Effect of the preparation conditions on the permeation of ultrahigh‐molecular‐weight polyethylene/silicon dioxide hybrid membranes

Porous ultrahigh‐molecular‐weight polyethylene/SiO₂ membranes were prepared by thermally induced phase separation (TIPS) with white mineral oil as the diluent and SiO₂ as an additive. Influential factors, including extraction method, SiO₂ content, and cooling rate, were investigated. The results suggest that the both porosity and pure water flux of the membranes by extraction of the solvent naphtha in the tension state with alcohol were the best among our research. With increasing SiO₂ content, the porosity, pure water flux, and pore diameter increased. However, with excessive SiO₂ content, defects formed easily. Moreover, SiO₂ improved the pressure resistance of the membranes. The cooling rate directly effected the crystal structure. A slow cooling rate was good for crystal growth and the integration of the diluent. Therefore, the porosity, pure water flux, and bubble‐point pore diameter increased with decreasing cooling rate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of ultrahigh‐molecular‐weight polyethylene membranes via a thermally induced phase‐separation method

Porous, flat membranes of ultrahigh‐molecular‐weight polyethylene were prepared as thermally resistant and solvent‐resistant membranes by the thermally induced phase‐separation method. Diphenyl ether and decalin were chosen as the diluents. The phase diagrams were drawn with the cloud‐point temperatures and the crystallization temperatures. According to the phase diagrams, scanning electron microscopy images, and porosities of the samples, the influential factors, including the polymer concentration, cooling rate, and viscosity, were investigated. Porous ultrahigh‐molecular‐weight polyethylene membranes with thermal and solvent resistance could be prepared with suitable diluents and cooling rates by the thermally induced phase‐separation method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of polyethylene‐graft‐maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh‐molecular‐weight polyethylene/copper composites

Ultrahigh‐molecular‐weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X‐ray photoelectron spectroscopy. The incorporation of PE‐g‐MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE‐g‐MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh‐molecular‐weight‐polyethylene‐matrix composites with the PE‐g‐MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic‐particulate‐filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004     

Homogenization in supercritical carbon dioxide enhances the diffusion of vitamin E in ultrahigh‐molecular‐weight polyethylene

Vitamin E stabilization of radiation‐crosslinked ultrahigh‐molecular‐weight polyethylene (UHMWPE) joint implants was successfully introduced to improve long‐term oxidation resistance. Current clinically available vitamin E stabilized UHMWPE implants were prepared by the postirradiation diffusion of vitamin E into 100‐kGy‐irradiated UHMWPE by a two‐step process, which included doping in pure vitamin E at an elevated temperature below the melting point followed by an annealing step at an elevated temperature in inert gas to homogenize the antioxidant throughout components of desired thickness. We hypothesized that the diffusion of vitamin E could be enhanced with supercritical carbon dioxide (SC‐CO₂) during homogenization without an increase in the surface vitamin E concentration, which would thus result in faster homogenization. Our hypothesis tested positive; crosslinked UHMWPE doped with vitamin E at 120°C and homogenized in SC‐CO₂ at 10–12 MPa had a greater penetration of vitamin E than those homogenized in inert gas. We attributed the faster diffusion of vitamin E in irradiated UHMWPE in SC‐CO₂ to the dissolution of vitamin E in the supercritical fluid and a rate of diffusion that was closer to that of the supercritical fluid in the polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheology behavior of high‐density polyethylene/diluent blends and fabrication of hollow‐fiber membranes via thermally induced phase separation

The phase‐separation behavior of high‐density polyethylene (HDPE)/diluent blends was monitored with a torque variation method (TVM). The torque variation of the molten blends was recorded with a rheometer. It was verified that TVM is an efficient way to detect the thermal phase behavior of a polymer–diluent system. Subsequently, polyethylene hollow‐fiber membranes were fabricated from HDPE/dodecanol/soybean oil blends via thermally induced phase separation. Hollow‐fiber membranes with a dense outer surface of spherulites were observed. Furthermore, the effects of the spinning temperature, air‐gap distance, cold drawing, and HDPE content on the morphology and gas permeability of the resultant membranes were examined. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Gas permeability and permselectivity of plasma‐treated polyethylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatments on rubbery polyethylene (PE) membranes on the permeation behavior for carbon dioxide (CO₂), O₂, and N₂ were investigated with permeability measurements. The NH₃‐plasma and N₂‐plasma treatments on PE membranes increased both the permeation coefficient for CO₂ and the ideal separation factor for CO₂ with respect to N₂. For O₂ transport, both the permeation coefficient for O₂ and the ideal separation factor for O₂ with respect to N₂ were increased. NH₃‐plasma and N₂‐plasma treatments on polymer membranes possibly bring about an augmentation of permeability and permselectivity simultaneously. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 383–387, 2006     

Modeling the oxidative degradation of ultra‐high‐molecular‐weight polyethylene

Understanding the sequence of reactions that occur in ultra‐high‐molecular‐weight polyethylene (UHMWPE) following ⁶⁰Co γ irradiation has been the focus of numerous experimental studies. In the study reported here, we have incorporated recent experimental findings into a mathematical model for UHMWPE oxidation. Simulation results for shelf aging and accelerated aging are presented. It is shown that very reasonable simulations of shelf‐aging and accelerated‐aging data can be obtained. It is also shown that simulations of shelf aging in reduced oxygen environments predict that the subsurface peaks of ketones will be shifted to the exterior surface. In vivo aging can be simulated if we assume that the oxygen level in the synovial fluid is about one‐eighth that of atmospheric levels. Some reduced irradiation doses are predicted to significantly reduce the ketone formation for shelf‐aging periods of up to 10 years. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 814–826, 2003     

High‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blend. I. The processing,thermal, and mechanical properties

Various blend ratios of high‐density polyethylene (HDPE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. Although the presence of HDPE in the blends enabled melt processing, the presence of UHMWPE helped to improve the toughness of the resulting blends. The processability of the blends was investigated with the Brabender torque, which was used as an indication of the optimum blend conditions. The blends were characterized with differential scanning calorimetry. The mechanical tests performed on the blends included tensile, flexural, and impact tests. A 50:50 (w/w) blend yielded optimum properties in terms of the processability and mechanical properties. The tensile property of the 50:50 blend was intermediate between those of HDPE and UHMWPE, but the strain at break increased 200% in comparison with that of both neat resins. The energy at break of the 50:50 blend revealed an improvement in the toughness. The fracture mechanism was also investigated with scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 413–425, 2005     

Modelling of biaxial ratcheting behaviour of ultrahigh‐molecular‐weight polyethylene with viscoplasticity theory based on overstress for polymers

Biaxial ratcheting behaviour of ultrahigh‐molecular‐weight polyethylene (UHMWPE) has been modelled using the viscoplasticity theory based on overstress for polymers (VBOP) with the modified Chaboche kinematic hardening rule. Investigated loading condition is: axial strain‐controlled cyclic loading of thin‐walled tubular specimen in the presence of constant pressure. To improve the circumferential strain ratcheting response of UHMWPE, changes designed to account for kinematic hardening and tangent modulus effects are proposed. Numerical results are compared with previously obtained experimental data. It is shown that modified tangent modulus improves the model responses. The biaxial ratcheting behaviour of UHMWPE is modelled quantitatively with VBOP. © 2015 Society of Chemical Industry     

Preparation and characterization of linear low‐density polyethylene/low‐density polyethylene/TiO2 membranes

Because of their special functions, the application of nanoscale powders has recently attracted both industrial and theoretical interest. In this study, nanoscale TiO₂, which exhibited a special UV absorption and consequent antibacterial function, was added to a low‐density polyethylene/linear low‐density polyethylene hybrid by melt compounding to yield functional composite membranes. TiO₂ exhibited an apparent induced nucleation effect on the crystallization of polyethylene, and the size of the crystallites decreased while the number increaed with the introduction of TiO₂; however, the crystallinity of polyethylene changed little. Also, TiO₂ exhibited an ideal dispersion in the membrane with an average size less than 100 nm, and this excellent dispersion provided the membranes extra UV absorption; moreover, the transparency of the membranes was maintained to satisfy common requirements. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 216–221, 2005     

Effect of the ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends on their physical properties

This study examined the effect of the ultradrawing behavior of gel film specimens of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE/low‐molecular‐weight polyethylene (LMWPE) blends on their physical properties. The concentration of a gel film approximated its critical concentration at a fixed drawing temperature; its achievable draw ratio was higher than that of other blend specimens with various concentrations. Noticeably, when about 5 wt % LMWPE was added to a UHMWPE/LMWPE gel film specimen, the achievable draw ratio of the gel film increased, and this contributed to an apparent promoting effect on its anticreeping properties and thermal stability. Therefore, when UL_B?0.9 was drawn to a draw ratio of 300, the anticreeping behavior was improved to less than 0.026%/day. Moreover, with respect to the thermal stability, when the same specimen was drawn to a draw ratio of 300, the retention capability of its storage modulus could resist a high temperature of 150°C, which was obviously much higher than the temperature of an undrawn gel film specimen (70°C). To study these interesting behaviors further, this study systematically investigated the gel solution viscosities, anticreeping properties, dynamic mechanical properties, thermal properties, molecular orientations, and mechanical properties of undrawn and drawn UHMWPE/LMWPE gel film specimens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/attapulgite fibers

An investigation of the influence of the contents of original and modified attapulgite (ATP) on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE)/ATP (FA_x) and UHMWPE/modified ATP (FA_mx) as‐prepared fibers is reported. Similar to what is found for the orientation factor values, the achievable draw ratios (D_ra) of the FA_x and FA_mx as‐prepared fibers approach a maximum value as the original ATP and/or modified ATP contents reach their corresponding optimum values. The maximum D_ra value obtained for FA_mx as‐prepared fiber specimens is significantly higher than that for FA_x as‐prepared fiber specimens prepared at the optimum original ATP content. Similar to what is found for the orientation factors and achievable drawing properties, the tensile strength (σ_f) and initial modulus (E) of both drawn F₂A_x and F₂A_mx fiber series specimens with a fixed draw ratio reach maximum values as the original and/or modified ATP contents approach the optimum values, respectively. The σ_f and E values of the F₂A_mx fiber specimens are always significantly higher than those of the corresponding F₂A_x fiber specimens prepared at the same draw ratios and ATP contents but without being modified. To understand the interesting ultradrawing, orientation and tensile properties of FA_x and FA_mx fiber specimens, Fourier transform infrared spectral, specific surface area, transmission electron microscopic and elemental analyses of the original and modified ATPs were performed. Copyright © 2012 Society of Chemical Industry     

Influence of different sterilization procedures on the morphological parameters and mechanical properties of ultra‐high‐molecular‐weight polyethylene

The objectives of this study were to examine the effects of the processing conditions, sterilization, and thermal treatment on the morphological and mechanical properties of ultra‐high‐molecular‐weight polyethylene (UHMWPE) in medical applications by means of thermal analysis, Fourier transform infrared spectroscopy, and nanoindentation. It is well known that manufacturing, irradiation, and thermal treatments significantly alter the microstructure of materials, which results in changes in their mechanical properties. UHMWPE was found to be barely sensitive to processing conditions but strongly influenced by sterilization treatments. Great emphasis was given to the characterization of the so‐called first generation of highly crosslinked UHMWPE because the thermal history of this material differed from that of γ‐irradiated materials. The physical and mechanical properties of UHMWPE were influenced as a result of γ and electron‐beam irradiation and the remelting procedure. Lower crystallinity, different lamellar thickness distributions, and lower hardness and modulus values were estimated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface modification of ultra‐high‐molecular‐weight polyethylene. II. Effect on the physicomechanical and tribological properties of ultra‐high‐molecular‐weight polyethylene/poly(ethylene terephthalate) composites

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching, with the aim of improving the performance of its composites with poly(ethylene terephthalate) (PET) fibers. In this article, we report on the morphology and physicomechanical and tribological properties of modified UHMWPE/PET composites. Composites containing chemically modified UHMWPE had higher impact properties than those based on unmodified UHMWPE because of improved interfacial bonding between the polymer matrix and the fibers and better dispersion of the fibers within the modified UHMWPE matrix. Chemical modification of UHMWPE before the introduction of PET fibers resulted in composites exhibiting improved wear resistance compared to the base material and compared to unmodified UHMWPE/PET composites. On the basis of the morphological studies of worn samples, microploughing and fatigue failure associated with microcracking were identified as the principle wear mechanisms. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of styrene–ethylene–butadiene–styrene and its synergetic effect with ethylene vinyl acetate on the mechanical,thermal, dielectric,and water‐treeing behaviors of crosslinked polyethylene

In this study, we investigated the effect of an aromatic polymer, styrene–ethylene–butadiene–styrene (SEBS), on the water‐tree resistance of crosslinked polyethylene (XLPE), and the synergetic effect of SEBS and ethylene vinyl acetate (EVA) was also investigated. The XLPE/SEBS and XLPE/SEBS/EVA samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, mechanical measurements, and an accelerated water‐treeing experiment, and the obtained results clearly show the relevant influence of SEBS and EVA, and as expected, the addition of SEBS and EVA was found to synergistically influence the water‐tree resistance of XLPE more positively in comparison with that without the addition of EVA. In addition, it also indicated that the blends possessed excellent dielectric behaviors, such as the dielectric constant and dissipation factor. The crystallization of the blends decreased with increasing SEBS content and addition of EVA. However, the melting temperature of the blends increased with the addition of SEBS and EVA, but the melting temperature of the blends decreased with increasing SEBS content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Temperature‐sensitive membranes prepared by the plasma‐induced graft polymerization of N‐Isopropylacrylamide into porous polyethylene membranes

A temperature‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAAm), was grafted onto porous polyethylene membranes by a plasma‐induced graft polymerization technique. A wide range of grafting was achieved through variations in the grafting conditions, including the postpolymerization temperature, time, monomer concentration, and graft‐reaction medium. The active species induced by plasma treatment was proven to be long‐living via a postpolymerization time of 95 h. Different solvent compositions, that is, water, methanol, benzene, and water/methanol, were used as reaction media, and water showed a much higher polymerization rate than the organic solvents. Based on the hydrophilicity of the active species, a mechanism explaining the solvent effect in plasma‐induced graft polymerization was examined. Characterizations by scanning electron microscopy, X‐ray photoelectron spectroscopy (XPS), and micro Fourier transform infrared showed that the grafted polymers were located on both the outer surface and inside pores of the membranes. The XPS analysis also confirmed that the polar amide groups tended to distribute more outward when grafted PNIPAAm was in its expanding state than when it was in its shrinking state. Water permeation experiments showed that the permeability of the grafted membranes varied dramatically with a slight temperature change in the vicinity of the lower critical solution temperature (LCST) of PNIPAAm. The effective pore radii of the grafted membranes above and below the LCST could be depicted by Hagen‐Poiseuille's law. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3180–3187, 2003     

Evaluation of the tensile properties and thermal stability of ultrahigh‐molecular‐weight polyethylene fibers

The thermal stability of ultrahigh‐molecular‐weight polyethylene (UHMWPE) should be paid attention in its applications, although the fiber has excellent flexible tensile properties. The measurements for two kinds of UHMWPE fibers, Dyneema SK65 (The Netherlands) and ZHF (Beijing, China), were carried out at different annealing temperatures and for different aging times. Experimental and regression analysis results showed that the aging behavior of the fibers followed an exponential attenuation with the annealing temperature and aging time. The critical temperature for the safe use of the fibers was equal to or lower than 70°C and depended on the glass‐transition temperature; this was validated by tensile tests. The difference between the two fibers in the thermal properties resulted from the intrinsic supermolecular structures of the two fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 310–315, 2005     

Influence of two‐stage drawing conditions on ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends

The influence of two‐stage drawing conditions on the ultradrawing behavior of the gel films of ultrahigh‐molecular‐weight polyethylene/low‐molecular‐weight polyethylene blends is reported in this article. The critical draw ratios (λ_c) of the gel films prepared near their critical concentrations were found to depend significantly on the draw ratio attained in the first drawing stage (D_1r) and on the temperature utilized in the second drawing stage (T_sec). After drawing the gel films to a fixed draw ratio in the first drawing stage, each two‐stage drawn gel film was made to exhibit a maximum λ_c (λ_cmax) by drawing the drawn gel film at its corresponding optimum T_sec. In addition, the optimum T_sec was found to increase significantly with the D_1r value of the drawn gel films. It is worth noting, on the other hand, that the λ_cmax of two‐stage drawn gel films increased consistently with an increasing D_1r until its value reached an optimum value of 160. These results clearly suggest that, as T_sec and D_1r are increased to their optimum values, the λ_cmax of the two‐stage drawn gel films can be improved further so as to be higher than those of the corresponding one‐stage drawn gel films. These interesting phenomena were investigated in terms of reduced viscosities of the solutions and by an analysis of the thermal, birefringence, and tensile properties of the drawn gel films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1890–1901, 2001     

Dispersion of carbon nanotubes in ultrahigh‐molecular‐weight polyethylene by melt mixing dominated by elongation stress

A novel melt‐mixing method and corresponding mixer for polymer materials are reported. The effects of carbon nanotube (CNT) loading, rotation rate and mixing time on the morphology and properties of CNTs/ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites were experimentally investigated in detail using the mixer. Homogeneous dispersion of CNTs in intractable UHMWPE is successfully realized without the aid of any additives or solvents. Differential scanning calorimetry results showed that the crystallinity increases 13.8% when 1 wt% of CNTs is added into the composites. The maximum crystallinity increased 13.5% and then decreased slightly with increasing rotation rate. The mixing time had little effect on crystallinity. Rheological tests reveal that the effect of CNT loading on the storage modulus/complex viscosity is a result of competition between the viscosity decrease due to the selective adsorption of UHMWPE onto CNT surfaces and the viscosity increase caused by the formation of an interconnected polymer–nanotube network. The storage modulus/complex viscosity decreased with increasing rotation rate/mixing time. This is a synergic result of the selective adsorption of the long molecular chains onto the CNT surface and their thermomechanical degradation. The results showed that the mixing process dominated by elongation stress is a simple, efficient green way to prepare CNTs/UHMWPE nanocomposites via melt mixing. © 2018 Society of Chemical Industry     

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

The continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O₂ plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005