In this article, the effect of adding titanium dioxide (TiO2) nanoparticles on impact strength and elongation at break of polypropylene/linear low-density polyethylene (PP/LLDPE) binary polymer matrix has been investigated. A 23 factorial design analysis was conducted to screen significant factors influencing the impact strength and elongation at break of polymer nanocomposites based on PP/LLDPE matrix. Three factors in two levels including LLDPE at 20 and 40 wt%, TiO2 nanoparticles at 2 and 4 wt%, and styrene–ethylene–butylene–styrene (SEBS as coupling agent) at 0 and 3 wt% were chosen for adding to matrix, and eight experiments were conducted for each response. Optimization of these factors was done for predicting maximum impact strength and elongation at break. It was observed that nanoparticles decreased impact strength. The presence of high levels of LLDPE and SEBS led to an increase in impact strength and elongation at break. From the analysis of variance, the most important parameters affecting impact strength and elongation at break were determined, and satisfactory prediction regression models were derived. In addition, the optimal condition of LLDPE and SEBS for the best combination of response variables was obtained at high level and for TiO2 at middle level.
Nascent ultrahigh molecular weight polyethylene (UHMWPE) is a thermoplastic material, consisting of nodular-fibrillar structure making it too much porous. At the present work, the effect of both particle morphology and chain entanglements on the sintering of UHMWPE was investigated. Neck growth for particles of three different commercial grades was determined as a function of time at isothermal sintering temperatures. A comparison between the experimental data and predictions from a theoretical model based on Maxwell constitutive equations revealed a complicated effect of particle size and morphology. It was observed that at early stages of sintering, Bellehumeur’s model was in an excellent agreement with the experimental data, while it was deviated at late stages when the neck growth ratio (y/a) exceeds 0.8. Unlike commercially entangled samples, melted disentangled powder particles did not flow toward each other even after a long time had elapsed. Disentangled UHMWPE pellets, sintered for 10 min near the melting temperature, showed great transparency indicating low air voids and developing the sintering process, while grain boundaries remained undeveloped for entangled pellets.
This work, conceived as a second step in the development of high-performance damping materials suitable for seismic application, describes the preparation and characterization of complex natural rubber-based composites containing hybrid nano- and conventional fillers. The cluster–cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. The same model was used to understand the mechanisms of energy dissipation. The damping coefficient was found to be in the sought range between 10% and 20% (at 0.5 Hz and high shear strain).
Polynorbornene rubbers (PNRs) used in this article were commercial compounds of polynorbornene filled with paraffin oil and fillers. The properties of PNR and ethylene-propylene-diene rubber (EPDM2650) blends with ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 were investigated. Blends were cured by sulfur and accelerator at 150°C and 160°C, respectively. Moving die rheometer, differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), and rubber process analyzer were used to examine the properties of the blends. The PNR exhibited significant reversion that was reduced by blending with EPDM. The thermal cross-linking of PNR occurred during hot air aging. The hot air aging resistance of PNR was improved by blending with EPDM. After 72 h of ozone aging, no obvious cracks were observed on the surface. The DMA results showed that the effective damping temperature range (tan ≥ 0.3) of vulcanized PNR was the broadest at 113°Cand then narrowed at higher temperature as the content of EPDM in the blend increased. With an increase in the ratio of EPDM, the glass transition temperature (Tg ) of EPDM moved to higher temperatures, as measured by DSC. The tensile strength of neat PNR is the greatest. PNR/EPDM = 75/25 blends showed yield behavior as the Tg of PNR moved to the higher temperature. These effects are attributed to a transfer of the extended oil from the PNR to the EPDM.
Commonly used shielding materials while X-ray imaging by clinical persons is based on lead but incessant contact with this toxic material can pave way to severe health problems. Polymer composites, embedded with lead-free additives, especially based on natural rubber can be chosen as a suitable alternative candidate due to its lightweight, cost-effectiveness and capability to absorb regular energy region of X-ray used in medical imaging. Rubber composites were prepared with modified rare earth oxides at different filler loadings. The characterization of the filler reveals that their size falls in the nanoregime, which, in turn, supplemented to the superior properties of the composites. Mechanical properties were found to increase with filler content. X-ray shielding studies were done at different tube voltages and thicknesses and the results prove the efficacy of materials to be considered as a promising shielding resource.
Although considerable progress has been made in recent years in field of polymer welding, challenges still remain in using a friction stir welding method to join polycarbonate (PC) composites. This research provides an investigation on the effect of welding parameters (tool’s travel and rotational speeds) on mechanical properties of PC nanocomposite weld lines. PC nanocomposites were prepared with different percentages of Al2O3 nanofiller using a twin screw extruder and injection moulded as sheets in order to ease the welding. Considering various parameters and their levels, optimization of Taguchi experimental design was carried out, an L 16 orthogonal standard array was selected and the effective parameter was calculated using analysis of variance of the results. The results indicated that nanoalumina percentage is the most effective parameter on the tensile strength of weld and tool’s travel speed and rotational speed are next effective parameters, respectively. According to signal-to-noise ratio, maximum weld tensile strength (89.5% of base material) is revealed when nanoalumina percentage, tool’s travel speed and tool’s rotational speed were chosen as 1 wt%, 12 mm/min and 1250 r/min, respectively.
A series of interpenetrating polymer network (IPN) hydrogels based on cross-linked natural rubber (XNR) and cassava starch (CSt) as biodegradable membrane material were synthesized via free radical polymerization in latex state using N,N'-methylenebisacrylamide (MBA) and maleic acid as cross-linkers. The IPN XNR/CSt hydrogels were confirmed and characterized by infrared spectroscopy, thermal analysis, and X-ray diffraction. The results showed that with increasing MBA content from 1.0 to 2.5 phr, cross-link density and gel fraction of XNR increased from 0.80 to 0.90 mol M–3 and from 19.7% to 30.5%, respectively. The gel fraction and tensile strength of the IPN XNR/CSt hydrogels also gradually increased as a function of MBA content but the water swelling and elongation at break decreased slightly. The IPN XNR/CSt containing 1.0 phr MBA displayed the highest water swelling of 82%. The weight retentions of IPN XNR/CSt hydrogels after soil degradations for 90 days increased from 48% to 56% with increasing MBA from 1.0 phr to 2.5 phr. The IPN XNR/CSt exhibited not only a good biodegradation but also high mechanical strength and flexibility. Also, the IPN XNR/CSt could be a promising candidate as a biodegradable membrane for longer released fertilizer application.
Polymer electrolytes consisting of poly(vinylidene fluoride-co-hexafluoropropylene) in combination with lithium triflate (LiCF3SO3) salt of varying concentration have been prepared using the conventional solution casting technique in the argon atmosphere. Structural electrical characterizations of the synthesized electrolytes have been performed using various imaging and spectroscopic techniques. The DC conductivities determined by complex impedance plots reveal gradual increase with increase in salt concentration up to a particular limit and decrease subsequently. The maximum DC conductivity obtained at 300 K is 1.64 x 10–4 Scm–1 for the electrolyte with a polymer to salt weight ratio of 1:1.8. The temperature-dependent conductivity followed a mixed Arrhenius and Vogel–Tamman–Fulcher type behaviour for the polymer electrolytes. From the Summerfield master curve plot, the conductivity of the solid polymer electrolytes is found to depend not only on ion dynamics but also on the segmental mobility of the polymer chains.
New efficient chelating polymers (CPs) based on waste polystyrene functionalized by itaconic acid moieties in absence and presence of montmorillonite clay have been prepared using high shearing effect homogenizer. The obtained CPs have been characterized using spectrophotometric and thermal analyses. The prepared CPs have been used as potential adsorbents for removal of different toxic metal ions from their aqueous solutions. The adsorption performance of the obtained CPs was found to match well with Langmuir adsorption isotherms. The highest sorption affinity of the obtained CPs toward different metal ions was for copper and lead.
In the present work, rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber (NBR). The sulfur and peroxide curing systems were introduced in cross-linking of rubber matrices. The research was aimed at the evaluation of magnetic filler content and type of curing system on the cross-link density, physical–mechanical and magnetic properties of prepared composites. The relationship between the composition of elastomers and cross-link structure within the rubber matrices, formed by applying different curing systems, was under investigation through strain–stress behavior of tested materials. The achieved results showed that ferrite behaves as a reinforcing filler in peroxide-cured composites based on NR, and in both, sulfur as well as peroxide-cured composites based on NBR. The results also demonstrated that the cross-linking degree and the type of cross-link structure as well as the composition of rubber matrices, to a large extent, influence the property spectrum of tested composite systems.
In this work, a novel polyurethane (PU) system based on poly(ethylene-butylene) adipate diol, 1,6-hexamethylene diisocyanate, 1,4-butanediol, and ascorbic acid was used to prepare scaffolds with potential applications in bone tissue engineering. Two fabrication methods to obtain porous materials were chosen: phase separation (PS)/salt particle leaching (PL) and solvent casting (SC)/salt PL. The calculated porosity demonstrated that scaffolds with a higher porosity were obtained (76–86%) using the PS/PL method. The morphology of pores was examined with the use of optical stereomicroscope and scanning electron microscope. The appropriate porosity, pore morphology, and swelling properties for bone tissue scaffolds were obtained for our novel PU system by the PS/PL method using 15 wt% solution of PU in the mixture of dimethylformamide (DMF)/tetrahydrofuran solvents and by SC/PL method from 20 wt% from DMF. The distilled water and saline water swelling for those samples was also appropriate for bone tissue scaffold application.
The effects of graft copolymers applied as compatibilizers for natural rubber/nitrile rubber (NR/NBR) blends at 50/50 (w/w) on cure characteristics, mechanical properties, thermal properties, oil resistance, and morphology were investigated. The graft copolymers of methyl methacrylate (MMA) onto NR initiated by benzoyl peroxide (NR-g-PMMA<BPO>) and by potassium persulfate (NR-g-PMMA<PPS>) under emulsion polymerization were synthesized and used to compatibilize the blends. The structures of the copolymers were characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. NR was blended with NBR via a two-roll mill at 70°C under the compatibilizer loading ranging from 0 to 10 parts per hundred of rubber (phr). The results showed that the tensile property and tear strength of the blends increased with the increasing amount of NR-g-PMMA<BPO> as a compatibilizer. Thermal aging determined in terms of tensile properties exhibited the smaller difference between before and after aging in an oven with the increasing compatibilizer loading. The morphology of the compatibilized NR/NBR vulcanizates was investigated by scanning electron microscopy of the tensile fracture surfaces, which exhibited the improvement of interfacial adhesion between the two rubber phases. The thermal properties of compatibilized NR/NBR vulcanizates were reported in terms of a glass transition temperature under differential scanning calorimetry and dynamic mechanical analysis. The incorporation of an appropriate amount of the compatibilizer into the blends apparently improved the oil resistance of NR. Among them, the blend filled with 7.5 phr of NR-g-PMMA<BPO> showed the lowest volume change in IRM 903 oil.
Coordination polymerization of styrene (St) using molybdenum pentachloride supported by phosphite ligand in the presence of metal organic compound was studied for the first time. The types of phosphite and co-catalysts significantly affected the catalytic activity of the molybdenum (V) (Mo(V)) active center and the number-average molecular weight (M n) of the resultant polymer. Among the examined catalysts, tri(nonylphenyl)phosphite (TNPP) ligand and AlOPhCH3(i-Bu)2 as co-catalyst provided the polymer with highest yield (up to 87.1%), metallocene as co-catalyst provided the polymer with highest M n (up to 5.32 x 105). The effect of [P]/[Mo] molar ratio on catalyst activity of the polymerization was discussed and the structures of Mo·TNPP complexes were preliminarily studied by infrared (IR) and ultraviolet spectroscopies. Besides, the polystyrene (PS) samples synthesized through bulk polymerization and solution polymerization were characterized by gel permeation chromatography, IR, carbon 13 nuclear magnetic resonance, and differential scanning calorimetry, respectively, and the results indicated both of the PS had high molecular weight (approximately 105) and atactic structure. All these results demonstrated that Mo(V) catalyst system was very effective for St polymerization.
Ethylene propylene diene monomer (EPDM)/calcium carbonate/bentonite (Bt) hybrid composites were prepared via a laboratory size two-roll mill. In this work, loading ratio of calcium carbonate to Bt was varied, that is, 30/0, 5/25, 15/15, 25/5 and 0/30 parts per hundred rubber. The effect of partial replacement of calcium carbonate with Bt on the curing characteristics, tear properties, morphology, aging and fatigue life of the hybrid composites was studied. On increasing Bt loading, cure time, scorch time and maximum torque of EPDM/calcium carbonate (CaCO3)/Bt composites decreased, whereas minimum torque increased. The tear strength and fatigue life of EPDM/CaCO3/Bt hybrid composites showed improvement with increasing Bt loading. The results also showed that the retention of aging of EPDM/CaCO3/Bt hybrid composites decreased with increasing Bt loading.
Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.
This article studies the enhancement in the properties of thermoplastic natural rubber (TPNR) reinforced by graphene oxide (GnO) and multiwalled carbon nanotubes (MWCNTs). TPNR is a blend of polypropylene and liquid natural rubber (NR), which is used as a compatibilizer and NR at a percentage of volume ratio 70:10:20, respectively. Using TPNR as the host matrix, a number of TPNR/carbon nanotubes (CNTs), TPNR/GnO, and hybrid TPNR/GnO/CNTs nanocomposites are processed and their mechanical, thermal, and electrical properties are characterized. The results extracted from tensile and impact test showed that tensile strength, Young’s modulus, and storage modulus of TPNR/GnO/MWCNTs hybrid nanocomposite increased as compared with TPNR composite and TPNR/GnO nanocomposite but lower than TPNR/MWCNTs nanocomposite. On the other hand, the elongation at break considerably decreased with increasing the content of both types of nanoparticles. Based on the experimental results, the thermal, electrical conductivity of a 0.5 wt% MWCNTs-reinforced sample increased as compared with a pure TPNR and other MWCNTs/GnO-reinforced composites. The improved dispersion properties of the nanocomposites can be due to altered interparticle interactions. MWCNTs, GnO, and MWCNTs–GnO networks are well combined to generate a synergistic effect that is shown by scanning electron microscopy micrographs. With the existence of this network, the mechanical, thermal, and electrical properties of the nanocomposite were improved significantly.
This article describes nanocomposites of triblock copolymer styrene–ethylene/butylene–styrene doping with 5 wt% of multiwalled carbon nanotubes (CNTs) prepared by melt mixing process. The selection of processing temperature was made according to the state of macrodispersion of CNTs within polymer matrix. Afterwards, the relationship between rotational speed, mixing time and electrical conductivity has been noted. It was confirmed that the temperature of 300°C and rotational speed of 100 r/min lead to significant decreasing of CNT agglomerations resulting in high electrical conductivity equal to 8.0 S/m.
Nonuniform networks were introduced into the nano-silica reinforced silicone rubbers, by co-cross-linking of silicone gum containing 0.05 mol% vinyl (GL) and gum containing 3 mol% vinyl (GH), so as to improve the mechanical properties. Their network characteristics were investigated by nuclear magnetic resonance measurement, swelling experiment, dynamic mechanical analysis, and rubber process analysis. Nonuniform networks displayed high tear strengths up to 41 kN m–1 and improved tensile strengths and elongations at break. Nonuniform networks with 7–10 phr of GH had optimal mechanical properties, since densely cross-linked domains scattered in base network and imparted maximum heterogeneity. In this structure, dense domains favored high modulus, while dominated long chains contributed to large extensibility. Hence, such structure could display large elongation before fracture while showing twice modulus upturns and stick-slip tearing characteristics, which were demonstrated by Mooney–Rivlin curves, tearing curves, and scanning electron microscopic images.
Epoxy (Ep) resin modified with carboxyl-terminated polybutadiene (CTPB) liquid rubber was investigated in this study. Fourier transform infrared verified the chemical reactions between oxirane ring of Ep and carboxyl groups of CTPB using benzyldimethylamine as a catalyst. The decrease of the thermal stability could be due to the lower thermal stability of CTPB compared with that of pure Ep. The mechanical results showed that CTPB-modified Ep was superior to that of the pure Ep, and the best overall mechanical properties were normally achieved with 20 phr of CTPB content. The impact strength of the system containing 20 phr CTPB increased by 193% due to the two-phase nature of the system. The dielectric constant and dissipation factor of the modified Ep obviously declined with the CTPB content compared with pure Ep, for instance, the dissipation factor remained less than 0.02 in wide frequency range.
Polyurethane(PU) nanocomposites were prepared using high shear mixing from castor oil, 4,4'-diphenylmethane diisocyanate, and modified clay (Closite 30B) as filler. The synthesis was carried out in bulk and without catalyst in the presence of clay. The clay percentage was varied from 1% to 5% by weight of the nanocomposite. The prepared nanocomposites were characterized using transmission electron microscopy (TEM), scanning electron microscopy, wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, mechanical and water absorption properties. TEM and WAXD results confirmed exfoliation upto 3% clay in the nanocomposite. Hydrogen bonding between clay and PU matrix was reflected in FTIR. The Young’s modulus improved more than 300% with addition of 4% clay but decreased further due to clay aggregation. The diffusivity and permeability decreased significantly for nanocomposites due to tortuous path offered by exfoliated clay platelets to diffusing water molecules.
The market for commercial polymer blends has grown steadily. A good blend should have strong interphases between different parts of the constituted polymers. Lack of strong interphases is a classical problem of the blend industry. Ethylene-propylene-diene monomer rubber (EPDM)/styrene-butadiene rubber (SBR) blends have a very good aging resistance and good compression sets. However, these rubbers are partially miscible. To improve the miscibility of EPDM and SBR in their blends, a Lewis acid, AlCl3,was used to form EPDM–g–SBR copolymer through Friedel–Crafts reactions. The existence of covalent bonds between EPDM and SBR macromolecules was studied by the cure traces of the blends, that is, Torque, Fourier transform infrared spectrums, differential scanning calorimetry (DSC) heat flow curves, thermogravimetric analysis curves, and scanning electron (SEM) micrographs. Subsequently, several blends with EPDM/SBR ratio of 40/60 and with various AlCl3 amounts were prepared and after curing, their mechanical properties were measured and compared. The results showed covalent bonds formed between SBR–EPDM and SBR–SBR macromolecules. An exothermic change in heat flow in the DSC curve was observed around 111.28°C,which can be attributed to the formation of carbocations in Friedel–Crafts reactions. Adding 2 phr AlCl3 had an efficient effect on EPDM–SBR and or SBR–SBR linkages. The mechanical properties of the cured blends, that is, tensile strength were lower when compared with corresponding values for prepared compound with SBR. Excellent compatibility between the two polymers and strong interphases were observed in SEM micrograph of the cured blend with 1 phr AlCl3.
Natural rubber from local zone in Colombia (San Juan) was compounded with three different commercial carbon black (N330, N550 and N660) at 25 and 50 phr. In order to evaluate the performance of new natural rubber compounds obtained from Colombia, a benchmarking was done with other natural rubber compounds from Central America (Guatemala). For this purpose, tensile strength, module at 100 and 300%, vulcanization rheometer curves, hardness and dispersion analysis were done for both natural rubber compounds. It was found that the new natural rubber compound from Colombia has similar properties and behaviour compared to Guatemala natural rubber (TSR). The Colombia natural rubber obtained is a new standard mix with high potential applications in the rubber industry in Colombia and other countries of region of South America.
Time-dependent thermodynamics was applied to steady-state melt flow of polyethylene. The steady-state viscosity behavior and first normal-stress difference were examined as a couple. The latter was a measure of the energy intensity (energy per volume); the time derivative of that was treated as the rate of energy production. In steady-state flow, viscosity decreased and the rate of the energy production increased with increasing shear stress. From the sign of the rate of production, steady flow was found to be in the stable region. The stress growth leading into steady-state flow was known from our previous work to be in the unstable region. This may be called pseudo-stable region. Under a constant rate of shear deformation, both shear stress and viscosity increased rapidly. A change into steady-state flow was interpreted to be the fracture point. The growth of the normal stress was slower than that of shear stress. The first normal-stress difference was a manifestation of deformation, which is a volume increase caused by shear stress. The volume increase led to fracture.
Composites of natural rubber (NR) reinforced with short carbon fibers (SCF) were prepared with two-roll open mill. Ozone treatment of carbon fibers was used to improve the interfacial interaction between fiber and matrix through chemical bonding and physical interlocking. The effect of treatment time on morphology and chemical component of SCF surface and mechanical properties of composites were thoroughly discussed. Results indicated that ozone treatment increased the surface roughness and the number of oxygen-containing groups. Compared with untreated SCF, tensile strength of NR-loaded SCF oxidized for 2.5 h reached the maximum values 26.9 MPa, and the increasing rate was 44.6%.
Hydrogenated nitrile butadiene rubber (HNBR) is cured by sulfur (S), dicumyl peroxide (DCP), and S donor, respectively. Effect of curing systems on vulcanization, mechanical properties, and cyclic compression of HNBR vulcanizates was investigated. The dependence of storage modulus (G') on strain was evaluated by Rubber Processing Analysis (RPA) analysis. The Mullins effect and degree of stress softening were also investigated by cyclic compression test. The energy dissipation of cyclic compression was calculated. The presumed mechanism of stress softening of HNBR was presented. The results show that the curing speed, torque, and G' are higher for S curing system compared with DCP and S donor. The elongation of break and hardness for S system are higher than that of DCP and S donor. The maximum compressive stress, stress softening, and dissipated energy decreased with the increasing number of cycles. The degree of stress softening for S is lower due to the bigger cross-link density and stronger filler–rubber interaction in S-cured HNBR.
Research on the structure and properties of room-temperature vulcanizated silicone rubber (RTV) composites with a type of incompletely condensed polyhedral oligomeric silsesquioxane (POSS) was conducted. Trisilanolphenyl POSS (TPOSS) was synthesized and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), proton nuclear magnetic resonance (1H NMR), and scanning electron microscopy (SEM). FTIR spectra suggested successful bonding of TPOSS. XRD analysis illustrated that POSS exhibited a crystal behavior while TPOSS had an amorphous structure. The chemical shift of 1H NMR at 7.1–7.8 ppm and 3.71–3.73 ppm further confirmed the structure of TPOSS. TPOSS particle was aggregated with large size observed from SEM Then, TPOSS was applied in RTV composites. Properties of RTV/TPOSS composites such as swelling behavior, tensile strength, elongation at break, thermal stability, and flame retardance were researched and compared. Results showed that the TPOSS were beneficial for increasing the cross-linking points and forming the effective three-dimensional networks in RTV composites. Tensile tests revealed that the tensile strength of RTV/TPOSS-3 was 20% higher than that of pure RTV, and the elongation at break of RTV/TPOSS-1 also showed an improvement. Thermogravimetric analysis studies demonstrated that RTV/TPOSS-5 presented the highest values of temperature at 5% mass loss and temperature at maximum mass loss rate of 437.5°C and 573.7°C, respectively. In addition, the residue of RTV/TPOSS-9 increased to 61.0%. Horizontal burning test found that the burning rate with 9% content of TPOSS was strikingly decreased by 66.4% compared with pure RTV.
Chitosan (Cts) was first modified with 4-cyano,4-[(phenylcarbothioyl)sulfanyl]pentanoic acid to serve as reversible addition–fragmentation chain transfer (RAFT) agent, and then the controlled grafting polymerizations of acrylic acid (PAA) were performed. The resultant copolymers were used as a stabilizing agent for preparation of colloidal silver nanoparticles (Ag NPs) in the range of 2–10 nm. Afterwards, montmorillonites (MMTs) were added to the solution of colloidal Ag NPs for improving thermal stability. Proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectrometry, energy dispersive X-ray spectroscopy, X-ray diffraction analysis, and scanning electron microscopy images demonstrate the successful synthesis of the graft copolymer. Their thermal behavior was examined by differential scanning calorimetry and thermogravimetric analyses.The antibacterial activity of Ag/Cts-g-PAA and Ag/Cts-g-PAA/MMT was investigated against Staphylococcus aureus, Escherichia coli, and Candida albicans by the disc diffusion method using Mueller Hinton agar. Antimicrobial tests show that Ag/Cts-g-PAA has much higher antimicrobial activity than Ag/Cts-g-PAA/MMT. This method would enable a wide variety of molecular designs to afford novel types of tailored hybrid materials composed of natural polysaccharides and synthetic polymers. The new hybrid materials were used as a stabilizing agent for preparation of Ag bionanocomposites with good antibacterial activity.
Polypropylene (PP)/poly(acrylonitrile–butadiene–styrene) (ABS) blends containing montmorillonite (MMT) compatibilized with polypropylene-grafted maleic anhydride were prepared by melt extrusion using twin screw extruder followed by injection molding. Mechanical properties were evaluated through tensile, flexural, and impact testing. The microstructure and formation of nanocomposites were assessed by scanning and transmission electron microscopy and X-ray diffraction (XRD). Incorporation of polypropylene-grafted maleic anhydride and MMT into PP/ABS blend led to higher strength and stiffness but at the expense of toughness. Scanning electron micrographs revealed a fine and homogeneous dispersion of ABS phase in PP matrix. Both XRD and transmission electron microscopic analysis revealed the formation of intercalated clay silicate layer in PP/ABS nanocomposites.
Isothermal and non-isothermal crystallization kinetics of polycyclohexylene dimethylene cyclohexanedicarboxylate (PCCE) were investigated via differential scanning calorimetry (DSC). Isothermal melt crystallization kinetics were analyzed using the traditional Avrami equation. Non-isothermal melt crystallization kinetics data obtained from DSC were analyzed using the extended Avrami relation and a combination of the Avrami equation and the Ozawa relationship. The glass transition temperature, equilibrium melting point, isothermal crystallization activation energy, and non-isothermal crystallization activation energy were determined. Furthermore, a predictive method based on the Nakamura model was proposed and was used to describe the non-isothermal crystallization kinetics based on the isothermal experimental data. The results suggested that the original Nakamura equation was not successful in describing the non-isothermal crystallization of PCCE over a wide range of cooling rates. It was found that the non-isothermal crystallization kinetics of PCCE, over a wide range of cooling rates, could best be described by modifying the differential Nakamura equation to include a varied Avrami index.
Segmented thermoplastic polyurethanes (PUs) were synthetized using polycarbonate diol as soft segment with a molar mass of 500 and as a hard segment 1,5-pentanediol with a combination of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, haze, transmittance, hardness, tensile properties and retention of tensile properties tests were employed to characterize the different PUs. The results of this study show that IPDI/HDI relation has a significant impact on the phase mixing, crystallinity and therefore on the PU’s properties. The variation of diisocyanate type ratio allows obtaining PUs of different nature from a high rubbery material with a high content in IPDI to high crystalline PU increasing the HDI content. Material transparency was also modified by decreasing the amorphous nature of the materials with the increase in the HDI content. The weather resistance of the final PU is related with the different isocyanate relation.
Epoxidized natural rubber (ENR)/multiwalled carbon nanotube (MWCNT) nanocomposites were prepared via in situ epoxidation of natural rubber (NR) using a molar ratio of formic acid/hydrogen peroxide to isoprene unit at 0.75/0.75 with five loadings of MWCNTs, ranging from 0.5–2.5 parts per hundred parts of rubber (phr), at 50°C for 4 h. Based on Fourier transform infrared spectra, the epoxide content of ENR in the nanocomposites was about 32.5–33.2 mole%. Accordingly, the products were referred to ENR30/MWCNT nanocomposites. The curing characteristics, mechanical properties (tensile properties, tear strength, and hardness), glass transition temperature (T g), thermal stability, and oil resistance of these in situ ENR30/MWCNT nanocomposites were investigated and compared with NR and neat ENR30. The results showed that the scorch and cure times of ENR30/MWCNT nanocomposites were the longest followed by NR and ENR30. The incorporation of an appropriate amount of MWCNTs into the in situ epoxidation apparently improved the properties of NR. Among them, the nanocomposites filled with 2 phr MWCNTs exhibited the highest mechanical properties, T g, thermal stability, and oil resistance. The mechanical properties of the in situ nanocomposites were also compared with those of the control nanocomposites prepared by adding MWCNTs directly in the prepared ENR30 latex. It was found that at similar MWCNT loadings, the in situ nanocomposites exhibited higher mechanical properties than the control nanocomposites.
This research shows the fungal degradation behavior of two series of composites: a series obtained with silver powder incorporated in sulfadiazine (SD)-based polyurethane urea and another series of composites that incorporates silver through polyurethane chain extension with silver SD. This article reports on the chemical structure variations characterized by Fourier transform infrared (FTIR) spectroscopy and the mechanical properties of these polymers before and after fungal exposure. Although silver SD—used as a chain-extender—ensures a more orderly dispersion of the silver throughout the hard segment of the polyurethane urea main chain, the FTIR results showed some changes on the surface of these composite films. Both silver composites exhibited higher fungal biodegradation resistance.
In the market of lighting technologies, light-emitting diodes (LEDs) gradually substitute conventional light sources. Because of their high energy efficiency and long lifetime, they are increasingly used in consumer products, interior and exterior lighting applications in the home and mobility sector as well as in industrial applications. The material properties in the surrounding area of the light-emitting semiconductor chip are crucial to the performance of LED. Although the energy efficiency of LED is higher compared to conventional light sources, temperatures exceed about 150°C close to the semiconductor chip. Especially in combination with high amounts of blue ultraviolet (UV) radiation, the materials for encapsulation cannot meet the requirements and reduce the lifetime of an LED significantly. Contrary to conventional materials, high transparent liquid silicone rubber (LSR) can resist high temperatures as well as UV radiation and offer a great freedom in design. This enables the combination of the encapsulation (primary optics) and the secondary optics in one component. The objective of an ongoing joint research project with various partners from the industry is the development of an innovative injection moulding process for high precision optics in LED applications made of LSR, which is analysed at the Institute of Plastics Processing (IKV), Aachen, Germany. Therefore, the LED board is placed in the injection mould and overmoulded with LSR. The goal is a highly integrated process with major emphasis on the reduction of components, mounting steps and costs. Furthermore, the combination of primary and secondary optics promises an improved effectiveness because losses in light power due to the transition of the primary and secondary optics are reduced.
The aim of this work was to combine the properties of chlorobutyl rubber (CIIR) and natural rubber (NR) in a binary blend for application in the inner liner of tubeless tires, using organomodified montmorillonite (Cloisite® 15A) as filler in order to improve the barrier property of the material. The maintenance of the mechanical and barrier properties of CIIR/NR 60/40 indicated that this blend can be used in the inner liner of tubeless tires, thereby reducing the cost of the final product, since the CIIR is 80% more expensive than NR.
A kind of bonding functional energetic thermoplastic elastomers (ETPEs) were synthesized as the binder of solid propellants using the mixture of chain extenders including diethyl bis(hydroxymethyl) malonate (DBM). The results showed that the mechanical properties of ETPEs decreased with increasing percent of DBM in the chain extenders. On the contrary, the work of adhesion between solid ingredients hexogen (RDX) and ETPEs increased. In order to test the comprehensive impacts of two elements, the RDX/ETPE propellants were prepared. The results showed when the percent of DBM was 25%, the overall properties of the propellants were optimum.
The gravimetric procedure was applied to investigate the solubility and diffusivity of supercritical carbon dioxide (SC-CO2) in cellulose acetate (CA). The solubility increases constantly in the initial period and reaches the dissolution equilibrium when the saturation time exceeds 10 h. The solubility decreases gradually from 14.29 wt% to 7.36 wt%, while the saturation temperature increases from 40°C to 70°C. The solubility increases by only 5.63%, while the saturation pressure grows from 10 MPa (12.62 wt%) to 30 MPa (13.33 wt%). The presence of cosolvents, especially ethanol, improves the solubility obviously. The diffusivity is not affected by pressure but increases with the solubility. Scanning electron microscopic images show that the cell densities increase with the content of ethanol, which implies that the higher solubility is in favor of the cell nucleation. The foamed CA with 10 wt% or 20 wt% ethanol has both low density and good impact properties.
The effectiveness of separate and combined incorporation of two natural, inexpensive, and nontoxic filler materials, kaolin and talc, at their various proportions in a bromobutyl rubber (BIIR) compound for a medical syringe plunger was investigated. The dispersion of kaolin was finer and more homogeneous than talc in BIIR. The curing was also enhanced in the presence of kaolin than talc. The difference in dispersion as well as reinforcing effects of the different fillers were reflected in the dynamic mechanical properties of the compounds. Tensile properties of the compounds were not significantly varied with varying kaolin/talc ratio of the compounds, however, tear strength decreased for higher contents of talc in the compounds. A significant synergistic reduction of compression set was achieved for 75/15 ratio of kaolin and talc in the rubber compound, very important for a plunger compound.
In this work, the effect of four factors including the nanoclay (NC) content, polyamide 6 (PA-6) content, compatibilizer type, and amount, as material variables on barrier properties of different high-density polyethylene (HDPE)/PA-6/clay nanocomposites, was described. Response surface method was used as a tool for experimental design. Different PA-6/clay nanocomposites were prepared by melt mixing of PA-6 at different clay loadings using a corotating twin-screw extruder. Subsequently, different PA-6/NC compounds containing different amounts of clay were melt mixed with HDPE to produce blow-molded containers under fixed processing conditions. In order to model the permeability, a neural network modelling approach in combination with a modified version of differential evolution was employed. The differential evolution modifications included, among others, a local search procedure based on backpropagation. The best models determined had a mean squared error in the testing phase of less than 0.1 and an average relative error lower than 12.2%, the difference between experimental results and predictions being within an acceptable range. This indicates that the methodology used was able to efficiently model the considered process.
The effect of natural rubber latex (NRL) on the properties of natural rubber/recycled chloroprene rubber (NR/rCR) blends was investigated. The properties of NR/rCR-NRL blends were compared with those of NR/rCR blends without the NRL. The addition of NRL showed an improvement in tensile strength, elongation at break, fatigue life, and swelling resistance with respect to those rubber blends without NRL. However, the gel content and glass transition of NR/rCR blends were not significantly affected by NRL. The scanning electron microscopic images showed better rCR dispersion in NR/rCR-NRL blends, indicating that the interfacial adhesion between NR and rCR blends was enhanced. A single tan is observed from the dynamic mechanical analysis supported that NRL can be used as compatibilizer in the NR-rich blend.
Magnetic particle-filled elastomeric composites are of significant importance in microwave shielding applications. An attempt has been made to enhance the microwave reflection properties of such composites by introduction of a magnetic filler concentration gradient along the thickness. Iron powder-filled functionally graded elastomeric composites (FGECs) are prepared by a construction-based method, wherein the volume fraction of iron powder is varied along the sheet thickness. The reflection losses of the uniformly dispersed elastomeric composites (UDECs) and of the FGECs, both employing same average amount of filler, has been measured through a reflection method with a vector network analyser, using the complex scattering parameter S 11. FGECs with equal sample thickness and filler volume fraction exhibit 2.5 times higher microwave reflection over a broader frequency range, as compared to that of the UDECs. For a volume fraction of 0.39, the reflection losses of FGECs and UDECs at 12.3 GHz are observed to be –50 dB and –19 dB, respectively. The corresponding frequency bandwidth for reflection loss ≤ –15 dB is observed to be 9.4 GHz for FGECs compared to that of 3.5 GHz for UDECs.
Rheological behavior has been treated in terms of the energy flow by coupling it with deformation and flow of material. The method follows time-dependent thermodynamics, which is different from Prigogine’s irreversible thermodynamics. We have examined the rate of energy production with particular attention to the physical meaning of the sign of the rate. Just as the sign of energy indicates in thermodynamics, whether or not the reaction is spontaneous, the sign of the rate indicates in time-dependent thermodynamics, whether or not the reaction is stable. In the stable region, the reaction is reversible. For a change from stable region to an unstable region, there is a discontinuity. Then, there is a pseudo-stable region, where a partial reversibility may be observed. This behavior involves yielding, which leads to fracture, like that seen in a longtime creep failure of a solid material. We have examined non-Newtonian flow of polyvinyl chloride plastisol, steady-state flow of high-density polyethylene melts, and its stress growth toward steady state.
Organically modified montmorillonite (OMMT) clay was intercalated with low-molecular weight polyethylene glycol (PEG) oligomer at melt stage. The intercalation behaviour of PEG into the OMMT clay galleries and its interaction with clay platelets were characterized with X-ray diffraction (XRD) and differential scanning calorimetric techniques. A natural rubber (NR)–organoclay nanocomposite (NROCN) was prepared by melt-compounding of NR with PEG-treated organoclay (P-OMMT) and other compounding chemicals using a laboratory-scale internal mixer. XRD analysis of the nanocomposites revealed the intercalation of NR molecules into the P-OMMT clay galleries and subsequent exfoliation during the melt-compounding process. Vulcanization characteristics of the NROCN, especially processing safety and optimum curing time, have been interpreted with reference to the organic modifier of the montmorillonite clay, PEG modification and the degree of exfoliation. Solid-state mechanical properties of P-OMMT clay-filled NROCN vulcanizates have shown a significant enhancement in stiffness and strength characteristics whilst without scarifying the elasticity of the nanocomposites. Results have been explained in terms of the degree of exfoliation, dispersibility of the organoclay and strain-induced crystallization of the natural rubber.
Citric acid (CA) was used as a grafted group onto polyurethane (PU) to form a CA-grafted PU series, with a control PU series containing free CA prepared for comparison. With an increase in the CA content, the enthalpy change during the melting increased for the PU and CPU series, and the glass transition temperature increased with the increase in CA content for the PU series but not for the CPU series. The tensile strengths of the PU series sharply increased with the CA content, whereas those of the CPU series did not. The PU series demonstrated better low-temperature flexibility and water permeability than the unmodified PU.
Natural rubber was reinforced with a short carbon fibers (SCFs) at different concentrations (0–20 part per hundred part of rubber (phr)). The composites were vulcanized by sulfur, then subjected to gamma radiation at different doses up to 40 kGy. Physico-mechanical properties of composites were studied. Also, thermogravimetric analysis was used to investigate the influence of the incorporation of SCF on the thermal properties of prepared composites. It was observed that the mechanical properties like tensile strength increases with increasing irradiation dose up to 30 kGy and fiber loading up to 15 phr, meanwhile the hardness and modulus increase with increasing fiber loading, but not affected by irradiation dose. Thermal stability of composites was increased by fiber loading content at constant irradiation dose. The morphological studies were made by means of scanning electron microscopy to investigate the structure change caused by the incorporation of SCF.
In order to analyze the differences in performance between two kinds of hydroxyl-terminated polyether (HTPE) binders, the curing reaction kinetics of the prepolymers and polyfunctional isocyanate (N-100) molecules and the thermal properties of the prepolymers and the corresponding polyurethane (PU) elastomers were studied by non-isothermal differential scanning calorimetry. The mechanical properties of PU elastomers were also studied by uniaxial tensile tests. With these data, the binder type could be chosen more appropriately for its application in rocket propellant formulations. The results showed that the reactivity of hydroxyl-terminated block copolyether (TPEG) with an isocyanate group is higher than that of hydroxyl-terminated random copolyether (PET). The chain flexibility of TPEG was less than that of PET, but the stereoregularity and crystallization ability of the former were superior. Compared to the prepolymers, the chain flexibility of the corresponding PU elastomers was reduced, and the crystallization ability became weaker such that their onset of crystallization was delayed. After the prepolymers were reacted with N-100, the thermal properties of PU elastomers remained consistent with their respective prepolymers. In summary, it was concluded that the mechanical properties of TPEG/N-100 PU elastomer films were found to be superior to the PET/N-100 films.
Acrylonitrile butadiene rubber (NBR) is widely used in seal applications due to its excellent oil resistance. In this article, carbon black-filled NBR composites, which differed in their acrylonitrile (ACN) and butadiene content ratios, were prepared and their curing characteristics and mechanical properties were investigated. Curing characteristics were investigated by measuring chemical kinetics and onset temperature of cross-linking reaction. Cross-linking density was measured by the volume swelling test. Mechanical properties, oil resistance, and compression set (CS) tests were also conducted. From these results, it was found that the microstructure in NBR polymer is closely connected to the curing characteristics and mechanical properties of the composite. On increasing the ACN content, Shore A hardness, tensile strength at break, elongation at break, oil resistance, and CS were raised, while, on the other hand cross-linking density, kinetics of cross-linking reaction, and bound rubber content were decreased.
Polymer composites containing nanofillers are among the most promising research fields for advanced materials. Carbon nanotubes (CNTs) are considered an ideal inclusion for polymer nanocomposites due to superior electrical, thermal, and mechanical properties which can be explained with the unique atomic structure of the nanotubes. Multi-walled carbon nanotubes (MWCNTs) are used as extremely strong nano-reinforcements for composites to produce a new generation of fiber-reinforced plastics with better application properties. In this experimental study, PP/MWCNT polymer nanocomposites with nanofiller concentrations in the range of 0.05–1 wt% MWCNT and the maleic anhydride amount from 0 to 7.5 wt% were investigated. An experimental study is conducted to examine the influence of MWCNT and compatibilizer contents on the thermal, mechanical, and viscoelastic properties of polypropylene (PP)/MWCNT nanocomposites. Extruded samples are characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and microindentation tests. Standard Berkovich indentation test determined by residual surface impression method based on load–displacement curves was used. DSC results show an increase in the crystallization temperature of maleinated PP with the increase of MWCNT contents proving the nucleation effect of CNTs. DMTA results prove the good modification properties of maleic anhydride in MWCNT/PP nanocomposites at 0.05 wt% nanotubes concentration. Elastic moduli, obtained from both DMTA and microindentation, are compared to investigate the difference between surface and bulk mechanical properties of nanocomposites with increasing nanotubes concentration. Measured values of elastic moduli are within comparable ranges, but the absolute values are different.
Polyamide12 (Nylon12)/natural rubber (NR) blend was prepared by melt mixing in a Brabender mixer using polystyrene/maleated natural rubber (PS/MNR) copolymer as a reactive compatibilizer. The influence of compatibilizer loading (1, 3, 5, 7, and 10 phr), shear rate (10–500 s–1), and temperature (200–220°C) on the flow properties (i.e., shear viscosity (), power law index, flow activation energy (Ea), and extrudate swell) of (Nylon12/NR)/(PS/MNR) blends was investigated. The blends showed pseudoplastic behavior from an evident increase of shear stress and a reduction of with increasing shear rate. The values of and Ea of the blends were also found to increase with the compatibilizer loading. It suggests that PS/MNR copolymer functioned properly and enhanced the compatibility and interfacial interaction between Nylon12 matrix and NR domains via the formation of amide and succinimide linkages at the interfaces. This reactive compatibilization also caused in a reduction of extrudate swell apparently due to slower elastic recovery of polymer chains.
Chitosan-based nanocomposites (NCs) at different modified multiwalled carbon nanotubes (MWCNTs) loadings were produced by solvent casting method. The effective dispersion of the MWCNT in polymer matrix is an important factor while making its NCs. The MWCNTs intrinsically tend to bundle and/or aggregate. For this reason, the MWCNT is modified to improve the dispersibility when incorporated into polymer matrix. In this study, the MWCNTs were modified with ascorbic acid or vitamin C (VC). The combined effect of MWCNT-VC and chitosan on the structural, crystallinity, interfacial interactions, and mechanical and thermal properties of the obtained NCs was investigated. Scanning electron micrographs showed that in the NC films, MWCNTs were dispersed homogeneously throughout the chitosan matrix. The tensile strength of chitosan film increased significantly with increasing the MWCNT-VC content.
Swelling elastomers are special polymers that increase in volume when exposed to water or oil. They have been successfully deployed in oil and gas wells for isolation of water-producing zones, partial replacement of cementing, slimming down of wells, and so on. Performance appraisal and design modifications cannot be attempted without knowledge of material response under specific field conditions. Results from an experimental investigation are presented here about the behavior of two commercial elastomers, one water swelling and one oil swelling. Of the one-month total testing time, one set of samples (for each elastomer type) was tested under acid for one day, and the other set without any acid exposure. Readings were taken at different stages of swelling to record the variation in volume, thickness, and hardness of elastomer samples. Test parameters were set to match existing conditions in a regional oil well. These results can be used to assess performance of elastomers under given well conditions and for modeling and simulation of seal behavior.
A novel constitutive characterization method for uncured rubber behaviour has been developed in this article. A systematic measuring procedure was designed to fully investigate the uncured rubber complex stress–strain behaviour under different deformation patterns, which integrated three kinds of tests – the uniaxial tensile, the compression test and the shear test. It can be found from the observed behaviour that the uncured rubber has similar but much pronounced non-elastic stress–strain relationship, which is highly non-linear and highly rate dependent. A generalized Maxwell model with modified Yeoh model is developed to constitutively describe the observed phenomena in which parameters are identified by an evolution optimization scheme. Good agreement can be found between the model and the test data. Another finding is that, similar to vulcanized rubber, multi-test data are needed to obtain compatible constitutive models. The test results, findings and the developed model help rubber engineers deeply understand the uncured rubber's mechanical behaviour and provide a base for rubber manufacturing simulation.
Fusion is a key parameter in achieving polyvinyl chloride (PVC) nanocomposites with desired properties. In the present research, a fuzzy logic (FL)-based model is developed to predict fusion time (FT) for the contents of nanoclay, processing aid, and calcium stearate in PVC processing. In order to have precise rules for the FL model, data mining algorithm RepTree is employed to detect dominating patterns among experimental data. The model parameters are then well adjusted using genetic algorithm. The modeling results show a correlation of 0.86 between predicted and observed values for FT. So, it proved reliability of the idea of employing the decision tree resulted from a data mining algorithm as the base knowledge of FL models. Also, applying genetic algorithm optimization, the correlation coefficient increased from a value of less than 0.83 to 0.86. The calculated correlation coefficient for the test data was 0.88, which denotes good model universalizing ability.
The overall goal of this project was to combine biochar (BC) with plastic and wood residue to create novel composite products. Little to no research has been conducted on combining BC with other materials to form a composite. In this research, BC was used as a partial and full replacement material for wood flour and was combined with polypropylene to manufacture composite materials. The resulting wood/BC/plastic composites were evaluated for various mechanical and physical properties. The composites fabricated with 25% BC had the highest average flexural strength and modulus of elasticity. Composites fabricated with 5% BC had the highest average tensile strength and tensile elasticity. Composites fabricated with 40% BC had the lowest average 24- and 48-h water absorption percentage. The findings suggested that BC has the potential to be a replacement for traditional wood in a variety of composite applications.
Two mixed-matrix membranes (MMM) for gas permeability test were prepared by introducing inorganic fillers (silica (SiO2) and magnesium oxide (MgO)) in the composite blend of epoxidized natural rubber (ENR) and polyvinyl chloride (PVC). Inclusion of SiO2 and MgO particles in the membranes resulted in pores formation as observed through scanning electron microscopy. Thermal study demonstrated that there were interaction between the fillers and polymer matrix with SiO2 exhibited better interaction. SiO2 was also observed to disperse more evenly in the membrane compared to MgO. The permeability of carbon dioxide (CO2) and nitrogen (N2) gases was measured in order to determine the effects of SiO2 and MgO in CO2/N2 separation performance of the ENR/PVC/filler membranes. CO2 was found to exhibit higher permeability compared to N2 for all the membranes. The gas permeability of ENR/PVC/SiO2 membrane was significantly higher than ENR/PVC/MgO and ENR/PVC membranes. Interestingly, despite having lower permeability, MgO-filled membrane exhibited higher CO2/N2 selectivity. When compared to the Robeson’s upper bound, it was found that introduction of fillers had improved gas separation performance of ENR/PVC membrane.
This article focuses on the calculation of transport parameters (number density of ions and time travel of ions between sites, mobility, diffusion coefficient, and number of transitions per unit time) of the lithium perchlorate (LiClO4)-doped poly(vinyl alcohol)/chitosan (PVA/CS) composites using Rice and Roth model. The thermal study reveals a decrease in glass transition temperature for LiClO4-doped PVA/CS composites. The highest ionic conductivity of 3 x 10–6 S cm–1 at room temperature is observed for the 20 wt% LiClO4-containing composite. The temperature-dependent conductivity follows Arrhenius relation and lowest activation energy of 0.153 eV is observed for highest conducting sample. The mechanical properties such as Young’s modulus, stiffness, and tensile strength decreases and its percentage elongation at break increases with increase in LiClO4-doping level in PVA/CS polymer matrix. The scanning electron microscopic images exhibit smooth and homogeneous surface of PVA/CS composite.
Application of ethylene–propylene-diene monomer (EPDM) grafted with glycidyl methacrylate (GMA), along with epoxidized natural rubber (ENR) was investigated for tire sidewall blend. The presence of ENR and EPDM-g-GMA improved physico-mechanical properties of the blends. The best results were obtained using 5 phr EPDM-g-GMA in the blend. Tensile and tear strength of the blend with 5 phr EPDM-g-GMA were 13.7% and 46.5% higher than conventional blend of tire sidewall, respectively. Ozone resistance in dynamic condition of NR/BR/ENR with 5 phr EPDM-g-GMA were 20% and 30% superior than NR/butadiene rubber (BR)/ENR/EPDM and conventional NR/BR with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylene, respectively. Improved mechanical and ozone resistance properties are due to better homogeneity of cross-link density and carbon black distribution in the blend.
The dispersion stability of silica aggregates in the rubber matrix is one of the concerns for silica-filled compounds. Silica aggregates tend to flocculate due to their poor compatibility with the rubbers and consequent strong tendency for self-association. The flocculation process can occur during compound storage as well as at the onset of vulcanization. This present work studies the kinetics of the flocculation process in silica-reinforced natural rubber (NR) compounds by following the changes of the storage modulus during thermal annealing under conditions applied for vulcanization. The results demonstrate that silica flocculation can be effectively suppressed by increasing compound dump temperature and amount of silane, as these result in a better degree of dispersion, higher degrees of hydrophobation, and filler–rubber interaction. The compounds containing highly dispersible silicas exhibit greater filler–rubber interaction, but their flocculation processes develop faster when compared to the compounds filled with conventional silicas. Epoxidation of NR clearly influences the filler–rubber interaction but shows no clear evidence of a change of flocculation rate.
In this study, our focus is on the compatibility behaviour of bio-based polyester blend with the addition of surface-modified oil palm fruit bunch fibres (OPFBFs). The surface of OPFBF has been modified using alkali, silane and acetic anhydride solutions. Surface-modified fibres are characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy analyses to identify the functionality, adhesion and phase morphology. Untreated and treated fibres are incorporated in the bio-based polyester blend with about 30% of fibre content. Surface-modified fibre biocomposites exhibit improved interaction between the polymer matrix and the fibre. Oil palm fibre-reinforced biocomposites exhibit enhanced thermal, mechanical and morphological properties with incorporation of surface-treated fibre. The OPFBF also acts as a reinforcement filler and adhesion material for the polyester blend.
Highly filled systems, such as dental materials and tires, have some exceptional properties that make them very special for particular scientists and engineers. In this study, the thermal and dynamic properties of highly nanosilica-filled polystyrene were investigated. Thermal study predicts a phase in the filled system, named as adsorbed polymer, that has a different glass transition temperature (T g) compared with the neat polymer. The adsorbed polymer seems to be responsible for special thermal properties of the highly filled system. The dynamic properties of the filled system are observed to have a similar trend as the thermal behavior at different particle sizes and concentrations, both increasing linearly with the increase of volume fraction of adsorbed polymer. However, at higher volume fractions or for smaller particles, this trend changes and the filler networking mechanism is considered to be the reason for this change. Effect of the filler network is studied through the Han plot and it is found that the contribution of the filler network to the dynamic behavior of the highly filled system increases by reducing the particle size and increasing the particle loading. Beside the particle size and concentration, the effect of filler surface physics on dynamic and thermal behavior of the highly filled system is investigated and it is found that surface modification of the particle surface with nonpolar groups tends to lower T g and volume fraction for the adsorbed phase and lower strength of the filler network. In this work, the samples were prepared using the method of stabilizing suspension in polymer solution. For viscoelastic investigation, the dynamic rheometry in sweep mode was chosen, also for studying the thermal behavior, differential scanning calorimetric tests were performed. In addition, in order to study the structure of filler in low and highly filled samples, atomic force microscopic imaging was employed.
This work focuses on the study of the hydrothermal aging of fiber-reinforced rubber composites. Physical and mechanical properties of different rubber composites as well as their influence with aging conditions were studied. Four rubber matrices were used (ethylene propylene diene monomer (EPDM), silicone, EPDM/silicone, and neoprene) to make composite samples reinforced with glass fibers. Accelerated aging in water was performed using a hot tub under controlled temperature for few months. The decrement in mechanical properties was linked to water infiltration and degradation of the fiber–matrix interface. After 6 months of accelerated aging, some samples showed an important deviation from original properties, while others retained nearly homogeneous properties with time.
In this work, thermoplastic polyurethane (TPU) elastomers reinforced with carbon nanosized particles were produced by a special melt blending technique. A TPU was melt blended with high-structured carbon black and carbon nanofibres (1 wt%). A miniature asymmetric batch mixer, which applies high shear levels to the melt, ensured good particles dispersion. The TPU material systems were then thoroughly characterized using thermogravimetric analysis, differential scanning calorimetry, tensile mechanical testing, electrical resistance measurements and flammability tests. The different nanofillers exhibited different influences on the TPU properties, these materials featuring interesting and improved multifunctional behaviours, with high propensity for large deformation sensors applications.
Dynamically cured 60/40 epoxidized natural rubber (ENR)/polyamide 12 (PA-12) and unmodified natural rubber (NR)/PA-12 blends with different types of curing systems (i.e. sulfur- and peroxide-cured systems) were prepared. It was found that mixing torque, shear viscosity, tensile strength, hardness, stress relaxation, thermal, and oil resistance properties of the ENR/PA-12 blends were higher than those of the NR/PA-12 blends. This is attributed to the chemical interaction between polar functional groups in ENR and PA-12 molecules which caused the formation of ENR-grafted PA-12. Smaller vulcanized rubber domains dispersed in the PA-12 matrix was observed in the dynamically sulfur-cured ENR/PA-12 blends. This is attributed to higher shear and elongational viscosities during mixing operation at high temperature. However, the peroxide-cured blends exhibited higher relaxation property, oil resistance, and cross-link density than those of the sulfur-cured blends due to strong reversion effect observed in the sulfur-cured system.
Nanocomposites were prepared by melt mixing in a twin-screw extruder 5% by weight of Cloisite® Na+, 15A or 30B, with an ethylene vinyl acetate/poly(vinyl chloride) (EVA/PVC) blend (90/10% by weight). The dispersion was assessed by X-ray diffraction (XRD), transmission electron microscopy (TEM), oscillatory rheometry, and dynamic mechanical analysis (DMA). XRD and TEM analyses revealed an intercalated morphology and an exfoliated morphology for the composites containing Cloisite 15A and 30B, respectively. Rheometrical and DMA data demonstrated that the presence of PVC in the blend not only improved the interaction with Cloisite 30B but also acted as a mechanical reinforcement.
The mechanical property, structure, and morphology of styrene–butadiene–styrene (SBS) thermoplastic elastomer under the combined fatigue and chemical aging conditions were investigated. The results indicated that under the fatigue condition alone, the tensile strength of SBS increased initially and then decreased with the increase in fatigue time. Cracks formed on the surface of samples. Through transmission electron microscopy analysis, it was found that the phase morphology was influenced by fatigue condition. However, there was no significant change in the molecular weight and chemical structure of SBS. Under combined fatigue and chemical aging conditions, the chemical aging process could be accelerated by the fatigue condition. Molecular weight and gel content significantly increased with the increase of fatigue condition. Under ultraviolet (UV) light irradiation alone, there was no crack on the surface of SBS. After adding the fatigue condition, a large deterioration formed on the surface of SBS sample. The chemical aging condition such as UV light and temperature could also promote the fatigue aging process. With the addition or increase of chemical aging condition, the tensile strength of SBS greatly decreased. The oxygen content and gel content significantly increased, and there were a lot of cracks forming on the surface of SBS sample.
Polybutadiene (PB) and hydroxyl-terminated PB were epoxidized using in situ-generated dimethyl dioxirane as an oxidant in the attendance of different concentrations of copper and lead (2-guanidinobenzimidazoliume) (GBH) complexes as the catalyst at 25°C. The potential of cis, trans, and vinyl double bonds toward epoxidation was considered in detail at various reaction times. The products were characterized using proton nuclear magnetic resonance and Fourier transform infrared spectroscopy techniques and data revealed that the formation of desired products were obtained without any side reaction. The results indicated the performance of calculated 0.252 mmol of GBH complexes in obtaining maximum epoxidation yield as well as selectivity in the epoxidation of cis double bonds in comparison with trans and vinyl ones.
Graft polymerization of isoprene onto styrene–butadiene rubber (SBR) was carried out in latex using p-menthane hydroperoxide and ferrous sulfate as an initiator. The effect of isoprene on vulcanization characteristics, mechanical, and thermal properties of isoprene-grafted SBR were investigated. The grafting of isoprene onto SBR was confirmed by attenuated total teflectance–Fourier transform infrared spectroscopy. The fatigue heat of the isoprene-grafted SBR mainly come from deformation and restructuring, while the smaller deformation of isoprene-grafted SBR will cause the heat lower. The results revealed that the glass transition temperature decreases with the grafting of isoprene and strengthen the Payne effect in grafted SBR.
The mechanical and damping properties of thermoplastic polyurethanes (TPUs) prepared by polyether–aromatic polyester polyols were studied. Dynamic viscoelastic properties (E' and tan ) were mainly investigated using a dynamical mechanical analysis. By increasing the content of the aromatic ester component of soft segment in each segmented PU, the value of tan increased, and the width of the peak narrowed with the same hard segment contents. It was desired that interaction between hard and soft segment in U-Fine (UF)-A and UF-B is uniform, and the degree of phase separation between hard and soft segment in UF-A and UF-B advanced in comparison with TPU-A. Tensile strength and abrasion resistance of UF-B (ester component content of polyether–ester polyol = 20.3 mol%) showed superior data compared with other commercial damping materials.
Embossing is an established process for the thermoplastic elastomers but not yet for the thermosetting elastomers. It has already been shown that hot embossing is a viable technology for imprinting microstructures in addition to curing thin silicone films at their gel point. It is one of the simplest, most cost-effective, and time-saving methods for replicating microstructures. In the present study, films made from liquid silicone rubber (LSR) formulations containing fillers are hot embossed under modified operating conditions. The use of such relatively hard silicone elastomers shows the versatility of this method that has been established for softer silicone elastomers. Also, as a proof of concept, a microstructured metal (nickel (Ni)) plate is used as an embosser for the films successfully. The ideal condition for hot embossing the LSR formulation (XLR 630 with titanium dioxide fillers) with a Ni embosser is 110°C preheating for 15–35 s, embossed with 2 bar pressure, and postheating for complete curing at 110°C for 3 min showing that the process is extremely fast.
The influence of blend composition and ethylene–propylene–diene terpolymer (EPDM) content on the processing parameters, phase structure and thermal behaviour of polypropylene (PP) and low-density polyethylene (LDPE) blends was studied. Processing parameters of blends in twin-screw extruder were followed by output (Q), torque (TQ) and back pressure (p), and apparent viscosity as given by TQ/Q and p/Q ratios, while the thermal behaviour was measured using differential scanning calorimetry. Phase structure was investigated using scanning transmission electron microscopy (STEM). The degree of crystallinity ( c) of PP phase decreased and c of LDPE phase increased with higher LDPE content in blends with and without EPDM. STEM micrographs of EPDM compatibilized PP/LDPE blends of compositions 80/20 and 20/80 showed particulate morphology, whereas in the blends of compositions 60/40 and 40/60 the morphology was co-continuous. The EPDM compatibilizer was localized on the interface.
Dielectric relaxation characteristics of multiwalled carbon nanotube (MWCNT)-reinforced chlorobutyl (CIIR) nanocomposites have been studied as a function of frequency (100–106 Hz) at different filler loadings (0, 2, 4, 6 and 8 phr) over a wide range of temperatures (30–120°C). The effect of MWCNT loadings and temperature on the dielectric permittivity ('), dielectric loss tangent (tan ), complex impedance (Z*) and electrical conductivity () was studied. The variation of ' with MWCNT loading has been explained based on the interfacial polarization of the fillers within a heterogeneous system. A significant effect of MWCNT loading on the real (Z') and imaginary (Z'') part of Z* was observed due to the relaxation dynamics of polymer chains at the CIIR-MWCNT interface. The non-linearity of CIIR nanocomposites has been studied from Nyquist plots. The dielectric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The permittivity and conductivity of the nanocomposites have been analyzed based on scaling theory at increasing temperatures. The frequency dependency and percolation phenomenon in the composites have been discussed in terms of . The percolation threshold ( crit) occurred at around 6 phr of MWCNT loading irrespective of temperature. The dispersion of MWCNT in the CIIR matrix and agglomeration of the filler at higher loading have been studied using scanning electron microscopic photomicrographs.
In this work, the potential of palm stearin alkyd as a cross-linking agent for rubber compounding was investigated. Alkyd carrying pendent –COOH groups was blended with epoxidised natural rubber (ENR50) via solvent casting technique at ambient temperature. Spectroscopic characterisations show that ENR50 and alkyd have interacted with each other via chemical reaction involving the epoxide of the rubber and –COOH of alkyd. Consequently, notable increase in the glass transition temperature (T g) and gel content of the blend was observed. In addition to the epoxide ring-opening reaction, the extent of cross-linking in the blend was further increased by means of ultraviolet (UV) curing. As a result, the UV-cured blends experienced lower percentage of swelling, produced higher percentage of gel, have higher cross-link density and higher T g. The cross-link density in the rubber/alkyd blend has increased from 3.0 x 10–6 mol cm–3 to 2.0 x 10–4 mol cm–3 after UV curing. This is clearly evidenced from the swelling test results, where ENR and alkyd are completely soluble in the solvent, but upon blending and subsequent UV irradiation, the blend produced >90% of gel and swelled by 318%. Findings from this work show that sustainable material such as vegetable oil could be utilised in development of cross-linking agent for rubber. Significant increase in the cross-link density of the UV-cured blend suggests that environment friendly compound such as alkyd has great potential to serve as an alternative to conventional compounds in rubber vulcanisation.
In this work, the morphology and crystallization behavior of polyamide 6 (PA6)/maleic anhydride-grafted-ethylene–propylene–diene rubber (MAH-g-EPDM)/high-density polyethylene (HDPE) blends with different ratios of the components were studied. In order to study the influence of both thermodynamics and kinetic factors, the interfacial tension between various polymer pairs was taken into account and two processing methods were used. Contact angle measurements and rheological relaxation time simulation were used to calculate the interfacial tension. It was found that because of the reaction between PA6 and MAH-g-EPDM, the value of interfacial tension of PA6/MAH-g-EPDM binary blends calculated by the contact angle measurement was not correct and the real value α = 0.97 mN m–1 was calculated by rheological relaxation time simulation. The two processing methods (one-step and two-step processing methods) led to different crystallization behaviors with different morphologies of the blends.
A series of polyurethane elastomers (PUEs) were prepared by the reaction of hydroxyl-terminated polybutadiene (HTPB) and toluene diisocyanate (TDI), the resultant PU prepolymer was extended with polydimethyl siloxane (PDMS). The conventional spectroscopic characterization of the synthesized samples using Fourier transform infrared spectrophotometer confirmed the structure of the proposed PDMS-based PU. Thermogravimetric analysis (TGA) was carried out to determine the thermal stability of the prepared PU samples. Surface properties of the synthesized material were studied determining the percentage of water absorption and equilibrium degree of swelling. The results revealed that by increasing the mole ratio of PDMS, the synthesized PUEs showed hydrophilic behavior while placing them in water and dimethyl sulfoxide solvent.
A new composite, kaolin/sodium alginate-grafted poly(acrylic acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid) (KL/SA-g-P(AA-co-AMPS)), was synthesized by intercalation graft polymerization of KL, SA, partially neutralized AA, and AMPS, using ammonium persulfate as an initiator and N,N'-methylenebisacrylamide as a cross-linker. The composite was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Possible mechanisms for the process of intercalation graft polymerization were speculated. The composite was used for the removal of heavy metal ions from aqueous solutions. Sorption behavior of heavy metal ions such as lead (Pb2+), cadmium (Cd2+), and zinc (Zn2+) on (KL/SA-g-P(AA-co-AMPS) was investigated. Maximal adsorption capacities for Pb2+, Cd2+, and Zn2+ ions were 834.7, 69.9, and 139.8 mg g–1, respectively. It was found that the adsorption of Pb2+ and Zn2+ ions was in agreement with the Freundlich model, whereas that of Cd2+ ion was consistent with both Langmuir and Freundlich models. Mechanisms for the adsorption process were also discussed. It indicated that chelation played an important role for the adsorption of Pb2+ ions, while ion exchange was decisive for the adsorption of Zn2+ and Cd2+ ions. It has been concluded that KL/SA-g-P(AA-co-AMPS) hydrogel composite offered excellent potential for the removal of heavy metal ions from contaminated water. In addition, the hydrogel composite could be regenerated and reused in wastewater treatment.
This article described the preparation of copper calcium titanate (CCTO)-modified poly(vinylidene fluoride) (PVDF) by solution casting, and its dielectric properties, breakdown strength and tensile properties. The phase structure, crystal type and surface morphology of the membrane were determined using the methods of Fourier-transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The results showed that the comprehensive performance of the CCTO/PVDF membrane treated with a coupling agent with a quality ratio of 2% was better than that of the membrane without coupling agent treatment. When the content of CCTO was increased to 20%, the surface structure of the membrane was compacted, and the membrane’s breakdown strength and dielectric properties were high.
The present research work was performed to study the properties of siloxane-based polyurethane (SPU) elastomers using aliphatic diisocyanate. SPU samples constituting of hexamethylene diisocyanate, hydroxyl-terminated polybutadiene, and polydimethylsiloxane (PDMS) were synthesized by two-step polymerization technique. Molecular engineering and surface characterization were carried out, and the outcome of the results was discussed. The conventional spectroscopic characterization of the synthesized samples using Fourier transform infrared spectroscopy confirms the existence of the proposed SPU structure. Surface properties of the synthesized material were studied determining the percentage of water absorption and equilibrium of the degree of swelling. It was found that by increasing the mole ratio of PDMS, the synthesized PU samples showed hydrophobic behavior while placing them in water and in dimethylsulfoxide solvent.
Auxetic materials exhibit a negative Poisson’s ratio behavior that makes them useful for a variety of structural applications by virtue of their ability to counterintuitively deform due to a reentrant cellular structure. This property allows the cellular material to expand laterally when pulled in the longitudinal direction or, conversely, contract laterally when compressed, with the manner of deformation of the internal structure depending upon the configuration of the cellular structure. The purpose of this research was to develop carbon black nanoparticle-reinforced natural rubber vulcanizates and to investigate the effects of carbon black reinforcement on the mechanical behavior of an idealized auxetic foam structure using modeling and numerical simulation techniques. This has been achieved by mechanically characterizing vulcanized natural rubber of various nanoparticle loadings and then using the test data to perform finite element (FE) simulations on the foam models. Material models have been developed in the FE simulation software ANSYS by curve fitting experimental data (hyperelastic) to theoretical material models. Large deformation analysis of this foam structure has been carried out to determine structural reorganizations and negative Poisson’s ratio effect in the foam structure.
A binary blend of acrylonitrile butadiene styrene–high-impact polystyrene (ABS–HIPS 50% wt) was prepared on a twin-screw extruder at 190–210°C. The different properties were then analyzed using tensile strength and impact tests, melt flow index, thermogravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). The analysis of mechanical properties showed a decrease in elongation at break and impact strength. FTIR analysis indicated heterogeneous distribution of the blend in injected pieces and scanning electron microscopic images show heterogeneous distribution of both ABS and HIPS phase. On the other hand, by varying the percentage of styrene–ethylene–butylene–styrene (SEBS) from 10 to 30% wt using a twin-screw extruder at 190–210°C, we have prepared ternary blends of ABS-HIPS-SEBS. The addition of SEBS to the binary system ABS–HIPS allowed us to increase the ductile properties (elongation at break and impact strength), as well as reducing the viscosity.
Different filler materials are widely used in industry both for obtaining better mechanical properties and decreasing the overall costs. In this study, several uniaxial tensile tests were conducted for 5.15% (MP1-GS1), 9.4% (MP2-GS2), and 13.4% (MP3-GS3) of glass spheres and mica powder-filled elastomer materials. In this research, the results obtained from tensile tests of samples made of natural rubber/styrene–butadiene rubber (NR/SBR)-based elastomer materials in which different amount of glass spheres (GS) and mica powder (MP) mixed were characterized using the finite element method. The values of forces and displacements obtained from the tests were transferred to ABAQUS 6.7 finite element analysis (FEA) software. Among all hyperelastic material models, Marlow’s model was found to be the most suitable one and was utilized as a material model in the FEA. Mechanical tests and the finite element results were compared with each other. Comparison of the results show that while the error percentage changed between 0.01 and 0.5% for the MP-filled samples, the error percentage changed between 0.25 and 0.5% for GS-filled samples. The effects of MP and GS filler materials on the mechanical properties of NR/SBR elastomer were compared. Maximum stress and strain values were observed in GS2 and MP2 materials.
2-Phenylimidazole (2-PZ) and polymethyl acrylic glycidyl ester (PGMA) are performed to fabricate a novel microcapsule latent curing agent of 2-PZ/PGMA by solvent evaporation method with 2-PZ as the core material and PGMA as the shell material. A novel single-component 2-PZ/PGMA/epoxy adhesive is also prepared by mixing 2-PZ/PGMA with epoxy resin matrix. The 2-PZ/PGMA microcapsules are characterized using scanning electron microscopy and granulometer. The curing kinetics and thermal properties of 2-PZ/PGMA/epoxy resin system are also investigated using differential scanning calorimeter, Fourier transform infrared spectrometer, and thermogravimetric analysis. Results show that 2-PZ/PGMA has good sphericity and narrow diameter distribution. The curing process of the 2-PZ/PGMA/epoxy resin system contains autocatalytic mechanism. Compared with that of pure epoxy, the presence of the 2-PZ/PGMA has little effect on thermal stability for the epoxy.
Aluminum nitride (AlN) microparticles treated by silane coupling reagent of -glycidoxy propyl trimethoxy silane (KH-560) are employed to fabricate AlN/epoxy (AlN/EP) composites. Initially, both the flexural and impact strength of the AlN/EP composites increased, but later decreased with excessive addition of AlN. The mechanical properties of the composites are optimal with 5 wt% AlN. The thermal decomposition temperature and the dielectric constant of the composites increased with the addition of AlN. The thermal conductivities of the AlN/EP composites improved with the increasing addition of AlN, and the thermal conductive coefficient is 0.98 W/mK with 70 wt%-treated AlN. For a fixed AlN loading, the surface treatment of AlN by KH-560 exhibits a positive effect on the thermal conductivities and mechanical properties of the composites.
Unsaturated polyester poly(fumaric-co-itaconic-co-butanediol) (poly(FA-co-IA-co-BD)) was prepared with fumaric acid (FA), itaconic acid (IA), and 1,4-butanediol (BD) by melt polycondensation, and its self-cross-linking kinetics was investigated through the percentage of insoluble gel fraction (Qs) and conversion degree of C=C (DC). The results showed that poly(FA-co-IA-co-BD) had the highest Qs and DC, when the mole ratio of FA and IA was 1:0.96, which meant that the polyester had the maximum extent of self-cross-linking. And the polyester had the maximum rate constant (k) and the smallest activation energy (Ea). The value of k was temperature dependent, and the higher the temperature, the higher the value of k. Thermodynamics parameters such as <img src="1.tif">, <img src="2.tif">, and <img src="3.tif"> were also discussed. The results showed that, <img src="1.tif"> > 0, the self-cross-linking reaction of the poly(FA-co-IA-co-BD) occurred at high temperature. The self-cross-linking reaction was an exothermic reaction, <img src="2.tif"> was equivalent to Ea. <img src="3.tif"> < 0, the product in the transition state was more ordered. When the mole ratio of FA to IA was 1:0.96, poly(FA-co- IA-co-BD) was the most ordered in the transition state and had the smallest <img src="3.tif">, and the C=C in the polyester self-cross-linked easily.
The aim of this work was to evaluate peroxide systems with and without coagents as cross-linking agents for rubber compounds in tires, which are usually prepared with sulfur. Natural rubber (NR) and styrene–butadiene rubber (SBR) formulations were prepared in open and closed mixers using an NR/SBR compound cured with sulfur as a reference. The physical properties (hardness, tensile strength, tearing, and abrasion) and dynamic mechanical behavior of the NR/SBR compounds cured with different cross-linking agents were evaluated. The NR/SBR compounds cured with only peroxide had poorer properties than did the vulcanized compound. On the other hand, the coagents were quite effective, and the NR/SBR compounds with BIS F40 + Retilink T40 (compound 10) or BIS F40 + T70A (compound 11) had properties similar to those of the reference compound. Compound 10 and the reference compound yielded similar tan values from dynamic mechanical analysis at 60 and 0°C, which are related to the rolling resistance and wet traction, respectively. The results demonstrate the possibility of using a peroxide/coagent NR/SBR compound instead of a sulfur-cured compound for tire tread applications without the loss of desirable properties and with lower costs and processing times.
This article describes an innovative method of coupling polyurethane elastomer (based on polyurethane glycolysate) with constructional steel, by implementation of a Glaspur®—glass lacquer containing latent polyurethanes and monosilane adhesion promoters. The commonly applied coupling agent is Cilbond® 45SF glue or its derivatives. Additionally, glycolysate was synthesised from polyurethane waste and 1,3-propylene glycol in 6:1 proportion. Results of examination confirm the usefulness of the above-mentioned glass lacquer for preparing laminar polyurethane–steel elements. Strength tests unequivocally present higher tear resistance of elements prepared with lacquer than couplings with Cilbond.
Ultrafine styrene–acrylonitrile random copolymer (SAN) nanofiber-based membranes were produced from N,N-dimethyl formamide solution by electrospinning. The purpose of this study was to find the optimum values of the electrospinning parameters and the influence of major significant parameters on the electrospun fiber morphology and the average fiber diameter (Davg) and its standard deviation using design of experiment. A backward elimination model for multiple regression analysis was employed to obtain quantitative interactions among selected electrospinning parameters and the final fiber diameter. The dependence of the Davg and morphology on the critical entanglement concentration was also studied. Morphology of the electrospun nanofiber mats were examined by scanning electron microscopy. Davg of electrospun SAN fibers increased considerably with increasing solution concentration. Fibers with diameters ranging from 40 to 650 nm were obtained. Analysis of variance was utilized to identify the statistically significant parameters (p < 0.05) and error variance.
Dielectric relaxation behavior of multi-walled carbon nanotube (MWCNT)-reinforced silicone elastomer nanocomposites has been studied as a function of filler loading in a wide frequency range (10-1–106 Hz). The effect of MWCNT loading on the real and imaginary parts of impedance is distinctly visible. The significant change in the impedance parameters on filler loading is explained on the basis of interfacial polarization in a heterogeneous medium and relaxation dynamics of polymer chains. The electrical modulus formalism has been used to investigate the conductivity and relaxation phenomena of the system. The frequency dependence of ac conductivity is explained using percolation theory. The existence of percolation phenomenon in the composites is discussed on the basis of electrical conductivity and morphology of the composites. The percolation threshold (as studied by electrical conductivity) occurs in the range of 4 phr of MWCNT loading. The scanning electron photomicrographs show agglomeration of the MWCNT above 4 phr concentration and formation of a continuous network structure.
A novel adhesion-enhancing polyhydrosiloxane containing acrylate groups (MPMS-PHMS) was prepared via the hydrolysis of 3-methacryloyloxypropylmethyldimethoxysilane and the ring-opening polymerization of octamethylcyclotetrasiloxane and tetramethylcyclotetrasiloxane, and was used as cross-linker for addition-cure silicone encapsulant (ASE) with a large amount of alumina as thermally conductive fillers. The chemical structure of MPMS-PHMS was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, silicon nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The effect of MPMS-PHMS on the properties of ASE was investigated. The results indicated that when using MPMS-PHMS as cross-linker, the cross-linking density of ASE was much higher than that of ASE using commercial poly(hydromethylsiloxane) cross-linker. It was also found that MPMS-PHMS not only markedly improved the adhesion strength of ASE to aluminum substrate but also significantly enhanced the mechanical properties of ASE. Appropriately increasing cure temperature and prolonging cure time were favorable to improve the adhesion strength of ASE. The optimal content of MPMS-PHMS was 10 phr, and the suitable cure temperature and time were approximately between 130 and 150°C and 2 h, respectively.
This work exhibits the synthesis and characterization of novel polymer/hybrid coatings for concrete protection. The coatings have been prepared by polymerization of vinyl acetate, butyl acrylate, or glycidyl methacrylate with hydroxyl ethyl methacrylate and toluidine as multiple shells in presence of poly methyl methacrylate (scrap) as seed particles and silica (natural sand) as inner core forming the corresponding C1, C2, and C3 coatings, respectively. The prepared polymer coatings have been characterized via Fourier transform-infrared spectroscopy, thermogravimetric analysis, transmission electron microscope, and SEM. The prepared coats have been tested on ready-made concrete slates. The polymer coatings have been applied with ease on dry concrete slates. Test results showed that the polymer coatings have good bonding strength with dry concrete surfaces ranging between 0.78 and 0.99 MPa. No failure was observed for more than 1 year with the coated concrete slates. The acid and base resistance as well as abrasion resistance of the coated concrete slates have been also evaluated and investigated. The performance of the prepared polymer coatings in 3% sulfuric acid and 20% sodium hydroxide solutions has proved the effectiveness of the prepared coatings in protecting the concrete slates.
Polyurethanes (Pus) were synthesized from castor oil and modified through transesterification by pentaerythritol, poly(-caprolactone)diol (PCL), and isophorone diisocyanate to form PU coatings. The ratio of NCO/OH groups used was 1:1. The effect of varying the PCL content on the physical properties of wood panel PU coatings was determined. The PU coatings were characterized using Fourier transform infrared spectroscopic analysis, and the physicochemical properties, such as tensile strength, elongation at the break, shore A hardness, and the results of a lap shear test, were reported. Thermal properties of the PU coatings were evaluated using differential scanning calorimetry and thermogravimetric analysis. In vitro PU degradation was related to the hard segment structure and polymer hydrophilicity.
Ethylene-propylene-diene monomer rubber (EPDM)-based ground wastes (W-EPDM) are reutilized as rubber matrix in plug material compounds for automotive applications. Production scraps of target product are ground to 35, 40 and 60 mesh in ambient conditions. Effect of particle size and the amount of W-EPDM is studied. A new trial product of maleated ethylene-propylene rubber (EPM) and bitumen are used to improve interphase adhesion of the waste and the virgin EPDM. Cure characteristics, physico-mechanical and aging properties of all compounds are determined. Micro structure of the vulcanizates is studied for explaining dispersion and interaction between different phases. Reutilization of W-EPDM causes some reasonable deterioration in cure characteristics and mechanical properties of the product. However, some systematic and alternative recipes for plug materials are suggested considering cost and environmental benefits.
The surfaces of high-modulus poly (p-phenylene-2, 6-benzobisoxazole) (HMPBO) fibres have been treated by a solution of polyphosphoric acid/acetic acid (PPA/AA). The single fibre pull-out strength, chemical compositions and surface morphologies of HMPBO fibres were tested and characterized by single fibre pull-out tests, contact angles, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscopy and thermogravimetric analyzer. Results show that this method has great potential in the surface treatment of HMPBO fibres.
The goal of the present work was to study the preparation and properties of rubber magnetic composites and investigation of strontium ferrite activity in examined materials. Three types of rubber matrices, namely butadiene rubber as non-polar elastomeric matrix, nitrile butadiene rubber (NBR) and NBR/poly(vinyl chloride) blend as polar elastomeric matrices, were compounded with strontium ferrite and other additives in order to prepare rubber magnetic composites. Ferrite dosage was given in modified and unmodified forms in concentration scale ranging from 0 to 100 phr. The influence of magnetic filler content on the mechanical properties of composites was investigated. Correlation between Wolf activity coefficient and Payne effect in relation to the mechanical properties of tested systems was discussed. The results revealed that the observed characteristics are dependent on the type of rubber matrix and also on the type of ferrite.
A graft copolymer, composed of maleic anhydride as side group and chlorinated polyvinyl chloride as backbone, was prepared via in situ chlorinating graft copolymerization. The effect of graft degree of the graft copolymer on the chain structure is discussed through proton nuclear magnetic resonance. The results of differential scanning calorimetry and thermogravimetic analysis showed glass transition temperature of the graft copolymer did not change with increase in graft degree, but thermal stability of the product improved much with increase in graft degree. The results of gel content measurements showed the increasing graft degree was favorable to prevent cross-linking reaction of the product.
Role of silane-treated stöber silica as reinforcing filler for nitrile rubber (NBR) has been studied. Stöber silica is synthesized by sol–gel method, and the surface of silica is modified with the treatment of silane-coupling agent viz. -mercaptopropyltrimethoxysilane (-MPS) in varying proportions. Average particle size of stöber silica of spherical shape in the range of 200 to 400 nm is evident from scanning electron microscopy (SEM). Surface modification of silica particle with silane-coupling agents decreases surface energy and reduces agglomeration of silica particles in rubber matrix. Stress–strain study and dynamic mechanical analysis of silica-filled composites are compared with the unfilled ones. Analysis of cross-linking density, mechanical properties, and storage moduli indicates a strong rubber–filler interaction in the silane-treated, silica-filled NBR composites. Silane treatment is found to be effective in uniform dispersion of silica in rubber matrix and in improving the mechanical properties of rubber composite. Different functionalities of organosilane at its both end improve the compatibility of silica with rubber matrix and offer better rubber–filler interaction.
This study aims at investigating the quaternary factors, namely zinc di-N-butyl dithiocarbonmate (ZDBC), sulfur, zinc oxide (ZnO), and potassium hydroxide (KOH) on the tensile strength and elongation of chlorinated nitrile latex film. Full factorial design analysis was employed to examine the factors and their combination two-way interactions with the tensile properties. The factors’ effect on the variability or the stability of the resulting latex films were analyzed as well. The results showed that KOH, which was used to adjust the pH of the latex system greatly affected the tensile strength of the latex film, whereas sulfur has minor influence on tensile strength. Meanwhile, KOH also interacted in combination with ZnO and sulfur to affect the elongation of the latex films. Addition of KOH changed the pH by affecting the electronic repulsion and gelling stability of the latex matrix. Consequently, the variability in tensile strength and elongation of latex film were according to the amount of KOH. Finally, the simple mathematical models with a regression range 0.73–0.86 were developed to relate the factors and the tensile properties of the latex.
In this study, isotactic polybutene-1 (iPB) was functionalized with glycidyl methacrylate (GMA) using di-tert-butyl peroxide as an initiator via a radical-initiated melt grafting reaction, while styrene (St) was used as a comonomer to enhance the grafting reaction. The effect of temperature, concentration of initial GMA and peroxide, and the addition of St comonomer on the final grafting degree, grafting efficiency, and the melt flow rate of the grafted polymer were studied. The results indicated that St was an effective comonomer. Moreover, the GMA grafted iPB had higher crystallization temperature and faster crystallization rate compared with the unmodified iPB based on the differential scanning calorimetric tests.
Ultrasonically aided extrusion of natural rubber (NR), styrene butadiene rubber (SBR), and NR/SBR blends with ratio of 70/30, 50/50, and 30/70 were carried out at various ultrasonic amplitudes up to 10 μm. A die pressure of NR and NR/SBR blends continuously decreased with increase of ultrasonic amplitude, while that of SBR showed a slight increase with increase in amplitude from 5.0 to 7.5 μm due to a dominant effect of SBR gel formation. Complex dynamic viscosity, minimum and maximum torque of curing curves of NR, SBR, and NR/SBR blends, and cross-link density and gel fraction of their vulcanizates were decreased by the ultrasonic treatment at an amplitude of 10 μm, due to the molecular chain scission. The latter also led to a decrease in the hardness, modulus at a strain of 100%, and abrasion resistance of NR and NR/SBR blends. However, the modulus and abrasion resistance of SBR showed an improvement at amplitude of 7.5 μm, due to a dominant effect of gel formation. Both the tensile strength and elongation at break of ultrasonically treated NR/SBR blends showed a maximum at amplitude of 5.0 μm, with the modulus at a strain of 100% not being affected. Morphological studies using the phase-contrast optical microscope and atomic force microscopy showed a reduction in the size of rubber phases and a better homogeneity of NR/SBR blend by the ultrasonic treatment at amplitude of 5.0 μm. Accordingly, the increase in both the tensile strength and elongation at break of ultrasonically treated NR/SBR blends at an amplitude of 5.0 μm is mainly ascribed to the lower size of rubber phases and improved uniformity of blend caused by the ultrasonic treatment.
Poly(butylene succinate) (PBS) was melt blended with maleic anhydride–grafted ethylene-propylene-diene terpolymer (EPDM-MAH) and maleic anhydride–grafted ethylene-1-butene copolymer (EB-MAH) to obtain thermoplastic elastomers (TPEs) containing a biodegradable polyester. PBS/EB-MAH blend showed lower modulus and excellent strain recovery compared to PBS/EPDM-MAH blend due to the smaller rubber particle size. Tensile strength of PBS/EPDM-MAH blend was found to be significantly improved by annealing because of the increased interfacial reaction between PBS matrix phase and EPDM dispersed phase and the increased cross-linking in EPDM. As the result, it was found that the annealing process is effective for the improvement of the mechanical properties of PBS/MAH-grafted rubber blends.
Dynamically vulcanized blends of 85/15 polystyrene (PS)/natural rubber (NR) were prepared by melt mixing in an internal mixer at 170°C using dicumyl peroxide (DCP). The concentration of DCP was varied from 0 to 4.2 milliequivalents (meq). It was found that dynamic vulcanization of the blend with 2.8 meq DCP significantly enhanced the Young’s modulus, flexural modulus, and impact strength, with a marginal improvement in tensile and flexural strengths. The SEM studies revealed that the morphology of the blends changed drastically on dynamic vulcanization. The dynamic mechanical studies showed that the storage modulus and the loss modulus were better for dynamically vulcanized blends with 2.8 meq DCP in comparison to other blends. The rheology studies reveal that the damping of the blend was reduced at the melt processing conditions at a DCP content of 2.8 meq and the blend was pseudoplastic in nature. The thermal stability of the dynamically vulcanized blend improved on dynamic vulcanization. Thus, dynamic vulcanization can be employed as a means of technological compatibilization technique for 85/15 PS/NR blend for overall improvement in properties.
In this study, the properties of ethylene–vinyl acetate (EVA) and EVA filled with aluminum (aluminum trihydrate; ATH) and magnesium hydroxide (MH) as halogen-free flame-retardant materials were studied. Scanning electron microscopic analysis revealed that MH in EVA matrix is platy in structure, considerably broad size distribution and well homogeneously distributed, whereas ATH particles are smaller and much more homogeneous in size. Addition of ATH or MH to EVA had an impressive affection on the thermal aging and flame tests but impaired the blend mechanical properties. This research explored that in comparison with ATH, addition of MH to EVA blends was more efficient and suitable in all mechanical, thermal, and flammability tests.
In the present study, characterization and morphological study of oil palm ash (OPA) and thermal properties of OPA-filled natural rubber (NR) compounds were carried out. The morphological study revealed that the OPA particle was irregular with rough surface and porous structure. Energy dispersive x-ray analysis and an x-ray fluorescence spectrometry indicated that silicon was the highest component in OPA. Fourier transform infrared analysis and x-ray diffraction indicated that the main mineralogical components in OPA were quartz and calcite. The study results of the OPA-filled NR compounds showed that the thermal resistance and retention properties after thermal ageing were notably enhanced with the addition of OPA and improved as the OPA loading was increased.
The grinding under the action of shear deformations of vulcanizates of oil-filled ethylene–propylene–diene elastomer cured by a sulfur-based system up to different degrees of cross-linking was studied. Monodisperse powders with a predominant fraction of particle sizes 0.315–0.63 mm were obtained. The effects of the cross-link density of the original vulcanizate on the content of sol fraction and the cross-link density of the rubber powder were estimated. The possibility of producing molding materials from rubber powders with enhanced rigidity using the method of high-temperature sintering was shown. The dependence of the structure and properties of molding materials on the parameters of rubber powders was studied. The mechanisms of the grinding and high-temperature sintering are proposed.
Graft copolymerization of silicone monomer—3-(trimethoxysilyl) propyl methacrylate (TMSPMA) grafted onto styrene–butadiene–styrene (SBS; SBS-g-TMSPMA) triblock copolymer was carried out by free radical polymerization, and the improvement of adhesive property of the grafted SBS for glass materials is the major purpose of this study. To gain the optimal reaction conditions and grafting effect, the effect of various factors, such as the monomer ratio and reaction time, on the grafting ratio and grafting efficiency (GE) of SBS-g-TMSPMA graft copolymers were investigated. In addition, various SBS-g-TMSPMA graft copolymers were coated on different substrates based on glass and their tensile strengths that were tested. The optimal graft condition for the SBS-g-TMSPMA was obtained when the molar ratio of TMSPMA to SBS was 1 and reaction time was 4 h. Their grafting ratio and GEreached to a maximum of 56.8% and 60.2%, respectively, and the tensile strength also reached maximum. In this article, we confirm that the higher the grafting ratio, the more the silicone-containing in the graft copolymer. Hence, the –Si–O–Si– bonding between SBS-g-TMSPMA and glass substrate was more intensive and tensile strength was stronger.
This article investigates the performance of polylactic acid (PLA)/polycaprolactone (PCL)/montmorillonite (MMT) nanocomposites toughened with metallocene-catalyzed linear low-density polyethylene (mLLDPE), in terms of mechanical, thermal, and morphological properties. All the results were compared and the influence of MMT and mLLDPE on the final properties was observed and reported. mLLDPE decreased the modulus and the strength of PLA/PCL and its nanocomposites due to its inherent lower rigidity compared to PLA/PCL nanocomposites. Moreover, incorporation of clay significantly increased mechanical and thermal stability of the nanocomposites. Scanning electron microscopic images confirmed that MMT acted as a compatibilizer, whereas it reduced the size of the droplets. It has been suggested that improvements in properties are related to good dispersion of clays within the matrix. However, further addition of MMT beyond 2 parts per hundred (phr) level decreases all the properties of PLA/PCL/mLLDPE/MMT nanocomposites. X-Ray diffraction patterns were used to discover the reason of reduction in the properties of PLA/PCL/mLLDPE/MMT at 4 phr. It was revealed that mLLDPE-toughened blends have intercalated structure below 4 phr MMT content as the interlayer spacing decreased at 4 phr MMT.
Different types of vulcanization systems play an important role towards thermal degradation of natural rubber (NR) compound. In this study, NR compounds were cured with efficient vulcanization (EV), semi-efficient vulcanization (SEV) and conventional vulcanization (CV) system in the presence of natural antioxidant (NA) obtained from oil palm leaves to compare the effectiveness of NA on the properties of NR vulcanizate, the same compound was prepared in the presence of commercial antioxidant, trimethylquinoline (TMQ). The samples were then subjected to tensile and tear test before and after ageing process. Both SEV/NA and EV/NA NR vulcanizates showed comparable results on mechanical properties before and after ageing process as compared to TMQ. Meanwhile, for CV systems, the result showed reduction in mechanical properties after a longer time of ageing due to the breakage of polysulphidic cross-link.
Low-density polyethylene, one of the most important polymer products, is commonly produced in high-pressure free radical polymerization processes. A dynamic model of the high-pressure polymerization of ethylene initiated by oxygen in tubular reactor is introduced, and a dynamic optimization problem is formulated for process start-up strategies. The present study proposes a kinetic model based on an assumed reaction mechanism. The model describes the rates of oxygen decomposition and propagation of free radical ethylene polymerization. The mass and heat balance equations in an adiabatic tubular reactor operated at a constant pressure of 2.4 kbars and a temperature range of 110–300°C are presented. Simulations of polymerization process predict temperature of the reaction mixture, response time for cooling water, and also conversion along the reactor length. Response time was obtained using different inputs of controlled variables. Values obtained from these simulations are compared with real data from the process unit (Polietilen, Dioki®, Zagreb, Croatia) and a model validation is confirmed. Improvement in reactor productivity and better understanding of few different start-up procedures is achieved.
Dynamically cured 40/60 epoxidized natural rubber (ENR)/thermoplastic polyurethane (TPU) blends with peroxide and three different types of sulfur curing system were prepared using an internal mixer. It was found that the blends with peroxide exhibited higher modulus, mixing torque, mixing temperature, hardness, and shear viscosity than the blends with the sulfur-cured systems (i.e. conventional (CV), semiefficient (semi-EV), and efficient sulfur vulcanization (EV)). This is attributed to peroxide-caused cross-linking reaction in both ENR and TPU phases. Furthermore, it was found that the dynamically CV-cured blends exhibited higher thermal resistance, relaxation behavior, cross-link density, oil resistance, and mechanical strength than those of the semi-EV and EV-cured blends. The dynamically CV-cured blends also exhibited the smallest vulcanized rubber domains dispersed in the TPU matrix. This is due to higher levels of cross-link density in ENR phase and possibly higher interfacial attraction. On the other hand, it is difficult to identify the spherical rubber particle in the peroxide-cured blend due to cross-linking reaction that occurs in the TPU matrix.
The present work involves the preparation of a new heteroaromatic azo polymer, poly(thiourea-azo-ether; PTAE) using 4,4'-oxydiphenyl bis(thiourea) and diazonium salt solution of 2,6-diaminopyridine. The polymer was easily processable using polar solvents and had high molar mass of 33 x 103 g mol-1. Various concentrations of azo filler and poly(styrene-butadiene-styrene; SBS) blends were then blended in solution phase. The effect of PTAE on processing, conductivity, morphology and thermophysical properties of elastomeric blends was investigated. Field-emission scanning electron microscopic micrographs of SBS/PTAE blends revealed fine dispersal of filler, good adhesion with the matrix and the development of conducting pathways. Accordingly, filler content from 10 to 60 wt% increased the conductivity from 0.77 x 10-1 to 1.43 S cm-1. Ultimate tensile strength of SBS/PTAE (26.94–28.12 MPa) was improved relative to pure SBS. A relationship between PTAE loading and thermal stability of the materials was also observed. The temperature at 10% gravimetric loss was increased from 461 to 499°C, while the glass transition temperature was enhanced from 135 to 147°C. Thermal and conducting data showed better results relative to pure elastomer but lower than the conducting filler. Fine balance of properties renders new materials better than the existing elastomeric blends used in a number of applications.
In this work, different contents of vinyl-terminated fluorosilicone oil (VFS oil) were blended with room temperature-vulcanized (RTV) polydimethylsiloxane (PDMS). Via rheological detection, the addition of VFS oil could increase the viscosities of VFS/PDMS/silicon dioxide (SiO2) blends, probably due to the interaction between incorporated fluorine atom and silanol on the surfaces of SiO2. The additional "structuring effect" was reduced by enhancing the shearing rate of the mixed gums containing VFS oil and the obvious shear-thinning property was helpful for enhancing the processability. The curing process and cross-linking degree test of VFS/PDMS/SiO2 blends suggested that the VFS oil could reduce the curing time and the induction time, but did not play a positive role in the cure depth using a platinum catalyst. Mechanical property tests showed that the VFS oil did not increase the tensile strength and elongation at break, and the hardness slightly decreased with increasing VFS oil content. The oil resistance property test showed that the oil resistance of the polysiloxane rubber was well improved by the incorporation of the VFS oil containing the functional group –CH2CH2CF3.
In this study, a rubber fender with the reduced dimensions of 1:10 of the original was simulated with ANSYS-Workbench finite element software to determine the deformations under compressive loads. Also, the rubber fender was tested by means of compression experiments for determining the actual performance values. Three different strain energy functions were used as the hyperelastic material model in the finite element analysis. The deformation results of simulations and experiments were compared against each other. In this regard, the most suitable strain energy potential was determined to be a hyperelastic material model for the rubber fender.
In the present article, an elongation viscosity equation of polymeric melts was derived based on the Moore dynamic model. The equation described the relationship between extensional viscosity and extension strain rate of polymer melts. The effects of the four parameters in this equation on the extension viscosity curves were analyzed in detail. The extensional viscosities of a low-density polyethylene (LDPE) and a linear LDPE as well as LDPE/glass bead composite melts at 170°C were estimated by applying this equation, and the predictions were compared with the measurement data under the same experimental conditions. The results showed that the estimations were in good agreement with the experimental data.
Conductive rubber composites based on ethylene acrylic elastomer (AEM) and conductive carbon black (CCB) were prepared by a two-roll mixing mill. From the transmission electron microscope photomicrographs, the uniform distribution of CCB aggregates and the interconnected CCB aggregates in the AEM matrix were observed. The bound rubber content of unvulcanized rubber was found to increase significantly with increasing CCB content. The effect of CCB concentration on the dynamic viscoelastic properties of AEM matrix was determined using a Rubber Process Analyzer (RPA 2000) in terms of strain sweep and frequency sweep of both uncured and cured AEM/CCB systems. The storage modulus (G') increased with an increase in CCB loading. In the case of strain sweep, the G' values decreased with strain amplitude for both the systems, but the G' was more for cross-linked AEM/CCB systems. The strain dependency of G' for CCB-filled AEM systems can be explained on the basis of the Payne effect. The complex viscosity (*) of these systems increased with CCB loading, and it decreased with strain amplitude, which is due to the shear thinning effect. The tan for unvulcanized and vulcanized systems increased with the strain; however, the value of tan was <1 throughout the experimental strain range, which explains the elastic nature of the cured systems. The G' increased with angular frequency for both the systems and the tan became independent upon the angular frequency after 10 Hz. The alternating current conductivity (AC) increased with an increase in CCB loading at all frequencies and the system achieves the percolation at 20 phr CCB loading, which is in accordance with the rheological percolation. The direct current conductivity (DC) also increased with an increase in CCB concentration.
The aim of this research was to develop a novel bio-based elastomer, chain-end functionalized polybutadiene (PBD), from epoxidized soybean oil (ESO), to be used as a processing aid for commercial PBD. This material was successfully synthesized in this study via post-living anionic polymerization of poly(butadienyl)lithium and ESO. The gel permeation chromatography revealed that the products had a mixture of molecular weights, comprising roughly three, two, and one times higher than that of the pure PBD. The majority of the molecules in the product had a two-fold higher molecular weight at the peak value (Mp) than the original PBD chain. The result obtained from the reaction of PBD anions with epoxidized methyl oleate indicated that the ester group showed the higher reactivity toward the PBD anion than the epoxide group. Therefore, the formation of bio-based elastomer from the PBD anions and ESO occurred via the nucleophilic substitution of PBD anion with the carbon atom of the ester group with the loss of the leaving group, the alkoxide, and then followed by nucleophilic addition of another PBD anion to the newly formed ketone, yielding an alcoholate anion. The alcoholate anion was then terminated by hydrogen abstraction from methanol, leading to the formation of chain-end epoxidized fatty acid ester functionalized PBD. The ring opening of the epoxide group of the ESO also took place simultaneously, yielding the product with the three-fold higher Mp than the original PBD. However, the ring opening of epoxide group was decreased when the size of the PBD anion and the amount of the ESO in the reaction were increased.
The aim of this research work is to establish a hot embossing process for addition curing vinyl-terminated polydimethylsiloxane (PDMS), which are thermosetting elastomers, based on the existing and widely applied technology for thermoplasts. To our knowledge, no known technologies or processes are commercially available for embossing microstructures and submicron structures on elastomers like silicones in large scale production of films. The predominantly used technologies to make microscale components for microfluidic devices and microstructures on PDMS elastomer is (a) reaction injection molding, (b) ultraviolet lithography, and (c) photolithography. We focus on hot embossing as it is one of the simplest, most cost-effective, and time-saving methods for replicating structures for thermoplasts. Addition curing silicones are shown to possess the ability to capture and retain an imprint made on it, 10–15 min after the gel point at room temperature. This property is exploited in the hot embossing technology.
Statistical methods are playing an important role in the design and analysis of engineering experiments. One such method called Taguchi method is found to provide sufficient information to optimize a process with the use of minimum number of experiments. This article presents systematic application of Taguchi method for optimizing the process parameters of compression moulding process. The response under consideration is flexural modulus. The study includes the use of recycled polyethylene terephthalate reinforced with fly ash cenospheres. The use of these recycled materials is promising to reduce the cost of the engineering parts and help nature by increasing waste utilization. A model for flexural modulus is designed and verified through experiments. The outcome from analysis of variance brings out the facts that moulding pressure, moulding temperature and weight fraction of cenospheres are the three most significant parameters of flexural modulus, contributing 59.44, 21.45 and 7.75%, respectively. The optimum set values for these parameters are found to be 5 MPa, 50°C and 15%. The proposed quadratic model for flexural modulus proves to be well in agreement with the experimental results.
Monomeric compounds that protect against ultraviolet (UV) exposure, e.g. 2-hydroxy-4-acryloyloxybenzophenone (HABP), 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate (BTEM), and 4-acryloyloxy-1,2,2,6,6-pentamethylpiperidine (APMP), were used as UV stabilizers for unsaturated polyester-based bulk molding compounds (BMCs). HABP and APMP were synthesized by reacting acryloyl chloride with 2,4-dihydro-xybenzophenone and 1,2,2,6,6-pentamethyl-4-piperidinol, respectively. The molded BMC samples were obtained using actual formulations containing these UV stabilizers, and the UV stability of the samples was estimated using a color difference meter. The results showed that HABP and BTEM afforded good protection against UV light, and these compounds showed a synergistic effect. APMP also showed a synergistic effect, but only when a small amount of the compound was used. These results were compared with the results obtained when copolymers of HABP and BTEM were used as UV stabilizers. The results showed that the polymerizable UV stabilizers demonstrated better protection against UV exposure, when they were added directly to the formulation of BMC, compared to the addition of copolymers as UV stabilizers.
Two polyurethane model compounds obtained from 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) or MDI and trisilanol isooctyl polyhedral oligomeric silsesquioxane (POSS) were synthesized and characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Moreover, polymerization kinetics of the samples obtained from an isocyanate-terminated prepolymer and BDO containing 0, 0.23, 0.57, 1.14 and 2.28 wt% of POSS were studied from oscillatory rheometry and differential scanning calorimetry. A higher thermal stability was observed for MDI + POSS when compared with MDI + BDO compound. The addition of 1.14 and 2.28 wt% of POSS increased the activation energy of polymerization. The polymerization mechanisms observed were nucleation and growth (A2) at the beginning of synthesis and diffusion controlled (Dn) at the last stage of conversion.
Extensive experimental studies on silica agglomerate breakup during compounding with polymer melts of various viscosities and polarities in a modular corotating twin-screw extruder were conducted. To avoid a subjectivity of the result, due to small size particles involved, silica agglomerates were characterized by measuring their mass average values. Increasing the screw speed, melt viscosity, and silica concentration were found to increase the silica agglomerate breakup. The effect of these parameters on agglomerate breakup was ranked as follows: silica concentration > polymer viscosity screw revolutions per minute (rpm). A good correlation between silica agglomerate breakage and power input was also found. Based on the experimental data and dispersion process, a composite modular kinetic model for evaluating silica agglomerate breakup during compounding in a corotating twin-screw extruder was tested. The kinetic constants of breakup and reagglomeration of silica agglomerates were calculated based on the stresses applied to the agglomerates and their cohesive strength. These constants for silica agglomerates were found to be not significantly different at high concentrations. The latter was in contrast to experimental data from available literature on compounding of calcium carbonate with polypropylene where the high reagglomeration kinetic constants of calcium carbonate in comparison with those of breakup played a major role in the agglomerate breakup. Comparison of the experimental and calculated results on the silica agglomerate size evolution during compounding with polymer melts indicated a reasonable agreement between them at high rotational speeds.
Sodium-montmorillonite (Mont-0) was partially/completely cation exchanged with appropriate amounts of cetyltrimethylammonium bromide to yield amphiphilic montmorillonites bearing different ratios of both hydrophilic and lipophilic segments. The lipophilicity/hydrophilicity range extended progressively up to the highly hydrophobic form (Mont-100), where all of the sodium cation content was replaced by the cetyltrimethylammonium cation. The produced amphiphilic forms can be arranged in the order of Mont-0 > Mont-25 > Mont-50 > Mont-75 > Mont-100, according to the decrease in hydrophilicity. Subsequently, the different montmorillonites were employed as reinforcing agents for acrylonitrile-butadiene rubber/styrene-butadiene rubber (50/50) rubber blend, which is known to be physically incompatible. We found from our previous reports that the mechanical properties of blends comprising a fixed loading of each montmorillonite form (20 phr) displayed remarkable improvements up to different levels indicating different compatibility influences between the rubber components by the inserted clays. In the current report, these results are intensively studied using dynamic mechanical thermal analysis and complemented by differential scanning calorimetry. Additionally, the network characteristics of the vulcanized rubber networks were determined for the neat blends (in absence of any clay) as well as for reinforced blends with different clay forms. Based on the obtained data, it could be concluded that the montmorillonite forms can bind both phases of the blend through interfacial interactions at the boundaries between the blend components but with different potentials. This effect was associated in the mean time by the hindrance of phase separation thus enhancing the compatibility. These findings were further supported using scanning electron microscopy, which confirmed that the compatibilization effect may have been achieved through lowering of the interfacial tension between the components.
A new type of synthesis route for the preparation of conducting chelating polymer composites (CCPCs) based on waste polystyrene grafted with acrylic (AA) and maleic (MA) acids in the presence of montmorillonite clay was investigated. The prepared composites were characterized using various techniques including Fourier-transform infrared spectroscopy, thermogravimetric analysis, light microscopy and x-ray diffraction analysis. The prepared composites of different AA and MA weight percentage (wt%) have been used as adsorbents for removal of toxic copper ions from their aqueous solutions. The copper uptake by the CCPC grafted with AA was found to be much higher than that of the CCPCs grafted with MA. The key parameters that can affect copper ion uptake such as time and pH were also investigated, and it was found that the increase in pH highly enhanced the copper uptake. The study was further extended to measure the alternating current (AC) conductivities of the prepared composites and their copper complexes which proved that the AC conductivities of the copper-free composites are higher than the AC conductivities of the composites complexed with copper ions.
Halloysite nanotubes (HNTs) have been used as a new type of filler for acrylonitrile–butadiene rubber (NBR) matrix. The NBR/HNT nanocomposites were prepared using a two-roll mill by adding 0–7 parts per hundred rubber (phr) HNTs, and the effect of the loading of HNTs on the curing behavior, mechanical, and microstructural properties were also investigated in this study. The cure characteristics showed that the cure time (t90) and scorch time (ts2) decreased, whereas the maximum torque (MH) exhibited an increasing trend from 0 to 7 phr. The tensile properties improved until optimum loading of HNTs (5 phr) and thermal stability increased with increasing HNT loading. The morphological study revealed the HNTs homogeneously dispersed inside the NBR matrix and good interaction occurred between HNTs and NBR.
Ethylene–propylene–diene monomer (EPDM) rubber/samarium borate (SmBO3)/polyolefin and EPDM/antimony-doped tin oxide (ATO)/polyolefin composites are aged at 150°C for different intervals. The addition of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) can delay the decrease in elongation at the break of EPDM/filler composites in the first 7 days of ageing. Moreover, the risen branch content of polyolefin can cause more crystals melt during ageing. It is found that acidic ATO particles would promote the formation of oxidative products during ageing. The substitution of SmBO3 by acidic ATO can boost the decrease amplitude of elongation at break of EPDM/filler/LDPE, EPDM/filler/LLDPE and EPDM/filler/HDPE in the first 7 days of ageing. The color change is correlated well with the variation in carbonyl index. The crystallinity is mainly influenced by the chemical cross-link points during ageing. The tendency of tensile strength is well consistent with that of swelling ratios, and the electric properties are correlated with increased polar groups and crystallinity.
Polymer blends of polypyrrole (PPy)-conducting particles dispersed in poly(ethylene-co-vinyl acetate) (EVA) matrix were prepared. The dielectric properties were determined, and we have examined how these properties depend on the relative concentration of the conducting (PPy) and dielectric (EVA) blends. The dielectric constant increases appreciably by increasing the PPy contents in the blend matrix. A previous proposed model by Tsangaris et al, for the calculation of effective dielectric constant, was tested and approaches the experimental values more closely for low PPy contents.
Histogram analyses of atomic force microscopy (AFM) phase images demonstrated changes in the surface composition of ethylene propylene diene–modified (EPDM) elastomeric formulations containing polybutadiene after exposure to hydrazine. It was determined by Fourier-transform infrared (FT-IR) spectroscopic analysis that the change in the surface composition is caused by hydrogenation of the vinylic double bonds of the polybutadiene coagent, stemming from diimide generation from hydrazine. The diffusion and subsequent reaction of hydrazine with two cured EPDM elastomeric formulations were investigated by mapping FT-IR spectroscopy. The depth of diffusion and reaction was determined by monitoring changes in the intensity of the vinyl group signal from the polybutadiene in the FT-IR spectra. The FT-IR analysis of horizontal microtome specimens and vertical ‘cross section’ of the EPDM samples showed that hydrazine diffused less than 200 μm into the elastomeric materials over a period of 40 weeks. Sequential proton nuclear magnetic resonance spectroscopy of the polybutadiene coagent showed that the vinyl groups in polybutadiene were hydrogenated when mixed with hydrazine at room temperature. The reaction of hydrazine with the polybutadiene coagent of the EPDM elastomeric material was corroborated by matrix-assisted laser desorption/ionization time of flight mass spectrometry as well. A model compound, 4-vinyl cyclohexene, was used to assess the relative hydrogenation rate of primary and secondary double bonds using gas chromatography/mass spectrometry.
This article presents an investigation about the polymer-modified bitumens (PMBs) containing styrene–butadiene–styrene (SBS) block copolymers with different structures, linear (SBS-L) and radial (SBS-R), semicrystalline copolymer ethylene–vinyl acetate (EVA), and terpolymer ethylene–butyl acrylate–glycidyl methacrylate, Elvaloy AM and Elvaloy 4170. The aim of the study was to establish the influence of the polymer type and content on the properties of PMBs for engineering applications and to evaluate the effectiveness of polymer modifiers. The results indicated that the polymer modification improved the rheological properties of bitumen, increased critical temperature, that is better resistance to permanent deformation was achieved as well as a wider temperature range in service. The degree of improvement generally increased with the polymer content but varied with the polymer type.
An experimental study was conducted to investigate the influence of ageing on the morphological, thermal and mechanical properties of virgin and two types of recycled (from technological and postconsumer wastes) modified polyolefin blends. Immiscible blends of virgin low-density polyethylene (LDPE) and polypropylene (PP) in weight ratio 1:1 were modified with the ethylene–propylene diene monomer (EPDM) rubber impact modifier. The efficiency of modification was investigated as a function of modifier content in the range from 7 to 15 wt%. The blends were prepared by extrusion using a corotating twin screw extruder Brabender DSE35/17D at melt temperature in the range from 150 to 200°C and a screw speed of 20 rpm. Compression-molded samples were subjected to natural and accelerated ageing and characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mechanical testing.
The experiments show that the ageing process deteriorates the mechanical properties of the PP/LDPE blends, and this is more clearly expressed in the blends of virgin material. The results show that the presence of the EPDM modifier delays the process of ageing in PP/LDPE blends. The DSC and SEM investigations confirm the structural changes in the examined compositions.
Natural rubber was reinforced with stearic acid-modified soy protein particles prepared using a microfluidizing and ball milling process. Longer ball milling time tends to increase the tensile strength of the rubber composites. Elastic modulus of the composites increased with the increasing filler concentration. The loss modulus and loss tangent indicated an increase in the amount of polymer immobilized by the modified soy protein. The extent of stearic acid modification affected the mechanical properties of the rubber composites. Compared with the unmodified soy protein, the microfluidized and stearic acid-modified soy protein filler improved the mechanical properties of the rubber composites.
A crystal silica was intermingled with an elastic ethylene-vinyl acetate polymer to fabricate an encapsulant and improve its thermal conductivity. The encapsulant showed not only an improved thermal conductivity and adhesiveness but also good thermal stability and tenacity. Its thermal conductivity with various sizes, dosage, and surface properties of silica (SiO2) was investigated using laser scattering method. The tenacity and adhesion properties were evaluated using dynamic viscoelasticity and peel strength, respectively. The integrated properties of the encapsulant were obtained while SiO2 reached to 80 wt portions in composite. Thermal conductivity of the composite was less dependent on the surface properties of SiO2.
Fly ash (FA) can be used as a filler in rubber vulcanizates to get rid off their waste. Polymer composite based on chlorinated styrene butadiene rubber (CSBR)/containing varying amount of FA composites has been developed by melt compounding followed by dicumyl peroxide vulcanization. The influence of increased loading of FA on the cure characteristics, mechanical properties, thermal stability, flame and oil resistance has been investigated. The increase in FA loading in CSBR matrices has been found to accelerate the curing process up to 37% compared to unfilled sample. The uniform distribution of FA in CSBR has been confirmed by scanning electron microscopy, which also explained the improved mechanical properties, flame and oil resistance of the composites. The diffusion rate of aromatic hydrocarbon solvents through the composite film is minimum for composites with 30 phr of filler and the rate is increased with increasing the filler content. Activation parameters are estimated and the molecular mass is calculated using Flory–Rehner theory. The sorption data are used to estimate the enthalpy, entropy and free energy of mixing. Mechanical properties such as tensile strength, modulus and hardness of the samples decreased after immersion in ASTM oil and the decreasing trend is lower for 30 phr FA-filled samples.
Poly(lactic acid) (PLA) and biodegradable elastomer were melt blended and molded in an injection molding machine. The crystallinity, viscoelasticity, thermal and mechanical properties of the molded blend and annealed blend samples were studied. Differential scanning calorimetry was used to evaluate the crystallinity and thermal property of all the samples. It was found that the melting temperature decreased as the amount of elastomer increased. Additionally, the presence of elastomer tended to increase the crystallinity of PLA at 10 and 20 wt%. The injection molding led to the diminishing of neat PLA crystallinity to be 20.79%; however, annealing could recover it to be 29.94%. This result was supported by x-ray diffraction and dynamic mechanical analysis tests. The complex viscosity and storage modulus of PLA melt decreased upon addition of elastomer. The elongation at break increased as the content of elastomer increased. However, the Young’s modulus and tensile strength decreased severely due to the addition of elastomer.
In this work, we report a melt blend of poly(lactic acid)(PLA)/epoxidized natural rubber (ENR) with liquid natural rubber (LNR). The LNR was synthesized by a photochemical degradation technique and used as a compatibilizer in the PLA/rubber binary blending systems. The PLA/ENR/LNR blends were melt-blended in a Haake internal mixer at 180°C and mixing speed of 50 r. min-1 for 15 min. It was found that the addition of LNR compatibilizer has improved the tensile strength and elongation at break for the compositions of the 40PLA/55ENR/5LNR blend system when compared with a noncompatibilized system (40PLA/55ENR/5NR). The elongation at break for the blend with 5% LNR compatibilizer showed a twofold increment compared with the blend without LNR. The increase in tensile strength and elongation at break were associated with the ability of LNR to promote the uniform dispersion between the natural rubber (NR) and PLA phases as observed in the scanning electron microscopic analysis. Moreover, the differential scanning calorimetric results indicated that the 40PLA/55ENR/5LNR showed the highest degree of crystallinity and thus contributed to improve their mechanical properties. Thermogravimetric analysis showed that two degradation transitions for both compatibilized and noncompatibilized blend systems due to higher degradation temperatures of ENR50 and NR parts. Fourier transform infrared spectroscopic analysis revealed that the PLA/ENR/NR and PLA/ENR/LNR blends were not miscible.
The overall objective of this study was to fabricate and characterize the properties of nanocrystalline cellulose/thermoplastic starch (TPS)-based nanocomposites. For the isolation of cellulose nanocrystals (CNCs) from cotton, it is subjected to alkaline treatment followed by acid hydrolysis. Then these CNCs were dispersed in TPS using a Fluko high-shear mixer in varying proportions, and the films were casted out of these nanocomposites using solvent casting technique. The CNCs were analyzed by transmission electron microscopy (TEM), wide-angle x-ray diffraction (WAXD) and Fourier transform infrared spectroscopy. TEM images of cellulose crystals extracted from cotton linters confirmed its nanodimensions with a size of 20–50 nm. WAXD results showed 2 peaks at 14.8°, 16.7° and 22.5° characteristic of the cellulose type-I crystalline structure. The films were analyzed by WAXD, scanning electron microscopy, thermogravimetric analysis (TGA) and moisture barrier properties. There was an increase in the thermal stability with increase in the cellulose crystals percentage as depicted by the TGA. The water vapor diffusivity decreased from 7.73 x 10-5 to 2.04 x 10-6 mm2 s-1. The improvements in these properties may be attributed to the good interaction between CNC filler and TPS matrix because of similar polysaccharide structures of cellulose and starch.
The aim of this article was to fabricate virgin polyvinyl chloride, polyethylene terephthalate, and low-density polyethylene blended with their corresponding recycled material in different ratios of virgin/recycled via injection molding and to evaluate their tensile strength, impact fracture, and hardness behavior. Raman spectroscopy was used to qualitatively study the characteristics of the recycled material in comparison with the virgin material. The impact testing method was the Charpy impact test, and for the hardness measurement, the shore D hardness method was used. The tensile tests were performed following the ATSM 683 standard. Scanning electron microscopy was used for chemical analysis and imaging to confirm the presence of contaminants.
Conducting plastics emerge as a new area of providing a cost effective and unique alternative material for applications ranging from consumer electronics to optoelectronics, solar cells, lighting, memory and a host of new photonic applications. In this work, an attempt has been made to produce conducting elastomeric thin films pertinent to optoelectronic applications. A thermoplastic elastomer, styrene butadiene rubber, is doped with suitable dopants by chemical-doping method. The spectroscopic analysis reveals the formation of conjugated sequences, which is responsible for high intrinsic conductivity in polymeric materials. The polystyrene segment of the elastomer seems to affect the doping rate and the length of the conjugated sequences formed. In this study, the electrical conductivity is found to increase from 10-13 S cm-1 to 10-1 S cm-1 upon doping, and the conduction mechanisms involved are also proposed.
Nanocomposites consisting of polyamide 6 (PA6) matrix with epoxidized natural rubber 50 (ENR-50) and organoclay-modified montmorillonite was prepared by melt blending in a twin-screw extruder followed by injection molding. The influence of varying amounts (0–30 phr) of ENR-50 loadings on ENR-50-toughened PA6 nanocomposites was examined. Morphological characterizations and mechanical and thermal properties of the blend and nanocomposites were investigated. Addition of ENR-50 resulted in a decrease in the tensile strength and modulus, while impact strength enhanced until a maximum at 10 wt% ENR-50. Thermal study revealed no significant change in the thermal properties with ENR-50 loadings. Exfoliated structure was observed using the x-ray diffraction patterns and was confirmed by transmission electron microscopic images. Scanning electron microscopic images revealed dispersed ENR-50 particles and increased rubber particles size with increasing ENR-50 loadings.
Segmented polyether–urethane/organically modified montmorillonite (O-MMT) nanocomposites were synthesized with poly(tetramethylene glycol) (PTMG), 4,4'-diphenylmethane diisocyanate (MDI), butane diol (BD), and a commercially available clay Cloisite-30B® (O-MMT). The state of dispersion of the clay crystals in the thermoplastic polyurethane elastomer (TPU) matrix was studied by X-ray diffraction and transmission electron microscopy (TEM). The phase-separated morphology of the TPU was revealed by high-resolution TEM (HRTEM) and atomic force microscopy (AFM). O-MMT caused a marginal increase in the glass transition temperature of the soft segments of the TPU and this increase is proportional to the amount of O-MMT in the nanocomposites. Differential scanning calorimetry (DSC) was employed to study the effect of O-MMT on the extent of phase separation in the TPU in these nanocomposites. Thermogravimetric analysis (TGA) results indicate a substantial improvement in the thermal stability of TPU by the addition of O-MMT. Tensile strength and elastic modulus are dramatically decreased by the incorporation of O-MMT into TPU, which is due to the hindrance of the phase-separation process by the exfoliated clay-layered crystals.
Styrene–butadiene rubber (SBR) was reinforced with silica (SiO2) by co-coagulating process. This study investigated the SiO2 amount, stirring time and pH value affecting the SiO2 content, curing characteristics and mechanical properties of SBR. Results showed that SiO2 content and reinforcing behavior were greatly influenced by the amount of SiO2 and pH value. The torque, tensile strength and elongation at break were optimal when the mass fraction of SiO2 was 21.5 wt%, stirring time was 6 h and pH value was 6.57. The utilized efficiency of SiO2 decreased with the increasing amount of SiO2 but increased with the increasing stirring time. The optimum cure time decreased with the increasing amount of SiO2. Both tensile strength and elongation at break decreased with the increasing pH value. Scanning electron microscopy observations showed that the SiO2 nanoparticles were distributed evenly in the SBR.
Blend nanocomposites of high-impact polystyrene and ethylene–vinyl acetate at a ratio of 3:1, with the addition of aluminum hydroxide Al(OH)3 and diphenyl 2-ethylhexyl phosphate (DPO) as fire retardants (FRs) and silica (SiO2) nanofiller were prepared by extrusion. Thermal decomposition, mechanism and kinetics of degradation of the studied samples were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The fire-retarded samples were characterized by following the degradation kinetics obtained from TGA data by recording the samples at four different heating rates. That enables us to determine one of the kinetic parameters, activation energy (Ea) of thermal decomposition. The effect of high concentration of FRs on morphology and properties of the studied samples were analyzed by scanning electron microscopy and mechanical properties. The obtained results show that the FRs delay thermal decomposition, particularly in combination with SiO2 nanofiller, which significantly contributes to slowing down the degradation process.
The effect of epoxidation and surface modification by acrylamide grafting on backing-required properties of peroxide prevulcanized natural rubber (PPNR)-based films was investigated. Backing-required properties including oxygen transmission rate (OTR), water vapor transmission rate (WVTR) and Young’s modulus were determined. In situ epoxidation of natural rubber (NR) latex was carried out using hydrogen peroxide/formic acid system. Both NR and epoxidized natural rubber (ENR) latexes were prevulcanized by tert-butyl hydroperoxide/fructose system before film casting. In the case of surface modification, acrylamide was grafted on PPNR surface by dipping the PPNR strip treated with O2 plasma into an aqueous solution of acrylamide monomer (AAm). Epoxidation showed more pronounced effect on the backing-required properties than surface grafting. As mole percentage epoxide increased, OTR decreased by 22–35%, whereas WVTR and Young’s modulus increased by 116–170% and 56–138%, respectively, depending on mole percentage epoxide. In the case of surface grafting, it was found that all OTR, WVTR and Young’s modulus were slightly higher than those of unmodified films.
The mechanical and thermal properties of polypropylene (PP)/ethylene octene copolymer (EOC)/wollastonite composites were investigated as a function of their composition in comparison to PP/EOC blends and native PP. PP was melt mixed with two loadings of EOC (20 and 30% (w/w)); and for the composites, each of these were mixed with three loadings of wollastonite (10, 20 and 30 parts by weight per hundred of the PP/EOC resin) on a twin-screw extruder and then injection molded. Both PP/EOC blends provided a higher elongation at break and impact strength but a lower tensile strength and modulus, storage modulus and flexural strength and modulus when compared with those of the neat PP. The addition of ultrafine wollastonite (particle size of 1200 mesh) into the blends increased the tensile modulus, storage modulus, flexural strength and modulus and impact strength in a dose-dependent manner. Thus, the combined use of EOC and wollastonite can provide balanced mechanical properties to PP. Moreover, thermogravimetric analysis showed that although the degradation temperatures of the composites were not improved, the char formation was remarkably increased with increasing wollastonite loadings.
The loop tack, shear and peel strength of cross-linked epoxidized natural rubber (ENR 50)-based adhesive were investigated. Coumarone–indene resin and toluene were used as the tackifier and solvent, respectively, throughout the study. Benzoyl peroxide was used to cross-link the ENR 50 adhesive at 80°C for 30 min. The dosage of benzoyl peroxide was varied from 1 to 5 parts per hundred parts of rubber (phr). The adhesive was coated on the polyethylene terephthalate substrate at various coating thickness using a SHEEN hand coater. Loop tack, shear and peel strength were determined by a Llyod adhesion tester operating at 30 cm min-1. The result shows that loop tack and peel strength of the ENR 50 adhesives indicate a maximum value at 2 phr of benzoyl peroxide dosage. This observation is attributed to the effect of optimum cross-linking of rubber chains that enhances the cohesive strength of the adhesive system. However, shear strength increases with increasing dosage of benzoyl peroxide, an observation that is associated with the steady increase in the cohesive strength resulting from increasing cross-linking of rubber chains. In all cases, the adhesion properties increase with increasing coating thickness.
Natural rubber latex waste was dried in an ambient temperature and was milled by a two-roll mill prior to blending with polystyrene (PS) for the purpose of recycling. These blends were prepared at different milled waste natural rubber latex (WNRL) and PS ratios, and the effect of PS content on the mechanical properties was investigated. As the PS content increased, the tensile strength and the Young’s modulus also increased, but the elongation at break decreased. The blend morphologies were observed using transmission electron microscope. A dynamically vulcanized natural rubber/PS blend and a natural rubber (NR)/PS blend were prepared and compared with WNRL/PS blend. WNRL/PS blend showed higher tensile strength and Young’s modulus compared with other blends.
Le Chatelier-Braun principle was modified for calculating the rate of free energy production [RFEP] in the flow of poly vinyl chloride (PVC) plastisol. At low-to-intermediate shear rate, viscosity decreases with increasing shear rate and reaches a minimum. The behavior was explained by the dominance of the rheological effect at the lower shear rates and that of the thermodynamic effect at the higher shear rates. In the former, viscous resistance was reduced by stress-induced phase separation into an immobilized layer and a mobile phase. In the latter the RFEP increases, reaching a maximum at the minimum viscosity. In the pseudo-plastic flow region, the flow is stable and the RFEP is negative. At shear rates higher than those at minimum viscosity, the immobilized layer dilates and then fractures when the stress becomes higher than the strength of the layer. Both dilatation and fracture are manifestations of flow instability and RFEP is positive, indicating insufficient resistance against failure of the immobilized layer. At super high shear rates, a plug flow takes place with a very thin layer of plasticizer lubricating at the capillary wall. Pseudo-plastic behavior may be explained by two different mechanisms. One is that a very small amount of particles are present in the lubricating layer. The particles are expelled from the layer with the increase in shear rate. The other possibility is that even though the lubricating layer consists of pure plasticizer, the layer increases in thickness in order to avoid excessive secondary flow such as eddy formation.
A biochar made from woody waste feedstock with low-ash content was blended with carbon black (CB) as filler for styrene–butadiene rubber. At 10% total filler concentration (w/w), composites made from 25% or 50% biochar showed improved tensile strength, elongation, and toughness compared with similar composites filled with CB. This demonstrates the potential to use renewable biochar as a partial substitute for CB in flexible, low-filler rubber composite applications.
The thermophysical properties of interior insulation in cars can depend strongly on mechanical compression of the insulation. No data exists presently on such dependence for this insulation. The main aim of this work was to measure the thermal conductivity and specific heat of different car interior parts (seat cushion, back cushion and leather–foam cover) in a temperature range of -20°C to +60°C and at four different compression values of 0%, 20%, 40% and 60%. Due to complicated mechanisms of material’s structure deformation under compression, theoretical predictions of these dependencies are very complicated. Therefore, experimental results have both scientific and practical interest.
Biodegradable sago starch/polyvinyl alcohol (PVA) films were developed using various percentage of silica. The effect of silica as filler on the mechanical properties, water resistance and degradation behaviour were investigated. Results showed that the 2.0 wt% of silica content in sago starch/PVA films exhibit higher tensile strength but lower elongation at break than films without additional silica. Water absorption and water vapour transmission were decreased with the addition of silica content. Biodegradability test revealed that the increment of silica content reduces the degradation process of sago starch/PVA films.
A series of aromatic polyimide–phosphoric anhydride composite membranes loaded with fumed silica (FS) nanoparticles were prepared from polyamic acid (PAA). First, the influence of the percentage loading of phosphoric anhydride (PA) on the proton conductivity of polyimide (PI) membranes was studied. The PA-PI film containing 45% of PA showed proton conductivity of 1.31 x 10-4 S/cm at 80°C, whereas the conductivity of neat PI films was 1.80 x 10-6 S/cm at room temperature. Next, the effects of the FS nanoparticles on the proton conductivity, the mechanical and thermal properties of the formulated PA-PI membranes were studied. Forty-five percent of the PA-PI membrane loaded with 1% FS (45% PA-PI/1% FS) showed an enhanced conductivity of 2.78 x 10-4 S/cm at 80°C when compared to the neat 45% PA-PI membrane. The tensile strength of the 45% PA-PI/1% FS nanocomposite membrane was comparable to the Nafion proton conductive membranes. The thermal analysis of 45% PA-PI/1% FS nanocomposite membranes showed that these membranes were thermally stable and suitable for high-temperature applications.
Natural oils have been used in the production of plastics for a long time. However, the number of studies dedicated to polyurethane research has shown an increase only recently. Usually, petrochemical components are used in polyurethane synthesis. Nowadays, there have been attempts made to replace polyols in polyurethanes with the modified oils and other natural raw materials. It is a promising and important scenario because the flexible segment of such polyurethanes can contain even up to 60 wt % of the novel ingredient. In the case of material evaluation for industry, one can additionally count on lowering the product price because natural oil is generally 2 to 3 times cheaper as compared to its synthetic equivalent. Oils most commonly used in industrial applications are soybean oil, palm oil, rapeseed oil, castor oil and tung oil. In this work the study results and the possibilities of applying natural oils in polyurethane synthesis are presented.
The damping properties of epoxidized natural rubber (ENR) are investigated by the dynamic mechanical analysis in this article. Time–temperature superposition of the isotherms give the change of the damping property with frequency of each cured ENR. Due to the existence of the intermolecular hydrogen bonds between ENR and phenolic resin, the cured ENR with phenolic resin as curing agent shows much broader effective damping (tan > 0.3) temperature and frequency range than that of using the other two curing agents, sulfur and peroxide curing systems, its effective damping temperature range reaches nearly 150°C and effective damping frequency range covers the range from 10-5 to 109 Hz. The influences of the phenolic resin types and contents on the damping property of ENR are also explored. The activation energies during the glass transition are calculated with the Arrhenius equation to demonstrate the change of the Tg of ENR cured by different phenolic resin contents.
The reclaiming of elastomer residues is one of the main problems of recycling materials. In this work, the efficiency of devulcanization of recycled ethylene propylene diene terpolymer (EPDM) was determined by subjecting the elastomer samples to 2, 3 and 4 min of microwaves exposure. Scanning electron microscopy and thermogravimetric analysis using different heating rates to determine the kinetic degradation parameters according to the Flynn–Wall–Ozawa and Criado methods were studied. The results obtained showed that up to 4 min devulcanization exposure period, the degradation temperature of EPDM did not exceed. Microwaves exposure caused modifications in the morphology and reduction in activation energy values upon increased samples exposure period. Degradation mechanisms were altered, mainly for the 4-min exposure period, where the nucleation mechanism shifts to diffusion, suggesting that the microwave method was able to promote the breakage of the elastomeric three-dimensional network.
The montmorillonite (MMT), Mont-0, was treated with different levels of appropriate corresponding amounts of cetyltrimethylammonium bromide to yield a variety of biphasic MMTs exhibiting different hydrophilic–lipophilic balance ranging gradually up to the highly hydrophobic form (Mont-100), which was proved using Fourier transform infrared spectra as well as x-ray diffraction, thus the produced forms can be arranged in the following order according to the decrease in hydrophilicity: Mont-0 > Mont-25 > Mont-50 > Mont-75 > Mont-100. In a following step, the obtained MMTs were attempted for use as reinforcing fillers that may exhibit in the mean time a compatibilizing effect, for acrylonitrile–butadiene rubber (NBR)/styrene–butadiene rubber (SBR) (50/50) rubber blend, which is known to be physically incompatible. The mechanical performance of the blends comprising different loadings of MMT forms demonstrated advancement in most of the cases accompanied by acceleration in rheometric characteristics indicating enhancement by different extents in compatibility between the phases. The results were explained on the light of the potential of these MMT forms to bind both phases of the blend through hydrophobic–hydrophobic interactions with the nonpolar part (SBR) and polar–polar interactions with the polar part (NBR) of the blend, which diminishes the molecular mobility of the macromolecular chains thus preventing progress in phase separation. These findings were additionally proved using scanning electron microscopy and XRD that confirmed a dependent contribution of both phases in interfacial interactions with the biphasic fillers as a function of the hydrophobization level.
Polybutadiene and hydroxyl terminated polybutadiene (HTPB) were epoxidized using in situ-generated dimethyl dioxirane (DMD) as an oxidant in the presence of nano-TiO2 at 25°C. Reaction time and different percentages of catalyst/Oxone® (w/w) were also examined. The capability of different kinds of double bonds to be epoxidized was studied in detail at various reaction times, and the products were characterized using nuclear magnetic resonance (1HNMR), 13CNMR, and Fourier transform infrared (FT-IR) techniques, with no side reaction being detected. The results indicate that using nano-TiO2 as a catalyst increases the epoxidation yield, especially of cis double bonds.
This work demonstrates the poly(ethylene terephthalate) (PET) washing process, which is the very important step in the overall PET recycling procedure. The samples of waste PET bottles were washed in sodium hydroxide at two different temperatures, that is, at 70 and 75°C, at a time intervals of 15 and 30 min. The cleaning efficiency of the washing processes was determined through the identification of the residual impurities and products of PET degradation. The samples before and after the washing procedure were characterized by gas chromatography/mass spectrometry (GC/MS), gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Due to low obtained oligomer molecular masses, it can be concluded that the degradation during all washing processes is not strong. Results show good purity of washed PET, especially at 75°C, due to very low content of adhesives, toxic compounds and formed monomers. The washing process carried out at 75°C for 15 min can be considered as the most successful. It results with low polymer degradation and the removal of the high quantity of contaminants in short time interval.
Superabsorbent hydrogels, polystyrene-graft-polyacrylic acid (PAA; PS-g-PAA), linear low-density polyethylene (LLDPE)-graft-PAA (LLDPE-g-PAA), and hydrogel composites, PS-g-PAA/bentonite (BT), were synthesized through emulsion polymerization using acrylic acid as a monomer, benzoyl peroxide as an oil-soluble initiator, and ammonium persulfate and sodium sulfite as a redox initiator in the presence of N,N-methylenebisacrylamide as a cross-linking agent. The superabsorbents were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The maximum water absorbencies for PS-g-PAA and PS-g-PAA/BT were 780 and 900 g g-1 in distilled water, respectively, while the water absorbency of LLDPE-g-PAA superabsorbent was 450 g g-1 in distilled water.
In this study, the influence of hybrid combination of fillers (carbon black in concentrations from 0 to 100 phr and conducting nickel (Ni) or cobalt particles in concentration 10 phr on the dielectric (dielectric permittivity and dielectric loss angle tangent)) and microwave (reflection coefficient, attenuation coefficient, and shielding effectiveness) properties of chloroprene rubber composites has been investigated in the wide frequency range (1–12 GHz). The results achieved showed that the hybrid combination of Ni powder and active furnace carbon black gives an opportunity of considerable increase in the dielectric permittivity and also a possibility for its adjustment varying carbon black content. The comparison in the behavior of prepared composites can be explained by the differences in some characteristics of two metals and influence of these differences on the real and imaginary parts of the complex dielectric permittivity and magnetic permeability.
This study evaluates the properties of the inter-cross-linked network of polyurethanes end-capped with multiacrylates groups and gum arabic blends obtained by a solution-mixing technique. The polyurethane acrylates have been synthesized from polytetramethylene ether glycol and 1,6-hexane diisocyanate with pentaerythritol triacrylate as the capping agent. Gum arabic 1%, 3%, 5% and 10% (by weight) was incorporated into the polyurethane acrylates matrix. The physical, thermal, morphological and mechanical properties of the blends were investigated. Data obtained from mechanical studies indicated that the introduction of gum arabic (until 5%) into the cross-linked polyurethane acrylates matrix improved the breaking strain values. The addition of gum arabic in the polyurethane acrylates network matrix induced a decrease in the water contact angle and in the water–polymer blend surface tension. The atomic force microscopy micrographs of the surfaces of cross-linked polyurethane acrylates–gum arabic blend matrix show the presence of a heterogeneous morphology, and its average roughness increases at high content of gum arabic. Thus, polyurethane acrylates–gum arabic blends can be used to produce composite materials with increased content of natural raw materials and improved hydrophilic–hydrophobic properties for various applications.
In this study, the effect of nanoclay and carbon black on the curing system of styrene-butadiene rubber (SBR)/butadiene rubber (BR) and natural rubber (NR)/BR blends were investigated. The dispersion of nanoclay and carbon black in blends was studied under the x-ray diffraction and scanning electron microscopy. Intercalated microstructure of SBR/BR blends is more stable than NR/BR blends. The presence of carbon black did not affect the dispersion state of nanoclay in NR/BR nanocomposites. By increasing the amount of nanoclay from 0 to 9 phr, the scorch time, optimum cure time, and difference between maximum and minimum torque were reduced in both the blends.
The effect of partial replacement of carbon black (CB) with halloysite nanotubes (HNTs) on the properties of natural rubber nanocomposites was investigated. Total hybrid fillers were kept constant at 40 parts per hundred rubber (phr) and were prepared using laboratory two-roll mill. Longer scorch and cure times were observed with the addition of more HNTs. The results also showed a decrement in tensile strength and tensile moduli besides causing an increment in swelling percentage. However, positive results were shown during elongation at break and fatigue life which indicates possible usefulness of HNTs in dynamic application of rubber products. Comparable thermal stability of nanocomposites with variable CB/HNTs ratios was shown in thermogravimetric analysis data.
The current work deals with the use of organic disulfides and organic mercaptanes as efficient reclaiming agents for ground tire powder (GTP). The efficiency of the reclaiming agents is investigated using different analytical tools. Determination of the number average of chain length and the iodine values. The degree of devulcaniztion of the reclaimed GTP gives distinct view for the reclaiming process. The highest performance for the current reclaiming conditions is found to be at 100°C, for 20 minutes using internal mixer plasticorder (Barabender). The tensile strength, of the compounded reclaimed GTP, confirms the performance of the reclaiming agent.
The influence of different talc contents on the thermal and mechanical properties of thermoplastic polyurethane/polypropylene (TPU/PP) blends was investigated. The compatibility and crystallinity of TPU/PP and TPU/PP/T blends were determined by differential scanning calorimetry (DSC). The DSC results indicated that the addition of PP in TPU/PP blends increased glass transition temperature (Tg), melting temperature (Tm) and crystallinity (c). The addition of talc has decreased Tm and c and increased Tg and crystallization temperature (Tc). The effect of talc content on Tg, Tm and c was insignificant, while Tc content increased. The Tg of nonfilled and talc-filled blends increased suggesting that the TPU and PP are partially compatible. Thermogravimetric analysis (TGA) showed improved thermal stability of all investigated nonfilled and talc-filled TPU/PP blends in the nitrogen atmosphere. In the air atmosphere only talc-filled TPU/PP 80/20 blends show a higher thermal stability, while thermal stability decreased for TPU/PP 50/50 and increased insignificantly for TPU/PP 20/80 blends. DSC and TGA results showed improved thermal properties of talc-filled TPU/PP blends when compared with nonfilled blends. The mechanical properties of talc-filled TPU/PP 50/50 and 20/80 blends improved in terms of tensile strength and Young’s modulus, while elongation of break decreased with the addition of talc and as the talc content increased.
The effects of electron beam irradiation dose (50–150 kGy) and the concentration of montmorillonite (MMT) clay (3–10 parts per hundred part of rubber (phr)) on the properties of acrylonitrile butadiene rubber (NBR) have been investigated. The dispersion of the layered silicates was assessed by x-ray diffraction and transmission electron microscopy. The morphology of NBR nanocomposites showed exfoliated clay layers at low clay content and a combination of exfoliated and intercalated clay layers at high clay content. The mechanical properties of NBR composites such as tensile strength (TS) and tear strength were remarkably improved by the incorporation of organoclay and electron beam irradiation, while elongation at break (Eb) was decreased. The increase in the TS of NBR nanocomposites increases with the increase in the clay content up to 10 phr, whereas the optimum gel content and TS of NBR composites were observed at 50 kGy irradiation dose. Thermogravimetric analysis studies showed that NBR/organo-MMT nanocomposites have higher decomposition temperatures in comparison with the NBR/Na+-MMT at 50 kGy irradiation dose.