Cold compaction molding and sintering of ultra high molecular weight polyethylene

Cold Compaction Molding and Sintering of Ultra High Molecular Weight Polyethylene (UHMWPE) has been examined as a function of particle size, sintering time and temperature, and cooling rate. Properties nearly equivalent to those obtained by compression molding can be obtained from samples with a fibrous particle morphology, sintered just above the melting point, with further improvement possible by control of particle size and addition of fine particles of normal molecular weight linear polyethylene. UHMWPE with a nodular particle morphology sintered poorly.     

Comparative studies of ultra high molecular weight polyethylene fiber reinforced composites

Ultra high molecular weight polyethylene fiber is a very promising material for making light-weight high strength and high impact resistant composites, especially for ballistic protective shields. Three commercially available materials designed specifically for ballistic applications are Spectra® woven cloth, Dyneema Fraglight® nonwoven felt, and Spectra Shield® Plus PCR prepreg were chosen for parallel comparisons. The high-temperature high-pressure sintering process was applied to all three materials. The physical, thermomechanical, and microstructural properties of the consolidated products were studied and compared, including their crystallinity, molecular orientation, impact resistance, interlaminar adhesion, flexural properties, and thermoformability. The differences in these materials and their structures are reflected in the different properties of the final products. The influence of different processing conditions on the properties also differs for each material. It is concluded that matrix free Spectra cloth composite has dominant advantages over the other two materials. POLYM. ENG. SCI., 47:1544–1553, 2007. © 2007 Society of Plastics Engineers     

Unusual rheology behaviour of ultra high molecular weight polyethylene/kaolin composites prepared via polymerization‐filling

The rheological behaviour of ultra high molecular weight polyethylene (UHMWPE)/Kaolin composites prepared by a polymerization‐filling process was investigated by conducting capillary and dynamic rheology tests. The results showed that the addition of Kaolin could significantly improve the processability of UHMWPE composites. The common viscoelastic flow was discovered for UHMWPE composites in capillary extrusion testing. The further discussion showed that the unique microstructure provided by polymerization‐filling of UHMWPE/Kaolin composites led to this unusual rheology behaviour. Copyright © 2003 Society of Chemical Industry     

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。     

超高分子量聚乙烯材料的研究进展

超高分子量聚乙烯(UHMWPE)是高性能聚烯烃材料的典型代表,稳定的线性长链结构使其具有高强度、耐冲击、耐磨损、自润滑、耐化学腐蚀、耐低温等诸多优异性能。近年,UHMWPE加工、改性技术日益扩展、优化,形成了多种多样的UHMWPE制品,广泛应用于军民各项领域。本文综述了UHMWPE在催化聚合、纤维、膜、管材、板材及型材等方面的最新进展,重点介绍在各领域应用、加工、改性等方面的研究成果和发展趋势。     

Solid state extrusion of ultra high molecular weight polyethylene. Processing and properties

The techniques of solid state coextrusion and powder extrusion have been employed for the deformation of ultra high molecular weight polyethylene. Chain folded and chain extended morphologies obtained under different crystallization conditions were coextruded within a nylon 11 casing acting as a processing aid at an extrusion draw ratio (EDR) of 5 at ≤ 120°C and 0.20 GPa. The powder was compacted and extruded at ≤ 128°C and 0.23 GPa up to an EDR of 24. The physical and mechanical properties of the extrudates were evaluated and found to be dependent on intial morphology. An extrudate from the chain-folded morphology gave a low modulus of 0.71 GPa, the chain-extended morphology a modulus of 6.7 GPa, and the compacted powder a modulus of 15 GPa.     

Preparation and properties of thermoplastic polyurethane/ultra high molecular weight polyethylene blends

The blends of thermoplastic polyurethane and ultra high molecular weight polyethylene (UHMWPE) were prepared by a co‐twin screw extruder. Phase separation morphology of the blends was confirmed by the SEM observations. The incorporation of UHMWPE is detrimental to the mechanical properties of the blends prepared from stiffer TPU, whereas is beneficial to that of TPU with low hardness. The tribological behaviors of neat TPU and its blends were studied by the means of a block‐on‐ring apparatus. It was found that UHMWPE could greatly improve the tribological properties of TPU matrix both under dry sliding and water lubricating conditions due to the excellent self‐lubricating property of the UHMWPE materials and furthermore improve the wear failure limit of TPU. POLYM. COMPOS., 36:897–906, 2015. © 2014 Society of Plastics Engineers     

Degradation of ultra high molecular weight polyethylene in vivo

Mechanical and thermal oxidation of UHMWPE used in the preparation of prosthetic implants is studied and the mechanisms of degradation are reported. Oxidation of new and retrieved prosthetic implants are studied by IR microscopy and clear evidence of oxidation in vivo is shown.     

J Integral measurements of ultra high molecular weight polyethylene

Fracture of ultra high molecular weight polyethylene (UHMWPE) contributes to damage modes occurring on the articulating surfaces of total joint replacement components. To minimize damage through the optimization of component design requires an understanding of the fracture behavior of UHMWPE. A fracture/mechanics approach was taken in which J integral tests were performed on three-point bend specimens of two thicknesses. J_IC was determined to be 99.5 kJ/m² and was independent of specimen thickness. The fracture surfaces for both specimen thicknesses showed extensive orientation and failure through multiple layers of material, suggesting that UHMWPE experiences plane stress conditions at the crack tip, regardless of thickness.     

浅谈超高分子量聚乙烯纤维的表面处理

超高分子量聚乙烯（UHMWPE）纤维是一种性能优异的高性能纤维,但由于其表面自身特点,限制了它的应用,所以通常对其表面进行处理,以提高与树脂的界面结合力。作者介绍了几种用于UHMWPE纤维表面处理的方法,如等离子处理法。     

超高分子量聚乙烯纤维防切割手套应用与市场分析

阐述了超高分子量聚乙烯(UHMWPE)防切割手套的加工及性能特点,并分析了市场发展趋势,对市场前景进行了展望。     

超高相对分子质量聚乙烯纤维热牵伸性能研究

就超高相对分子质量聚乙烯纤维热牵伸过程的拉伸比和牵伸温度对纤维力学性能的影响进行了试验.研究结果表明,拉伸比4.5～6.0和牵伸温度144～150℃是最适合超高相对分子质量聚乙烯纤维热牵伸的关键参数,纤维力学性能可以达到拉伸强度35 cN/dtex和拉伸模量1 100 cN/dtex以上.     

Effect of gamma ray irradiation on processability and properties of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (UHMWPE) has been widely used in many fields due to its outstanding properties. However, it is virtually impossible to be processed by the conventional method due to its high molecular weight and very tight chain entanglement. To solve this problem, a new method was proposed in this article. Gamma ray irradiation was adopted to cause the oxidation degradation of UHMWPE. The degraded products which generated in situ and dispersed in UHMWPE evenly were utilized as self‐lubricant and heat transfer intermediary. These low molecular weight fractions thus could improve the processability of UHMWPE. The effects of irradiation dose on the structure and properties of UHMWPE were studied by fourier transform infrared (FTIR) spectroscopy, gel content measurement, wide angle x‐ray diffraction (WAXD), Haake torque rheometer, mechanical properties measurements and sliding wear tests. The experimental results showed that gamma ray irradiation caused oxidation degradation of UHMWPE. Under appropriate irradiation condition, the processability of UHMWPE could be improved substantially while most of its excellent properties could be kept. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characteristics of nano-B4C/PVA particles and ultra high molecular weight polyethylene composites

In-situ mechanical process for preparation of the polyvinyl alcohol (PVA) coated nano-B₄C powder was investigated by using a high-energy ball mill. The produced PVA coat on the surface of nano-B₄C particles was observed by x-ray diffraction (XRD) and confirmed by TEM images. The average particle size of the produced nano-B₄C/PVA particles was in the range of several tens to hundreds of nanometers depending on the milling conditions. The polymer composites were fabricated by hot pressing ultra high molecular weight polyethylene (UHMWPE) powder mixed with nano-B₄C/PAV and micro-B₄C powders, respectively. Nano-B₄C/PVA dispersed UHMWPE shows slightly lower crystallinity and stiffness than micro-B₄C dispersed UHMWPE based on differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) evaluations.     

Melt characterization of ultra high molecular weight polyethylene using squeeze flow

A method for determining the melt viscosity and molecular weight of ultra high molecular weight polyethylene (UHMWPE) is described. The method, based on squeeze flow, was used to characterize seventeen UHM W-PE samples varying in molecular weight from 0.6 × 10⁶ to 5.1 × 10⁶ and in viscosity from 2.9 × 10⁶ to 3.4 × 10⁹ poise. A correlation between melt viscosity and molecular weight was demonstrated, but the reliability of a molecular weight determination decreased somewhat as molecular weight increased. As a predictor of melt processability, the method provides the speed and simplicity heretofore lacking in UHMW-PE characterization by solution viscosity while retaining high reproducibility.     

Uniaxial tensile creep behaviour of ultra high molecular weight linear polyethylene

The present paper examines the room temperature constant-load uniaxial tensile creep response of two ultra high molecular weight linear polyethylene (UHMW LPE) materials and compares it with that of a normal molecular weight linear polyethylene (NMW LPE). It was found that at all stress levels examined, the magnitude of creep deformation is significantly higher in UHMW LPE than in NMW LPE. Possible reasons for this behaviour are explored. Potential techniques for improving the tensile creep behaviour (i.e. decreasing the creep deformation) of LPE are discussed.     

Microstructural origin of physical and mechanical properties of ultra high molecular weight polyethylene processed by high velocity compaction

Ultra High Molecular Weight Polyethylene (UHMWPE) is a semi-crystalline polymer with exceptional wear and impact properties, but also a very high melt viscosity, owing to its extremely long chains. Therefore, UHMWPE is non-melt processable and its processing is long and expensive. However, a new process, High Velocity Compaction (HVC), allows processing UHMWPE within short processing times via sintering. Several high velocity impacts are applied to a powder-filled die to provide self-heating. The sintering is then obtained by local fusion/recrystallization. In this study, the physical and mechanical properties of UHMWPE processed by HVC are investigated. Ductile UHMWPE with a high modulus was obtained. The particular microstructure of the material resulting from the sintering by fusion/recrystallization has then been characterized. It appears that mechanical properties of HVC-UHMWPE are governed by the microstructure induced by processing conditions, and hence can be adjusted for a given application.     

The forming properties of high molecular weight polyethylene

The formabilities of cold-rolled high molecular weight polyethylene (HMWPE) sheets have been studied by measuring their plastic anisotropy ratio (R value), strain-hardening exponent (n value), strain distribution, and the forming limit diagram (FLD). The deep drawability of the polymer is improved by rolling. After 40% or more reduction in thickness by cold rolling, the HMWPE sheet could be deep-drawn into a cylindrical cup. The results of R value measurement indicate that the R value is responsible for improved drawability. Cold rolling also increases the n value but decreases the strain gradient. Stretch forming tests have also been carried out, and the results show that cold working could also improve the stretchability of this polymer. The results of the FLD are in agreement with the other properties studied. The mechanical properties, environmental stress cracking resistance, and shape, size, and property stability of the deep-drawn HMWPE cups have also been investigated.