Thermal degradation behavior and flame retardant mechanism of poly(vinyl chloride) plasticized with a soybean-oil-based plasticizer containing phosphaphenanthrene groups

This represents the first description of a flame retardant plasticizer based on soybean oil containing phosphaphenanthrene groups (PSPE). This additive has been prepared and applied in the generation of flame retardant PVC materials. The molecular structure of PSPE was characterized using FT-IR, 1H NMR and 31P NMR spectroscopy. The thermal degradation behavior and flame retardant performance of PVC blends plasticized with different amounts of DOP and PSPE has been examined based on mass loss, LOI values, morphologies of residues, smoke production rate (SPR), smoke extinction area (SEA), mass loss rate (MLR) and heat release rate (HRR), thermal degradation processes and modes of flame retardant action has been proposed. The results showed that the addition of PSPE promotes the formation of high quality char residue. Replacement of DOP with PSPE provided PVC blends which exhibited high thermal stability; Td, T50, Tp1 and Tp1 of 291.3 °C, 325.8 °C, 283.0 °C and 461.8 °C, respectively, were observed. The degradation of PSPE released PO2 and HPO2 radicals and a series of long chain fatty acid, which provided abundant carbon sources and acid sources for PVC blends. The flame retardant effect was mainly in the condensed phase.