Influence of Ultraviolet Light-Induced Photooxidation on the Surface Chemistry and Biodegradability of Aliphatic...

This study examines the environmental degradation of polyamides (PAs) with varying methylene group content from the perspective of polymer surface chemistry. PA4, PA6, PA11, and PA12 films were subjected to ultraviolet (UV) exposure to simulate environmental photooxidation, and subsequent changes in surface morphology and wettability were analyzed using laser microscopy and contact angle measurements. After 4 weeks of UV exposure, PA11 and PA12, which contain longer alkylene chains, exhibited more pronounced and denser surface cracks than PA4 and PA6. UV exposure increased the surface wettability of all samples, indicating photooxidation, as confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The photooxidation rate followed the order: PA4 < PA6 < PA11 < PA12. Biodegradation was assessed by immersing pristine and UV-exposed films in extracted seawater. While pristine PA4 and PA6 developed biofilms, indicating biodegradation, PA11 and PA12 remained resistant. However, UV exposure rendered PA11 and PA12 biodegradable, likely due to the formation of lower-molecular-weight, soluble photooxidation products that facilitated microbial attack. UV exposure also enhanced the biodegradability of PA4 and PA6. Wide- and small-angle X-ray scattering analyses revealed that both photooxidation and biodegradation predominantly affected the amorphous regions of the polymers. These findings highlight the role of surface chemistry in the environmental fate of polyamides and the potential for UV-induced degradation to influence their biodegradability.