Epoxidized soybean oil: A sustainable solution to polyvinyl chloride recycling challenges

Abstract Recycling process of polyvinyl chloride (PVC), a widely used plastic, is important in order to reduce its harmful environmental impacts and contribute to the circular economy. Thermal degradation of PVC during mechanical recycling significantly reduces its final properties and requires optimization of its thermal stability. In this context, this paper examines the performance of epoxidized soybean oil (ESBO) as a secondary heat stabilizer to improve the thermal and mechanical properties of PVC during the simulated recycling process through repeated extrusion processes. Two different PVC formulations prepared without and with ESBO were subjected to multiple extrusion, granulation, and film casting cycles five times to simulate the recycling process. The research involved characterizing cast films after each extrusion cycle to assess the effects of ESBO. Fourier transform infrared spectroscopy indicated that the ESBO does not chemically interact with the PVC yet effectively maintains its structural integrity after multiple extrusions. Colorimetric analysis revealed that yellowing and discoloration are reduced by the incorporation of ESBO and the optical properties of PVC films containing ESBO are maintained even after recycling. The dE* value, which shows a significant color change for the reference films without ESBO (REF), started from 20 and increased to 38 at the end of five extrusion cycles. With the addition of ESBO, dE* values remained lower than REF films throughout all cycles. The thermal stability findings determined via thermogravimetrical analysis, Congo red, and oven aging tests indicated that ESBO acted as a heat stabilizer for PVC over all extrusion cycles. It increased stability time and degradation temperatures, delayed thermal aging, and minimized the effects of thermal treatment. Rheological and mechanical tests showed that ESBO decreased torque requirements during extrusion, increased the degradation time, enhanced flexibility, tensile strength, and modulus, and maintained mechanical properties throughout repeated extrusion. These outcomes prove the performance of ESBO as a sustainable additive to improve the durability, thermal stability, and processability of PVC, addressing crucial challenges in its recycling. Highlights The mechanical recycling of PVC is simulated via repeated extrusion. The effects of ESBO on the thermal and mechanical stability were determined. ESBO maintained the thermal stability of PVC under repeated extrusion. ESBO is a sustainable additive for PVC that improves mechanical strength.