Biodegradable and biocompatible nanocomposites of poly(ε-caprolactone) with hydroxyapatite nanocrystals:: Thermal and mechanical properties

Nanocomposites of poly-(epsilon-caprolactone) (PCL) with hydroxyapatite nanocrystals (HAP) prepared through the solvent-cast technique were characterized by means of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile tests. Such composites are of great importance to make bone-like substitutes as HAP nanocrystals have similar composition, morphology, and crystal structure as natural apatite crystals. The TEM micrograph reveals the nanocrystals dispersed homogeneously in the matrix at a microscale level. The solvent-cast samples commonly show much higher melting points and crystallinity than the melt-quenched samples, due to a lower undercooling as well as more sufficient time to crystallize. For both cases of samples, the melting point decreases slightly with HAP content while the level of crystallinity attained by the PCL component is not hindered by the nanocrystals. Both the glass transition temperatures and the nonisothermal crystallization temperatures are composition dependent. The tensile modulus increases with increasing HAP content while the yield stress is almost invariant with composition. Theoretical prediction of the modulus based on Halpin-Tsai equations shows excellent agreement with the experimental result. By analysis of the variation in fracture stress and strain with composition, a ductile-to-quasi-brittle transition is revealed to be operative for the nanocomposites, as also can be seen by SEM. (C) 2002 Wiley Periodicals, Inc.