Partially Bio-Based and Biodegradable Poly(Propylene Terephthalate-Co-Adipate) Copolymers: Synthesis, Thermal Properties, and Enzymatic Degradation Behavior

A series of partially bio-based and biodegradable poly(propylene terephthalate-co-adipate) (PPTA) random copolymers with different components were prepared by the melt polycondensation of petro-based adipic acid and terephthalic acid with bio-based 1,3-propanediol. The microstructure, crystallization behavior, thermal properties, and enzymatic degradation properties were further investigated. The thermal decomposition kinetics was deeply analyzed using Friedman's method, with the thermal degradation activation energy ranging from 297.8 to 302.1 kJ/mol. The crystallinity and wettability of the copolymers decreased with the increase in the content of the third unit, but they were lower than those of the homopolymer. The thermal degradation activation energy <i>E</i>, carbon residue, and reaction level <i>n</i> all showed a decreasing trend. Meanwhile, the initial thermal decomposition temperature (<i>T_d</i>) was higher than 350 °C, which can meet the requirements for processing and use. The PPTA copolymer material still showed excellent thermal stability. Adding PA units could regulate the crystallinity, wettability, and degradation rate of PPTA copolymers. The composition of PPTA copolymers in different degradation cycles was characterized by ¹H NMR analysis. Further, the copolymers' surface morphology during the process of enzymatic degradation also was observed by scanning electron microscopy (SEM). The copolymers' enzymatic degradation accorded with the surface degradation mechanism. The copolymers showed significant degradation behavior within 30 days, and the rate increased with increasing PA content when the PA content exceeded 45.36%.