Oxidized (GO) and expanded (G-Exp) graphite were employed to prepare composites with ultrahigh molecular weight polyethylene (UHMWPE) matrix using masterbatches of polyethylene with different compositions. The materials and a blend of UHMWPE/HDPE were prepared by extrusion and their properties were evaluated. The effect of carbon fillers on the crystalline structure, thermo dynamic-mechanical (DMTA) and thermal properties (melting and crystallization temperatures) of the composites were discussed. The thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements showed that the addition of masterbatch with GO and G-Exp significantly increased the crystallite size of composites, increasing the temperatures of melting, degradation, glass transition and the degree of crystallinity of polyethylene. DMTA analysis indicated the storage and loss moduli of composites in relation to neat UHMWPE, the blend and UHMWPE/composites. SEM micrographs showed a flatter, continuous and uniform surface meaning a compact lamellar structure. The present work resulted in interesting findings on the effects of GO on the crystalline structures, mechanical and thermal properties of UHMWPE, which can lead to generalizations useful for future work.
Abstract. The asymmetric arylimino pyridine Ni(II) catalysts have been examined with different substituents including diisopropyl, diethyl, fluoro, and chloro groups. The influence of these substituents and variation of ethylene pressure on the catalytic activity, crystalline structure, as well as on thermal properties of polyethylene has been investigated. The result show that complexes with substituent alkyl groups, which provide the increased electron density on the metal center ( o -diethyl and o-diisopropyl) exhibit higher activity, compared to those with electron acceptors substituents (o-fluoro and o-chloro).
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