Fabrication of Bismuth Oxychloride Nanosheets Decorated with Chitosan and Phytic Acid for Improvement of Flexible Poly(vinyl chloride) Flame Retardancy

Abstract

A novel green composite flame retardant, bismuth oxychloride nanosheet decorated with chitosan and phytic acid (BiOCl@CS-PA) was prepared in order to improve the fire safety of flexible poly(vinyl chloride) (PVC). Introducing phytic acid (PA) is aimed at promoting the flame retardancy of BiOCl nanosheets in condensed phase using the synergistic effects. Chitosan (CS) not only acts as a bridge between BiOCl and PA, but also increases residue as a charring agent. Adequate characterizations verified that the BiOCl@CS-PA has been prepared successfully. When 3 wt.% of BiOCl@CS-PA was imparted into the PVC matrix, the resultant PVC composite can pass V-0 rating in the UL-94 test. Additionally, cone calorimetry test demonstrated that 3 wt.% of BiOCl@CS-PA reduced the first peak heat release rate and inhibited the pronounced peak heat release rate of PVC matrix between 300–400 s in comparison with the BiOCl nanosheets, indicating a further improvement in flame retardancy of PVC/BiOCl@CS-PA composite with the help of PA in the condensed phase. Microstructure and morphology of the char residue of PVC/BiOCl@CS-PA were analyzed to reveal the flame retardant mechanism. The results indicated that the joint action of PA and CS improves the quality of the char layer, which contributes to improving the flame retardancy in condensed-phase.