Thermomechanical Devulcanization of Highly Filled EPDM Rubber Waste: Process Optimization, Selectivity Assessment, and Preliminary Industrial Scale-Up

Devulcanization of ethylene–propylene–diene monomer (EPDM) rubber is a promising strategy to improve the circularity of vulcanized automotive rubber waste. However, selective sulfur crosslink cleavage while preserving the polymer backbone remains challenging, particularly in highly filled industrial compounds. In this work, highly filled sulfur-cured EPDM waste from automotive sealing-profile production was thermomechanically devulcanized using 2,2′-dibenzamidodiphenyl disulfide (DBD) and hexadecylamine (HDA). Laboratory-scale experiments were performed in an internal mixer, followed by preliminary industrial-scale trials in a single-screw extruder. Crosslink density was determined using the Flory–Rehner equation with Kraus correction, and selectivity was assessed by Horikx analysis, supported by ATR-FTIR and rheometry. At laboratory scale, DBD showed optimal performance at 1 phr and 200 °C, reaching approximately 86% devulcanization, while higher DBD loading reduced efficiency. HDA reached approximately 85% devulcanization at 3 phr and 280 °C. Horikx analysis indicated preferential crosslink scission under optimized conditions, although mixed reclamation behavior was still observed. Industrial scale-up with 1 phr DBD at 200 °C achieved approximately 60% devulcanization, while HDA was less effective. The lower performance observed at the industrial scale highlights the challenges of translating laboratory-optimized conditions to industrial processing, although the individual contributions of specific processing parameters could not be determined from the available data.