Environmental and thermal aging studies on plastics and biopolymers : changes in mechanical properties and emissions of volatile organic compounds (VOCs)

Abstract

Plastics, especially biopolymers, degrade in response to environmental conditions such as UV radiation, heat, and moisture, resulting in surface changes and decreased in mechanical properties. As biopolymers replace traditional plastics, evaluating their long-term environmental impact is critical. This study aims were to investigate the effects of extended environmental aging on the surface and mechanical properties and the emission of volatile organic compound of biopolymers, including polybutylene adipate terephthalate (PBAT), poly (lactic acid) (PLA), polybutylene succinate (PBS) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH).Biopolymers samples were prepared by melting and compounding in a twin-screw extruder, followed by injection moulding into dumbbell-shaped specimens.

The changes in the structural, chemical, thermal, and mechanical characteristics of the biopolymer before and after were investigated by FT-IR, TS, TG-FTIR and Py-GC/MS. The visual appearance of biopolymers after exposure to accelerated aging for 1000 hours was studies. Photo-oxidation led to the formation of chromophores and double bonds, leading to PBAT, PHBH and PBS change color from white to yellow. PLA, which was before transparent due to its amorphous structure, became opaque white because of UV-induced cold crystallization. After 1500 hours of aging, tensile strength in PBAT increased by 12%, while for PBS and PHBH tensile strength decreased by 72% and 12%, respectively. PLA showed the highest decrease after 1000 hours due to UV-induced photodegradation and hydrolysis. Strain at break decreased significantly in PBS (98%), PBAT (64%), and PHBH (60%) after 1500 hours.

FTIR spectroscopy confirmed the presence of carbonyl groups in PBS, PLA, and PBAT by revealing C=O and C-O bond peaks at 1710 cm−1 and 1046-1100 cm−1, respectively. To evaluate the effect of photooxidation, the carbonyl index was measured using FTIR analysis, which effectively measures oxidative degradation. The carbonyl index of the biopolymers decreased with aging indicating a gradual decrease in oxidative breakdown. TG-FTIR of biopolymers showed the present of degradation products majorly oligomers, unsaturated carboxylic acids, CO2, CO, and H2O.

VOCs analysis revealed that no toxic emissions such as benzene or toluene were emitted from the recycled plastics before and after aging. The study showed that the highest concentration of VOCs was 3-formyl-benzoic acid in PBAT, 2-butenoic acid in PHBH, 2,5-furandione in PBS, and 1,4-dioxane-2,5-dione in PLA. The absence of harmful substances indicates that emissions are within acceptable levels, showing Py-GC/MS's efficiency in monitoring environmental safety.