Epoxidized Cassia fistula Seed Oil as Bio-Based Plasticizer for Poly(vinyl chloride) Soft Films

The soft poly(vinyl chloride) (PVC) films were prepared by a solution casting method using the epoxidized form of the oil (ECFSO) extracted from the seeds of Cassia fistula (a nonedible source), dioctyl phthalate (DOP), and DOP + ECFSO mixtures as plasticizers. The plasticization effects were evaluated in terms of thermal and mechanical properties, wide-angle X-ray scattering (WAXS) measurements, migration, and volatility of the plasticizer from the films. The use of ECFSO or its binary mixtures with DOP as plasticizers resulted in better thermal stability, improved mechanical properties, and a drastic decrease in the glass transition temperature (Tg) of the films as compared to DOP plasticized ones. The WAXS profiles showed no significant change in the order of the arrangement of PVC chains, and therefore the plasticization effects are mainly attributed to the enhanced chain mobility. The detailed analysis of the ATR-FTIR spectral measurements on the PVC films revealed major changes in the stretching frequencies of C═O of the plasticizers and HC–Cl of the PVC chains. Density functional theory (DFT) calculations and their careful analysis clearly establish the presence of hydrogen bond type interactions of the hydrogens of the −CH2Cl units of the hydrogenated repeat unit of the PVC with carbonyl and epoxy groups of the ECFSO plasticizer. Due to these hetero interactions, the migration of the plasticizer to the surface and solvent phase was found to be the lowest. The ECSFO based plasticizers have a good potential to partly or fully replace the DOP for producing high performing and environmentally safe PVC soft films.