Abiotic surface degradation induced by ozonation on poly (lactic acid) (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends

Biopolymers have emerged as sustainable alternatives to conventional plastics, showing advantages like biocompatibility, biodegradability, and non-toxicity [1]. Nevertheless, their aging processes under service life conditions still need a deeper evaluation [2], [3]. This study examined films of three commercial compositions for rigid/flexible packaging based on poly (lactic acid) (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends under oxidative degradation conditions.

Commercial PLA/PBAT films, of 100 µm thickness, were exposed to short- (0 - 2 h) and long-term ozone aging (24 - 96 h) in an Anseros SIM 6050 T chamber at 40 ^oC and 300 pphm of ozone concentration. Analytical characterisation included measurements for surface hydrophilicity (WCA), microscopic morphology (SEM), chemical structure (FTIR-ATR), thermal properties (DSC), and mechanical performance.

Ozonation caused significant variations in surface properties after long-term ozone treatment, demonstrated by a constant decrease in WCA. A 96 h treatment led to abiotic degradation revealed by chemical structure analysis, where carbonyl and carboxyl indices were reduced by 17% and 16%, indicating degradation of oxidised functional groups and products, along with mild chain scission. Surface morphology showed surface changes with initial oxidation, reinforcement and re-degradation tendencies. These changes were limited to surface modifications, as slight bulk changes were reported in thermal properties. Mechanical performance improved, with the aging factor increasing from 0.5 to 0.9 to 1.14 - 1.30, suggesting that structural stability was maintained. Phase distribution within the polymer matrix influenced the extent of abiotic degradation. The progressive increase in additives such as plasticisers and inorganic fillers likely buffered the effects of ozone treatment.

Short- and long-term treatments promoted oxidative degradation of biodegradable film surfaces. Only long-term exposure led to macroscopic surface damage, altering morphology, chemical structure, and hydrophilicity, without affecting deeper layers, while maintaining thermal properties and slightly enhancing mechanical performance.

ACKNOWLEDGEMENTS

Authors acknowledge funding from the Agència Valenciana de la Innovació (AVI) through the INNEST/2022/295 project.