Melting of ultrahigh molecular weight polyethylene

On heating in DSC, samples of UHMWPE show a single, fairly sharp, melting endotherm which may be increased to a peak temperature of 147°C and 77% crystallinity by annealing at elevated temperatures. An irreversible conversion of nascent to folded crystals, between 134 and 142°C, was observed by heating nascent UHMWPE powder in the calorimeter. In the presence of n-hexatriacontane, the melting endotherm of UHMWPE was depressed and broadened and the conversion of nascent to melt-crystallized polyethylene facilitated on heating. A melt-crystallized mixture of ordinary linear polyethylene (HDPE) and UHMWPE was not resolved on remelting. After annealing this mixture for 12 h at 130°C, HDPE was fractionated and the melting of UHMWPE was sharpened. Crystals of UHMWPE, prepared from dilute solution in xylene, show a single sharp melting endotherm and high crystallinity, but the melting peak is reduced in temperature compared to nascent crystallized powder.     

Roller drawing of ultrahigh molecular weight polyethylene

The roller drawing of ultrahigh molecular weight polyethylene (UHMW-PE) sheets were carried out in the roller temperature T_r range of 100–140°C. In addition to the roller drawing in the solid state (T_r = 100°C), we attempted to crystallize the molten UHMW-PE sheet under the roller-drawing process (T_r = 100–140°C). The tensile and dynamic viscoelastic properties, the molecular orientation, and the microstructure of the roller-drawn UHMW-PE sheets were investigated. The mechanical properties of UHMW-PE sheets were much improved by crystallization during the roller drawing process at T_r = 140°C. The sheets roller-drawn at T_r = 135 and 140°C exhibited c-axis orientation to the draw direction and (100) alignment in the sheet plane. However, at T_r = 100°C the elastic motion of the amorphous chains induces the twinnings of lattice, which enhances the transition to the (110) alignment in the sheet plane. The dynamic storage modulus below γ-dispersion temperature showed good correlation with crystallinity and orientation functions, while taut tie molecules and thick crystallites play an important role in the storage modulus above γ-dipersion temperature.     

Viscous behavior of ultrahigh molecular weight polyethylene solution

The viscous behavior of the decalin solution of ultrahigh molecular weight polyethylene (UHMEPE) was studied. The influence of the concentration of polymer as well as the temperature was investigated. The flow curve can be described by the power-law model. The dependence of the viscosity on the temperature can be described by the Arrhenius–Frenkel–Eyring equation. The dependence of viscosity on the concentration can also be described by a power-law correlation. The addition of aluminum stearate increased the activation energy of flow of the solution. The viscosity of UHMWPE solution was decreased at lower concentration and increased at higher concentration of UHMWPE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:289–293, 1997     

Microstructure of biaxially drawn ultrahigh molecular weight polyethylene

The microstructure of ultrahigh molecular weight polyethylene (UHMW-PE) sheets biaxially drawn in the molten state was investigated by means of wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and electron microscopy. The crystallographic c-axis tended to be oriented in the sheet plane by the biaxial drawing in the molten state. The microstructure of the biaxially drawn UHMW-PE was shown to depend upon molecular weight of UHMW-PE. The biaxially drawn sheet of higher molecular weight (M_v = 2,700,000) showed a fibrous structure, while the lower molecular weight sample (M_v 700,000) had a lamellar structure. The result of DSC measurements suggested that a small number of nucleating extended chain crystals was produced by biaxial melt drawing of the UHMW-PE sheet with higher molecular weight.     

超高分子量聚乙烯改性研究进展

综述了近年来超高分子量聚乙烯（PE?UHMW）改性的最新研究进展,包括采用辐照交联法、填充改性法及共混改性法等进行摩擦性能改性,和采用涂层改性法、等离子体改性法等进行纤维表面性能改性,并讨论了摩擦性能改性与纤维的表面性能改性研究面临的挑战。     

Wetting of oriented and etched ultrahigh molecular weight polyethylene

Highly oriented gel‐spun ultrahigh molecular weight polyethylene (UHMWPE) fibers possess many outstanding properties desirable for composite materials but their adhesion to such matrices as epoxy is poor. This article describes the combined effects of drawing and surface modification on the bulk and surface properties of gel‐cast UHMWPE films emphasizing the effects of etching on both undrawn and drawn films. Drawing the films yields a fibrillar structural hierarchy similar to UHMWPE fibers and a significant increase in orientation, melting point, modulus, and strength. The effects of drawing on bulk properties were more significant than those of etching. The poor adhesion of epoxy to the smooth, fibrillar, and relatively nonpolar drawn film surface improves significantly with oxidization and roughening on etching. The interlaminar shear failure occurred cohesively in the UHMWPE, and thus the interlaminar shear failure strength was greater for the drawn UHMWPE with its greater tensile strength. Nitrogen plasma etching yielded the best results, both removing any low molecular weight surface layer and etching the UHMWPE beneath. Oxygen plasma etching enhanced wetting but was too harsh, causing extensive surface degradation and a significant reduction in mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 405–418, 1999     

Sliding wear behaviour of oriented ultrahigh molecular weight polyethylene

The impact of processing‐induced chain orientation on the sliding wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The orientation of the molecular network of UHMWPE was done by means of uniaxial tension up to different residual strains. We found that high residual strain levels (higher than 0.45) enabled the sliding dissipated energy of UHMWPE to be decreased in dry conditions. In particular, oriented UHMWPE with a residual strain of 0.85 exhibited, at 500 000 sliding cycles in dry conditions, a decrease in volumetric wear loss by a factor of 3.3 and 19.4 compared with the reference UHMWPE tested in directions parallel and perpendicular to the chain direction, respectively. It is argued that oriented UHMWPE exhibits less adhesion during interfacial wear than the reference material, and hence orientation of UHMWPE bulk may be an alternative treatment to crosslinking for dry sliding conditions. In the case of sliding testing conducted in Ringer's solution, the benefit of the initial chain orientation was quite weak due to a lubrication effect of the solution that markedly limited the effect of chain orientation on the sliding behaviour.     

超高分子量聚乙烯树脂的溶胀性的检测分析

通过上海化工研究院设计的在线检测装置对超高分子量聚乙烯(UHMWPE)溶胀过程中的温度、黏度进行测试,形成了UHMWPE树脂溶胀工艺的检测方法,对黏均分子量分别为3.261×106(A),3.833×106(B),3.455×106(C)3种不同树脂的溶胀温度、溶胀时间、溶胀比等参数进行了分析。结果表明:A,B,C树脂的溶胀温度分别为121,120,119℃;对溶胀釜加热系统设定统一温度,釜内温度达120℃时,A,B,C树脂的溶胀时间分别为60,30,3 min,溶胀比分别为2.37,2.51,2.31。     

超高相对分子质量聚乙烯接枝丙烯酸的制备

以丙烯酸为单体,采用γ射线辐照引发技术制备了超高相对分子质量聚乙烯接枝丙烯酸(UHMWPE- g-AA);利用傅里叶变换红外光谱和差示扫描量热法表征了接枝物的结构和热性能;用化学滴定法测定了接枝物的接枝率;研究了UHMWPE-g-AA对聚酰胺(PA)1010/UHMWPE-g-AA/UHMWPE共混物力学性能的影响。实验表明：接枝物在1716cm~(-1)处有明显的羰基特征吸收峰,说明AA分子确实被接枝到UHMWPE分子链上;接枝率随单体浓度、辐照剂量及辐照时间的增加而增加;加入UHMWPE-g-AA后,UHMWPE与PA1010的相容性得到了改善,PA1010/UHMWPE-g-AA/UHMWPE共混物的缺口冲击强度是PA1010/UHMWPE共混物的1.5倍,达到72J/m。     

Hot rolling and quench rolling of ultrahigh molecular weight polyethylene

The mechanical properties, the crystal orientation, and the microstructure of hot rolled and quench rolled ultrahigh molecular weight polyethylene (UHMW-PE) were investigated. The tensile strength of hot rolled and quench rolled UHMW-PE sheets increased with increasing draw ratio. The crystallographic axes a, b, and c of the rolled sheets tended to be oriented to the normal direction (ND), the traverse direction (TD), and the rolling direction (RD), respectively. The small-angle X-ray scattering patterns with incident X-ray beam parallel to TD suggested the presence of inclined lamellar structure in the RD–ND plane. At the initial stage of rolling, partial breakup of crystallites along the (100) plane was observed. The lamellar structure is deformed by the slippage mechanism along the (100) plane in the chain direction.     

Characterizations of ultrahigh molecular weight polyethylene nanocomposite films with organomica

Ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites with various organoclay contents were prepared by using the solution intercalation method. Up to a clay loading of 4 wt%, the clay particles were found to be highly dispersed in the UHMWPE matrix without any agglomeration of particles. However, for a clay content above 6 wt% some agglomerated structures form in the polymer matrix. The melting transition temperatures (T_ms) and ultimate strengths of the hybrids increase with increasing clay content; the maximum values of these properties were obtained for the hybrid containing 2 wt% of the organoclay. However, the thermal degradation stability and initial modulus are at their maximum values when the amount of organoclay in the hybrid is 4 wt%. The oxygen permeability, coefficient of thermal expansion (CTE), and transmittance at 400 nm were found to monotonically decrease with increases in the clay loading in the range 0 to 10 wt%. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

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     

Oxidation of gamma‐irradiated ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene (UHMWPE), the current polymer of choice in orthopedic prosthetic devices, is typically sterilized by exposure to Co‐60 gamma irradiation prior to packaging for long‐term storage. However, the exposure to Co‐60 irradiation generates free radicals along the polymer chain that can participate in a series of reactions commencing with the oxidation of the free radicals to form reactive peroxy radicals. This study was undertaken to identify the role of hydroperoxide species in shelf‐aged and accelerated aged UHMWPE samples by using a nitric oxide derivatization technique. It is shown that the concentration of hydroperoxides did not change appreciably with shelf aging. However, during accelerated aging the hydroperoxide concentration increased to a plateau and then decreased, suggesting its role as an intermediate in the process. By contrast, the concentrations of carbonyl species continued to increase during shelf aging and accelerated aging. The effects of several packaging materials on the oxidation characteristics were also investigated. A vacuum foil package is shown to be effective in preventing oxidation to a significant extent during accelerated aging. However, accelerated aging after removal from the foil pack resulted in oxidative degradation. Extended vacuum to remove dissolved oxygen and a 5‐week room‐temperature healing process in the foil pack were shown to be ineffective in reducing oxidative degradation. It also was shown that increased moisture content in the aging environment did not affect the degradation process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2525–2542, 2000     

Rolling and roll-drawing of ultrahigh molecular weight polyethylene reactor powders

Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.     

凝胶纺丝法制备超高分子量聚乙烯/高分子量聚乙烯纤维延伸性能的研究

用凝胶纺丝法制备了超高分子量聚乙烯(UHMWPE)/高分子量聚乙烯(HDPE)纤维,探讨了添加不同种类高分子量聚乙烯对凝胶初生纤维在后续延伸过程中延伸性能的影响。结果表明在固定制备条件时,当超高分子量聚乙烯(UHMWPE)/高分子量聚乙烯(HDPE)的质量比在最适当质量比时,高分子量聚乙烯的分子量为1.5～2.0×104时,所制备的凝胶初生纤维的可延伸比达最大值。     

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 behavior of gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends at varying drawing conditions

A systematic study of the influence of the drawing temperature and rate on the ultradrawing properties of film samples prepared from gel solutions of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends is reported. At a fixed drawing rate, the achievable draw ratios reached a maximum value when each film specimen was drawn at a temperature near its optimum temperature (T_op). It is interesting to note that the T_op values of each film sample increased consistently with the drawing rate. The achievable draw ratio of each film sample drawn at a constant rate and a temperature near T_op is referred to as the D_raop, which reached another maximum value as the drawing rates approached an optimum value. Dynamic mechanical analysis of the film sample exhibited an extraordinary high transition peaked at temperature near 95°C, which is again very close to the T_op value found for the film sample drawn at a relatively low rate. On the other hand, the birefringence values and tensile strengths of the film specimen were found to improve significantly with the draw ratios, although the improvement of these properties reduced significantly at high draw ratios. Moreover, both the drawing temperature and rate showed beneficial influence on the birefringence, and tensile strengths of the drawn film specimens. Possible mechanisms accounting for these interesting deformation properties are suggested.     

Properties of bamboo flour/high-density polyethylene composites reinforced with ultrahigh molecular weight polyethylene

In order to improve the properties of bamboo-plastic composites (BPCs), bamboo flour/high-density polyethylene (HDPE) composites were reinforced with ultrahigh molecular weight polyethylene (UHMWPE). The effects of UHMWPE on properties of composites were studied. The crystallinity of composites decreased slightly. Compared with non-UHMWPE added bamboo powder/HDPE composite, the composite with 6 wt % UHMWPE, showed decrease in water absorption to 0.41%, whereas its tensile strength and flexural strength increased to 34.51 and 25.88 MPa, respectively, a corresponding increase of 34.59 and 12.87%. The temperatures corresponding to initial degradation temperature (T_initial) and maximum degradation temperature (T_max) of the composite increased from 282.7 and 467.4 °C to 288.5 and 474.7 °C respectively. Scanning electron microscopic images showed that UHMWPE was well dispersed and fully extended as long fibers in the composite, forming a “three-dimensional physically cross-linked network structure,” which contributed to the improved properties of the composites. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48971.     

Study on processing of ultrahigh molecular weight polyethylene/polypropylene blends

The processing of ultrahigh molecular weight polyethylene (UHMWPE) by the addition of polypropylene (PP) and high‐density polyethylene (HDPE) was investigated. The results show that the addition of PP improves the processability of UHMWPE more effectively than does the addition of HDPE. UHMWPE/PP blends can be effectively processed with a twin‐roller and general single‐screw extruder. In the extrusion of UHMWPE/PP blends, PP is enriched at the surface of the blend adjacent to the barrel wall, thus increasing the frictional force on the wall; the conveyance of the solid down to the channel can then be carried out. The melt pool against the active flight flank exerts a considerable pressure on the UHMWPE powder in the passive flight flank, which overcomes the hard compaction of UHMWPE. The PP penetrates into the gaps between the particles, acting as a heat‐transfer agent and adhesive, thus enhancing the heat‐transfer ability in the material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 977–985, 2004     

A conducting composite of polypyrrole with ultrahigh molecular weight polyethylene foam

Through a chemical polymerization of pyrrole inside ultrahigh molecular weight polyethylene (UHMWPE) foam, a conducting polymer composite was obtained. To produce conductive polymer foams, successive imbibiting of reactives, FeCl₃ and pyrrole in tetrahydrofuran solutions, were carried out. The conductive polymeric materials were characterized by FTIR, DSC, and SEM. Mechanical property measurements were carried out on the films prepared by the compression molding of the conductive foam polymers. These films showed rather high tensile strength compared to pure UHMWPE. Conductivity determined by a two‐probe technique showed that it increased with the pyrrole content in the UHMWPE foam matrix. The compression molding, however, resulted in a considerable reduction in the conductivities. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1843–1850, 1999