Sintering of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (UHMWPE) is a high performance polymer having low coefficient of friction, good abrasion resistance, good chemical resistance etc. It is used in shipbuilding, textile industries and also in biomedical applications. UHMWPE is processed by powder processing technique because of its high melt viscosity at the processing temperature. Powder processing technique involves compaction of polymeric powder under pressure and sintering of the preforms at temperature above its melting point. In this study, we report our results on compaction and sintering behaviour of two grades of UHMWPE with reference to the powder morphology, sintering temperatures and strength development.     

超高分子量聚乙烯的生物摩擦学

结合超高分子量聚乙烯(UHMWPE)的磨损机制,综述了通过改性,如离子注入、填料改性等,提高UHMWPE的耐磨性研究,并对其发展方向进行了有益探讨.     

Crystal ageing in irradiated ultra high molecular weight polyethylene

Medical grade ultra high molecular weight polyethylene (UHMWPE) of two molecular weights has been γ irradiated in air to give received doses of 3.5 and 10 Mrad and aged in air for 25 months. Differential scanning calorimetry and wide and small angle X-ray diffraction (WAX and SAX) techniques and transmission electron microscopy have been used to characterize the materials. Polymer from an orthopaedic component, retrieved 10 years after implantation, has been subjected to the same analytical programme. The X-ray diffraction data shows that following irradiation two events occur with time, first a crystal refinement process, indicated by pronounced sharpening of the SAX peak, and secondly growth of a new crystal population of reduced lamellae thickness compared to the original crystal structures, shown by the development of a bimodal SAX pattern. Following irradiation crystallinity increases with time and this second crystal population makes a significant contribution to that increase. The retrieved component shows full development of these processes. It is considered that these crystallographic changes with time are responsible for the observed time dependent changes in the mechanical properties of air irradiated UHMWPE.     

超高分子量聚乙烯纤维的发展状况

介绍超高分子量聚乙烯纤维的结构性能,发展历程和现状.描述了纤维的生产工艺方法和用途,介绍了国内外主要生产厂商产品,以及国内外对超高分子量聚乙烯纤维的改性方法和应用.     

Fatigue characteristics of ultra high molecular weight polyethylene with different molecular weight for implant material

In order to investigate the effect of molecular weight on fatigue characteristics in the ultra high molecular weight polyethylene (UHMWPE), tension–tension fatigue tests of notched specimens were carried out in the present study. The effects of frequency and stress ratio on the fatigue characteristics were also investigated and fractography was discussed. The fatigue strength does not increase with increasing molecular weight. The fatigue strength might be influenced by the high degree of crystallinity in spite of the decreased tie molecule density in this study. Almost no effect of frequency on the number of cycles to failure can be observed. However, the higher the frequency, the higher the crack tip temperature. The effects of heat and strain rate on the fatigue strength must be considered in polymer materials. At a high stress ratio, the stress–number of cycles to failure (S–N) curves shift to high number cycles to failure side. Both stress amplitude and mean stress influence the fatigue life of UHMWPE. © 2001 Kluwer Academic Publishers     

Observations of residual sub-surface shear strain in the ultrahigh molecular weight polyethylene acetabular cups of hip prostheses

Analysis of bearing surfaces of explanted cups can help to determine the wear mechanisms that are responsible for generation of wear debris. In this study a microscope polariscope was used to detect residual subsurface shear strains, deformation and subsurface cracks in explanted Charnley acetabular cups. The wear surfaces were compared to an acetabular cup from a hip joint simulator test. The six explanted cups that were studied had all failed after long periods of implantation, with penetrations ranging from 2.1 to 3.8 mm. The explanted and simulator cups both had a smooth, high-wear region. High residual subsurface shear strains were found in the high-wear region of most cups, with certain cups possessing subsurface cracks running parallel with the surface 5–10 m deep, close to the areas of high residual subsurface shear strain. This was caused by plastic deformation and subsurface fatigue of the polymer surface.     

Enhanced wear performance of ultra high molecular weight polyethylene crosslinked by organosilane

Ultra high molecular weight polyethylene (UHMWPE) crosslinked by organosilane was thermal compression molded. The organosilane used was the tri-ethyloxyl vinyl silane. Its gelation, melting behavior, crystallinity, mechanical and wear-resisting properties were systematically investigated. The results showed that the gel ratio of UHMWPE increases with the incorporation of organosilane. At a low content of organosilane, the melting point and crystallinity of the crosslinked UHMWPE increase, and hence the mechanical and wear-resisting properties are improved. However, at a high content of organosilane, these performances of the crosslinked UHMWPE become worse. At 0.4 phr silane, the wear resistance of crosslinked UHMWPE reaches its optimum value.     

HAP／UHMWPE生物复合材料的制备与微观结构

通过化学共沉淀．水热合成法制备纳米级羟基磷灰石（HAP），再用自制模具制备出羟基磷友石／超高分子量聚乙烯（UHMWPE）复合材料．通过SEM观察、X射线分析、DSC测试、热重分析以及力学性能测通过其超长分子链获得网状结构，为材料提供机械强度，HAP在复合材料中试，研究了HAP／／UHMWE复合材料的微观组织和力学性能．结果表明：UHMWPE分布比较均匀，并被包裹在UHMWPE超长细链形成的层层网状结构之中．随着HAP含量的增加，复合材料的熔点下降，熔融热焓有所降低，UHMWPE的结晶度降低了．随着HAP体积含量的增加，复合材料的拉伸强度和抗弯强度均下降，从30．1MPa降到21．5MPa以及从63．1IMPa降到46．7MPa，而弹性模量有所上升，从1．6GPa上升到4．1GPa．     

超高分子量聚乙烯纤维表面紫外接枝聚合改性研究

以二苯甲酮(BP)为引发剂,采用新型二步紫外接枝法在超高分子量聚乙烯(UHMWPE)纤维表面接枝了丙烯酸(AA)、甲基丙烯酸(MAA)等活性单体,利用全反射傅里叶变换红外光谱(ATR-IR)、电子显微镜(SEM)分析证明了接枝层的存在,此外还通过紫外吸收光谱(UV)、全反射傅里叶变换红外光谱(ATR-IR)、热裂解色谱质谱分析(Py-GCMS)对反应机理进行了分析.探索了接枝条件对接枝率的影响,接枝改性后的超高分子量聚乙烯纤维的粘结性能和亲水性能大大提升,其中界面剪切强度提升160.9％,水接触角从112.0°下降为67.88°.     

超临界CO2改性UHMWPE/PP共混物性能的研究

采用超临界CO2作为增塑剂,与聚丙烯(PP)结合对超高分子量聚乙烯(UHMWPE)进行挤出共混,分析超临界CO2对其性能的影响.结果表明:随着螺杆转速的增加,共混物的拉伸强度呈下降趋势,冲击强度随着螺杆转速的增加呈现先降低后升高的趋势.有超临界CO2条件下的共混物的力学强度值均高于无超临界条件下的.SEM照片显示,超临界CO2的加入使UHMWPE/PP共混物的界面模糊,相容性增加,且超临界CO2使共混物中出现少量的微孔,从而使制品密度降低但并没有影响其力学性能.DSC表征说明,超临界CO2的加入可以使共混物的结晶度增加.     

A study on the tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) coated with a Ni-P layer

The tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been investigated using friction and wear tests at room temperature (25 °C) and also at a low temperature (-20 °C) in air, vacuum or CO₂ saturated vapour for UHMWPE rubbing against itself and also against a steel counterpart. A sticking phenomenon took place in saturated CO₂ vapour at low temperature (-20°C), which was produced by severe adhesion between the UHMWPE polymer rubbing pair. The sticking phenomenon was prevented by a Ni-P coating deposited on the surface of the UHMWPE by means of high-speed electro-plating. Non-continuous transfer films of UHMWPE on the Ni-P surface layer and the steel surface were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The studied coating has a solid lubrication character, so that its sliding friction coefficient and relative wear weight loss of the pin w _t, decreased; the wear mechanism changed from adhesive wear to surface fatigue wear. It is concluded that the tribological behaviour of the UHMWPE polymer could be improved with a metallic coating, such as the Ni-P coating used in this study.     

Improving the ballistic performance of ultra high molecular weight polyethylene fiber reinforced composites using conch particles

A new method was proposed to improve ballistic impact performance of unidirectional ultra high molecular weight polyethylene (UHMWPE) fiber plate (UD plate) by adding shell particles in matrix. The complex micro-laminate structure of these bio-composite materials was studied. It was revealed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR) spectra that modified shell particles were uniformly dispersed in the matrix. The results of ballistic tests and temperature adaptation tests demonstrated that the bulletproof property of the modified UD plate was improved by 20%.     

Comparative wear under four different tribological conditions of acetylene enhanced cross-linked ultra high molecular weight polyethylene

In this study, the wear of ultra high molecular weight polyethylene (UHMWPE) (Grade RCH 1000) crosslinked by gamma irradiation in acetylene was compared to virgin (non-irradiated) UHMWPE using four different wear configurations: (i) unidirectional motion with a smooth counterface, (ii) multidirectional motion with a smooth counterface, (iii) unidirectional motion with a rough counterface and (iv) multidirectional motion with a rough counterface. ©©1999©Kluwer Academic Publishers     

Effect of annealing process in water on the essential work of fracture response of ultra high molecular weight polyethylene

The toughness of ultra high molecular weight polyethylene (UHMWPE) before and after annealing process in water was investigated by the essential work of fracture (EWF) method. Annealing in water at 80 °C for various aging periods of the 5 mm thickness with various ligament lengths single edge notched tension (SENT) specimens was performed in hot water. Tensile tests were performed at 2 mm/min constant deformation rate at room temperature in order to determine EWF parameters. After tensile tests, the fracture cross-sections of SENT specimens were investigated by scanning electron microscope (SEM). From the 60th day of annealing process in water, it was seen that the fracture toughness of the material decreased while water absorption in samples increased.     

Characterization of silane coated hollow sphere alumina-reinforced ultra high molecular weight polyethylene composite as a possible bone substitute material

Silane coated hollow sphere alumina ceramic particles were moulded with ultra high molecular weight polyethylene (UHMWPE) to form a series of composites with alumina weight percent in the range from 15 to 50. The composites were prepared in a cylindrical mould using powder-processing technique. The composites were characterized for mechanical properties using destructive and non-destructive ultrasonic testing methods. The physical properties of the composite were determined and compared with those of cortical bone.