Physical properties and enzymatic hydrolysis of poly( l-lactide)–CaCO 3 composites

Abstract

Amorphous poly( l-lactide) (PLLA) composite films with calcium carbonate (CaCO 3) particles were prepared by solution-casting using methylene chloride as a solvent, followed by quenching from the melt. The effects of volume fraction, surface treatment and size of the CaCO 3 particles on the physical properties and enzymatic hydrolysis of the composite films were investigated. The Young's modulus of all the composite films containing 10 wt.% of the CaCO 3 particles was higher than that of the pure PLLA film, regardless of the surface treatment and the size. On the other hand, the tensile strength of the films did not change on addition of 10 wt.% of the CaCO 3 particles, excluding that containing the CaCO 3 particles surface-treated with rosin acid, which was lower than the tensile strength of the pure PLLA film. Hydrolysis studies in the presence of proteinase K revealed that the enzymatic hydrolysis rates of the PLLA composite films containing 5 and 10 wt.% of the CaCO 3 particles were much higher than that of the pure PLLA film, regardless of the surface treatment and the size. This is attributable to the enzymatic hydrolysis at the interface between the PLLA matrix and the CaCO 3 particles of the composite films as well as on their surface, as shown by scanning electron microscopy. Addition of amounts of CaCO 3 particles exceeding 10 wt.% led to a drop in the enzymatic hydrolysis rate, probably because the CaCO 3 particles covered the film surface and therefore disturbed the adsorption and/or scission processes of the enzyme.