Preparation and characterization of porous titanium dioxide sulfonated polystyrene composite microspheres with amphiphilicity

Porous particles with amphiphilicity were prepared by a nonpolymeric pore‐formation process with the sulfonation of polystyrene microspheres. Nano titanium dioxide (TiO₂) particles were then grafted onto the surface via a sol–gel method to finally form the composite particles. The effects of the mass ratio of ethanol (EtOH) to water, temperature, and solubility parameter on the pore‐formation process is discussed in detail. The morphology, porous structure, and wetting properties of the particles were studied by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and contact angle measurement. The results show that porous sulfonated polystyrene (SP) microspheres could be fabricated at 60°C with a 1 : 1 mass ratio of EtOH–water and a solubility parameter of 29.69 MPa^1/2. The TiO₂ particles were determined to be grafted onto the SP microspheres by physical‐bond interaction on the basis of FTIR analysis. The contact angles for both water (aqueous‐phase) and various organic solvent (oil‐phase) droplets with different polarities on the surface of compressed tablets of TiO₂–SP powder were all lower than 30°; this indicated excellent amphiphilicity in the composite particles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crystallization behavior of ultrahigh‐molecular‐weight polyethylene/polyhedral oligomeric silsesquioxane nanocomposites prepared by ethylene in situ polymerization

A [3‐t‐Bu‐2‐O? C₆H₃CH?N(C₆F₅)]₂TiCl₂ catalyst (bis(phenoxyimine)titanium dichloride complex – FI catalyst) was immobilized on disilanolisobutyl polyhedral oligomeric silsesquioxane (OH‐POSS) to prepare ultrahigh molecular‐weight polyethylene (UHMWPE)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites during ethylene in situ polymerization. The dispersion state of POSS in the UHMWPE matrix was characterized by X‐ray diffraction measurements and transmission electron microscopy. It was shown that the OH‐POSS achieved uniformed dispersion in the UHMWPE matrix, although its polarity was unmatched. The isothermal and nonisothermal crystallization behavior of the nanocomposites was investigated by means of differential scanning calorimetry. The crystallization rate of the nanocomposites was enhanced because of the incorporation of POSS during the isothermal crystallization. POSS acted as a nucleus for the initial nucleation and the subsequent growth of the crystallites. For nonisothermal studies, POSS showed an increase in the crystallinity. The crystallization rate of the nanocomposites decreased because the presence of POSS hindered the crystal growth. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40847.     

Two‐stage drawing process to prepare high‐strength and porous ultrahigh‐molecular‐weight polyethylene fibers: Cold drawing and hot drawing

High‐strength and porous ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers have been prepared through a two‐stage drawing process. Combined with tensile testing, scanning electron microscopy, and small‐angle X‐ray scattering, the mechanical properties, porosity, and microstructural evolution of the UHMWPE fibers were investigated. The first‐stage cold drawing of the gel‐spun fibers and subsequent extraction process produced fibers with oriented lamellae stacks on the surface and plentiful voids inside but with poor mechanical properties. The second‐stage hot drawing of the extracted fibers significantly improved the mechanical properties of the porous fibers because of the formation of lamellar backbone networks on the surface and microfibrillar networks interwoven inside to support the voids. With various processing conditions, the optimized mechanical properties and porosity of the prepared UHMWPE fibers were obtained a tensile strength of 1.31 GPa, a modulus of 10.1 GPa, and a porosity of 35%. In addition, a molecular schematic diagram is proposed to describe structural development under two‐stage drawing, including void formation and lamellar evolution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42823.     

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     

Friction and wear properties of graphene oxide/ultrahigh‐molecular‐weight polyethylene composites under the lubrication of deionized water and normal saline solution

Ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE composites reinforced with graphene oxide (GO) were successfully fabricated through a new step of liquid‐phase ultrasonic dispersion, high‐speed ball‐mill mixing, and hot‐pressing molding technology. When the GO/UHMWPE composites were lubricated with deionized water (DW) and normal saline (NS) solution, their friction and wear properties were investigated through sliding against ZrO₂. The worn surface and wear volume losses of these composites were studied with scanning electron microscopy, X‐ray photoelectron spectroscopy, and a Micro‐XAM 3D non‐contact surface profiler. The results show that the microhardness of the GO/UHMWPE composites was improved by 13.80% and the wear rates were decreased by 19.86 and 21.13%, whereas the depths of the scratches were decreased by 22.93 and 23.77% in DW and NS lubricating conditions, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39640.     

Single‐walled carbon nanotube/ultrahigh‐molecular‐weight polyethylene composites with percolation at low nanotube contents

To mix single‐walled carbon nanotubes (SWCNTs) with a polymer and to achieve low percolation thresholds, a low‐viscosity liquid has been required in order to achieve sufficiently good dispersion. In this article, data are presented which show that percolation occurs at ～0.14 wt % carbon nanotubes and the dispersion procedure does not involve dispersing the SWCNTs in a low‐viscosity liquid. Specifically, ultrahigh‐molecular‐weight polyethylene powder was mixed with a powder containing nanotubes and catalyst support, e.g., the powder contains 93% silica and 7% SWCNTs. The powder blend is compression molded into sheets using high pressure and temperature. Because of the very high viscosity of the resin, the nanotube/silica mixture largely stays segregated at the interface as shown by scanning electron microscopy. A significant drop in tensile properties (modulus, tensile strength, and elongation at break) occurs with filler incorporation. Non isothermal crystallization measurements indicate that this filler does not nucleate crystallinity when mixed in this manner; although there is a definite sharpening of the melt endotherm indicating that crystallites with smaller lamellar thicknesses are reduced significantly with filler addition. The addition of filler also slightly reduces the overall fractional crystallinity measured after a constant cooling rate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

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     

Preparation of Sn‐doped CdS/TiO2/conducting polymer fiber composites for efficient photocatalytic hydrogen production under visible light irradiation

Sn‐doped CdS/TiO₂ heterojunction was synthesized on the conducting polymer fiber mat by hydrothermal method. The conducting polymer fiber mat was made by electrospinning from polyvinylidene fluoride, styrene‐maleic anhydride copolymer, and nano‐graphites as conducting fillers. The Sn‐doped CdS/TiO₂ heterojunction was characterized by XRD, XPS, SEM, TEM, TGA, and UV–Vis absorption spectra. Under simulated solar light irradiation, a combination of Sn‐doped CdS/TiO₂/conducting polymer was found to be highly efficient for photocatalytic hydrogen evolution from splitting of water. The photocatalytic hydrogen production efficiency was up to 2885 μmol h^?1 g^?1cat. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42300.     

Blending ultrahigh‐molecular‐weight polyethylene and poly(ethylene/10‐undecen‐1‐ol) in one nascent particle

Ultrahigh‐molecular‐weight polyethylene (UHMWPE)/polar polyethylene (PE) composites were blended in one nascent particle by in situ polymerization with a hybrid catalyst. Polystyrene‐coated SiO₂ particles were used to support the hybrid catalyst. Fe(acac)₃/2,6‐bis[1‐(2‐isopropylanilinoethyl)] was supported on SiO₂ for the synthesis of UHMWPE, whereas [PhN?C(CH₃)CH?C(Ph)O]VCl₂ was immobilized on a polystyrene layer to prepare a copolymer of ethylene and 10‐undecen‐1‐ol (polar PE). Importantly, the core part of the supports (the polystyrene layer) exhibited pronounced transfer resistance to 10‐undecen‐1‐ol; this provided an opportunity to keep the inside iron active sites away from the poisoning of 10‐undecen‐1‐ol. Therefore, UHMWPE was simultaneously synthesized with polar PE by in situ polymerization. Interestingly, the morphological results show that UHMWPE and the polar PE were successfully blended in one nascent polymer. This improved the miscibility of the composites, where most of the chains were difficult to crystallize because of the strong interactions between the PE chains and polar chains. The blends showed an extremely low crystallinity, that is, 9.9%. Finally, the hydrophilic properties of the polymer composites were examined. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46652.     

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     

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     

Effect of polyethylene glycol on the performance of ultrahigh‐molecular‐weight polyethylene membranes

Porous, flat membranes of ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared by thermally induced phase separation, with mineral oil as a diluent and poly(ethylene glycol) with a weight‐average molecular weight of 20,000 (PEG20000) as an additive. Through the control of the rheological behavior, crystallite size, and pore structure, the influential factors, including the diluent, poly(ethylene glycol) (PEG) content, and cooling rate, were investigated. The results suggested that PEG could decrease the viscosity of UHMWPE/diluent apparently. The crystal density decreased when mineral oil was added, which made the melting point and crystallinity of UHMWPE lower. The crystallization rate and crystallinity also increased with the addition of PEG. However, the addition of excess PEG restrained crystal growth. PEG20000 in membranes could be extracted absolutely through the soaking of the membranes with fresh water for 7 days. With increasing PEG content, both porosity and pure water flux first increased and then decreased, reaching a maximum at a PEG mass fraction of 10%. The cooling rate had a direct effect the crystal structure. A slow cooling rate was good for crystal growth and diluent integration. Therefore, the pure water flux increased along with the temperature of the cooling medium, whereas porosity first increased and then decreased, reaching a maximum at 40°C. © 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     

Ultradrawing properties of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends prepared at various formation temperatures

The ultradrawing behavior of ultrahigh‐molecular‐weight polyethylene/low‐molecular‐weight polyethylene film specimens prepared at various concentrations and formation temperatures was studied. The critical draw ratio (D_rc) of UL_?0.7 film specimens was found to depend significantly on the formation temperature used to prepare the film specimens. At any fixed drawing temperature, the D_rc values of UL_?0.7 specimens prepared at various formation temperatures increased significantly as the formation temperatures were reduced. In fact, with an optimum drawing temperature of 95°C, the D_rc values of UL_?0.7 specimens prepared at a formation temperature of 0°C reached 488, about 50% higher than that of UL_?0.7 specimens prepared at a formation temperature of 95°C. These interesting phenomena were investigated in terms of the thermal, birefringence, and tensile properties of these undrawn and drawn UL_?0.7 specimens. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3728–3738, 2003     

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     

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     

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     

Control of the interfacial properties of ultrahigh‐molecular‐weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment

This work aims to explore the use of lightweight magnesium alloys as an advanced composite material in conjunction with lightweight thermoplastic materials, such as ultrahigh‐molecular‐weight polyethylene (UHMWPE). High throughput, environmentally friendly, atmospheric plasma treatment methods were used to control the interfacial properties and improve the adhesion behavior of metallic/UHMWPE composites. Helium‐oxygen dielectric barrier discharges were used, and the plasma‐activated UHMWPE surfaces were characterized through analytical and mechanical characterization methods. Oxygen content on the treated polymer surfaces increased 18.1–36.0%. A reduction in silicon content combined with characterization through microscopy reveal a preference for the attack of the matrix over the polyethylene fibers. Wetting angles for the treated samples decreased as much as 53.7%. Treated UHMWPE/Mg hybrid samples exhibited lap shear strengths up to 113.7% greater than the control. Both the plasma‐induced surface functionalization with oxygen‐containing polar groups (carboxyl, carbonyl, and hydroxyl groups) and the preferential mild etching of the polymer matrix over the fibers lead to the improvement in adhesion. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

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     

Preparation and characterization of composites of polyethylene with polypyrrole‐coated wollastonite

Composite sheets of polyethylene and polypyrrole‐coated wollastonite were prepared by extrusion and compression molding. Four compatibilizers were also evaluated, poly(ethylene‐co‐methyl acrylate) (EMA), maleated polyethylene (MAPE), poly(ethylene‐co‐vinyl alcohol) (EVOH), and poly(vinyl alcohol) (PVOH). The composite materials were characterized using X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy (SEM), Raman spectroscopy, and mechanical properties determined by tensile tests. SEM micrographs showed that significantly improved interactions occurred between the PE matrix and polypyrrole‐coated wollastonite particles in the presence of EMA, MAPE, and EVOH. Raman spectroscopy confirmed that the polypyrrole coating on the wollastonite particles was not thermally degraded during melt processing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008