Papers by Keyword: Ultra High Molecular Weight Polyethylene

Abstract: This work aims to provide a review of available published literature that explores the opportunities to improve the quality of fused deposit modelling (FDM) products, particularly in medical applications. The paper presents details concerning the basis of the technology, process parameter settings and their responses, and reviews the properties of common FDM engineering/bio-materials and the available methods applied for improving their performance. Based on the researches which have been reviewed, FDM technology works within a complex environment from process parameters. Thus, it can achieve good results only with the proper settings for these parameters according to the properties of the material used. Improving the polymers is essentially based on the correct selection of additive materials, which can particularly enhance the key property/properties in the matrix material. This review provides a brief insight into FDM technology, provides an idea of the process parameter settings, the available materials and ways of modifying their properties to consequently improve the quality of FDM products.

Abstract: Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to γ-irradiation. Correlations were found between the mechanical properties and ortho-positronium lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of γ-irradiation on positronium formation is discussed.

Abstract: The ultra high molecular weight polyethylene (UHMWPE) has a molecular mass of the order of a millions of grams per mole. So, UHMWPE presents prominent properties, for instance, abrasion and impact resistance. However, due to its very high viscosity in the melt state, the preparation of composites by conventional extrusion and injection molding is not possible. Therefore, in this work we studied the possibility of incorporating montmorillonite (MMT) into the matrix of the UHMWPE in the solid state, via high energy milling. The formulations were prepared in Attritor mill by milling UHMWPE reactor powder and MMT. The samples were characterized by bulk density, XRD, AFM and SEM. Results show that this route of processing was effective to incorporate MMT into the matrix of UHMWPE.

Abstract: In order to investigate the biotribology behavior of a novel artificial joint pair composed of a carbon/carbon composite femoral head and an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup, a hip joint simulator was employed to predict the clinical wear behavior with a constant load and a lubricant of newborn calf serum. The worn surface and the wear particles generated were analyzed by scanning electron microscopy and laser particle size analyzer. The results showed that the worn surface of UHMWPE had a ripple-like morphology with plentiful furrows. The wear particles generated had various morphologies with a size concentrated at about 15 μm.

Abstract: In this study, blends of ultra high molecular weight polyethylene/high density polyethylene/polyethylene glycol (UHMWPE/HDPE/PEG) and the composites containing Hydroxyapatite (HA) as reinforcement filler were prepared via single screw extruder nanomixer followed by compression moulding. PEG (2phr) was used as processing aid and HA loadings were varied from 10 to 50 phr. HDPE and PEG were introduced to improve the extrudability of UHMWPE. Rheological behavior was studied via capillary rheometer while flexural and izod impact tests were conducted in order to investigate the mechanical properties of the blends and composites. Melt viscosity of the blends was found to decrease with increasing shear rate indicating a pseudoplastic behaviour. Incorporation of PEG shows a synergism effect on the reduction of blends viscosity. Blend of 40% UHMWPE/ 60% HDPE/ 2 phr PEG was chosen as the optimum blend composition with a balance properties in terms of the mechanical properties and processability. The incorporation of HA fillers from 10 to 50 phr into the blend resulted in the increase of flexural modulus and flexural strength with a slight decline of impact strength values. It can be concluded that the composites having adequate strength and modulus within the range of cancellous bone properties were succesfully developed to be used as biomedical implant devices.

Abstract: The effect of ultrahigh molecular weight polyethylene (UHMWPE) on solid particle erosion behaviour of aramid fabric reinforced-epoxy (A-E) hybrid composites was investigated. The aramid fabric reinforced-epoxy hybrid composites have been fabricated with and with out UHMWPE filler. The solid particle erosive wear was evaluated at different impingement angles from 300 to 90 0 at constant velocity and at constant standoff distance .The silica sand of size 30 -50 and 60 -80 μm was used as erodent. The results show erosive rate of UHMWPE filled aramid- epoxy composite shows lowest value. The presence of UHMWPE in epoxy matrix gives good bonding between filler and matrix. The morphologies of eroded surface were examined by the SEM in order to establish the erosion mechanism of the composites.

Abstract: In order to understand the influence of gamma-irradiation, accelerated aging and Vitamin-E addition on the fatigue crack growth properties of UHMWPE, fatigue crack growth tests of UHMWPE plates using compact tension specimens were carried out. The specimen conditioned in -irradiation and accelerated aging (the -aging specimen) has faster fatigue crack growth rate than the virgin specimens. For the Vitamin-E added specimen (the VE specimen), however, K threshold of the -aging VE specimen is smaller than that of the VE specimen. This result shows that the addition of Vitamin-E reduced the decrease of K threshold by -irradiation and accelerated aging.

Abstract: Carbon nanotubes (CNT) have been shown to enhance the engineering properties of plastic fibers in ballistic-resistant garments enabling the garments to withstand very high impact forces while remaining to be lightweight. Previous study shows that by reinforcing ultra high molecular weight polyethylene (UHMWPE) fibers with a small amount of carbon nanotubes, the fibers are simultaneously toughened and strengthened. In this paper, we study the mechanical properties of carbon nanotube reinforced ultra high molecular weight polyethylene (UHMWPE) by using micromechanics-based Mori-Tanaka model. Results show that the addition of small amount of carbon nanotubes as reinforcement can substantially improve the mechanical properties of the UHMWPE fibers.

Abstract: This paper presents a methodology for assessing the in-vivo degradation mechanisms of articular components of total hip replacement (THR) prostheses of Charnley type. The experimental procedure revealed that common features can be observed even if the clinical cases under investigation were quite different with regard to the demographic data. It particularly emphasises the detrimental effects of foreign bodies on the damage of the articulating surfaces. These foreign bodies can migrate into the joint space before embedding definitely into the Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular cup surface where they further participate to a third body wear mechanism accelerated by a progressive increase of the femoral head roughness. Our experimental results underline, from a practical point of view, the need for careful manufacturing and clinical handling of porous surfaces, advocate for a systematic assessment of retrieved components, particularly when changed because of unexplained wear, and make questionable the clinical use of multifilament trochanteric cables.