Chemoenzymatic Synthesis of Epoxidized Cottonseed Oil as a Sustainable PVC Plasticizer

Poly(vinyl chloride) (PVC), one of the most consumed commodity thermoplastics, relies heavily on the usage of plasticizing agents to confer versatilities. Biobased plasticizers that are biocompatible, nontoxic, and biorenewable have captured much attention as a sustainable alternative to the conventional phthalate for PVC plasticization. Epoxidized cottonseed oil (ECSO), derived as a byproduct of the cotton fiber industry, was synthesized through a safer and more selective solvent-free chemoenzymatic epoxidation reaction of cottonseed oil (CSO) using Novozym 435. The epoxidation reaction products were studied by 1H NMR, FTIR, and acid number titration, and a varying amount of purified ECSO (0–100 phr) was incorporated into PVC films through solvent casting. The effects of ECSO on the glass transition temperature (Tg), thermal stability, and mechanical properties of the films were examined. The average Young’s modulus dropped up to 330-fold from 1.78 GPa to 5.27 MPa, and the average elongation at break increased up to 80-fold from 3% to 266%. The Tgs decreased from 85.3 °C to the lowest of −25.6 °C, which is well below room temperature and consistent with the flexible and rubbery behaviors. In contrast, unmodified CSO was unable to provide effective plasticization, and a Tg of 76 °C was seen on the second differential scanning calorimetry (DSC) heating. The degradation onset temperature showed an up to 21 °C improvement for ECSO plasticized PVC film, whereas the incorporation of unmodified CSO reduced it. XRD analysis indicated that both CSO and ECSO were initially mixed with PVC chains at a molecular level before heating and emphasized the role of epoxy in the effective plasticization and stabilization of PVC, where intimate mixing alone was insufficient. The findings from this study demonstrate the feasibility and scalability of producing ECSO using sustainable chemoenzymatic epoxidation and provide critical insights into its working mechanisms as an effective bioplasticizer.