EPDM recycled rubber has excellent heat resistance, ozone resistance and weather resistance, and can be used alone or in combination with EPDM rubber to produce high-hardness rubber products, effectively reducing raw material costs and production energy consumption. In actual production, carbon black is the main raw material to improve the hardness of rubber products, but the use of carbon black in large quantities will lead to the problem of mixing and processing difficulties. How to design a high-hardness EPDM compound formula with EPDM reclaimed rubber as the main raw material to achieve a balance among hardness and processing performance.
1. Rubber raw material selection
Compared with EPDM rubber, EPDM reclaimed rubber has better processing performance. When EPDM reclaimed rubber and EPDM rubber are used together to prepare high-hardness rubber, it is recommended to choose low-Mooneson rubber to ensure that a large amount of carbon black can maintain low rubber viscosity and good processing performance without or less softener. When choosing EPDM, you also need to pay attention to the ethylene content and diolefin content of the raw rubber.
Ethylene content is the key factor affecting the hardness of EPDM, which is generally controlled among 60%~70% to balance the hardness and processing performance. It is recommended to choose EPDM raw rubber with moderate diene content for high-hardness EPDM rubber products, too high diene content may lead to reduced processing performance and scorching risk, while too low will affect the resilience of the rubber compound.
2. Key points of design of vulcanization system for high-hardness EPDM recycled rubber products
The high-hardness EPDM recycled rubber compound generally requires that the vulcanization system should have good processing safety, and the selection matches the diene content to achieve higher processing safety. If the diolefin content in the EPDM is low, it may be necessary to choose a sulfidation system that does not depend on the diolefin cross-linking point, such as a peroxide sulfing system. If the diolefin content is high, a sulfur-accelerator vulcanization system can be chosen.
The design of the vulcanization system of high-hardness EPDM recycled rubber compound also needs to consider the physical properties, heat resistance, aging resistance and other performance indicators of the rubber after vulcanization, as well as the convenience of processing technology.
3. Key points of design of reinforcing system for high-hardness EPDM recycled rubber products
To improve the hardness of EPDM recycled rubber, it is recommended to choose medium or medium and low reinforcing carbon black as reinforcing agent, or use carbon black with different reinforcing properties to obtain high E4LYY312 hardness of rubber by filling a large number of materials, which can obtain good resilience and low compression set while maintaining the hardness of rubber compounds. Although the hardening effect of high-reinforcing carbon black is obvious, the rapid expansion of the viscosity of the rubber compound and the increase of heat generation will bring difficulties to the processing of high-hardness rubber compounds, so it is not recommended to use this kind of carbon black filling for high-hardness EPDM recycled rubber products.
4. Key points of design of softening system for high-hardness EPDM recycled rubber products
On the premise of ensuring the hardness of EPDM recycled rubber, in order to give the rubber better elasticity, it is recommended to use an appropriate amount of softener, but the dosage should not be too much, and even no softener can be added in some formulas.
When using EPDM reclaimed rubber as the main raw material to prepare high-hardness rubber, it is necessary to balance the relationship among the hardness of the rubber and the processing performance, so some formulations can use processing aids in moderation, such as WB212, Aflux42, FL, PE wax and petroleum jelly, etc., which can reduce the viscosity of the rubber, improve the lubricity and fluidity on the metal surface, and reduce power consumption and heat generation.
For products with a hardness requirement of more than 85, hardeners can be used, e.g. in combination with NR, SBR or liquid polybutadiene rubber with a high sulfur content; Combined with thermoplastic polymers such as polyethylene, polypropylene, and high-crystallinity ethylene-octene copolymers; In combination with SBR resins with high styrene content (HS - SBR); In combination with a thermosetting phenolic resin (PF) containing a curing agent (accelerator H); A system that combines peroxide with a high content of active additives.
To design the formula of high-hardness EPDM recycled rubber products, it is necessary to comprehensively consider the selection of raw rubber, the control of ethylene and diene content, the dosage of reinforcing agents and softeners, the use of processing aids, hardening agents, etc., and continue to discuss related issues with you in the future.
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