Characterization of poly(lactic acid)/hydroxyapatite prepared by a solvent-blending technique

Abstract

Poly(lactic acid) (PLA) was solvent blended in a chloroform solution using multiple weight fractions of hydroxyapatite (HAp) (5, 10, and 20 wt%). A miniature laboratory mixing extruder equipped with a ribbon die was used to produce thin ribbons of PLA/HAp biocomposites. The dynamic mechanical parameters (storage modulus (G′), loss modulus (G′′), complex viscosity (η*), and degree of crystallinity) increased with increasing HAp loading. In vitro hydrolytic degradation of the PLA biocomposites was conducted in a 0.01-M phosphate-buffered saline solution at 37°C. The presence of HAp tended to increase both the hydrolytic degradability of the PLA and the crystallinity, possibly resulting from the hydrophilicity of the HAp. The thermal stability of the PLA was slightly higher in the composites with HAp. Following hydrolytic degradation, several microholes and cracks appeared on the surface of these biocomposites, as observed by scanning electron microscopy. The Coats–Redfern method was used to evaluate the thermal degradation kinetics of the biocomposites with support from a chemical reaction model. From this evaluation, the activation energies of the biocomposites were found to exceed that of the neat PLA. These energies were observed to decrease after the hydrolytic degradation process.