Vulcanization Temperature Impact on Cross‐Linking Density and Compression Set of Sulfur‐Cured Ethylene–Propylene–Diene Monomer

ABSTRACT The aim of the research was to find a fast and reliable measurement method for the prediction of functional properties such as compression set (CS) of rubber profiles. Research shows that the best method for testing network density and crosslinks structure for a finished product, such as complex car seals, is equilibrium swelling. Measurements of cross‐linking density in the temperature range of 150°C–200°C revealed the decrease of cross‐linking density with increase of temperature. Thermal degradation of accelerators responsible for cross‐linking density degradation with temperature was analyzed by thermogravimetry and differential scanning calorimetry. Results showed that the accelerators were stable up to 200°C. Following cross‐linking density reduction with increasing vulcanization temperature, CS was tested. Its optimum was found at 170°C. Based on the finding that cross‐linking density is not the only factor influencing CS, the network structure was studied by thiol–amine analysis. It was confirmed that the optimum of CS was directly linked with the structure, that is, sulfidity, of network crosslinks. Discovery of the CS optimum at vulcanization temperature shows that CS may correspond to the highest percentage of disulfide bond in the network structure and optimization of CS is possible also by processing conditions of rubber compounds.