Rabeh Elleithy

High density polyethylene/graphite nano-composites for total hip joint replacements: Processing and in vitro characterization

The main objective of the present study is to investigate how the thermal, rheological, mechanical and cytotoxicity behavior of High Density Polyethylene (HDPE) can be changed by the addition of graphite nano particles (GNPs) at different contents. The HDPE/GNPs composites were prepared using melt blending in a co-rotating intermeshing twin screw extruder. The in vitro tests results showed that the original material (HDPE) and all HDPE/GNPs composites do not exhibit any cytotoxicity to the WISH cell line. The microscopic examination of the nano-composite tensile-fractured surface found a good distribution of GNPs in the HDPE matrix. The Differential Scanning Calorimetry (DSC) results indicated that the crystallization percentage increased by adding GNPs to HDPE up to 4%. The XRD patterns of the HDPE/GNPs composites showed an increase in peak intensity compared to neat HDPE. This increase echoed the crystallinity results obtained from DSC. The rheological tests showed that the complex viscosity of the HDPE increased as the percentage of GNPs increased due to the restriction of the molecular mobility. The tensile test results showed that with increasing the GNPs content, Youngs modulus and the yield strength of the HDPE/GNPs composite increased while the strain at fracture decreased. Finally, the preliminary results of the abrasion test indicated that the abrasion rate decreased by increasing the GNPs ratio up to 4% content. The prepared HDPE/GNPs composites appear to have fairly good comprehensive properties that make them a good candidate as a bearing material for the total joint replacement.

Formation of Vinylidene in Polypropylene/Ethylene Vinyl Acetate (PP/EVA) Blends During Degradation

The effect of natural exposure and artificial weathering on selected properties of PP/EVA blends was investigated. The vinyl acetate concentration decreased with exposure time due to acetylation. The most pronounced effect of radiation is associated with oxidative degradation. The cross-linking of PP/EVA blends was attributed to the formation of vinylidene group. Weathering decreased the tensile strength, elongation at break, and Youngs modulus of the naturally and artificially exposed blends. This reduction was the result of blends’ molecular weight reduction due to the degradation induced by weathering.

Different factors affecting the mechanical and thermo-mechanical properties of HDPE reinforced with micro-CaCO3:

In this study, we manufactured the HDPE/micro-calcium carbonate (CaCO3) composites. A twin screw extruder was used to melt blend different loadings of CaCO3 masterbatch, from 5% to 20%, with HDPE. Furthermore, injection-molded samples were manufactured using different molding conditions, namely pressure and cooling time. The presence of CaCO3 increased the viscosity and the stiffness of the composites. The viscoelastic analysis indicated that adding more than 15% on the CaCO3 masterbatch apparently affected the way the material behaves, as indicated by an abrupt change of some properties of the composite containing 20% masterbatch. As the molding pressure and cooling time increased, the shrinkage of the molded samples decreased. The tensile strength and the ductility of the composite decreased as the content of the CaCO3 increased and as the cooling time or the molding pressure decreased. The fracture surface of all samples had the characteristic dimples of polyethylene fracture; however, neat resin showed extensive fibrillation which was absent at high loadings of CaCO3.

Improvements in barrier properties of poly(ethylene terephthalate) films using commercially available high barrier masterbatch additives via melt blend technique

Poly(ethylene terephthalate) films which contained commercially available masterbatch additives were prepared by melt processing. Three different commercially available additives were selected, of which two of them significantly improved the oxygen and water vapour barrier properties. The additives did not significantly alter the optical, crystallization and melt rheological properties. The diffusion mechanism of oxygen and carbon dioxide gases through the polymer matrix is also explained. This article discusses the improvements in barrier properties of poly(ethylene terephthalate) films which can be used for food packaging applications with emphasis on preparation, characterization, properties and diffusion mechanism.