Recycling of EPDM rubber via thermomechanical devulcanization: Batch and continuous operations

• Devulcanization using a two-roll mill, an internal mixer and a twin-screw extruder. • According to horikx's theory, high selectivity and degree of devulcanization (75 %). • Devulcanizates outperformed cryo-rubber during their application in virgin rubber. • Circular strategy, retaining mechanical properties at 50 wt% recycling rate. Thermomechanical devulcanization is a possible solution for the circular economy of EPDM rubber, as it removes covalent crosslinks from vulcanizates, resulting in a material similar to uncured rubber mixes. In this paper, sulfur-cured EPDM rubber was treated with thermomechanical stimuli: a) processing on a two-roll mill and in an internal mixer, and b) twin-screw extrusion. Horikx's analysis indicated a 75 % decrease in crosslink density with little polymer chain degradation. The resulting devulcanizates and non-devulcanized rubber crumb were added to the original rubber mix, yielding samples with 0, 25, 50, 75 and 100 wt% recycled rubber contents. Revulcanizates with up to 50 wt% devulcanizate content retained the tensile strength of the original rubber with a slight increase in modulus. Ultimately, batch devulcanization had the most promising results, and extrusion devulcanization was also more beneficial than using non-devulcanized rubber crumb. Crosslink density and morphological tests also support these findings.