Sponge foam rubber products are a kind of elastomer material with porous structure processed from rubber as the main raw material, with low density, light texture, good elasticity, soft feel, and not easy to transfer heat, and are widely used in various fields such as automobiles, shoes, home appliances, daily life, etc., and have good effects of shock absorption, sound insulation, and heat insulation.As a renewable resource for waste rubber recycling, reclaimed rubber has low price and good performance, and can be used alone or combined with natural rubber and synthetic rubber to produce sponge foam rubber products, which requires a reasonable design of vulcanization system.
1. The vulcanization rate of reclaimed rubber matches the foaming speed
When using reclaimed rubber to produce sponge foam rubber products, the vulcanization process involves the interaction among vulcanizing agent and accelerator, so the variety and amount of vulcanizing agent directly affect the vulcanization rate of reclaimed rubber and the performance of sponge foam rubber products. During the vulcanization and heating process of reclaimed rubber, two main reactions will occur: the decomposition of the foaming agent to produce gas and the cross-linking of the reclaimed rubber under the action of the vulcanizing agent.
The gas precipitated by the foaming agent is initially dissolved in the rubber compound, and when the gas dissolution reaches saturation, the rubber material foams under the gas pressure, and the hole structure is fixed by vulcanization cross-linking. Therefore, the vulcanization rate is required to be adjusted so that the tensile expansion force on the pore wall generated by the precipitated gas E4LYY94 is slightly greater than the resistance of the pore wall itself to the stress. If the gas phase formation rate is too fast, the rubber material will not have time to vulcanize, and the bubbles will burst, resulting in a decrease in foaming pressure; If the vapor phase formation rate is too slow or the vulcanization rate is too fast, the compound will complete the vulcanization and shaping before forming a porous structure; The curing rate of the vulcanizing agent must match the foaming rate.
2. Vulcanization system and compounding agent commonly used in the production of sponge foamed rubber products from reclaimed rubber
(1) Sulfur vulcanization system
When the sulfur vulcanization system is used in the foamed rubber products of reclaimed rubber sponge, it is recommended to choose thiuram super accelerator, and the dosage is controlled among 0.5-2 parts, which is more than the number of pores of thiazole or sulfenamide accelerator alone; generally, sulfur alone is used without the accelerator, and the sulfur binding rate can be accelerated by the foaming agent; when the accelerator and the foaming agent exist at the same time, the binding rate of sulfur may be accelerated or slowed down.
When the sulfur-accelerator system is used in the combined production of sponge foamed rubber products from natural rubber/reclaimed rubber, the mixing of foaming agent AC in the rubber compound containing accelerators DM, thiuram and AZ will reduce the sulfur binding rate by about 33%, and the vulcanization time needs to be extended by 30%-50%; The reclaimed rubber compound containing the accelerator DPG is vulcanized by the foaming agent AC, and the sulfur binding rate is not affected. When using the blowing agent DPT, the blowing agent and accelerator will activate each other, and the time to reach the maximum vulcanization can be shortened by 50%-75%.
(2) Peroxide vulcanization system
Peroxide vulcanization can be used in the production of sponge foam rubber products using EPDM reclaimed rubber, and the peroxide vulcanization system has more stringent requirements for temperature and time. The suitable vulcanization temperature range is 130-190°C, otherwise the polymer will be degraded or under-crosslinked. The curing time needs to be determined according to the half-life of the peroxide at the sulfidation temperature, usually 5-10 times the half-life. For example, at 150°C, if the half-life of peroxide is 1 minute, the vulcanization time should be controlled in the range of 5-10 minutes.
There are many types of sponge foam rubber products with reclaimed rubber as the main raw material, such as foam sealing strips, sponge gaskets, etc. When using reclaimed rubber to produce sponge foamed rubber products, it is necessary to reasonably select vulcanizing agents and accelerators according to the types of raw rubber, product performance requirements and production process conditions to ensure the coordination of vulcanization and foaming processes, and reduce more raw material costs and production energy consumption on the premise of ensuring the performance of foamed products.
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