Ionizing radiation effects on polymer biodegradation

Plastic waste has become a major worldwide environmental threat. In this view, we exposed to gamma radiation six different polymer films, characterized by a different biodegradation rate; their surface properties along with the effect on their biodegradation rate in compost were investigated. Two polyesters, poly(butylene succinate) (PBS) and poly(propylene cyclohexane dicarboxylate) (PPCE), were selected as biodegradable and slow-degrading polymers; on the other hand, commercial films of high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polyethylene terephthalate (PET) were chosen as recalcitrant polymers. The samples were irradiated in air and water at absorbed doses up to hundreds of kGy. Surface properties were analyzed by means of water contact angle (WCA) measurements and the composting tests were performed up to 180 days. WCA measurements revealed positive changes that could affect the polymer biodegradability. For polyesters, the wettability is highly increased when the samples are irradiated in water. PE wettability is increased for all the absorbed doses, while PET is not affected. In general, the degradability in compost of the considered systems is increased: PBS degrades faster when irradiated in water while PPCE degrades in both irradiation conditions. HDPE and LDPE do not evidence relevant variations in the surface morphology after 180 days in compost but a difference in the thermal properties suggests a beginning of the degradation process. PET degradability appears to be not affected after 180 days in compost, even after irradiation up to 1 MGy. The research suggests that the radiation-induced degradation could be an effective pre-treatment to enhance the biodegradation rate of some polymeric systems.