Castor Oil-Based Polymer Films with Superior Mechanical, Thermal, and Optical Properties

In pursuit of global sustainability goals, there is a growing need for high-performance biobased polymer films. Herein, plant-derived castor oil (CO)-based cross-linked films were prepared following a three-step strategy: (1) the self-stabilized precipitation polymerization of styrene and maleic anhydride to prepare poly(styrene-alt-maleic anhydride) (SMA); (2) the esterification reaction of SMA and CO to prepare CO-grafted SMA (SMA-g-CO); and (3) the preparation of SMA-g-CO/poly(ethylene glycol) (PEG) films through solution-blending, casting, and heat-induced curing. By varying the molecular weights of SMA and PEG, the grafting amount of CO, and the feed ratio of SMA-g-CO to PEG, a series of CO-based films were successfully prepared, with the highest biomass content reaching up to 63.4 wt %. The microstructure, mechanical properties, thermal properties, optical performance, toxicity, and solvent resistance of the films were investigated systematically. SMA-g-CO/PEG films possessed excellent tensile strength (up to 70 MPa), good mechanical performance retention after reprocessing, and a high glass transition temperature (up to 184.2 °C). The films also demonstrated intriguing and stable photoluminescence behavior, contributing to outstanding UV-shielding and visible light-transmitting properties. Thus, the present work enables the effective conversion of renewable CO into high-performance SMA-g-CO/PEG films with great application potential in constructing a circular economy.