High strength and bioactive hydroxyapatite nano-particles reinforced ultrahigh molecular weight polyethylene

Nano-sized hydroxyapatite (HA) particles reinforced UHMWPE composite was developed for biomedical applications. The biocomposite with HA volume fraction of 0.5 was successfully processed by combined swelling/twin-screw extrusion, compression molding, and then hot drawing. SEM and EDAX characterization revealed that HA nano-particles were homogeneously dispersed in UHMWPE. WAXD showed that hot drawing effectively oriented the UHMWPE chains along the drawing direction. The composite exhibited tensile strength of 100 ± 22 MPa after hot drawing, which was comparable to that of cortical bone. The composite also exhibited great ability of inducing calcium phosphate precipitates on its surface in simulated body fluid, which was widely accepted as an indication of bioactivity.     

Ultradrawing gel films of blends of ultrahigh molecular weight polyethylene and low molecular weight polyethylenes with different molecular weights

The ultradrawing behavior of five series of gel films prepared from the blends of one ultrahigh molecular weight polyethylene (UHMWPE) and five other low molecular weight polyethylene (LMWPE) resins with varying molecular weight is reported. The critical draw ratio (_c) of each of the five UHMWPE/LMWPE gel film series were found to depend significantly upon the amount of LMWPE present in each of the gel film series. The presence of optimum amounts of LMWPE in each of the five gel film series can significantly improve their _c values, and this improvement in _c can further be enhanced with the addition of an optimum molecular weight of LMWPE. These interesting phenomena were investigated in terms of reduced viscosities of the solutions, thermal analysis, birefringence and tensile properties of these undrawn and drawn gel films.     

Tensile force at break of gel-spun/hot-drawn ultrahigh molecular weight polyethylene fibres

Fibres obtained by gel spinning of ultrahigh molecular weight polyethylene (UHMWPE) were drawn to various ratios, and the improvement of the tensile strength of the hot-drawn filaments with increasing draw ratio has been studied. The tensile force at break of gel-spun/hot-drawn UHMWPE fibres appeared to be constant for draw ratios exceeding λ=30. From scaling arguments, full chain extension is expected at this draw ratio. On the basis of development of the physical properties during drawing, it is concluded that little disentangling occurs up to λ=30. Beyond this point, slippage of chains through entanglement hooks becomes predominant. The observed constant tensile force at break can be explained by this drawing mechanism.     

超高分子量聚乙烯架桥纤维与裂缝的交互微观力学

使用拉曼光谱研究了架桥纤维与裂缝微观力学,以超高分子量聚乙烯(UHMWPE)纤维为例,将纤维搭桥试样进行微拉伸试验,着重分析架桥纤维的止裂作用和架桥纤维/环氧树脂界面的应力分布,并对不同位置架桥试样的裂缝扩展速度和应力分布进行分析,并进一步运用剪切滞后模型,对架桥纤维在不同拉伸载荷下的应力分布进行了拟合分析,结果表明:架桥纤维能够分散部分外载应力,对于裂纹扩展具有显著的止裂作用。在低于UHMWPE纤维最大应变拉伸时,发现在裂缝中心位置处架桥纤维所承受的应力最大,其应力不超过2GPa,而基体树脂的应力可达到12GPa,架桥纤维/基体界面的应力传递达不到100%。以UHMWPE为架桥的应力传递模型呈"正抛物线"型,应力分布存在于粘结区、脱粘区和架桥区。     

不同层数的超高分子量聚乙烯纬平针织复合材料冲击损伤

研究了不同层数超高分子量聚乙烯(UHMWPE)纤维/环氧树脂纬平针织复合材料的冲击性能,并讨论了其冲击损伤模式。复合材料板分别为4、6、8层纬平针织结构,采用真空辅助树脂传递模塑(VARTM)工艺层合而成,以不同的冲击能量(10~55J)冲击复合材料板直至层合板被穿透,得到冲击能量与吸收能量关系图以及接触力-挠度曲线。分析了不同冲击能量下,复合材料中织物的损伤形式和破坏过程。研究结果表明:在3种针织结构复合材料中,8层纬平针织结构承受载荷的能力最强,6层纬平针织结构次之,4层纬平针织结构最差;随着冲击能量的增加,3种试样的冲击挠度均增大;基体开裂、纤维断裂是试样被渗透时有效的损伤模式,基体和纤维断裂是试样被穿孔时有效的损伤模式。     

超高分子量聚乙烯的静电纺丝研究

应用静电纺丝技术制备了直径为纳米级的UHMWPE超细高性能纤维.使用液体石蜡为溶剂,对二甲苯为萃取剂进行UHMWPE静电纺丝研究,通过SEM、DSC、FT-IR和XRD对电纺UHMWPE纤维的外观形貌、化学结构和物质组成分别进行了分析,并通过强力拉伸试验对束纤维强力进行了测试.     

石墨烯多壁碳纳米管/超高分子量聚乙烯导电复合材料的制备及性能

为了比较超高分子量聚乙烯(UHMWPE)在单一填充和混合填充时, 复合材料导电性的差别。在超声和肼的作用下, 通过对氧化石墨烯(GO)、 多壁碳纳米管(MWCNTs)和超高分子量聚乙烯水/乙醇分散液减压蒸馏及热压制备了隔离型MWCNTs/UHMWPE、 石墨烯(GNS)/UHMWPE和MWCNTs-GNS/UHMWPE导电复合材料。经SEM、 TEM测试发现, 导电填料分散于UHMWPE颗粒表面, 热压后形成隔离结构。隔离型的MWCNTs/UHMWPE和GNS/UHMWPE复合材料均表现出较低的导电逾渗(0.148%和0.059%, 体积分数,下同), 但MWCNTs/UHMWPE复合材料的电导率(2.0×10^-2 S/m, 1.0%, 质量分数, 下同)明显高于相同填料含量下的GNS/UHMWPE复合材料。 MWCNTs-GNS/UHMWPE复合材料表现出了更低的逾渗(0.039%) 和较高导电性能(1.0×10^-2 S/m, 1.0%), 其拉伸强度和断裂伸长率随填充剂含量的增加呈现出先上升后下降的趋势。     

The influence of magnetic field on ballistic performance of aramid fibre and ultrahigh molecular weight polyethylene

An innovative method is introduced here whereby using two sets of arrays of rare earth magnets aligned opposite each other in order to create a repulsion force owing to the like poles when facing close to each other. Ballistic test samples of aramid fibre (Kevlar K29) and ultrahigh molecular weight polyethylene (UHMWPE) were sandwiched by two sets of opposing magnets. Ballistic test was conducted using a gas gun with a 7.62 mm diameter projectile at a velocity ranging from 160 to 220 m/s. High speed camera was used to capture the ballistics testing and it shows that the magnetic repulsion force created by the opposing rare earth magnets managed to suppress the projectile from advancing into the front face of the aramid fibre. Similarly, when magnets were used, the UHMWPE sample shows the projectile perforated through the first few sheets and finally rested on the last sheet showing partial perforation.     

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     

超高分子量聚乙烯纤维/水性聚氨酯复合材料层压板抗软钢芯弹侵彻性能及其损伤机制

选用碳纳米粒子(CNPs)原位改性和未改性的超高分子量聚乙烯(UHMWPE)纤维作为增强纤维,水性聚氨酯(WPU)作为树脂基体,采用缠绕-复合-热压工艺制备单向(UD)正交结构的UHMWPE纤维/WPU复合材料层压板.基于X射线计算机断层扫描(CT)技术,研究UHMWPE纤维/WPU复合材料层压板在7.62mmx39m...     

三元层状陶瓷Ti_3AlC_2/超高分子量聚乙烯复合材料的制备及性能

为了增强超高分子量聚乙烯(UHMWPE)的性能,研究采用表面改性的Ti_3AlC_2填充UHMWPE,通过热压成型制备了Ti_3AlC_2/UHMWPE复合材料。采用SEM观察复合材料的微观结构,表明Ti_3AlC_2均匀分散在UHMWPE基体中,表面处理后的填料与基体界面熔合较好;热分析结果表明,Ti_3AlC_2的添加降低了UHMWPE的结晶度和结晶热焓,同时提高了聚合物的热传导性;DMA分析结果表明,添加Ti_3AlC_2有效地提高了Ti_3AlC_2/UHMWPE复合材料的抗蠕变性能,得益于无机粒子改善了复合材料的硬度和刚性,提高了复合材料抗外界应力变形能力;摩擦学性能分析表明,适量的Ti_3AlC_2(质量分数≤15wt%)填充UHMWPE能有效提高复合材料的减磨抗摩性能,同时磨痕表面形貌分析结果表明,Ti_3AlC_2/UHMWPE复合材料的摩擦磨损机制由粘着磨损向磨粒磨损转变。     

The influence of sterilization technique and ageing on the structure and morphology of medical-grade ultrahigh molecular weight polyethylene

The effects of four sterilization treatments (gamma radiation in nitrogen, electron-beam radiation, ethylene oxide gas, and no sterilization) on the structure and morphology of ultrahigh molecular weight polyethylene (UHMWPE) were monitored as a function of ageing time in air for a period of 1.5 y. Characterization techniques employed include differential scanning calorimetry, density gradient column, transmission electron microscopy, and small-angle X-ray scattering. Ethylene oxide gas does not affect the structure of the polymer. Both forms of radiation lead to measurable alterations of the material's structure, including an increase in crystallinity, an increase in density, and the enhancement of lamellae crystalline stacking. Most changes in structure occur in the first few months with little differences observed upon subsequent ageing in air. The sharpness of the crystalline–amorphous boundaries decreases with time for irradiated UHMWPE and is believed to be linked to the oxidation of the polymer. © 1998 Chapman & Hall     

Effect of grafting cellulose acetate and methylmethacrylate as compatibilizer onto NBR/SBR blends

Compatibilizer is used for improving of processability, interfacial interaction and mechanical properties of polymer blends. In this study acrylonitrile butadiene rubber (NBR) and styrene-butadiene rubber (SBR) blends were compatibilized by a graft copolymer of acrylonitrile butadiene rubber (NBR) grafted with cellulose acetate (CA) i.e. (NBR-g-CA) and acrylonitrile butadiene rubber (NBR) grafted with methylmethacrylate i.e. (NBR-g-MMA). Compatibilizers were prepared by gamma radiation induced grafting of NBR with cellulose acetate (CA) and methylmethacrylate (MMA) were added with different ratios to NBR/SBR (50/50) blend. The compatibilized blends were evaluated by rheometric characteristics, physico-mechanical properties, swelling behavior, scanning electron microscope (SEM) and thermal analysis. The results showed that, the blends with graft copolymer effect greatly on the rheological characteristics [optimum cure time (Tc₉₀), scorch time (Ts₂), and the cure rate index (CRI)]. The physico-mechanical properties of the investigated blends were enhanced by the incorporation of these graft copolymers, while the resistance to swelling in toluene became higher. SEM photographs confirm that, these compatibilizers improve the interfacial adhesion between NBR/SBR (50/50) blend which induce compatibilization in the immiscible blends. The efficiency of the compatibilizer was also evaluated by studying the thermogravimetric analysis.     

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.     

A novel approach to the chemical stabilization of gamma-irradiated ultrahigh molecular weight polyethylene using arc-discharge multi-walled carbon nanotubes

A complete study was made of the stabilization of gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) using arc-discharge multi-walled carbon nanotubes (MWCNTs) as inhibitors of the oxidative process. MWCNTs were efficiently incorporated into the polymer matrix by ball milling and thermo-compression processes at concentrations up to 5 wt% and subsequently gamma irradiated at 90 kGy. Raman spectroscopy demonstrated the generation of radicals on the walls of the MWCNTs and that the G/D ratio was altered by their generation. The same spectra showed interactions between the polymer chains as a series of shifts are observed in the UHMWPE bands. The effect of the MWCNTs as inhibitors for the oxidative process of the UHMWPE was evaluated by means of Electron Spin Resonance (ESR) and Fourier Transformed Infrared Spectroscopy (FTIR). ESR detection of the radiation-induced radicals proved the radical scavenger behaviour of MWCNTs. FTIR measurements were performed to ascertain the influence of the irradiation and of the accelerated ageing protocol in the oxidation index of the polymer and the composites. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite when compared to pure UHMWPE. A comparison is made between composites obtained using MWCNTs produced by the carbon vapour deposition and arc-discharge methods.     

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.     

Radiation-induced grafting of glycidyl methacrylate onto cotton fabric waste and its modification for anchoring hazardous wastes from their solutions

Ion exchange adsorbents based on cellulosic fabric wastes carrying sulfonic acid and amine functional groups were synthesized by radiation-induced graft polymerization of glycidyl methacrylate (GMA) with subsequent chemical modification of the epoxy groups of poly-GMA graft chains with sodium sulfite/H₂SO₄ and triethylamine, respectively. The conversion of epoxy groups into the functional groups was investigated. Factors affecting on grafting process such as radiation dose, monomer concentration and solvent were studied. The synthesized adsorbent and its applications in the removal of different types of hazardous pollutants e.g. acidic dye, cobalt, dichromate and phenols from aqueous solution were also studied.     

Drawing of virgin ultrahigh molecular weight polyethylene: An alternative route to high strength/high modulus materials

The synthesis of ultra-high molecular weight polyethylene films and the production of high strength/high modulus tapes and filaments drawn directly from the virgin polymer are described. The study particularly focuses on the effect of the polymerization temperature on the deformation behaviour of the virgin UHMW polyethylene films. These results are discussed within the framework of the entanglement concepts for deformation of weakly bonded macromolecules. The developrnent of the room temperature Young's modulus and the tensile strength with draw ratio is presented and compared with modulus and tenacity/draw ratio relations observed for melt and solution crystallized polyethylene.