Improving Interfacial Adhesion of PLA/Lignin Composites by One-Step Solvent-Free Modification Method

To clarify the effects of lignin as a biodegradable filler added into the PLA matrix, PLA/lignin composites with or without silane coupling agent of gamma-(2,3-epoxypropoxy)propy trimethoxysilane (KH560) were prepared by a one-step solvent-free modification method. The effects of KH560 as a compatibilizer on the morphology, chemical structure, crystallization behavior, thermal degradative behavior as well as mechanical strength of the PLA/lignin composites were analyzed in detail. It was found that, after modification by KH560, the fractured surfaces of composites became smooth, suggested sufficient bonding between the lignin and PLA in the composites with KH560 coupling agent molecules. This result further proved by 1H NMR and ATR spectra of the composites that lignin and PLA formed stable chemical bonds with KH560. Due to the toughening effect of KH560, mainly affect the molecular chain mobility, the thermodynamic properties of LG-KH560/PLA composites were all reduced. When compared to the conventional solution modification method of adding silane coupling agents into PLA/lignin, the composites were synthesized via a single-step reactive extrusion modification procedure in this work showed relatively low tensile strength, which mainly because the existence of the free radicals due to coupling agents result in the composite's deterioration and subsequent weakening of the tensile properties.