Epoxidized isosorbide-based esters with long alkyl chains as efficient and enhanced thermal stability and migration resistance PVC plasticizers

Abstract

The development of a bio-based plasticizer with good plasticizing performance, migration resistance, and thermal stability for polyvinyl chloride (PVC) is still a notable challenge due to the trade-off between molecular weight and compatibility. Herein, epoxidized isosorbide-based esters featuring multiple epoxy groups were prepared via the esterification of isosorbide with various aliphatic acids with C-18 alkyl chains (oleic acid, linoleic acid, and linolenic acid) followed by epoxidation. The resulting epoxidized isosorbide-based esters were utilized as PVC resin plasticizers, and the overall performance of these plasticized PVC specimens was investigated in detail. Moreover, the esterification reaction was optimized and 1-propylsulfonic-3-methylimidazolium hydrogensulfate ionic liquid was selected as the catalyst. After the reaction was complete, the ionic liquid and product were in separate phases, enabling facile catalyst recycling in a simple, convenient, and environmentally friendly process. The most superior plasticizing effect was achieved by epoxidized isosorbide linolenate (EGLA-ISB). In comparison to the PVC samples plasticized with dioctyl terephthalate (DOTP), those plasticized with EGLA-ISB demonstrated a 15-fold increase in thermal stability during isothermal testing (a PVC/50EGLA-ISB film had a low weight loss of approximately 1.5% after heating at 200 °C for 120 min). Furthermore, the initial thermal decomposition temperature of the PVC plasticized by EGLA-ISB increased by almost 40 °C (up to 306.9 °C) compared to pure PVC, and a higher elongation at break (387%) was also observed. The excellent performance of the PVC plasticized by EGLA-ISB was attributed to the C-18 alkyl chains and multiple epoxy groups of EGLA-ISB, which improved its PVC compatibility, enhanced the thermal stability of the PVC.