STRUCTURE DEVELOPMENT AND CONTROL OF INJECTION-MOLDED HYDROXYLAPATITE-REINFORCED STARCH EVOH COMPOSITES/

This article reports on the development of novel composites of starch- based polymers reinforced with hydroxylapatite (HA). Two different gra des of blends of starch and ethylene vinyl alcohol copolymers were rei nforced with up to 30% (wt) of sintered and nonsintered HA. The initia l compounding stage was carried out either in a rotating drum or by tw in-screw extrusion (TSE). Compounds were injection molded using both c onventional molding and a shear-controlled orientation in injection mo lding (Scorim) technique. It was possible to obtain composites with ve ry good mechanical properties, approaching those of cortical bone. The best results were achieved for 30% sintered HA composites processed b y TSE and Scorim, due to the in situ formation of HA fibers, and the d evelopment of molecular orientation and more compact microstructures i n the moldings. This was confirmed by SEM analysis of the fracture sur faces, x-ray diffraction, and Raman spectroscopy. The biodegradability of the composites was also assessed and was found to be faster than t hat of the matrix. (C) 1997 John Wiley & Sons, Inc.