Phosphorous-containing flame retardant plasticizer based on Cassia fistula seed oil and their application in poly(vinyl chloride) films

Abstract

The need for safety and sustainability has prompted the development of flame-retardant bio-based plasticizers from renewable resources. In this study, an efficient phosphorous-containing flame retardant plasticizer (ECFSO-P) for poly(vinyl chloride) (PVC) was synthesized using Cassia fistula seed oil and characterized by fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and proton nuclear magnetic resonance (1H NMR) spectroscopies. In replace of the dioctyl phthalate (DOP), the ECFSO-P was employed as a flame retardant plasticizer to produce poly(vinyl chloride) (PVC) blends. The PVC blends were prepared using ECFSO-P, DOP, and ECFSO-P + DOP blends as plasticizers. The PVC blends with different concentrations of DOP and ECFSO-P were investigated with thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical properties, fire retardant performance, crystallinity, leaching, volatility, and density functional theory (DFT) studies. The TGA results showed that the thermal degradation temperature of PVC blends plasticized with ECFSO-P reached 230.6 ºC. The glass transition temperature, Tg decreased to 34ºC as determined by DSC, when DOP was completely replaced with ECFSO-P. When PVC was plasticized with ECFSO-P only, the tensile strength and elongation at break reached 6.41 and 508.83, respectively. The leaching and volatility properties of ECFSO-P plasticized PVC blends were better than DOP plasticized film. Limited oxygen index (LOI) and smoke density rating (SDR) values were increased by 6.7% and 17.4%, respectively. The WAXS profiles showed that ECFSO-P did not alter the order of crystallinity among the PVC chains. As expected, the hydrogen bonding interactions between plasticizers and the -CH-Cl units of PVC were confirmed by DFT calculations.