Highly efficient flame-retardant plasticizers for flexible poly(vinyl chloride) via the synergism of integrated isocyanurate, DOPO and poly (ε-caprolactone)

Polymer materials with flame retardancy are essential for human and environmental safety, yet conventional flame retardants often compromise the mechanical or thermal properties of polymers due to poor matrix compatibility. In this study, flame retardants based on isocyanurate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were covalently integrated with the biodegradable polymer poly(epsilon-caprolactone) (PCL) to create flame-retardant star PCL (STPD) plasticizers for poly(vinyl chloride) (PVC). The structure-property relationship of STPDs was systematically investigated, with a focus on their flame-retardant performance in PVC systems using limiting oxygen index (LOI), UL-94 vertical burning, and cone calorimeter tests. The optimized STPDs not only imparted exceptional flame retardancy to flexible PVC but also maintained its mechanical and thermal properties. The underlying flame-retardant mechanism, attributed to the synergistic effect of isocyanurate, DOPO, and PCL, was thoroughly elucidated. This work demonstrates that STPDs represent a promising class of eco-friendly, high-performance flame-retardant plasticizers for flexible PVC applications.