Chemoenzymatic Modification of Polyolefins: Surface Oxidation and Identification of Degradation Products

Sammanfattning

Global plastic production exceeds 400 million tons annually, with polyolefins accounting for nearly half. Their highly stable hydrocarbon backbone makes them highly resistant to degradation, leading to environmental accumulation and significant contributions to plastic pollution. Conventional recycling methods are insufficient to address these challenges, highlighting the need for more sustainable alternatives. This study investigates chemoenzymatic modification of polyolefin films, including LDPE, LDPEa (LDPE with antioxidants), LLDPE and HDPE. Chemical pretreatments, KMnO4/HCl, Fenton oxidation and UVC-Fenton were combined with enzymatic treatment using bacterial (Bacillus Subtils, L.CotA) and fungal (Myceliophthora thermophila, L.MT), laccases in a TEMPO-mediated system. The resulting modifications of the polymer backbone, surface morphology, elemental composition and thermal properties were evaluated using FTIR, SEM, EDX, DSC, HPLC and GC-MS. Following chemoenzymatic treatment, FTIR revealed oxidation of the polymer backbone. The highest calculated carbonyl index values were 2.50 for KMnO4/HCl combined with L.CotA and 2.01 for Fenton oxidation combined with L.MT. Additionally, UVC treatment enhanced Fenton oxidation and enzymatic treatment with both L.CotA and L.MT. SEM analysis revealed visible surface modification in the form of cracks and particle clusters, EDX confirmed an increase in oxygen content and DSC measurements indicated slight decreases in melting temperature and crystallinity. GC-MS analysis of the reaction mixtures identified oxidised degradation products ranging from C2-C20. L.CotA primarily generated longer oxidised oligomers, suggesting more surface limited modification, whereas L.MT produced a broader range of compounds, including short chain hydroxy acids and polyoxidised intermediates, indicating more extensive modification. These degradation products demonstrated great potential for upcycling into biodegradable polymer or other industrial applications. Overall, LDPE and LDPEa films proved most susceptible to the modification.