This article describes and evaluates the basic properties and the damp heat (85%RH, 85℃) aging behaviour of a 400 µm thick titanium dioxide filled polyoxymethylene film for potential use as backsheet in photovoltaic (PV) modules. The polyoxymethylene monolayer was characterized using analytical methods and technological tests. The stabilizer package contained Tinuvin 234, Tinuvin 770 and Irganox 245. The less than 1 wt% pigmentation resulted in 0.680 solar optical reflectance. The slightly anisotropic mechanical properties elastic modulus and strength were within the requirements for backsheets. Damp heat exposure triggered degradation, stabilizer loss and lead to optical properties degrading (yellowing). However, neither premature embrittlement nor a critical loss of ultimate mechanical properties was found after 5005 h of aging. Hence, polyoxymethylene was classified as a potential candidate for backsheet core layers.
In this work, polystyrene microspheres (PSMS) and PSMS-based polymer nanocomposites have been prepared. PSMS were first synthesized by dispersion polymerization of styrene monomer. The microsphere-coated-multi-walled carbon nanotube (PSMS/MWCNT) nanocomposite was prepared by incorporating MWCNT into PSMS matrix. Aniline monomer was then introduced by means of in situ oxidative polymerization (PANI) route to PSMS, MWCNT, and PSMS/MWCNT. Fourier transform infrared spectroscopy depicted the composite formation of PANI and MWCNT with PSMS matrix. PANI polymer was successfully polymerized in PSMS matrix and on carbon nanotube walls. According to scanning electron microscopy, all nanocomposites exhibited core-shell morphology. Glass transition temperature (Tg) of PSMS/PANI, PANI/MWCNT, and PSMS/PANI/MWCNT were found as 245℃, 287℃, and 289℃, while maximum decomposition temperature (Tmax) was 387℃, 575℃, and 580℃, respectively. Tetrahydrofuran was shown to be a suitable solvent for dispersing the nanocomposite. Toluene can also be used as suitable solvent for these nanocomposites. X-ray diffraction analysis depicted amorphous form of PSMS; however, PANI and MWCNT reduced the amorphous nature of the microspheres. PANI/MWCNT showed the highest crystallinity among all nanocomposites. Moreover, PSMS/PANI/MWCNT nanocomposite revealed electromagnetic interference shielding effectiveness of ~23.2 dB.
This paper focuses on wrinkle development in decorative film laminates during heating operations with the goal to understand their driving factors and develop strategies to overcome such defects. The study looked at temperature and heating rate effects on the wrinkling behavior of a commercial black-out film laminated onto a metal substrate. The 135℃ threshold temperature identified for our film under which no wrinkles formed, related to the stiffness of its different construction layers. Heating rate was also noted by this study to be an important parameter in wrinkling; values between 1℃ and 350℃/min were tested. It was possible to exceed the threshold temperature stated above without wrinkling when the heating rate was sufficiently low (closer to 1℃/min, though less than 50℃/min was often sufficient depending on the final temperature). The heating rate effect is believed to be related to the time-dependent viscoelastic response of the compliant layer in relation to building thermal stresses.
Polypropylene/multiwall carbon nanotube composites with 1, 9, 81, and 729 layers were prepared with a novel microlayer extrusion technology. The influences of multiwall carbon nanotube dispersion and orientation on crystallization behavior, mechanical properties, and thermal stability of composites were investigated. The results indicated that homogeneous dispersion and improved multiwall carbon nanotube orientation in matrix were obtained with more layers. The tensile strength, Young’s modulus, and elongation at break of polypropylene/multiwall carbon nanotube composites with 729 layers increased by 77%, 78%, and 149%, respectively, compared with 1 layer composites. The 81 and 729 layer samples displayed obvious double yielding points on the stress–strain curves. Furthermore, thermogravimetric analysis showed that the composites with more layers exhibited better thermal stability than the 1 layer composites. These results suggest that multiwall carbon nanotube dispersion and orientation in a matrix can be effectively improved through microlayer extrusion.
The packaging of a lithium polymer secondary battery involves a wrapping process of an aluminum/polymer laminate film that uses heat sealing. Heat sealing time and sealing block width are important variables in creating packaging requirements for optimal battery performance and safety. In this study, a heat transfer analysis is performed using finite element method to investigate the temperature distribution of the sealing block over the course of the heat sealing process. Heat sealing time and sealing block width were the variables of interest for the heat transfer simulation in order to identify optimal manufacturing conditions. Through the analysis, we successfully identified a minimum heat sealing time less than 3 s and 1.5 mm width of the sealing block that optimizes both the rate of battery production and lithium polymer battery capacity. To validate the quality of heat sealing properties, visual inspection and restrained packaging tests were performed.
The process dynamics of single-screw extrusion on mixtures of polypropylene (PP) and recycled PP were studied using a statistical, design of experiments (DoE) approach. For a conventional screw design, the barrel temperature, screw speed and two vastly different melt viscosity polypropylene mixtures were selected as the independent factors, whilst melt pressure, mass output, screw torque and temperature rise at the die due to shear heating were the dependent responses. A central composite design (CCD) in the framework of response surface methodology (RSM) was constructed, and an analysis of variance (ANOVA) was carried out to determine the significance of the response surface models. The resulting statistical and response surface predictions have demonstrated that the low viscosity component concentration in the blend is a dominating factor on melt pressure and screw torque, apart from the expected effect of screw speed on output. Viscous heating is affected only by screw speed and recycled polypropylene concentration. Furthermore, the predictions have identified a wider process operating window with increased low-viscosity component concentration. The data confirm that statistical tools make quantitative predictions for the effects of experimental process variables, in accordance with the expected qualitative trends towards process optimisation, providing scope towards its application in scaled-up industrial processes.
We present a theoretical analysis of calendering of Ellis fluid based on lubrication approximation. The equations governing the flow are nondimensionalized and solved to get closed form expressions of velocity and pressure gradient. Runge–Kutta algorithm is employed to compute the pressure distribution. The operating variables which are used in the calendering process, i.e. roll-separating force, power input to the rolls and exiting sheet thickness are calculated. The influence of the material parameters on the velocity profile, pressure gradient, pressure distribution and operating variables is shown graphically and discussed in detail.
In this study, a new diacid monomer containing amide, imide, and sulfone functional groups was successfully used to synthesize a new poly(ether-amide) for membrane-based gas separation applications. The synthesized poly(ether-amide) was soluble in organic solvents, has high thermal stability (up to 460℃ under nitrogen atmosphere, for 10% weight loss), and high glass transition temperature (Tg = 274℃). This poly(ether-amide) was combined with different amounts of surface-modified zinc oxide nanoparticles to provide organic–inorganic nanocomposites. The optically transparent and flexible membranes of these hybrid nanocomposites were prepared. The obtained materials were characterized by Fourier transform-infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, field emission-scanning electron microscopy, and transmission electron microscopy techniques. Transmission electron microscopy of the nanocomposite film with 15 wt% zinc oxide confirms that the nanoparticles are well dispersed in the polymer matrix. Thermal gravimetric analysis data indicated that the hybrid materials had better thermal behavior with increasing surface-modified zinc oxide nanoparticles nanoparticle content. The poly(ether-amide)/surface-modified zinc oxide nanoparticles nanocomposite film mechanical properties improved with increasing surface-modified zinc oxide nanoparticles content. The permeability and selectivity of the poly(ether-amide)/zinc oxide membranes as a function of the surface-modified zinc oxide nanoparticles weight percentage were studied, and the results indicated that the CO2 and CH4 permeability increased with increasing zinc oxide content. In general, the membranes prepared from these polymers showed very good permeability and permselectivity for a pair of gases.
This paper presents the exact solution for calendering a third-order fluid under lubrication approximation. The solution obtained is valid for all values of the third-order fluid parameter. This exact solution is compared to the perturbation solution. The results show that the perturbation solution is valid for very small values of the third-order fluid parameter. Therefore, no significant deviation from the corresponding results of the Newtonian fluid is observed with the perturbation solution. The interesting quantities for mechanically designing a calendering system such as the force separating the two rolls and total power input into both rolls are calculated and shown graphically for large third-order fluid parameter. The material’s rheological features modify the pressure, flow characteristics, and all other operating variables significantly. In fact, the nip region pressure increases with increasing third-order fluid parameter. The exiting sheet thickness, power input, and roll separating force also increase with increasing third-order fluid parameter.
The antimicrobial activity of films made of poly(
This article is concerned with the effect of the individual viscoelastic relaxation modes of a polymer melt on its behavior in polymer melt extrusion film casting process. We compare the predicted versus experimentally obtained film necking or neck-in profile as a function of draw ratio. The predicted necking profile was obtained using well-established one-dimensional isothermal flow kinematics and consisted of using two different phenomenological constitutive equations, upper convected Maxwell and Phan-Thien–Tanner, with a discrete spectrum of relaxation times. The numerical simulations, containing the two different phenomenological constitutive equations, provided an insight into the effect of the slow and the fast relaxing modes on the stresses, strains, and strain/extensional rates that develop in the molten polymer film as it is stretched from the die exit to the chill-roll. The slow relaxing modes follow trends that are directly proportional to strain (similar to Hookean solids), whereas the fast relaxing modes follow trends that are directly proportional to the stretch rate (in accordance with Newton’s law of viscosity). Comparing the numerical predictions with the experiments showed that predictions using the upper convected Maxwell constitutive equation best described the long-chain branched polymers (like low-density polyethylene, which shows extensional strain hardening) in the extrusion film casting process. On the other hand, predictions using the Phan-Thien–Tanner constitutive equation best described the linear polymers (like linear low-density polyethylene, which does not show noticeable extensional strain hardening) in the extrusion film casting process.
We synthesized graphene oxide (GO) using a modified Hummer’s method, and then blended it into polyvinyl chloride (PVC) and amino-functional PVC (PVC-4ABA) matrices. GO was added to 0.5 g PVC at 0.01, 0.05, 0.1 and 0.5 g. The PVC/GO matrix was modified using 4-aminobenzoic acid (4ABA) at 0.01, 0.05, 0.1 and 0.5 g per 0.5 g PVC. This gave four amino-functional PVC/GO series and one PVC/GO series nanocomposite membranes that were prepared by a solution blending route. The filler and the modifier (4ABA) content effect on the PVC membrane properties were investigated. Fourier transform infrared spectroscopy confirmed the GO functional groups and PVC modification with 4ABA. According to scanning electron microscopy, a unique two-way layered structure was observed for modified PVC and GO composites. XRD explained the conformation of PVC/GO and modified PVC/GO nanocomposites. GO crystallite size and its interlayer distance between sheets were also studied. The XRD peak at 2 = 10.8° with interlayer spacing of 0.81 nm was calculated with the Bragg equation. GO particle size was calculated (Scherrer formula) as 7.78 nm. XRD results revealed fine interaction between modified PVC and GO compared with unmodified PVC composites. Glass transition temperature (Tg) of non-modified PVC/GO nanocomposite was 202℃, whereas modified nanocomposite with similar GO loading had Tg equal to 212℃. Higher filler content gave better hydrophilic membranes as determined by solvent content, porosity, and shrinkage ratio. PVC-4ABA-0.5/GO 0.5 membrane with a low contact angle (25°) is a fine option for water purification. The overall results suggest that the higher modifier concentrations developed better interaction between the nanofiller and PVC.
Multi-layer flexible PVC films used in this study were produced via the micro-layer co-extrusion technology and the influences of micro-layer co-extrusion technology on plasticizer migration of flexible PVC were investigated. It was shown that the morphology of PVC molecule chains changed from the coiled state into the linear ordered state. The linear alignment is more compact with evenly dispersed additives in the PVC matrix after micro-layer co-extrusion. The volatility stability, solvent extraction stability, exudation stability, and film tensile strength were tested. The results indicated that, films made by micro-layer co-extrusion technology showed excellent plasticizer migration stability and mechanical properties, due to the ordered PVC molecule chains and the even additive dispersion.
In this study, films from polyethylene and coated calcium carbonate blends were generated and the effects of calcium carbonate type, calcium carbonate loading and stretching temperature were investigated for roughness, morphology, crystallinity, pore size distribution, water pressure resistance and water vapor permeability of the films. The results showed that both breathability and waterproofness properties were only achieved with calcium carbonate possessing small particles (CC2 type) at both 25 and 50℃. Stretching at 80℃ led to ruptures in the films independent of calcium carbonate and loading amount employed. Increasing the calcium carbonate level provided better breathability performance without affecting the waterproofness considerably.
The aim of this work was to fabricate the nanocomposite films based on poly(vinyl alcohol) and investigate their thermal stability, mechanical and optical properties of nanocomposite films. For this purpose, first, the titanium dioxide nanoparticles surface was modified simultaneously with biocompatible citric acid and vitamin C to prevent their agglomeration in the poly(vinyl alcohol)matrix. Afterward, the modified titanium dioxide nanoparticles were embedded into the poly(vinyl alcohol)matrix via solution casting along with ultrasonic method. The prepared nanocomposite films were characterized by different analyses such as Fourier transform infrared, X-ray diffraction and thermal gravimetric analysis. Fourier transform infrared emphasized the presence of citric acid and vitamin C on the titanium dioxide surface as well as their interaction with nanoparticles. Poly(vinyl alcohol) nanocomposites thermal degradation temperature increased by 100℃, tensile strength 300% and E-modulus 200%.
This paper presents a dual-scale model, which couples the macroscopic flow field of the film-casting process and the microscopic crystallization behavior of the material. In this dual-scale model, the finite difference method is used to calculate the macroscopic flow field variables such as temperature, extensional rate, and draw tension, while the Monte Carlo method is employed to predict the evolution of the crystallinity and the development of the crystal morphology. The effect of draw ratio during film-casting on the morphology of isotactic polypropylene crystallization is investigated both experimentally and numerically. Based on the fairly good agreement between the experimental results and simulation predictions, we conclude that the dual-scale modeling and simulation presented in this paper can well predict the film-casting process and give users more detailed insight into the flow field and morphological evolution.
Shape memory polyurethanes are synthetic materials with great potential to respond to external stimulus. Desired properties of shape memory polyurethanes can be achieved by blending with other polymers or varying the hard and soft segments. In this study, structure, morphology, mechanical, thermal and electrical conductivity properties of a shape memory blend reinforced with multi-walled carbon nanotube were investigated. One blend component was polyethylene glycol and toluene diisocyanate polyurethane, and the second component was either polystyrene or nitro-functional or amino-functional. The fundamental chemical and physical linkages were confirmed by Fourier transform infrared spectroscopy. Field emission scanning electron microscopic images demonstrated the generation of polyurethane–polystyrene interpenetrating polymer network over multi-walled carbon nanotube surface. The tensile strength and modulus were found to increase systematically with increasing filler content in all series and was higher for polyurethane/polystyrene amino-functional/multi-walled carbon nanotube composites. The stress-bearing capacity and mechanical properties were enhanced due to a matrix made up of two different chemically interlinked polymers. On the whole, using amino-functional polystyrene showed better physical and shape memory properties. Electrical conductivity was superior for composites with polystyrene amino-functional matrix, compared with neat blend and other composite. The polyurethane/polystyrene amino-functional/multi-walled carbon nanotube 0.5 electrical conductivity tested at 1.08 S cm–1. The polyurethane/polystyrene amino-functional/multi-walled carbon nanotube composites showed remarkable thermally triggered shape memory behavior to the extent of 95%. Electric field-triggered shape recovery of the polyurethane/polystyrene amino-functional/multi-walled carbon nanotube sample was found to be 96%. The synergetic effect of the fine electrical conductivity and high mechanical strength renders the composites as high-performance shape memory materials.
In this paper, synthesis and characterization of polymer intercalated carbon nanotube buckypaper for improved structural, morphological, electrical, and thermal properties have been discussed. Resin-infiltration technique was opted for the preparation of polyvinylchloride intercalated poly(ethylene glycol) -modified-multi-walled carbon nanotube buckypaper. The effect of increasing purified nanotube (purified multi-walled carbon nanotube) and functional nanotube (functional multi-walled carbon nanotube) content on the properties of BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube and BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube buckypaper composites was investigated, while using same amount of polymer. Results indicated better interaction between polyvinylchloride and functional multi-walled carbon nanotube due to hydrogen bonding relative to polyvinylchloride and purified multi-walled carbon nanotube where no chemical link was present between the two. Fourier transform infrared spectroscopy results confirmed the modification of functional multi-walled carbon nanotube, and formation of buckypaper composite. Scanning electron microscopy micrographs showed better network formation in BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube samples and intercalation of polymer can be seen forming polymer-coated functional multi-walled carbon nanotube network. Thermal stability was found to be improved by the increment of multi-walled carbon nanotube and the difference between the thermal stability of functional multi-walled carbon nanotube and purified multi-walled carbon nanotube buckypaper was also prominent. The maximum degradation temperature (Tmax) of functional composite BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 (469℃) was higher relative to non-functional BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube 0.05 (461℃). The glass transition temperature of BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 was found as 249℃, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 depicted higher Tg of 271℃. Amorphous character of polymer/carbon nanotube -buckypaper composite showed a trend towards crystallinity according to X-ray diffraction results. Purified multi-walled carbon nanotube-based buckypaper presented conductivity up to 1.91 x 10–1 S cm–1, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.01–0.08 had increased conductivity up to 9.88 x 10–1 S cm–1.
Carbon nanotubes (CNTs) have long been recognized as the stiffest and strongest man-made material known to date. Owing to high electrical conductivity, CNTs have also gained interest in the area of electrical appliances and communication related applications. Moreover, carbon nanofibers (CNFs) depict fine electrical and mechanical profile. Due to their miniscule size, excellent mechanical, electrical, and thermal properties, CNTs can only be beneficial if they are homogeneously dispersed and embedded into light-weight engineering polymer matrices. Adding small amounts of CNTs strongly improve the electrical, thermal, and mechanical properties of the composites. In order to enhance their chemical affinity to polymer matrices, chemically modifying the graphitic sidewalls and tips is necessary. This article reviews the processing technology and improvement of various properties of carbon nanotube-reinforced thermoplastic polyurethane (PU) composites. Initially, the structure, morphology, mechanical, thermal, and electrical properties of nanotubes are described. Then various strategies for fabricating PU/CNTs composites and their properties are discussed. To conclude, recent developments in the field of mechanical, thermal, and electrical properties of thermoplastic PU reinforced with nanotubes and nanofibers are reviewed. A brief account regarding the toxicity and environmental safety aspects of carbon nanomaterials is also included in this article.
The high-density polyethylene microporous membrane was prepared based on melt-stretching mechanism and the influence of annealing time on the structure and properties of initial annealed film and final microporous membrane was investigated using scanning electron microscopy, differential scanning calorimetry, and capillary flow porometer. It was found that compared with that without annealing, the main melting peak after annealing for 3 h moved to higher temperature. The corresponding lamellar thickness and elastic recovery values were increased by 13.7 and 30.6%, respectively. The porosity and air permeability property of final microporous membrane were increased by 48.0 and 42.9%, respectively. With increasing the annealing time from 3 to 4 h, the lamellar thickness was decreased from 21.0 to 20.6 nm and the corresponding porosity showed a little decrease from 64.1 to 63.6%. With increasing annealing time, more chains in the amorphous regions were induced to crystallize, resulting in higher lamellar thickness and uniform lamellae distribution. The higher the grown crystalline part was, the higher the pores induced during stretching were, resulting in better air permeability property. Therefore, annealing the polyethylene cast film under 125℃ for 3 h is sufficient to obtain final microporous membrane with better properties.
A facile route has been opted to synthesize carbon nanotubes/polyazopyridine/nanodiamonds nanocomposites. In-situ oxidative polymerization of conducting monomer in presence of nanodiamonds (functional nanodiamonds and non-functional nanodiamonds) and carbon nanotubes (functional carbon nanotubes and non-functional carbon nanotubes) resulted in nanocomposites. The physical characteristics of resulting nanocomposites were studied using various techniques such as Fourier transform infra-red spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction spectroscopy. Field emission scanning electron microscopy examination revealed the polymer fibrillars formed network structure with ordered arrangement of nanodiamonds. Fourier transform infra-red spectroscopy confirmed the structure of carbon nanotubes/polyazopyridine/nanodiamonds nanocomposite. Functional carbon nanotubes/polyazopyridine/functional nanodiamonds showed higher 10% degradation temperature (T10) 489℃ and glass transition temperature 229℃ relative to non-functional carbon nanotubes/nanodiamonds having T10 482℃ and glass transition temperature 221℃. Measured electrical conductivity (4.5 S cm–1) of functional carbon nanotubes/polyazopyridine/functional nanodiamonds nanocomposite was also remarkably improved by the incorporation of functional nanodiamonds relative to non-functional carbon nanotubes/polyazopyridine/non-functional nanodiamonds (3.9 S cm–1).
In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.
In this study, we have reported poly(benzimidazole-amide) containing flexible moieties such as ether, fluoro, and siloxane. The poly(benzimidazole-amide) synthesis was carried out by the condensation of 4-(3,4-diaminophenoxy)benzene-1,2-diamine, bis(carboxypropyl)-tetramethyldisiloxane, and 2,2-bis(4-aminophenyl)hexafluoropropane in the presence of polyphosphoric acid at 160℃. Afterwards, poly(benzimidazole-amide) was blended with sulfonated polystyrene and 0.1–2 wt.% titania nanoparticles-grafted-multi-walled carbon nanotubes for the formation of hybrid proton exchange membranes for fuel cell (poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes) for fuel cell. Inclusion of titania modified multi-walled carbon nanotubes influenced the membrane performance by modifying the microstructure, mechanical properties, as well as water retention and proton conductivity properties of proton exchange membranes (PEM). The hybrid membranes were doped with phosphoric acid before subjecting to various characterizations. Field emission scanning electron microscopic study depicted typical blend morphology in which titania nanoparticles-grafted-multi-walled carbon nanotubes were partially embedded in the matrix and seemed to be pulled out of the matrix surface during fracturing. The phase separated structure was accountable for the water retention and higher proton conductivity. The tensile stress and modulus of acid doped poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes nanocomposites increased from 65.1 to 72.5 MPa and 9.5 to 15.2 GPa, respectively, with the increasing titania nanoparticles-grafted-multi-walled carbon nanotubes loading (0.1–2 wt.%). The glass transition temperature of phosphoric acid doped poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes 0.1–2 membranes increased from 227 to 236 C. They also had higher ion exchange capacity of 2.5–3.7 mmol/g and proton conductivity of 2.3–3.1 S/cm at 80℃ (higher than perfluorinated Nafion®117 membrane 1.1 x 10–1S/cm). A H2/O2 fuel cell using poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes 2 (ion exchange capacity 3.7 mmol/g) showed better performance than that of Nafion® 117 at 40℃ and 30% relative humidity.
Liquid–liquid phase separation of polyethylene/ethylene vinyl acetate copolymer binary blends was investigated employing rheometry, mechanical experiments, optical, and electron microscopy as well as thermal analysis. The observed phase diagram has shown that the studied polyethylene/ethylene vinyl acetate blends possess upper critical solution temperature behavior, i.e. phase separation of two components occurs in the molten state before polyethylene crystallization begins. Moreover, the interfacial interaction of phases was found to be dependent on the blend composition, and it varies considerably by the occurrence of phase inversion. In the solid state, however, the miscibility of phases is controlled by the melt temperature and cooling rate of final process. In addition, it was confirmed that imposing restrictions on phase separation leads to a noticeable improvement in the toughness of blends.
Biopolymer films have been prepared by continuous aqueous tape casting, using dextran–water solutions. The effect of dextran concentration and solution temperature on the flow behavior was studied by steady and dynamic rheological measurements. Rheological measurements revealed that increasing dextran concentration strongly increased viscosity, while increasing temperature reduced the viscosity marginally, limiting the film processing techniques to tape casting. Elastic effects were also seen in the biopolymer rheology studies, and no changes in the fluid internal microstructure were detected in the rheological measurements. The effect of casting speeds on the biopolymer film thickness was experimentally determined and compared with a pseudoplastic fluid model. Mechanical properties of the biopolymer films presented an isotropic behavior. Adding sorbitol as an external plasticizer produced more elastic films but induced an anisotropic response on the elongation at break.
We have first prepared non-woven, nanofibrous membranes from nano-diamond (ND) particles and multi-walled carbon nanotube-filled poly(azo-pyridine) by electro-spinning. Then, these membranes were used to obtain epoxy composites reinforced with them. Friedel-Crafts acylation and in situ polymerization were adopted to graft polyamide on multi-walled carbon nanotube (MWCNT) surface to form MWCNT-PA using -Phenyl--caprolactone. For the preparation of nanofiber, poly(azo-pyridine) (AP) was also synthesized in this work. MWCNT-PA was then electrospun with new AP and ND to yield two types of nanofibers, i.e. MWCNT/AP/PA and ND/MWCNT/AP/PA. Afterward, bisphenol A diglycidyl ether (DGEBA) matrix was reinforced with electrospun nanofiber to form two types of nanocomposites, with and with out ND. Scanning and transmission electron microscopy revealed non-woven nanofibrous membranes of MWCNT/AP/PA/DGEBA and ND/MWCNT/AP/PA/DGEBA. Compared with MWCNT/AP/PA/DGEBA 3 (3 wt.% MWCNT/AP/PA nanofibers) in DGEBA (323.6 MPa), the tensile strength for ND/MWCNT/AP/PA/DGEBA film reinforced with 3 wt.% ND/MWCNT/AP/PA nanofiber (359.4 MPa) was found to increase. Thermal stability of ND/MWCNT/AP/PA nanofiber reinforced epoxy was higher with T10 537–552°C and Tg 297–302°C relative to MWCNT/AP/PA/DGEBA system. Inclusion of ND in the system also increased the electrical conductivity of nanofiber web ND/MWCNT/AP/PA/DGEBA composites from 3.8 to 6.2 S cm–1.
Functional and non-functional graphite-based polymer nanocomposites have been fabricated via layer by layer polymerization. Functionalization of graphite was achieved by the oxidation of natural graphite, in which widening of the gap between graphite layers occurred facilitating the monomers to polymerize into the graphite galleries. Fourier transform infrared results confirmed the deposition of layered polymers on graphite. The elemental analysis by energy dispersive X-ray spectroscopy also revealed the composite structure. The morphology of resulting nanocomposites was studied by scanning electron microscopy. Non-functional graphite-based nanocomposites showed rough surface topology while in case of functional graphite-based nanocomposites, deposition of polymers on graphite sheets was observed. The presence of graphite nanosheets in multi-layered nanocomposites was confirmed by the appearance of X-ray diffraction peak at 2 = 26.75°. Thermogravimetric analysis of multi-layered nanocomposites functional graphite/polypyrole/polyethylene glycol/poly(styrene-co-maleic anhydride)cumene terminated/4,4'-methylenedianilin (F-G/PPy/PEG/PSMA/MDA) showed higher degradation temperature for 10% weight loss at 475°C compared with non-functional graphite/polypyrole/polyethylene glycol/poly(styrene-co-maleic anhydride)cumene terminated/4,4'-methylenedianilin (NF-G/PPy/PEG/PSMA/MDA) at 453°C. The electrical conductivity of the fabricated nanocomposite F-G/PPy/PEG/PSMA/MDA was increased with functional filler up to 14.4 S cm–1.
In this paper, the study of a non-Newtonian material when it is dragged through the narrow region between two co-rotating rolls is carried out. The conservation of mass and momentum equations based on lubrication theory are nondimensionalized and solved for the velocity and pressure fields using the perturbation technique. By considering the influence of the material parameter, the dimensionless leave-off distance in the calendering process is determined. The leave-off distance is expressed in terms of eigen value problem. Quantities of engineering interest like maximum pressure, the roll-separating force, and the power transmitted to the fluid by rolls are calculated. It is observed that the material parameter has great influence on detachment point, velocity, and pressure distribution, which are useful for the calendering process.
The polyvinylidene fluoride cast film was prepared with different melt-draw ratios by a cast extrusion process. The structure and properties of the prepared films were characterized by differential scanning calorimetry, X-ray diffraction, Fourier transform infrared and scanning electrical microscopy. The results showed that with increasing melt-draw ratio, the crystalline orientation increased and the crystalline morphology transformed from spherulites to parallel lamellae perpendicular to the extrusion direction. At the same time, necking behavior in the stress–strain curves disappeared and strain-hardening behavior became apparent. The lamellae thickness distribution became uniform. The polarized Fourier transform infrared results also indicated the existence of some β-phase for the samples with different melt-draw ratios.
A sulfonated polyamide (PA-S) was first synthesized through polycondensation of sulfonated 4,4'-oxydianiline and terephthaloyl chloride. The sulfonation of polystyrene (PS-S) was conducted using a mild sulfonating reagent (98% H2SO4). Two categories of mechanically robust and thermally stable nanocomposites, based on multi-walled carbon nanotube (MWCNT) and silica nanotube (SiNT), i.e. PS-S/PA-S/MWCNT and PS-S/PA-S/SiNT, were prepared by solution blending. Scanning electron micrographs showed good dispersion of filler and adhesion of matrix on the surface of nanotube. Accordingly, a symmetric membrane structure with dense porous top layer, porous sublayer, and fully developed micropores at the bottom were observed. The porous membrane structure was accountable for the excellent water retention capability, and so, higher proton conductivity of new hybrids. Increasing the amount of nanotube from 0.5 to 2 wt.% increased the ultimate tensile stress of functional PS-S/PA-S/MWCNT nanocomposites 51.8–62.2 MPa compared with non-functional filler (33.4 MPa) and PS-S/PA-S/SiNT. A rapport between nanotube loading and thermal stability of the materials was also observed as the glass transition in PS-S/PA-S/MWCNT nanocomposites increased from 202 to 206°C. MWCNT-based blend membranes had higher ion exchange capacity (IEC), around 2.99–3.42 mmol/g. Novel membranes with high IEC value achieved high proton conductivity of 1.28–2.23 S/cm in a wide range of humidity values at 80°C which was higher than that of perfluorinated Nafion®117 membrane (1.1 x 10–1 S/cm) at 80°C (94% relative humidity; RH) which was used as benchmark. Moreover, a H2/O2 fuel cell using the PS-S/PA-S/MWCNT (IEC 3.42 mmol/g) also showed better performance than that of Nafion®117 at 40°C and 30% RH.
This study describes a process technology to maintain or improve the gas barrier property of ethylene vinyl alcohol (EVOH) barrier films after flexing. EVOH and polyethylene-grafted maleic anhydride (PE-g-MA) multi- and microlayer samples with 5, 19, and 35 layers were produced in a coextrusion line. Flexing was performed using a Gelbo flex tester (400 flexes). After flexing, pin hole tests were performed on the film and only those with fewer than two pin holes were re-tested for oxygen transmission rate (OTR). Pin holes decreased after 400 Gelbo flexes as the number of layers increased. The OTR on these films demonstrated that thin EVOH barrier layers can improve film flex crack resistance. This proves that for a given barrier resin total thickness the flex barrier property can be increased dramatically by microlayering.
The oxygen permeation properties of polypropylene nanocomposites were examined to compare their oxygen-barrier performance as affected by temperature (25–50°C), relative humidity (0–50% RH), and nanoparticle contents. Polypropylene/clay, polypropylene/ZnO composites and polypropylene/clay/ZnO ternary nanocomposites were prepared with different compositions by melt compounding to determine the optimum amount of nanoparticles. The results showed that at low temperatures, the effect of both clay and ZnO nanoparticles on oxygen barrier properties of polypropylene was very low. The resulting PP nanocomposites showed increase in oxygen permeability as temperature increased, with an Arrhenius behavior, and activation energy of 43.9–44.7 kJ/mol. The differential scanning calorimetry results indicated that the addition of clay and ZnO nanoparticles in composites slightly decreased melting temperature (Tm) and crystallinity (Xc%). It was found that ternary nanocomposite prepared by incorporating 5 wt% of nanoclay and surface treated 1 wt% ZnO to polypropylene had the lowest gas permeability and its oxygen permeability was 24.5% lower than that of pristine polypropylene at 50°C.
Multilayer films of a conventional linear low-density poly(ethylene/α-octene) (LLDPE) and a metallocene linear low-density poly(ethylene/α-hexene) (mLLDPE) copolymers were produced by cast co-extrusion process. Coextruded films were obtained by varying the position and the relative thicknesses of the two polymers. Mechanical (tensile and impact) tests, permeability, haze and hot tack measurements were carried out on the produced films in order to verify the effect of layer composition and position on the performances of the coextruded samples. Thermal and atomic force microscopy characterizations of the three-layer structures were also performed to correlate the resulting morphology with the film properties. The experiments demonstrated that, at fixed composition, the structures having the mLLDPE copolymer as external layers exhibit generally better mechanical performances and a widening in the sealability temperature window due to a lowering of 5°C in the seal-initiation temperature, with only a small increase (max 3.5%) in the film haze percentages. The oxygen permeability values do not seem to be significantly affected by the structure composition and layout.
A high molecular weight (27 x 103 gmol–1) poly(azo-ether-imide) has been fabricated in this study. Well-aligned poly(azo-ether-imide) fibers and poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers-based nanocomposite were then produced by electrospinning via self-reinforcement. Transmission electron microscopy showed that the poly(azo-ether-imide)–multi-walled carbon nanotube electrospun nanofibers were uniform and almost free of defects. Scanning electron microscopy indicated the wrapping of matrix over the bundles of nanofibrs. The as prepared electrospun nanofibers were utilized as homogeneous reinforcement to enhance the tensile strength and toughness of films. The tensile strength and tensile modulus of poly(azo-ether-imide) film reinforced with 3 wt% poly(azo-ether-imide)–multi-walled carbon nanotube nanofibers were 18% and 23% higher as compared to those of the poly(azo-ether-imide) film reinforced with 3 wt% neat poly(azo-ether-imide) nanofibers. The significant enhancement in the overall mechanical properties of the poly(azo-ether-imide)–multi-walled carbon nanotube nanofibers reinforced polyimide films was ascribed to good compatibility between the electrospun nanofibers and the matrix as well as high nanofiber orientation in the matrix. The homogeneous alignment of poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers was also studied using scanning electron microscopy micrographs. Moreover, the thermal stability of poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers reinforced polyimide was superior having 10% gravimetric loss at around 602–617°C and glass transition temperature in the range of 241–263°C relative to the neat polymer and poly(azo-ether-imide) nanofiber-based system. This study demonstrated the fabrication of high performance and high toughness polyimide nanocomposites by using this facile self-reinforcement method.
Two grades of 5 mm thick polypropylene (PP) sheets, one having linear polymer chains (PP-TF-1) and the other having long-chain branches (PP-TF-2), were drape formed, using moulds of different parameters. Single-sided heating of sheet was found to be suitable only at lower depths of draw. Double-sided heating gave good part shape conformance at all depths of draw. PP-TF-2 was found to have lower crystallinity than PP-TF-1, suggesting that it would have a lower sagging tendency and would give parts with more uniform wall thickness distribution. This was confirmed in formability studies. At higher depths of draw, an increase in draft angle was found to give more uniform wall thickness distribution, maintaining reasonable values of wall thickness. At lower depths of draw, draft angle was found to have no influence on product quality. Irrespective of material characteristics and other mould parameters, only moulds with generous values of corner radii gave strong corners.
A computational model to design plastic food packaging is proposed. The model minimizes the cost of the multi-layer structure satisfying the specific product requirements, using a heuristic optimization algorithm. The product requirements are defined by the expected shelf life, the storage conditions, the water sorption isotherms of foods and the maximum allowable gain or loss of gases (O2, CO2, N2, etc.) and moisture for the packaged food. In order to assure the food shelf life, these product requirements should be fulfilled to estimate the maximum permeance values of the plastic package. The computational algorithm automatically generates different multi-layer film structures that satisfy the product requirements. This algorithm combines different polymeric materials taking into account the barrier properties and cost of each layer, the compatibility between layers, the maximum number of layers and the minimum and maximum film thickness for each layer. Temperature and relative humidity corrections for the permeance calculations are considered.
Permeance calculations of several barrier films are compared with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) measurements. The optimization model algorithm is evaluated by means of standard numerical routines and numerical benchmarking.
Rice husk and nanoclay (montmorillonite)-filled low-density polyethylene composite films were prepared by extrusion blown film. Maleic anhydride-modified polyethylene was used as compatibiliser in various concentrations ranging from 0 to 8 parts per hundred. X-ray difractograms showed an increase in interlayer spacing of montmorillonite from the use of compatibiliser when compared to the uncompatibilised composites; an increase of 20, 33, 36 and 38% for 2, 4, 6 and 8 parts per hundred, respectively, of maleic anhydride-modified polyethylene. With the incorporation of maleic anhydride-modified polyethylene, a better dispersion of the fillers was also achieved, as confirmed by scanning electron microscopy. The compatibilised composite films showed improved tensile and barrier properties. The addition of 4 parts per hundred of the compatibiliser resulted in an improvement by 22% in tensile strength. Furthermore, oxygen barrier property of the composite films improved more than twofold by adding 4 parts per hundred of maleic anhydride-modified polyethylene. This improvement in tensile and barrier properties is due to an increase in the interfacial adhesion between the fibre and matrix and better dispersion of impermeable nanoparticles.
Poly(azo-pyridyl-urethane)/multi-walled carbon nanotube (PAPU/MWCNT) nanocomposites were prepared by first synthesizing polyurethane followed by solution dispersing MWCNT in the matrix. We have used two different MWCNTs: the first set of MWCNT contained carboxylic acid group (MWCNT-COOH) and the second set contained acid chloride group (MWCNT-COCl). Afterward, these MWCNT particles were used in the preparation of PAPU/MWCNT nanocomposites. In the first set of nanocomposites, MWCNT-COOH and PAPU were just physically mixed and were designated as PAPU/MWCNT-A. In the second set of nanocomposites, PAPU chains were tethered onto the surfaces of MWCNT-COCl particles and designated as PAPU/MWCNT-AC. Two types of nanocomposites were thus fabricated, including acid functionalized nanotube-based non-tethered PAPU/MWCNT and acid chloride functionalized MWCNT-based tethered system. We have incorporated hydroxyl end-terminated polyurethane via "grafting to" approach to acid chloride functional MWCNT through esterification. Fourier transform infrared spectra confirmed that the matrix was covalently attached to sidewalls of nanotube. Various nanotube loading levels and surface-modified groups were considered to regulate mechanical, thermal and electrical performance of PAPU/MWCNT. The experimental results showed that a moderate loading level of 5 wt. % MWCNT produced the maximum tensile strength (63.1 MPa) in tethered nanocomposites, while the presence of surface carboxylation of MWCNT relatively decreased the tensile strength (49.7 MPa). Comparative studies based on scanning and transmission electron microscopy of the chemically bonded samples revealed unique nano-fibriller morphology. Dynamic mechanical analysis of nanocomposite films showed an increased segmental rigidity with Tg of 144–153°C in the tethered system relative to pristine PAPU (133°C). Addition of acid chloride functional MWCNT also contributed to an enhancement in the conductivity (2.9–4.7 S cm–1), relative to PAPU/carboxylated MWCNT (2.0–2.7 S cm–1).
In this article, three linear low-density polyethylenes having different molecular structures were selected and films were produced from them using a semi-industrial cast film extrusion line. Rheological and gel permeation chromatography measurements were performed on the resins to assess their molecular structure. Mechanical, physical and sealability properties of the films were evaluated and the results were discussed with regard to the molecular structure of the resins. It was found that molecular weight and distribution of short-chain branching (comonomer) on the backbone of polyethylene chains are the main factors that control sealability, flexural cracking and mechanical properties. Placement of comonomer on medium length chains generated crystals with expanded unit cell that show lower melting peak. Sealing was controlled by crystal size distribution, chain diffusion and entanglement formation at the interface. linear low-density polyethylenes with lower melting point and boarder molecular weight distribution showed lower seal and hot tack initiation temperatures. Polydispersity along with molecular weight contributes to toughness and puncture resistance. Flexural cracking resistance was observed to be related to crystallinity, tie chain density and more importantly to the amorphous phase fraction. The amorphous part could absorb flexing energy and hinders crack initiation and propagation. Seal through contamination (caulkability) was found to be related to flowability and elasticity of the melt.
In the current effort, heteroaromatic azo-polymer, poly(thiourea-azo-ether) was prepared using 4,4'-oxydiphenyl bis(thiourea) and diazonium salt solution of 2,6-diaminopyridine. Poly(thiourea-azo-ether) was then exploited as a matrix to synthesize new hybrid materials. Varying carbon nanotube content was melt blended with the azo-matrix. The effect of filler loading on processing and other thermo-physical properties of poly(thiourea-azo-ether)/multi-walled carbon nanotube was investigated. Homogeneous dispersion of multi-walled carbon nanotube in a polymer matrix plays a crucial role in the preparation of polymer composites based on interfacial interaction between multi-walled carbon nanotube and the polymer matrix. Field emission scanning electron microscopy micrographs revealed fine dispersal of filler and adhesion of matrix on the surface of nanotube. Accordingly, filler content from 1 to 5 wt.% increased the electrical conductivity from 2.3 to 4.8 S cm–1. Ultimate tensile strength of functional hybrids 37.39–41.23 MPa was improved relative to non-functional multi-walled carbon nanotube in matrix. Furthermore, the tensile modulus considerably increased from 9.9 to 13.3 GPa. A connection between filler loading and thermal stability of the materials was also observed. Ten percent gravimetric loss was increased from 592 to 599°C, while glass transition was enhanced from 201 to 221°C. The addition of small amount of functional multi-walled carbon nanotube strongly improved the electrical, thermal and mechanical properties of nanocomposites. The melt processing technology was so found outstanding for the improvement of the properties of multi-walled carbon nanotube-reinforced polymer nanocomposites.
The relationships between crystallization characteristics and heat sealing properties of high-density polyethylene (HDPE) films were determined. HDPE with a 1.1 g/10 min melt flow index (MFI) (190°C, 2.16 kg) was melt mixed in a twin-screw extruder with a 0.04 g/10 min MFI HDPE. The high molecular weight HDPE (HMW HDPE) concentration was varied between 1 and 20 wt%. The HDPE blends were cast into a 50 µm thick film. The films were heat sealed at 125°C and 128°C. The seal bar pressure was kept constant at 0.13 MPa. The heat seal time was varied from 0.5 to 2.0 s. Heat-sealed strength was measured by T-peel test. The molecular structure development during the heat seal process was evaluated by differential scanning calorimeter and wide-angle X-ray diffraction. The HMW HDPE decreased the film heat seal strength when sealed at 125°C. However, at 128°C the presence of up to 10 wt% reduced the heat sealing time.
Recent research has shown that the resistance against crack initiation and propagation of polyethylene blown films depends on density, chain branching and crystal orientation next to the processing parameters. To assess low-density polyethylene blown film fracture toughness with different thicknesses, the essential work of fracture method has been conducted in this study. The thickness of the investigated low-density polyethylene films was regulated by the draw down ratio, which causes low-density polyethylene crystal orientation with the chain axis parallel to the machine direction at higher draw down ratios, influencing mechanical parameters and the fracture toughness. The crystal orientation was measured by X-ray diffraction. Blown films with thicknesses equal to or greater than 200 µm exhibit no preferred orientation, which is consistent with various calculated mechanical and fracture mechanics parameters. Films of less than 200 µm thickness show preferred machine direction crystal orientation and a distinct thickness influence on mechanical and fracture mechanics parameters.
We report a comparative analysis of three-layered poly(ethylene terephthalate) films. The first set of three-layered films was prepared entirely from virgin poly(ethylene terephthalate). The second set of films was prepared from a recycled poly(ethylene terephthalate) core layer and virgin poly(ethylene terephthalate) skin layers. The resistance of the films to impact was tested using the free falling drop dart method. The selected strength properties of various thicknesses of these films were also tested. It was shown that the poly(ethylene terephthalate) film containing a layer of recycled polymer has properties similar to the film obtained from virgin polymer and can thus be successfully used in the manufacturing of packaging materials.
An aromatic azo-polymer, poly(thiourea-azo-naphthyl), has been synthesized using 1-(5-thiocarbamoylaminonaphthyl)thiourea and diazonium salt solution of 2,6-diaminopyridine. Poly(thiourea-azo-naphthyl) was easily processable using polar solvents and had high molar mass, 57 x 103 g/mol. Electrically conducting and mechanically and thermally stable polymer/multi-walled carbon nanotube nanocomposites were obtained via melt processing technique. Fine distribution of multi-walled carbon nanotubes in a polymer matrix played an essential role in the preparation of polymer/multi-walled carbon nanotube nanocomposites based on interfacial interaction between multi-walled carbon nanotubes and polymer matrix. Field emission-scanning electron microscopy images revealed good dispersion of filler and adhesion of matrix on the surface of multi-walled carbon nanotubes. Accordingly, increasing the amount of multi-walled carbon nanotubes from 1 to 5 wt% increased the electrical conductivity from 2.42 to 4.11 S cm–1. Percolation behavior of the composite was also studied. Tensile modulus for 1 wt% nanocomposite was 4.2 GPa, which increased up to 6.8 GPa on 5 wt% filler addition. A relationship between nanotube loading and thermal stability of the materials was also observed. Ten percent gravimetric loss increased from 502°C to 538°C in the presence of 1 wt% multi-walled carbon nanotube. Similarly, glass transition increased from 227°C to 245°C in the presence of 5 wt% multi-walled carbon nanotube. Enhancement of the physical properties of multi-walled carbon nanotube-reinforced polymer nanocomposites was accredited to the non-covalent interactions (– interactions and secondary bond forces).
In this paper, an analysis has been presented for the calendering process of incompressible magnetohydrodynamics Newtonian fluid. The lubrication approximation is used to simplify the equations of motion. Exact solutions for velocity profile, pressure gradient, flow rate per unit width, rate of strain, shear stress, maximum shear rate and shear stress at the roll surface are obtained. The value of , the distance from the nip to the point where the sheet leaves the rolls, is calculated using Newton–Cotes formula along with the regula-falsi method. Numerical results are presented for pressure distribution, power transmitted to the fluid by both rolls, force separating the two rolls using Newton–Cotes formula with regula-falsi method and Simpson’s rule for different values of magnetic parameter, M, and the corresponding values of . Some results are shown graphically. It is found that the magnetic field provides the controlling parameter to increase or decrease power transmission, separation force and distance between attachment and detachment points, which are useful for the calendaring process.