Effect of the individual and combined use of cardanol-based plasticizers and epoxidized soybean oil on the properties of PVC

The cardanol-derived plasticizers cardanol acetate (CA) and epoxidized cardanol acetate (ECA) were prepared from a renewable resource, cashew nut shell liquid (CNSL), and their plasticization efficiencies were investigated. The thermal decomposition temperatures of the cardanol derivatives were higher than that of the common petroleum-based plasticizer di-2-ethylhexyl phthalate (DOP) in the order ECA > CA > DOP. The tensile strains of the PVCs containing CA and ECA were ca. 705–810%, and the tensile strengths were ca. 17.4–19.1 MPa, which were higher than those of PVC containing DOP. The results of a Fourier transform infrared spectroscopy (FT-IR/ATR) and dynamic mechanical analysis (DMA) showed that the compatibility of ECA with PVC was excellent, and the Tg of PVC containing 50 phr of ECA decreased to 27.4 °C. In studies on the combination of a primary plasticizer with epoxidized soybean oil (ESBO), it has been shown that the addition of small amounts (5 phr) of ESBO to ECA improves not only the thermal stability but also the mechanical properties, despite the insufficient compatibility of ESBO and PVC. It can be inferred that the mixture of ECA and ESBO improves the affinity of ESBO and PVC, thereby reducing the polymer chain interactions. Finally, in the leaching tests, the weight loss of PVC containing 50 phr of ECA was reduced to 2%, confirming that ECA is highly resistant to migration to water. As a result, the combination of two biobased plasticizers, ECA and ESBO, could be a good candidate to replace DOP.