The crosslink density of elastomers is the essential property that determines many other but especially the mechanical product properties. Different raw materials, especially recycled and bio-based materials, influence the vulcanization and may change the crosslink density when they are used as a substitute to conventional raw materials. Aim of this study is to develop a procedure that allows the reliable determination of the crosslink density in highly filled EPDM compounds as basis for future investigations focussed on substitution with sustainable materials in this compound. Unfortunately, experiences with other rubber compounds like tire treads cannot be directly applied here because of the use of other filler types and amounts as well as the differences in the polymer with regard to active sites (available double bonds). Equilibrium swelling, Flory-stress-strain-measurements, freezing point depression and temperature-scanning-stress-relaxation are applied to a model EPDM compound with high filler and softener amount as typically used for sealings. For sensitivity investigation the amount of the crosslink agent sulfur was varied. Furthermore, the influence of different accelerators was investigated. All methods are able to determine the crosslink density but with different standard deviations due to measurement errors. Partially, they can be optimized for this use case. Based on the results a combination of Flory-stress-strain-measurements and freezing point depression was chosen to be used in the future.

Tire wear is a main contributor to microplastics. As we cannot fully avoid tire wear, otherwise we could not brake and stop, new solutions are needed to address this problem. Not only on roads tire wear is released to the environment, even more can be found at airports. The advantage there is that the Tire Wear Airstrip Particles are gathered while cleaning the pavement. This collection is an opportunity to recycle and add new value to it. Whereas rubber powder is a common way to recycle and reuse end-of-life-tires as raw material in rubber compounds, the question is if TWAP is reusable in the same or similar way. In this study TWAP and rubber powder from truck tire treads are analyzed and compared with regard to their morphology, particle size distribution and composition. The particle size distribution of TWAP is broader than rubber powder containing also much smaller particles. The mineral content of TWAP is about 60%. These minerals can be residues of the pavement, brake wear but also rubber ingredients. In comparison to rubber powder, the impurities of TWAP are expected to have an impact with regard to potential applications and should be better separated.

Every aircraft leaves tire wear particles on the ground of airports at take-off and landing. To maintain good grip properties, the pavement must be regularly cleaned up. The gathered Tire Wear Airstrip Particles (TWAP) normally get disposed by burning. As they are very similar to rubber powder the question is if they might be used as a secondary raw material to keep them longer in the loop in the sense of circular economy. In this study TWAP gathered by the cleaning of the runway of an airport in Germany are compared to ambient ground rubber powder from truck tire treads. Both are analyzed microscopically with regard to their morphology, particle size distribution and chemical composition by calcination with following elemental characterization of the ash by Energy-Dispersion-X-ray Analysis (EDS) in the Scanning Electron Microscope (SEM) and Thermal Gravimetric Analysis (TGA). The particle size distribution of TWAP is broader than rubber powder containing also much smaller particles. The mineral content is about 60% of the gathered TWAP. These minerals can be residues of the pavement or break wear and to a smaller amount from the rubber ingredients. Although the TWAP on their own are similar to rubber powder, the impurities they contain may have an impact with regard to potential applications.