Design of a hybrid zinc-polyamide complex and phosphorus-modified Mg(OH)2 for enhanced fire safety and thermal stability of plasticized PVC nanocomposites

A hybrid additive system was developed to simultaneously enhance the thermal stability and flame-retardant performance of plasticized poly(vinyl chloride) (PVC). A zinc-containing Schiff-base polyamide complex (ZSPC) was synthesized through coordination of Zn 2+ ions with an imine-based polyamide ligand, while magnesium dihydroxide (MDH) nanoparticles were surface-modified using a DOPO-based dicarboxylic acid. PVC nanocomposites containing individual and combined additives were fabricated via solution casting. Structural and morphological analyses confirmed the successful incorporation and relatively uniform dispersion of both additives within the PVC matrix. Thermogravimetric analysis (TGA) revealed an improvement in thermal resistance for the hybrid systems, with the temperature of maximum dehydrochlorination (T max1 ) increasing from 270 °C for neat PVC to 287 °C for the hybrid nanocomposite containing 10 wt% additives, along with an increase in char yield from 10% to 16%. Improved resistance to heat degradation was confirmed by thermal aging at 180 °C, as evidenced by delayed discoloration of the hybrid nanocomposites as compared to pristine PVC. Flame-retardancy tests demonstrated an enhancement, as the limiting oxygen index (LOI) enhanced from 26.5% to 31.3%, and the hybrid nanocomposite achieved a UL-94, V-0 grade, compared to no rating for neat PVC. The hybrid nanocomposites maintained acceptable mechanical performance, showing moderate tensile strength retention with only a slight reduction in elongation at higher additive contents.