Fabrication of low-fire-hazard flexible poly (vinyl chloride) via reutilization of heavy metal biosorbents

As a naturally abundant biopolymer, chitosan is considered to be a suitable adsorbent for stannate (SnO₃ ²⁻) in tin plating wastewater. However, mass transfer of the adsorbent and its recycling remain challenging problems. Though flexible poly(vinyl chloride) (PVC) is highly flammable due to the addition of plasticizers, the traditional flame retardant, antimony trioxide (Sb₂O₃), is potentially harmful. In this study, chitosan was anchored onto the surface of PVC resin to adsorb SnO₃ ²⁻ from wastewater. Thereafter, tin-doped chitosan-coated PVC resin was readily recycled and processed into a flexible PVC composite (modified fPVC). The limiting oxygen index value of the modified fPVC increased to 33.1%, and the peak heat release rate decreased to 161 kW/m². In addition to reducing fire hazards, this approach also decreased the content of harmful hydrogen chloride gas released during the combustion of modified fPVC. Meanwhile, the tensile properties of modified fPVC were enhanced compared with those of the Sb₂O₃-treated sample. These results indicated the synthesis of an eco-friendly Sb₂O₃-free flexible PVC composite that poses a low fire hazard.