Thermomechanical degradation of PLA-based nanobiocomposite

Abstract

Nanobiocomposites are a new class of biodegradable polymer materials with nanometric dispersion of inert particles in a biodegradable polymer matrix that show very interesting properties often very different from those of conventional- filled polymers and also biodegradability. An important issue in the applications of the biodegradable polymers is their easy degradability during processing due to the thermomechanical stress or to the presence of humidity. In this work, the thermomechanical degradation behavior of a nanobiocomposite made by a PLA-based blend and an organomodified montmorillonite has been investigated. The degradation kinetics has been followed by means of rheological, mechanical and morphological characterization. In particular, the influence of temperature and of the presence of humidity have been considered. The presence of the nanoparticles slightly increases the thermomechanical degradation of the pure matrix and in particular with increasing time and temperature processing. In the more severe conditions, indeed, the organomodifier undergoes some slight decomposition of the organomodifier of the clay because of the Hoffmann elimination. The radicals formed through this decomposition enhance the degradation of the matrix. However, this decomposition is at the first stage, and the evolved CO2remains entrapped in the clay increasing the level of intercalation and causing also some exfoliation. Then the morphology of the nanobiocomposite changes because of the processing conditions. Moreover, the thermomechanical degradation remarkably increased if the materials are not pre-dried because of the hydrolytic degradation of the biodegradable polyesters of the matrix.