Effect of chlorinated phosphate ester based on castor oil on thermal degradation of poly (vinyl chloride) blends and its flame retardant mechanism as secondary plasticizer
A novel flame retardant chlorinated phosphate ester based on castor oil (CPECO) was synthesized. Chemical structure of CPECO was characterized with FTIR, 1H NMR and 31P NMR. The application of CPECO as a secondary plasticizer for poly (vinyl chloride) (PVC) not only gained satisfied flame retardancy and mechanical properties, but also substituted for dioctyl phthalate (DOP) partly. Flame retardant properties of PVC plasticized with CPECO was explored with LOI tests, SEM, TGA, TGA-FTIR, TGA-MS and cone calorimeter tests. The results showed that LOI value of plasticized PVC blends could increase from 23.6% to 35.4%. TGA-FTIR and TGA-MS detected that the main pyrolysis products of PVC blends were H2O, HCl, CO2, CO and C6H6. Cone calorimeter tests showed that peak heat release (pHRR) of plasticized PVC blends could decreased from 379.00 to 289.00 kW m−2, total heat release (THR) decreased from 31.78 to 19.12 MJ m−2. The flame retardant mechanism of plasticized PVC blends could be concluded that phosphorous-containing components generated from pyrolysis of CPECO could promote formation of char residual. The char residual was blown by evolving gases which produced a foaming and expansion of the char layer. The carbonaceous char layer is effective to slow mass and heat transfer between the gas and condensed phases and to protect the underlying material from further combustion. The glass-transition temperature (Tg), mechanical properties of PVC blends and migration stability of CPECO were investigated.