Synthesis and Properties of Isosorbide-Based Eco-friendly Plasticizers for Poly(Vinyl Chloride)

In this study, isosorbide-based eco-friendly and effective plasticizers were synthesized and characterized. Isosorbide esterification was conducted using fatty acids with different alkyl-chain lengths; the optimal degree of isosorbide esterification was obtained after 6 h reaction at 220 °C with a short alkyl-chain fatty acid in the presence of the catalyst Ti(OBu)4. Isosorbide-based plasticizers of C12 or more alkyl-chain lengths exhibited low compatibility and did not form PVC sheets. An esterified isosorbide with long alkyl-chain length was epoxidized to enhance its plasticizing properties and enable low-cost production; the high epoxidation degree (91%) indicated efficient epoxidation by formic acid and hydrogen peroxide. The synthesized plasticizers, according to the alkyl-chain length, were used to fabricate PVC sheets; subsequently, their mechanical and thermal properties were analyzed. As the alkyl-chain length of the synthesized plasticizer increased, the tensile strength and modulus increased, while the elongation decreased. Furthermore, as the plasticizer content increased, the tensile strength and elongation decreased, while the plasticization efficiency increased. As the alkyl-chain length of the plasticizer increased, the molecular weight increased and the smaller molecules generated more free volume in the PVC chain. The thermal stability of the synthesized isosorbide-based plasticizers improved on increasing their alkyl-chain length, and was higher than that of a commercial plasticizer. Thus, the plasticizers synthesized in this study, particularly isosorbide di epoxidized oleate, could be used as eco-friendly and effective plasticizers for practical PVC applications.