超高分子量聚乙烯基纳米复合材料的导热性能研究

通过添加导热系数较高的纳米AIN、C纤维来制备超高分子量聚乙烯复合材料,采用Hot Disk导热系数仪测试了其导热系数,同时分析了不同添加物及其含量对导热系数的影响.结果表明,制备的超高分子量聚乙烯复合材料的导热性能有明显提高.在本实验条件下,当纤维的添加量达到20%时,复合材料的热导率为0.8969 W·m-1·K-1,比纯超高分子量聚乙烯提高了150%.     

The plastic deformation of ultra-high molecular weight polyethylene

Gel-spun filaments of different initial morphologies have been subjected to controlled drawing at elevated temperatures. The drawn samples have been examined by high-resolution scanning electron microscopy. The deformation mechanism at temperatures up to 120° C is very similar to crazing, especially in the case of unoriented gel-spun filaments. Filaments exhibiting a shish-kebab morphology offer the opportunity of examining the deformation of elementary fibrils in a quantitative way. The transformation of individual lamellae into fibrils is the initial deformation mode, which is followed by slip of fibrils at a later stage. This is concluded from a comparison of experimental data and model calculations of the maximum draw ratio. Drawing at 144° C results in the formation of globular aggregates of lamellae, with a characteristic long period of 40 nm. This long period persists until all the globules have been converted, by micronecking, into aggregate fibrils of extended-chain character. On a molecular scale, the various processes can be described as the temperature-dependent flow behaviour of an entanglement network.     

Impact fatigue response of ultra-high molecular weight linear polyethylene

The impact fatigue response of ultra-high molecular weight linear polyethylene (UHMW LPE), in a special test, has been examined and the results are presented in this paper. In an attempt to understand the influence of high molecular weight on impact strength, identical measurements were made on a normal molecular weight linear polyethylene (NMW LPE). UHMW LPE is found to have a superior impact and impact fatigue behaviour to the NMW LPE. Almost all of the UHMW LPE materials perform equally well in the present impact fatigue test. However, one of the high bulk density UHMW LPE materials, resin G, performs quite poorly. Photomicrographs of the free surface of this material show that this may result from poor interparticle fusion during compression moulding.     

超高分子量聚乙烯纤维级专用料的开发

超高分子量聚乙烯(UHMWPE)纤维具有许多卓越的性能,被广泛应用于工业及一些特殊领域.本文对国内UHMWPE纤维用原料的性能以及纤维的性能进行对比分析,包括原料的分子量、颗粒形态、热性能以及纤维的力学性能,为开发UHMWPE纤维级专用料提供参考,以提高国产UHMWPE纤维的性能.     

自增强高密度聚乙烯/超高分子量聚乙烯复合材料制备与表征

用自制模具制备出自增强高密度聚乙烯(HDPE)/超高分子量聚乙烯(UHMWPE)棒材.通过SEM观察、X射线分析、DSC分析以及力学性能测试,研究了挤出自增强HDPE/UHMWPE棒材微观结构和力学性能.研究结果表明,在HDPE和UHMWPE最佳配比为8:2的情况下,自增强试样的拉伸强度、抗弯强度和弹性模量分别为168.5、164.8MPa和4.9GPa,比未增强试样分别提高了534.9%、261.2%和408.3%.与普通模压试样相比,自增强试样内部有大量的微纤结构和串晶互锁结构,结晶度获得提高,(110)面和(200)面的峰值均获得提高,并且熔点向高温区发生漂移.     

聚全氟乙丙烯改性超高分子量聚乙烯的性能研究

以纯超高聚乙烯(UHMWPE)为基础原料,添加高密度聚乙烯、乙烯-丙烯酸酯共聚物、纳米SiO₂等改性剂,制备了UHMWPE改性混合物。研究了聚全氟乙丙烯(FEP)的加入和用量,对UHMWPE改性混合物力学性能及磨耗性能、熔融性能及热性能的影响。结果表明:添加FEP前后,改性混合物体系中纳米粒子都有较好的分散,拉伸强度和冲击强度以及热性能变化不大,但添加FEP后聚合物体系的磨耗几乎下降了50%,熔融性有一定的改善。当FEP用量较少时,随着FEP用量的增加,改性混合物的拉伸强度和冲击强度都上升;当FEP用量超过2%时,随着随着FEP用量的增加,改性混合物的拉伸强度和冲击强度都下降;在FEP用量达到2%时,改性混合物的磨耗是最低的。     

Deformation mechanisms during uniaxial drawing of melt-crystallized ultra-high molecular weight polyethylene

The crystal deformation mechanisms during solid-state uniaxial drawing of melt-crystallized ultra-high molecular weight polyethylene (UHMW-PE) film have been studied as a function of draw ratio. At higher draw ratios (3) the fine slip processes during uniaxial drawing of melt-crystallized UHMW-PE result in a single-erystal-like (1 0 0) [0 0 1] texture, whereas the normals to the lamellae are inclined by more than 45° with respect to the applied force. It is postulated that in melt-crystallized UHMW-PE the coarse slip process is predominantly restricted due to the fold plane restraints, preventing lamellae from breaking up and rotating with their normals towards the draw direction. The inclination of lamellar normals with respect to the draw direction prohibits further drawing because shear stresses act perpendicular instead of parallel to the lamellar normals.     

Electrical properties of graphene nanoplatelets/ultra-high molecular weight polyethylene composites

Graphene nanoplatelets (GNPs)/ultra-high molecular weight polyethylene (UHMWPE) composites with a segregated structure had been fabricated using ethanol-assisted dispersion and hot compression at 180 °C. A percolation threshold of 3.5 wt% was achieved because of the formation conductive network. The positive temperature coefficient (PTC) and the negative temperature coefficient (NTC) effects of GNPs/UHMWPE composites had been investigated. The PTC behavior enhanced with increasing GNPs content but this was not always the case. The maximum PTC effect was observed in GNPs/UHMWPE composites (GNPs, 3.8 wt%) with the relatively low room temperature resistivity and the relatively high peak resistivity. The structure for GNPs/UHMWPE composites was examined by the SEM. The fact revealed that the slight interaction between GNPs and UHMWPE matrix may be changed by thermal cycles, and this can explain why thermal cycles could increase PTC and NTC intensity.     

Medical-grade ultra-high molecular weight polyethylene: past,current and future

Ultra-high molecular weight polyethylene is a semi-crystalline polymer (45–60%) with six decades of orthopaedic applications. This polymer has a high fracture toughness (30?kJ?m^?2) which comes from the molecular weight and the chain entanglements. Adverse alteration of the properties may lead to the part's pre-mature failure. This paper reviews the current manufacturing methods, and their effect on the properties of the polymer. The review also focused on the attempts of enhancing the polymer properties. The main cause of failure is implant loosing owing to the polymeric wear particles. Many manufacturers have attempted to enhance the wear and oxidation properties of the polymer, and the outcome of the new technologies is critically reviewed. Finally, the review explores the potential for future developments.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Mechanical properties of ultra-high molecular weight polyethylene fibres in relation to structural changes and chain scissioning upon spinning and hot-drawing

Gel- and suspension-spun fibres of ultra-high molecular weight polyethylene have been subjected to hot-drawing at 148° C. It has been found that for these fibres and drawing conditions, strength and modulus are uniquely determined by the draw ratio, analogous to observations by Capaccio et al. [1] for melt-spun fibres. Draw ratios of 100 could be achieved, leading to a tensile strength at break of 3.8 GPa and a Young's modulus of 120 GPa. Chain scissioning occurs both in spinning and hot-drawing. There seems to be a limiting molecular weight of approximately 1.5×10⁶. Extraction of the low molecular weight polyethylene from the as-spun fibres by controlled swelling, whereby an entanglement network of only the very long chains remains, substantially reduced the drawability of the fibres and only a draw ratio of 40 and a tensile strength of 1.7 GPa could be attained for such filaments.     

Crystal twinning in simultaneous biaxial stretching of gelation-crystallized ultra-high molecular weight polyethylene

Structure and orientation development in simultaneous biaxial stretching of gelation-crystallized ultra-high molecular weight polyethylene (UHMWPE) was examined by means of X-ray pole figures. The dry gel film exhibits a stacked lamellar structure similar to single-crystal mats with preferential crystalc-axis orientation normal to the film surface. The biaxially stretched gelationcrystallized films reveal a complex crystal orientation of (1 1 0), (2 0 0) and (0 2 0) planes. The detailed analysis of these pole figures manifests the occurrence of crystal twinning in addition to the orientation of crystallites. Crystal transformation of orthorhombic to monoclinic structure was not observed during biaxial stretching. The orientation distribution functions of crystallites were calculated assuming affine deformation. The orthogonality of crystal 1 1 0-c axes and crystala-c axes was further assumed to be conserved during the crystal twinning and biaxial orientation, respectively. Model simulation with contributions of 30% crystal twinning and 70% crystal orientation yields the best fit with the X-ray pole figures of biaxially stretched UHMWPE films. The affine model appears to be valid up to a biaxial draw ratio of 1.8×1.8, after which the results deviate from ideality with increasing draw ratio.On leave from Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan.     

Micellar morphology and its plastic deformation behaviour in ultra-high molecular weight polyethylene

Highly oriented samples from ultra-high molecular weight and normal high-density polyethylene (UHMWPE, HDPE) were prepared under the same experimental conditions. The morphology of the UHMWPE, investigated by transmission electron microscopy, was found to be oriented micellar, while the HDPE samples had a shishkebab morphology. Tensile test experiments under cyclic loading conditions exhibit a strain-hardening effect (increase in stress for the onset of plastic deformation) for HDPE, while the UHMWPE shows a decrease in Young's modulus, which is attributed to similar molecular mechanisms as for the Mullins effect in particle-filled elastomers.     

Tribological behavior of ultra-high molecular weight polyethylene in a hip joint simulator

In this paper effects of various injection molding parameters on tribological properties of ultra-high molecular weight polyethylene (UHMWPE) were investigated. The tribological properties like coefficient of friction and wear rate were obtained from the experimental results of hip simulator which was designed and fabricated in the laboratory. Bovine serum was used as a lubricant in this study. In addition, the hardness of the specimen was also investigated as well. The injection molding parameters that varied for this study are melt temperature, injection velocity and compaction time. The results show that contact loads and melt temperature were mostly influenced the tribological behavior of UHMWPE. A wear mechanism map was developed to study the dominant wear mechanism that influences the wear behavior of UHMWPE. SEM was employed to study the worn out morphologies of UHMWPE. The dominant wear mechanisms that are dominated through our study are ironing, scratching, ploughing, plastic deformation, and fatigue wear.     

The fracture process of ultra-high strength polyethylene fibres

The fracture behaviour of ultra-high strength polyethylene fibres has been investigated in dead load tests as well as by electron microscopical observation of the fracture surfaces. It was found that the fracture process in the fibres involves an activation energy of about 60 to 75 kJ mol^–1, which implies that the strength is mainly determined by the lateral bond strength between the molecules. Fracture is initiated at surface irregularities, such as kink bands, which leads to the formation of cracks with a fibrillated fracture surface. In this process the individual fibrils are cut through at topological defect regions in such fibrils, containing a relatively high concentration of trapped entanglements and chain ends. The ultimate strength of the polyethylene fibres was found to be inversely proportional to the square root of its diameter. Extrapolation to zero diameter yields a strength of 26 GPa for flawless fibres, which equals the theoretical strength of polyethylene.     

Hierarchical constraint distribution of ultra-high molecular weight polyethylene fibers with different preparation methods

The hierarchical constraint characteristics of ultra-high molecular weight polyethylene (UHMW-PE) fibers with different structures were evaluated by in situ wide-angle X-ray diffraction (WAXD) measurement during heating. Two UHMW-PE fibers were used in this study, an original gel-spun fiber and a processed fiber that was tensile-drawn from the original fiber above the static equilibrium melting temperature of PE. A difference in fiber processing induced change in constraint distribution attributed to morphological heterogeneity. The original gel-spun fiber, which had a heterogeneous structure, induced the constraint distribution because of the obvious existence of skin and core. In contrast, the tensile-drawn fiber, which had a homogeneous structure formed by the fusion adhesion between twisted single yarn surfaces, depressed the constraint distribution. These results demonstrate that a difference in fiber processing induces change in hierarchical characteristics with different structural dimensions.     

Flexural fatigue resistance of ultra-high molecular weight polyethylene at ambient and low temperature

Specimens of ultra-high molecular weight polyethylene have been subjected to flexural fatigue tests at −40° and 23°C, and the temperature of some of the specimens recorded throughout the test. It is found that when the specimen life exceeds 10⁶ cycles, the temperature of the specimen stabilizes. However, if the temperature of the specimen does not reach equilibrium with the testing temperature, the specimen life is short (< 10⁴ cycles). The stabilization of the speciment temperature is related to a critical stress level, which is different for each testing temperature.     

Elastic flow instabilities and shish-kebab formation during gel-spinning of ultra-high molecular weight polyethylene

The flow behaviour during gel-spinning of semi-dilute solutions of ultra-high molecular weight polyethylene in paraffin oil was investigated in relation to fibre strength and morphology. Shish-kebab morphologies observed in the as-spun filaments originate from a solidification of long flow units already developed in the polymer solution during spinning. These flow units consist of alternating bundles of elongated molecules and highly entangled clusters of unoriented molecules. Extrudate stretching leads to a demolition of these long flow units by elastic flow instabilities. As a result, the tensile properties after hot-drawing of the fibres are strongly reduced. The inclusion of 1 wt% aluminium stearate in the spinning solution preserves the long bundle-like flow units even at high take-up speeds during extrusion. This additive suppresses the adsorption of the polyethylene on the die-wall and avoids the generation of elastic turbulences. Filaments with a strength between 2.5 and 3.0 G Pa can be obtained from these doped solutions after hot-drawing, in spite of high winding speeds up to 300 m min⁻¹ in the spinning process.     

The effect of sterilising radiation on the properties of ultra-high molecular weight polyethylene

The effects of sterilising radiation on the properties of ultra high molecular weight polyethylene have been measured by tensile testing, dynamic mechanical analysis and differential scanning calorimetry. It was found that tensile modulus and yield stress both increased with increasing radiation dosage, while elongation at fracture showed an inverse relationship. A general increase in shear storage modulus and decrease in relative damping with dosage was also observed. These results are discussed in terms of radiation-induced cross-linking and the morphological data produced from the calorimetry experiments. Whilst the individual changes observed could be explained in terms of standard radio-chemistry, they did not correspond directly to the phenomena observed in high radiation dose work.     

A structural study on solid state drawing of solution-crystallized ultra-high molecular weight polyethylene

The influence of solid state drawing of solution-crystallized ultra-high molecular weight polyethylene on the structure has been studied. Results obtained by different wide-angle and small-angle X-ray techniques support a deformation mechanism, which was partially described by Peterlin. An extended mechanism is proposed, which not only explains the orientational effects observed via WAXS and SAXS fairly easily, but can also account for the constancy of the long period, the steady decrease of the meridional SAXS intensity, the increase in crystallinity and the increase in the longitudinal crystallite size as the draw ratio increases (starting from a draw ratio of 10). Furthermore, the observed changes in lateral apparent crystal sizes as well as the stress-strain behaviour during the drawing process can be understood easily in terms of this model.