Hydrolytic degradation of PLA/Posidonia Oceanica green composites: A simple model based on starting morpho-chemical properties

Abstract

In this work, we studied the degradability of PLA-based biocomposites containing Posidonia Oceanica flour at different loading levels and aspect ratios. Hydrolytic tests were carried out in neutral (pH = 7.4) and alkaline (pH = 10) environment. Time-dependent evolution of some key features, including residual mass and solution uptake, was monitored, and correlated with the changes observed in both morphology and chemical structure of the matrix. The results pointed out that biocomposites degraded much faster than neat PLA in both conditions, up to lose 70% of their initial weight after 1000 h immersion. A complex mechanism was unveiled, evidencing the crucial role of the fillers, capable of both imparting degradation to PLA during processing with enhancement of hydrophilicity and offering preferential gateways for solution penetration through filler-matrix interface by capillarity and swelling-aided polymer cracking. Based on data collected, we propose a new model allowing to predict the triggering and final extent of degradation pathways by considering starting morphological and chemical features of composites via the use of a novel yet simple indicator of chemical stability, which we called morphochemical parameter.