Compatibilization and Plasticization of Poly(Lactic Acid) by Eco-Friendly Castor Oil-Based Plasticizers

To address the inherent brittleness of polylactic acid (PLA) that restricts its application in flexible packaging and to avoid the drawbacks of petroleum-based plasticizers such as toxic residues and non-biodegradability, PLA/castor oil (CO)/castor oil glycidyl ether (COGE) blends were prepared via one-step melt blending method. The results indicated that CO and COGE was compatible and both showed good affinity with PLA, thus multiple intermolecular hydrogen bonds were formed among three components, effectively improving the movability of PLA chains. COGE not only significantly improved the dispersion of CO in the PLA matrix and reduced the size of dispersed phases, but also enhanced the interfacial adhesion of the blends through its ring-opening reaction with PLA. Due to the enhanced mobility of molecular chains, the glass transition temperature decreased, the crystallinity slightly increased, and the melt viscosity of the blends significantly decreased. The elongation at break of the PLA/CO/COGE (85/6/9) blend reached 176.24%, which was 18 times greater than that of pure PLA, meanwhile, the Young’s modulus decreased by less than 15%, demonstrating a balance between high rigidity and preferable ductility. This synergistic plasticizing strategy provides a practical approach for the development of flexible PLA materials for biodegradable packaging and disposable products.