Mechanochemical Treatment of Waste Poly (Vinyl Chloride) for Alcohol Halogenation by Ball Milling and Triboelectric Material

Polyvinyl chloride (PVC), one of the most extensively produced polymers, has raised significant environment and public health concerns due to its persistence in ecosystem, long-term accumulation and associated toxicity. The well-established mechanical recycling approach for treating waste PVC often result in polymer degradation and release of hazardous by-products, such as corrosive HCl. We envisage that mechanical recycling in tandem with a halogenation reaction provide a new solution to waste PVC management. Herein, we demonstrated that PVC plastic could serve as chlorination reagents, in combination with triboelectric catalyst, to achieve efficient halogenation of alcohols under ball milling condition. The triboelectric catalyst, TiO2, mediates the single electron transfer process that promotes the dehydrochlorination of PVC, thereby enabling the in-situ chlorination of alcohols. This strategy was applicable to a variety of aliphatic and benzylic alcohols, yielding the corresponding organic chlorides in moderate to excellent yields. In particular, the yield of benzyl chloride reached 95% after 4 h of ball milling. Structural analysis confirmed that polymer formed by dehydrochlorination of PVC contained olefin, carbonyl and aromatic structures. Additionally, Cl could be completely removed, and the molecular weight decreased from 65.0 kDa to 4.6 kDa after recycling and reusing PVC five times. This mechanochemical approach was also successfully applied in real plastics applications and scale-up experiments. Overall, this method provides inspiration for using PVC as a chlorine source to initiate chemical reactions through mechanochemical approaches.