Thermal Effect on the Formation of Polyethylene Greenhouse Plastiglomerates from Microplastics

This study examined the impact of photodegradation and thermal degradation on polyethylene (PE) microplastics (MPs) through the analysis of their wettability, surface morphology, sand adhesion, and physical changes after exposure to UV radiation (72 and 130 h) followed by heating at 250 °C. The results of water contact angle (WCA) measurements indicated that photodegradation reduced hydrophobicity, with the sample photodegraded for 130 h (P130) exhibiting the lowest angle (64.4°) prior to heating. After heating, all samples showed a decrease in hydrophobicity, except for the P130 sample, which exhibited a slight increase in the contact angle. Scanning electron microscopy (SEM) analysis revealed changes in the polymer structure that became more pronounced with increasing photodegradation time, with the P130 sample showing more significant surface damage. The formation of plastiglomerates was observed, particularly in the samples photodegraded for 72 h (P72), as these samples exhibited greater adhesion to sand due to the presence of more polar functional groups, such as carbonyls. The P72 sample showed the greatest weight increase (1659%) after sand adhesion, while the original sample exhibited the largest area reduction (72%) after heating. FTIR analysis confirmed the formation of oxidized groups, such as carbonyls and hydroxyls, in the photodegraded samples and highlighted the effects of photodegradation and thermal degradation on the polymer structure. This research demonstrates the combined influence of photodegradation and thermal stress on the physical and chemical properties of PE microplastics.