Influence of soy protein isolate on the thermal stability of poly(vinyl chloride) in the presence or absence of calcium and zinc stearates

The influence of soy protein isolate (SPI) and its mixture with calcium stearate (CaSt2), and zinc stearate (ZnSt2) with various ratios on the processing thermal stability of poly (vinyl chloride) (PVC) was investigated by measuring dehydrochlorination rate of PVC (DHC), visual color comparison, and thermogravimetric analysis (TGA). The results suggested that SPI acted as a long-term thermal stabilizer like CaSt2 to absorb HCl released from PVC, which is due to the primary amine (-NH2) and polyols containing hydroxyl groups in SPI. Moreover, SPI improved the stabilization effect of the traditional CaSt2/ZnSt2 stabilizer, and the combination of SPI and CaSt2/ZnSt2 at certain ratios exhibited desirable stabilization efficiency in prolonging the discoloration time.