Application skills of precipitated silica in reclaimed rubber products
According to the production methods, white carbon black can be mainly divided into precipitated white carbon black and fumed white carbon black. The precipitated white carbon black is mainly used as a reinforcing agent for natural rubber and synthetic rubber, with significant reinforcement effect. Precipitation white carbon black is called hydrated silica and silicon dioxide, also known as active silicon dioxide. It has high specific surface area, high structure and high activity. When using recycled rubber to produce rubber products, especially light colored and colored rubber products, precipitated silica has more advantages than carbon black and other light colored inorganic fillers.
Application of precipitated silica in rubber products industry
Precipitation silica is a reinforcing filler material prepared by the reaction of silicate and inorganic acid precipitation. After adding a small amount of silica to ordinary rubber, the mechanical strength, wear resistance and aging resistance of the product are significantly improved, and it is widely used in the rubber product industry. In practical application, more than 65% of precipitated silica is used in the rubber industry, mainly in footwear and tires.
After the use of white carbon black for rubber parts in footwear materials, the product hardness, tensile strength, tear strength, abrasion resistance, skid resistance and adhesion are significantly improved, especially in light color, color translucent and transparent soles (including outsole, midsole, band rubber, etc.). Adding proper amount of white carbon black to the tire tread and carcass rubber will help to improve the tear resistance and adhesion between rubber and cord.
2. Relationship between physical properties of precipitated silica and properties of reclaimed rubber
Recycled rubber can replace a certain proportion of high priced raw rubber to produce rubber products on the premise of ensuring product quality. It is the mainstream raw material to reduce raw materials and production costs in the industry. When the reclaimed rubber JS-185 is used to produce rubber products, the particle size, specific surface area, surface properties, etc. of precipitated silica will affect its reinforcement effect in the reclaimed rubber, as well as the process of mixing and vulcanization of the reclaimed rubber.
(1) Particle size: theoretically, the smaller the particle size of white carbon black is, the better the dispersion in the recycled rubber is. The larger the effective contact area with the rubber compound is, the more obvious the reinforcement effect is. However, if the particle size is too small, the plasticity of the compound will decrease and the extruding performance will become worse.
(2) Structure: the greater the structural degree is, the more branch chain structures of precipitated silica in the aggregation state will be, and more energy will be consumed to destroy the branch chain structure; In order to ensure the uniform dispersion of silica with high structure in the recycled rubber, the mixing time should be appropriately extended.
(3) Specific surface area: theoretically, the larger the specific surface area of precipitated silica, the better the penetration of rubber and accelerator, and then a series of physical and chemical reactions occur. However, in actual production, the larger the specific surface area, the higher the adsorption rate and activity of white carbon black, which can absorb more accelerants and accelerate the decomposition of accelerants. Therefore, it has a strong delaying effect on the vulcanization of rubber compound. At this time, it is necessary to appropriately increase the amount of accelerants to improve the vulcanization speed.
In actual production, diethylene glycol, glycerol, triethanolamine and other active agents can also be used appropriately in the formula of recycled rubber products to reduce the adsorption of - OH group on the surface layer of white carbon black on accelerator molecules.
(4) Moisture: the moisture of precipitated silica includes free water and bound water. The content of bound water in white carbon black is generally controlled at 4% - 7%, and the reinforcement effect is better; The content of free water is controlled at 6% - 8%, which has a good isolation effect on white carbon black molecules, effectively prevents the re aggregation of the rubber compound, and can be evenly distributed in the rubber compound during mixing, improving the performance and accelerating the curing speed.
(5) PH value: The acidity and alkalinity of precipitated silica have a great impact on the vulcanization of the rubber compound. The acidic silica will delay the vulcanization of the rubber compound, while the alkalinity will promote the vulcanization, but too high alkalinity will be detrimental to the reinforcement. In actual production, white carbon black with slightly acidic pH is more favorable to the tensile and wear resistance of rubber compound.
3. Precautions for using precipitated silica for reclaimed rubber
When precipitated silica is used in the production of recycled rubber products, the influence of silica on the processing technology and finished product index of recycled rubber products must be comprehensively considered, appropriate silica products shall be selected, and the dosage shall be reasonably controlled; When using recycled rubber to produce low-cost rubber products, avoid using too much precipitated silica in combination with the cost budget.