Enhancement of flame retardancy and physical property for poly(vinyl chloride) having renewable cardanol-based self-polymerizable phosphonate under heat treatment process

Abstract

Considering the drawbacks of conventional plasticizers used for poly(vinyl chloride) (PVC), it is imperative to develop bio-based additives. Herein, bis(cardanyl) phenylphosphonate (CP), which is not only a flame retardant but also a plasticizer for PVC, was designed and synthesized from cardanol. The flame retardancy and flexibility of PVC improved with an increase in the CP content (wt%) because of the presence of the phosphonate group and long alkyl chain of CP, respectively. Meanwhile, we found that CP can be self-polymerized by heat treatment and that the cross-linked network of CP leads to an additional enhancement in the flame retardancy of PVC by inducing anti-dripping property and the formation of graphitized char layer. Also, the flexibility of the PVC films was preserved without deteriorating its transparency. CP with self-polymerization properties is a promising candidate to improve the thermal stability, flame retardancy, and flexibility of PVC while maintaining its transparency and migration stability.