Bismuth stannate nanoparticles for enhancing fire safety of flexible polyvinyl chloride: Preparation, evaluation, and mechanism

Abstract

To replace traditional toxic Sb2O3 flame retardants, Bi2Sn2O7 (BSO) nanoparticles were prepared by a co-precipitation method and used as flame retardants of flexible polyvinyl chloride (PVC) for the first time. Structural characterization revealed that as-prepared BSO nanoparticles had a cubic phase with an average diameter of 20 nm. Under 3 wt% loading, the PVC/BSO composite gained a limiting oxygen index of 29%, very close to 29.5% of PVC/Sb2O3. In particular, the PVC/BSO composites passed the UL-94V-0 rating, while PVC/Sb2O3 failed. The PVC/BSO composite also showed better heat and smoke suppression performance than Sb2O3, with a 27.4% decrease in peak heat release rate and a 39.9% decrease in total smoke production, compared with the PVC matrix. The excellent performance is attributed to following two reasons: In the gas phase, similar to Sb, Bi can form BiCl3, which dilutes the combustion gas and captures hydroxyl radicals; In the condensed phase, Sn in BSO helps form more protective char residue with the least pores and the highest degree graphitization. In addition, the tensile strength and elongation at break of PVC/BSO were also slightly superior to those of PVC/Sb2O3. In conclusion, BSO nanoparticles will be a promising substitute for toxic Sb2O3 flame retardants.