Study on gel‐spinning process of ultra‐high molecular weight polyethylene

An ultra‐high molecular weight polyethylene (UHMW‐PE) fiber was prepared by gel spinning using general kerosene as the solvent and gasoline as the extraction solvent. The process of the phase separation of gel as‐spun, spun under various spinning conditions, was investigated. Its extracting and drying process were also studied. The results reveal that the gel as‐spun, spun under a lower spin draft and a lower spin quenching temperature, extracted in times and dried under free‐shrinkage, exhibits a good afterdrawability that eventually endows the fiber with excellent mechanical behaviors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 670–675, 1999     

超高分子量聚乙烯溶解均匀性研究

超高分子量聚乙烯纤维生产工艺中,超高分子量聚乙烯溶解设备普遍使用双螺杆挤出机。文章研究了如何使用双螺杆挤出机,具体涉及到螺纹元件的组合、双螺杆挤出机的转速以及各区温度控制等关键技术,制备溶解均匀的超高分子量聚乙烯溶液,以达到纺丝要求。     

Improvement of the tribological behavior of ultra‐high‐molecular‐weight polyethylene by incorporation of poly (phenyl p‐hydroxyzoate)

Ultra‐high‐molecular‐weight polyethylene/poly (phenyl p‐hydroxyzoate) composites (coded as UHMWPE/PPHZ) were prepared by compression molding. The effects of the poly (phenyl p‐hydroxyzoate) on the tribological properties of the UHMWPE/PPHZ composites were investigated, based on the evaluations of the tribological properties of the composites with various compositions and the examinations of the worn steel surfaces and composites structures by means of scanning electron microscopy and transmission electron microscopy. It was found that the incorporation of the PPHZ led to a significant decrease in the wear rate of the composites. The composites with the volume fraction of the PPHZ particulates within 45% ～ 75% showed the best wear resistance. The friction coefficient of the UHMWPE/PPHZ composites decreased with increasing load and sliding velocity, while the wear rates increased with increasing load. This was attributed to the enhanced softening and plastic deformation of the composites at elevated load or sliding velocity. The UHMWPE/PPHZ composites of different compositions had differences in the microstructures and the transfer film characteristics on the counterpart steel surface as well. This accounted for their different friction and wear behaviors. The transfer film of the UHMWPE/PPHZ composites appeared to be thinner and more coherent, which was largely responsible for their better wear resistance of t composite than the UHMWPE matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2336–2343, 2005     

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology,mechanical properties and mechanism

As linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m^?2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry     

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     

超高分子量聚乙烯纤维的表面处理

综述了超高分子量聚乙烯（UHMWPE）纤维复合材料界面的重要性,总结了表面改性方法对UHMWPE纤维以及UHMWPE／树脂界面的影响。     

Influence of high molecular weight component on the hierarchical crystalline structures of injection‐molded bars of polyethylene

A small amount of high molecular weight molecules can have a dramatic influence on the flow‐induced crystallization kinetics and orientation of polymers. To elucidate the effects of the high molecular weight component under a real processing process, we prepared model blends in which high density polyethylene with a high molecular weight and wide molecular weight distribution was blended with a metallocene polyethylene with a low molecular weight and very narrow molecular weight distribution. To enhance the shear strength, gas‐assisted injection molding was utilized in producing the molded bars. The hierarchical structures and orientation behavior of the molded bars were intensively explored by using scanning electron microscopy and two‐dimensional wide‐angle X‐ray diffraction, focusing on effects of the high molecular weight component on the formation of the shish kebab structure. It was found that there exists a critical concentration of high molecular weight component for the formation of a shish kebab structure. The threshold was about 5.5–7.0 times larger than the chain overlap concentration, suggesting an important role of entanglements of the high molecular weight component. Moreover, the rheological properties of molten polyethylene melts were studied by dynamic rheological measurements and a critical characteristic relaxation time for shish kebab formation was obtained under the processing conditions adopted in this research. © 2013 Society of Chemical Industry     

Preparation and characterization of novel ultra‐high molecular weight polyethylene composite fibers filled with nanosilica particles

Ultrahigh molecular weight polyethylene (UHMWPE)/nanosilica (F₂S_y) and UHMWPE/modified nanosilica (F₂S_mx‐y) as‐prepared fibers were prepared by spinning of F₂S_y and F₂S_mx‐y gel solutions, respectively. Modified nanosilica particles were prepared by grafting maleic anhydride grafted polyethylenes onto nanosilica particles. The achievable draw ratios (D_ra) of F₂S_y and F₂S_mx‐y as‐prepared fibers approached a maximal value as the original and modified nanosilica contents reached corresponding optimum values; the maximal D_ra value obtained for F₂S_mx‐y as‐prepared fiber specimens was significantly higher than that of the F₂S_y as‐prepared fiber specimens prepared at the optimum nanosilica content. The melting temperature and evaluated lamellar thickness values of F₂S_y and F₂S_mx‐y as‐prepared fiber series specimens decrease, but crystallinity values increase significantly, as their original and modified nanosilica contents respectively increase. Similar to the achievable drawing properties of the as‐prepared fibers, the orientation factor, tensile strength (σ_f) and initial modulus (E) values of both drawn F₂S_y and F₂S_mx‐y fiber series specimens with a fixed draw ratio reach a maximal value as the original and/or modified nanosilica contents approach the optimum values; the σ_f and E values of the drawn F₂S_mx‐y fiber specimens are significantly higher than those of the corresponding drawn F₂S_y fiber specimens prepared at the same draw ratios and nanosilica contents but without being modified. To understand the interesting ultradrawing, thermal, orientation and tensile properties of F₂S_y and F₂S_mx‐y fiber specimens, Fourier transform infrared, specific surface area and transmission electron microscopy analyses of the original and modified nanosilica were performed in this study. © 2012 Society of Chemical Industry     

Thermal and dynamic mechanical properties of vitamin E infused and blended ultra‐high molecular weight polyethylenes

Vitamin E (or α‐tocopherol) is an alternative via to thermal treatments to achieve oxidative stability of gamma or electron beam irradiated ultra‐high molecular weight polyethylenes (UHMWPE) used in total joint replacements. Our aim was to study the effects of vitamin E on the molecular dynamics and microstructural properties of UHMWPE. We hypothesized that the antioxidant would plasticize UHMWPE. Vitamin E was incorporated into UHMWPE at different concentrations by diffusion and blending and detected by ultraviolet and infrared spectroscopies from 500 ppm and 4000 ppm, respectively. Dynamic mechanical thermal analysis was used to characterize the influence of this antioxidant in the relaxations of the raw material. Differential scanning calorimetry and transmission electron microscopy served to characterize thermal and microstructure properties, respectively. Vitamin E concentrations above 3% by weight significantly reduced the degree of crystallinity and increased the melting transition temperature of raw UHMWPE. The presence of increasing concentrations of α‐tocopherol introduced and/or strengthened the beta relaxation, which was also shifted toward gradually lower temperatures and had rising activation energies up to 188 kJ/mol. In addition, the gamma relaxation remained unaltered on vitamin E addition. Therefore, no plasticizing effects of vitamin E on the molecular dynamics of UHMWPE could be confirmed from mechanical spectroscopy data. However, the α relaxation was modified in intensity and location due to the changes in the degree of crystallinity introduced by the incorporation of vitamin E. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of ultra‐high molecular weight polystyrene with rare earth–magnesium alkyl catalyst system: general features of bulk polymerization

Bulk polymerization of styrene (St) with an in‐situ‐activated Ziegler‐catalyst containing neodymium 2‐ethylhexyl phosphonate [Nd(P₂₀₄)₃], magnesium–aluminum alkyls and hexamethyl phosphoramide (HMPA) was studied. The new rare‐earth catalyst exhibited high activity for polymerization of styrene, and its catalytic efficiency reached 14 730 g PSt/g Nd. The influence of reaction parameters, such as Mg/Nd, Mg/Al, St/Nd molar ratios, temperature, etc, on the catalyst performance was examined in detail. The molecular weight of the resulting polystyrene is ultra‐high (M_W = 40 × 10⁴ ∼ 120 × 10⁴ g mol⁻¹) and the distribution of molecular weight is broad (M_W/M_n = 2.1 ∼ 2.8). The microstructure of the polystyrene was characterized by IR and ¹³C NMR spectroscopies and found to be atactic. © 2001 Society of Chemical Industry     

Studies on nonisothermal crystallization of ultra–high molecular weight polyethylene in liquid paraffin

The nonisothermal crystallization kinetics for ultra–high molecular weight polyethylene (UHMWPE) in liquid paraffin (LP) systems was investigated through differential scanning calorimetry (DSC) measurement. The influence of UHMWPE concentration and cooling rate on crystallization mechanism and spherulitc structure as implied by the modified Avrami equation and Mo's analysis was determined, whereas the Ozawa's approach fails to describe the crystallization behaviors of these UHMWPE‐diluent systems. As a result, in the modified Avrami analysis, it was found that the Avrami exponent is constant around five at various concentrations of UHMWPE and cooling rates. Further, the value of F(T) in the Mo's approach increases with the increasing of relative crystallinity and UHMWPE content in the blends. The nonisothermal crystallization kinetics presented here are the first for UHMWPE‐diluent systems. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

High density polyethylene/ultra high molecular weight polyethylene blend. II. Effect of hydroxyapatite on processing,thermal, and mechanical properties

Hydroxyapatite (HA) is part of bone mineral composition. Several attempts have been made to incorporate HA into high density polyethylene (HDPE) to produce bone replacement biomaterials since neat HDPE is not suitable as bone replacement. The blending of HDPE with ultra high molecular weight polyethylene (UHMWPE) up to 50% by weight was performed with the aim of improving the toughness of composites. Reinforcement of blend with HA of up to 50% by weight was carried out. Methods of characterizing the composites included density, differential scanning calorimetry, thermal gravimetric analysis, ash content, and morphological examination using scanning electron microscope. For the mechanical properties of the composites, tensile, flexural, and impact tests were carried out. Incorporation of HA into HDPE has resulted in the brittleness of the composites. Blending of HDPE with UHMWPE in the presence of HA was found to improve the mechanical properties and promote a ductile failure of the resulting composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3931–3942, 2006     

高分子量HDPE薄膜级树脂的开发

综述了国内外高分子量高密度聚乙烯薄膜级树脂的性能、生产工艺、代表牌号、市场、应用领域和发展趋势,重点介绍了几种代表性的生产工艺,并根据我国该薄膜级树脂生产和消费现状,提出了今后发展的建议。     

Effects of carbon nanofibers on crystalline structures and properties of ultrahigh molecular weight polyethylene blend fabricated using twin‐screw extrusion

Melt mixing in an extruder with polymers is an effective approach for forming nanocomposites, allowing mass production applications. The intent of this study is to investigate carbon nanofiber composites with ultrahigh molecular weight polyethylene (UHMWPE) matrix using the twin‐screw extruder. To decrease the high viscosity of UHMWPE, a low density polyethylene (LDPE) was added into the UHMWPE. The effects of carbon nanofibers (CNFs) on the crystalline structures and properties of the nanocomposites were analyzed. The differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) measurements showed the addition of CNFs decreases the degree of crystallinity, but does not impart significant effects on the crystalline structure of the UHMWPE/LDPE blend. Tensile test results showed that the nanocomposite with loading of 3 wt % CNFs had an increase of 38% in tensile strength and 15% in modulus. The thermal stability and thermal conductivity of UHMWPE/LDPE blends were also enhanced by the addition of CNFs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

纤维专用超高相对分子质量聚乙烯的结构与性能

研究了纤维专用国产超高相对分子质量聚乙烯(简称GN)的基本性能、力学性能、定伸应力、相对分子质量及其分布、聚集态结构等,并与进口同类产品GUR4022进行了对比。结果表明:GN与GUR4022的相对分子质量较为接近、密度基本相同、拉伸强度相差不多;GN的拉伸弹性模量为711 MPa,高于GUR4022;GN的聚集态结构与GUR4022较为接近,表面形貌为一定尺寸分布的类球体,GN的分子结构与GUR4022比较接近。与GUR4022的可纺性对比研究表明,GN的可纺性良好,经过3级拉伸后,当拉伸倍数达到45倍时,GN具有较好的取向结晶性能,拉伸强度与GUR4022接近,达到了高强度、高模量的要求。     

Extrusion of ultrahigh molecular weight polyethylene under ultrasonic vibration field

The effects of polypropylene (PP) and ultrasonic irradiation on the processing and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE) are studied. The results show that PP can effectively improve the fluidity and mechanical properties of UHMWPE. The Izod notched impact strength increases from 92 kJ/m² for pure UHMWPE to 109.2 kJ/m² for the blend of UHMWPE with 10 wt % PP. The Young's modulus increases from 528 MPa for pure UHMWPE to 1128 MPa when 25 wt % PP is contained in the blend, and the yield strength also rises when PP is added. The application of ultrasonic vibrations during extrusion can prominently decrease the die pressure and apparent viscosity of the melt, thus increasing the output of extrudate. An appropriate ultrasonic intensity and irradiation time can further promote the mechanical properties, while an overdose of irradiation destroys them. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2628–2632, 2003     

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λ_c) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 149–159, 1998     

Ultradrawing of blend films of ethylene-dimethyl-aminoethyl methacrylate copolymer and ultra-high molecular weight polyethylene prepared by gelation/crystallization from solutions

Copolymer ethylene-dimethyl-aminoethyl methacrylate (EDAM) with 3.9% DAM side groups and ultra-high molecular weight polyethylene (UHMWPE) were blended in decalin solvent. The hot homogenized solution was poured into an aluminum tray to form gels and the decalin was allowed to evaporate from the resultant gels under ambient condition. Surprisingly, the resultant dry blend films could be elongated to more than 200-fold (λ=200) even for the blend film with 90% EDAM content (9/1 composition), although the maximum draw ratio of EDAM homopolymer films was 1.6-fold (λ=1.6). The mechanism of the great drawability was dependent upon the content of EDAM. The drawability for the 9/1 composite films was attributed to large crystal lamellae of UHMWPE ensuring crystal transition from a folded to a fibrous type. Accordingly, EDAM chains were independent of ultradrawing of UHMWPE and kept a random orientation under ultra-drawing process. The storage (Young's) modulus was 10 GPa at 20 °C. In contrast, EDAM chains within the 1/1 composite films were oriented drastically together with UHMWPE crystallites. The modulus of the 1/1 composition at 20 °C reached 68 GPa, which was higher than the value (40 GPa) of polypropylene films with λ=100. Such considerable difference of modulus due to EDAM content was analyzed in relation to the gelation/crystallization from solutions.     

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     

Effect of aluminoxane on molecular weight and molecular weight distribution of polyethylene prepared by an iron‐based catalyst

A series of aluminoxanes, tetraethylaluminoxane (TEAO), tetraalkylaluminoxane (TAAO), Et₂AlOB(4 ? F ? C₆H₄)OAlEt₂ (BTEAO) and ethyl‐iso‐butylaluminoxane modified with p‐fluorophenylboric acid (BEBAO), were prepared and their effects on molecular weight (MW) and molecular weight distribution (MWD) of polyethylene prepared by the iron‐based catalyst [(ArN?C(Me))₂C₅H₃N]FeCl₂ (Ar?2,6‐dimethylphenyl) ( 1 ) were investigated. It was found that TEAO and BTEAO were highly efficient activators for iron‐based catalysts and introducing the branched bulky group (eg iso‐Bu) into the aluminoxane activator could improve the MW of the resulting polyethylene. The MW of polyethylene produced by activators modified by p‐fluorophenylboric acid was higher than for other aluminoxane activators. The TEAO‐ and TAAO‐based polyethylene exhibited attractive bimodal MWD, and the lower MW fraction of bimodal MWD was shown to be produced in the early stage of polymerization due to chain transfer to the aluminium activator. Copyright © 2004 Society of Chemical Industry