Degradation of UV-pretreated polyolefins by latex clearing protein from Streptomyces sp. Strain K30.

Plastic products made of polyethylene (PE), polypropylene (PP), and polystyrene (PS) are widely used in daily life and industrial production. Polyolefins-which have a very stable structure and do not contain any active molecular groups-are difficult to degrade and pose a serious global environment threat. This study selected latex clearing protein (Lcp) derived from Streptomyces sp. Strain K30. The natural substrate of the enzyme is rubber (cis-1, 4-polyisoprene), and the site of action is the carbon‑carbon double bond. Lcp was incubated with UV-irradiated polyolefin PE, PP and PS (UV-PE, UV-PP, and UV-PS containing carbon‑carbon double bonds) for 5 d at 37 °C. The results showed that UV-PE-Lcp was more fragmented than UV-PE-blank; the Fourier transform infrared spectroscopy results showed that UV-PE-Lcp and UV-PP-Lcp produced new active groups (e.g., -OH and -C=O); however, the effect on UV-PS was not significant. Scanning electron microscopy results showed that the treated group had more obvious roughness, cracks, and pits than the control group. The results of high-temperature gel permeation chromatography showed that the average molecular weight (M) of UV-PE-Lcp and UV-PP-Lcp decreased; the M of UV-PE5-Lcp was reduced by 42.02%. The results of gas chromatography-mass spectrometry showed the production of ketones. Therefore, the Lcp latex clearing protein degrade UV-oxidized polyolefin plastics and has great potential for PE and PP degradation but may not be suitable for PS. Furthermore, other Lcps (such as Lcp, Lcp) can also degrade UV-PE.