EPDM reclaimed rubber has excellent resistance to high and low temperatures, ozone resistance, and weather resistance, and is widely used in the production of various sponge rubber products, such as automotive door and window sealing strips, foam rubber sheets, and cushioning pads, effectively reducing raw material costs. When using EPDM reclaimed rubber to produce sponge foam rubber products, is it better to choose inorganic or organic foaming agents? What issues should be considered when designing the EPDM reclaimed rubber sponge foam rubber formula?
1. For EPDM reclaimed rubber, sponge foaming rubber products, choose inorganic or organic foaming agents?
The decomposition of inorganic foaming agents is an endothermic reaction with a slow decomposition rate, and the decomposition gas in the rubber has high permeability; The decomposition of organic foaming agents is an exothermic reaction, rapidly decomposing after reaching a E6LYY129 temperature, with stable gas output. The main gas produced is nitrogen, which has low permeability to rubber. Relatively speaking, the decomposition temperature of organic foaming agents is closer to the vulcanization temperature of rubber, resulting in better processing stability and gas emission stability. The decomposed nitrogen can generate bubbles in the rubber to produce sponge rubber, so EPDM reclaimed rubber sponge products mainly use organic foaming agents.
2. What should be noted when choosing foaming agents for producing sponge foam rubber products with EPDM reclaimed rubber?
When producing sponge rubber products using EPDM reclaimed rubber as the main raw material, vulcanization rate directly affects the sponge rubber's density (foaming rate), water absorption rate (increased water absorption rate due to increased porous bubbles), and whether the skin condition is good. It is essential to ensure that foaming speed matches vulcanization speed; The balance among vulcanization speed and foaming speed of sponge rubber is very important.
EPDM reclaimed rubber foams before vulcanization, causing gas to escape from the rubber surface, resulting in insufficient foaming and an uneven surface; Vulcanization occurs before foaming, increasing the viscosity of the compound and making foaming difficult, resulting in insufficient foaming. Prolonged low-temperature, low-speed vulcanization leads to thin surfaces and many pores in foamed products made from EPDM reclaimed rubber; High-temperature, short-duration, high-speed vulcanization causes the surface of EPDM reclaimed rubber sponge rubber to be thick, resulting in more closed pores.
3. What are the commonly used foaming agents for producing sponge foam rubber products from EPDM reclaimed rubber?
(1) Foaming agent OB (OBSH)
When using EPDM reclaimed rubber to produce sponge foam rubber products, especially during extrusion vulcanized foam, it is recommended to use the foaming agent OB (OBSH), which is non-polluting. It should be noted that the foaming agent OBSH has a low gas output, so even with large use, it cannot produce sponge adhesive with a high foaming ratio. Moreover, increasing the amount can significantly delay vulcanization; For EPDM reclaimed rubber sponge products, the typical dosage is 5-10 parts.
(2) Foaming Agent AC (ADCA)
Foaming agent AC is one of the commonly used foaming agents for EPDM reclaimed rubber products. It has fine particles and disperses easily in rubber. It can be used for both atmospheric and pressurized blowing and has a relatively high decomposition temperature. When used alone, its decomposition temperature is 200°C. Metal oxides, organic acid salts, as well as urea and urea derivatives can all lower the decomposition temperature, which can be reduced to 130-180°C. This foaming agent produces a large amount of foam, enabling the production of EPDM reclaimed rubber sponge rubber with a high foaming ratio and good skin surface. It should be noted that the foaming agent AC is easily affected by moisture in the rubber, significantly hindering vulcanization.
(3) Foaming agent H
Foaming agent H features high gas output, high foaming efficiency, and low product collapse. It is very common in EPDM reclaimed rubber sponge rubber products, decomposes at 200°C, but under the action of stearic acid, its decomposition temperature can drop to around 130°C. It should be noted that the heat of decomposition of foaming agent H is relatively high, so when using EPDM reclaimed rubber to produce thick sponge products, careful handling is required; Decomposition products have a foul odor; adding urea or urea derivatives can reduce the odor.
(4) Urea
When using EPDM reclaimed rubber to produce sponge foam rubber products, urea mainly serves as a foaming additive for foaming agents such as H, and also promotes vulcanization.
When using EPDM reclaimed rubber to produce sponge foam rubber products, the vulcanization rate of the compound must match the decomposition rate of the foaming agent. Since the decomposition rate of foaming agents is greatly affected by additives and difficult to adjust, the type of foaming agent (such as AC, OBSH, etc.) is often determined first, and then the vulcanization system is adjusted to adapt.
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