A strategy to prepare internally-plasticized poly(vinyl chloride) by grafting castor oil onto the PVC chain with three different isocyanates as intermediate bridges

In this work, three types of internally-plasticized poly(vinyl chloride) materials (PVC-H-C, PVC-TH-C, PVC-IP-C) were prepared by grafting castor oil onto the PVC chain with three different isocyanates as intermediate bridges, respectively. The three different isocyanates were hexamethylene diisocyanate (HDI), trimer of HDI (THDI), and isophorone diisocyanate (IPDI). This method does not need any castor oil pretreatment. The effects of different isocyanates on the plasticizing ability of the internally-plasticized PVC and the thermal stability of the whole material were discussed. The grafting of castor oil onto PVC with hexamethylene diisocyanate (HDI) as the intermediate bridge has the best plasticizing effect among the three types of internally-plasticized poly(vinyl chloride) materials, as the elongation at break reaches 294%, and the glass transition temperature is lower than that of pure PVC from 75 to 58 °C. It is worth mentioning that the thermal stability is optimized when HDI trimer (THDI) is used as the intermediate bridge, which may be related to the triazine ring contained in THDI. Moreover, this PVC material (PVC-TH-C) also has higher decomposition activation energy when the mass loss is 40% and releases less HCl and benzene gas during thermal degradation. The three types of internally-plasticized PVC all show excellent migration resistance, and almost do not migrate in the petroleum ether environment.