Ground Tire Rubber (GTR) is a product obtained by grinding of worn tire treads before retreading or by cryo or ambient temperature milling of End-of-Life-Tires (ELT). The amount of ELT is continuously increasing. Therefore new ways for their recycling need to be found.

EPDM compounds often find application in automotive as car body sealings. They mostly have a high content of fillers – active and inactive. Chalk is an inactive filler with higher density. With the current pressure to reduce the CO₂ foot print of the products further weight reduction with impact on rolling resistance as well as use of secondary / recycled raw materials is needed in order to get closer to the climate goals. The challenge is to close the loop in the sense of circular economy, what is not trivial at all for elastomers.

The aim of this study is to evaluate if chalk can be substituted by Ground Tire Rubber in EPDM sealing compounds and if yes to which extent. Different types of GTR are incorporated in an EPDM model compound as partial or complete substitute of chalk. The raw compounds and the vulcanizates are characterized to identify the limits. In general, it can be seen that increasing amounts of GTR and larger particles degrade the properties. The Ground Tire Rubber also influences the vulcanization kinetics. The process safety window is reduced up to 50 % and the vulcanization time up to nearly 80 %. The compounds with about 30 % substitution with the finer Ground Tire Rubber show partially similar or even better properties than the reference.