Accelerated weathering of poly(lactic acid) and its biocomposites: A review

Abstract

Currently, poly(lactic acid) (PLA) and its natural fiber biocomposites have a growing interest as a sustainable and biodegradable alternative to conventional polymers. Their intrinsic susceptibility to weathering degradation limits their applications. This review discusses the accelerated weathering of PLA and how fillers, reinforcements, and additives affect photo-degradation. The changes in molecular weight, thermal and mechanical properties, as well as surface morphology, are highlighted. Moisture causes hydrolytic degradation of PLA and biocomposites, especially due to the hydrophilicity of lignocellulosic fibers. Temperature promotes thermal annealing of the polymer, increasing its crystallinity. The main process occurring in photo-degradation is the random chain scission via the Norrish II mechanism, preferentially on the amorphous regions. Degradation causes changes in mechanical properties, particularly when the molecular weight importantly decreases. Reinforcements could attenuate the loss in mechanical properties, depending on its structural integrity and the state of interfacial adhesion. UV stabilizers can be considered, but leaching of potentially toxic additives to the environment during degradation is a concern. It is important to establish mathematical models to predict the decrease of molecular weight and mechanical properties by combining the effect of temperature, irradiance, and humidity to predict the long-term behavior of these materials.