Cardanol with a Covalently Attached Organophosphate Moiety as a Halogen-Free, Intrinsically Flame-Retardant PVC Bio-Plasticizer

Plasticizers that enable flexible polyvinyl chloride (PVC) are usually combustible, restricting the application of PVC in fire-prone scenarios. In this context, intrinsically flame-retardant plasticizers displaying dual function continue to be the focus of intensive research. Despite their efficiency, the majority of these dual-functional plasticizers previously reported contain halogen elements, which, once ignited, emanate toxic and potentially carcinogenic substances, along with toxic gases and smoke, polluting the environment, damaging the biota, and threatening human health. Here, we report a strategy to obtain a halogen-free, intrinsically flame-retardant PVC bio-plasticizer that harnesses the phenolic hydroxyl of naturally occurring cardanol and covalent attachment of an organophosphate moiety. When combined with di-(2-ethylhexyl) phthalate (DOP), the organophosphate-containing cardanol is qualified as a co-plasticizer, while endowing the PVC materials with flame retardancy. Unlike inorganic flame-retardants, the engineered cardanol is compatible with PVC such that the mechanical properties of the PVC materials are not compromised. The rationale underlying the present effort may provide guidance for developing sustainable alternatives to halogen-containing plasticizers to address the sustainability challenge now confronting PVC industry.