Non-Conventional Processing Routes on the Development of Anisotropic and Biodegradable Composites of Starch Based Thermoplastics Reinforced with Bone-Like Ceramics

Abstract

Biodegradable thermoplastic blends of com starch with ethylene vinyl alcohol copolymers (40/60 mol/mol) were reinforced with bone-like ceramics (hydroxylapatite, HA) in amounts up to 30% by weight. The materials were compounded either in a rotating drum, RD, or in a corotating twin-screw extruder, TSE. Then tensile samples were processed by conventional injection molding or using a shear controlled orientation in injection molding (Scorim) technique. By using the later technique it was possible to induce anisotropy (copying bone structure) into the moldings and, for HA amounts up to 20%, to obtain simultaneously higher values of stiffness and ductility (results of tensile tests). The goal of matching the minimum stiffness of cortical bone (around 7 GPa) was accomplished for 30%HA composites processed by TSE + Scorim. Furthermore, the composites degradation was studied in simulated physiological solutions. It was found that an increase in the HA concentration lead to a faster degradation rate, indicating thatboth the matrix and the reinforcement are being degraded by body fluids. This chapter reports the development of starch IHA thermoplastic composites that may be molded in complex shapes (injection molding) and that show promising mechanical properties. It gives special attention to the compounding of the materials by corotating twin-screw extrusion, TSE. Also non-conventional composite processing routes, including shear controlled orientation in injection molding (Scorim)IO,ll were used to attain the required mechanical performance.