Characterization of hydrolytic degradation of polylactic acid/rice hulls composites in water at different temperatures

Hydrolytic degradations of polyactic acid/rice hulls (PLA/RH) composites with various rice hulls contents due to water absorptions at 23, 51 and 69 degrees C were investigated by studying the thermal properties, chemical composition, molecular weight, and morphology of the degraded products. The results have attested that the stability of PLA/RH composites in water depends slightly on rice hulls contents but it is significantly influenced by water temperature. Water adsorption in 30 days at 23 degrees C was between 0.87 and 9.25% depending on rice hull contents. However, at thermophilic temperatures, the water adsorption and degradation of these products were increased significantly. Saturations were achieved in less than 25 and 9 days at 51 degrees C and 69 degrees C, respectively, while hydrolytic degradation was demonstrated by an increase in fragility and development of crystallinity. At 69 degrees C, there were significant reductions of the decomposition and glass transition temperatures of the polymer by 13 degrees C. These changes were associated with the reduction of the molecular weight of PLA from 153.1 kDa to similar to 10.7 kDa due to hydrolysis of its ester group.