The UV Aging Properties of Maleic Anhydride Esterified Starch/Polylactic Acid Composites

Esterified starch/polylactic acid (ES/PLA) blending composite was prepared by melting extrusion with maleic anhydride esterified starch and PLA as the raw materials. The composite was accelerated aging by using UV aging box, and its properties were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo gravimetric analysis (TGA) and mechanical testing machine. FT-IR and SEM results show that the infrared absorption peak intensities of C-O, C-H, and C=O in aged samples decrease gradually with increasing aging time. The damage degree of surface and internal of aged samples increases gradually. XRD analysis results show that after aging treatment, the crystalline diffraction peak of thermoplastic esterified starch at 2 theta = 21 degrees disappears and the diffraction peaks of PLA at 2 theta = 16.5 degrees appear, indicating that the hydrolysis rate of esterified starch is greater than that of PLA. The crystallinity of PLA in aged sample shows an increasing trend at first followed by a decreasing one along with the increasing time of aging treatment, suggesting that the hydrolysis of amorphous regions of PLA is more preferential than its crystalline regions. Because of the influence of crystal structure and the change of composition structure, the initial decomposition temperature of aging test specimen gradually increases with the extension of aging time. The maximum decomposition rate temperature and residual mass increases at first, and then decrease after the aging time extending to 1 600 h. As the aging time increases, the damage degree of combination interface between esterification starch and PLA is exacerbated, resulting in the tensile strength and bending strength of aged specimen decreasing gradually.