Comparative study of N-vinyl pyrrolidone and cyclic ketene acetal copolymer degradation under alkaline, enzymatic, or wastewater conditions

Abstract

The (bio)degradability of cyclic ketene acetal (CKA)-containing polymers is dependent on the polymer structure and degradation conditions. Copolymers of N-vinyl pyrrolidone (NVP), with different CKA comonomers and architectures, were subjected to (bio)degradation under alkaline, enzymatic and wastewater conditions. Grafting CKA-co-NVP moieties onto a poly(ethylene oxide) (PEO) backbone promoted the enzymatic hydrolysis of CKA esters and improved the overall polymer biodegradability. Limited biodegradation was observed for poly(CKA-co-NVP) in the presence of wastewater sludge during an industrial biodegradability test under OECD 301F guidelines. Under less stringent test conditions poly(CKA-co-NVP) achieves small, yet non-negligible biodegradation. Structural analysis of the degradation products shed light into the degradation mechanisms, revealing CKA ester hydrolysis in all cases, while in presence of wastewater sludge, additional CKA end-group oxidation was clearly observed. However, effective amide hydrolysis or pyrrolidone unit biodegradation was not detected, with pyrrolidone-containing segments persisting through the biodegradation test.