EPDM reclaimed rubber is made by processing EPDM mastication rubber, uncured EPDM rubber, or discarded EPDM rubber products, retaining the basic properties of the original EPDM rubber. It can partially replace raw materials in rubber product manufacturing, effectively reducing material costs. When producing rubber products like seals, gaskets, and vibration dampers using a combination of EPDM rubber and EPDM reclaimed rubber, the rubber compound needs to have low compression set. So, what factors affect the compression set performance of EPDM/EPDM reclaimed rubber compounds?
1. EPDM rubber content affects the compression set of EPDM/reclaimed rubber
When producing rubber products with strict compression set requirements using a mix of EPDM and EPDM reclaimed rubber, increasing the amount of original EPDM rubber reduces the cured compound's compression set. EPDM reclaimed rubber is made from EPDM scrap or used EPDM products and is a mixture of rubber, carbon black, various softeners, and additives. Compared to pure EPDM, reclaimed rubber has relatively lower elasticity. Properly increasing the EPDM content in the formulation can improve the elasticity and recovery performance of the rubber compound.
2. Carbon black content affects the compression set of EPDM/reclaimed rubber
In compounds using EPDM and EPDM reclaimed rubber, carbon black is the most common reinforcing agent, directly affecting the physical and mechanical properties of the vulcanized rubber. Compared to highly abrasive carbon blacks and channel blacks, semi-reinforcing carbon black is more widely used in low compression set EPDM reclaimed rubber products.
The more carbon black used, the more particles physically adsorbed and bonded to the rubber macromolecular chains. When the external force is removed, stress relaxation is slower, and elasticity decreases. Especially when carbon black exceeds a critical amount, the compression set of the EPDM/reclaimed mixture rises significantly.
3. Antioxidant system design affects the compression set of EPDM/reclaimed rubber
When using a blend of EPDM and EPDM reclaimed rubber as the main material, thermal-oxidative aging can harden the rubber and reduce elasticity. A proper antioxidant system can improve aging resistance. Common antioxidants include Antioxidant D, RD, and MB. Note that Antioxidant D is more toxic and should be handled carefully.
A combined antioxidant system with RD and MB works well. Increasing the amount of MB in the mix reduces the changes in tensile strength and elongation after aging in hot air, improving thermal aging performance. However, adding RD and MB significantly increases the compression set, and the effect becomes more pronounced as the MB content rises.
In actual production, the compression set of EPDM/EPDM reclaimed rubber compounds is influenced by multiple factors. Therefore, when designing rubber formulations, it’s important to consider the specific working conditions and performance requirements. One should: appropriately determine the EPDM/reclaimed rubber ratio, choose semi-reinforcing carbon black and strictly control its amount, and select suitable antioxidants with proper dosages. This ensures aging resistance while minimizing compression set, resulting in EPDM products with both cost advantages and excellent sealing performance.
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