(255w) Study on Accelerated Aging of Biodegradable Poly(butylene adipate-co-terephthalate) Films for Mulch Applications

Poor weatherability is one of the bottlenecks for large-scale applications of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) mulch films. Herein, PBAT-based films were subjected to accelerated weathering test under laboratory simulated conditions for investigation of their aging behaviors. During the aging, crosslink structures in the films were formed rapidly by recombination of free radicals formed via Norrish I chain scission. In addition, the content of butylene terephthalate (BT) units increased because water-soluble butylene adipate (BA)-rich segments were formed and washed away by water spay due to the susceptibility of aliphatic ester groups to Norrish II chain scission or photo-oxidation. Such structural changes resulted in significant performance reduction including a significant increase in T_g, decrease in T_m, and rapid deterioration of tensile properties. Incorporating a UV absorber 1164 into PBAT-based films effectively depressed both Norrish I and II chain scissions and the subsequent degradation reactions, thus greatly improving the weatherability of PBAT films. The gel formation, changes in composition and transition temperatures, and deterioration of mechanical properties were all effectively suppressed. Addition of either hindered phenolic antioxidant 1010 or hindered amine light stabilizer 944 improved the weatherability as well, but the effects were inferior to 1164 as they could only depress the degradation reactions following Norrish I.