EPDM recycled rubber retains the basic performance characteristics of original EPDM rubber, offering good resistance to high and low temperatures, ozone, weathering, and water. It can be used to produce rubber waterproof gaskets, reducing raw material costs. However, in producing waterproof gaskets, EPDM recycled rubber is not simply a direct replacement for the original rubber. Whether the gasket can maintain long-term sealing depends on whether the recycled rubber’s specifications, formulation, and vulcanization process are properly matched. There are three key points to pay attention to:
1. Choosing EPDM recycled rubber for waterproof gaskets shouldn’t just be about price
When choosing EPDM recycled rubber for EPDM waterproof gaskets, you shouldn’t only chase the lowest price. It’s recommended to choose recycled rubber based on gasket hardness, tensile strength, permanent compression set, water resistance, and operating temperature. For gaskets used in regular static water sealing, recycled rubber with moderate Mooney viscosity, low impurities, and good fineness is preferable. For gaskets under long-term compression, with high requirements for resilience and permanent deformation, recycled rubber with higher EPDM content is recommended.
Rubber gasket manufacturers also need to consider the quality stability of recycled rubber. Significant differences among batches can lead to changes in Mooney viscosity, scorch time, and vulcanization speed, which can cause variations in finished product size and sealing performance.
2. Key points in designing reinforcement/filler and softening systems for EPDM recycled rubber gaskets
EPDM waterproof gaskets need a certain hardness and strength. Using recycled EPDM rubber, you can adjust the compound’s hardness and strength through reinforcement and filler system design. However, using too much filler is not better. Excessive reinforcing agents like carbon black and fillers like calcium carbonate can reduce elasticity, making gaskets difficult to fully recover after compression and affecting long-term sealing. The amount of softeners should also be controlled to avoid lowering the strength and compression resistance of vulcanized EPDM recycled rubber.
3. Key points for mixing and vulcanization of EPDM recycled rubber gaskets
(1) Mixing: When using recycled EPDM rubber, ensure the rubber, fillers, softeners, and vulcanization system are evenly dispersed. Adding powder too quickly or improper temperature control can cause poor dispersion or local scorching. Temperatures after adding vulcanizers and accelerators must also be strictly monitored.
(2) Vulcanization: The vulcanization conditions for EPDM recycled rubber gaskets should be based on the rubber’s cure curve rather than using fixed time mechanically. Under-vulcanization can lead to insufficient strength and poor shape retention, while over-vulcanization can make the rubber hard and reduce elasticity. When producing gaskets of different thicknesses, the heat transfer rate must also be considered; vulcanization parameters for thin products can’t simply be applied to thicker products.
4. Vulcanization formula for gaskets using both EPDM and recycled EPDM rubber
EPDM rubber 60 parts, recycled EPDM rubber 40 parts, zinc oxide 5 parts, stearic acid 1 part, carbon black N330 90 parts, white carbon black 5 parts, naphthenic oil 80 parts, accelerator M 1 part, TMTD 1.5 parts, sulfur 1 part; total 284.5 parts.
Using recycled EPDM rubber reasonably in gaskets primarily made of EPDM not only reduces raw material costs but can also improve the mixing and processing performance of the rubber. Choosing the right recycled rubber and combining it with a proper filler system, softening agents, and mixing/vulcanization process ensures that cost reduction translates into real product profit. Simply lowering the purchase price of recycled rubber can result in high permanent compression set, unstable dimensions, or inconsistent batch performance, leading to higher costs from rework and customer complaints.
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