Home    Company News    Application of silica in rubber

Application of silica in rubber

Hits: 221 img

(1) Mixing and dispersion of rubber compound
Due to its large specific surface area, white carbon tends to aggregate twice. In addition, it is easy to absorb water in the air, which makes it easy to generate strong hydrogen bond association between hydroxyl groups, further improving the cohesion between particles. Therefore, the mixing and dispersion of white carbon black is much more difficult than that of carbon black. In addition, it is easy to generate gel when mixing in large quantities, which hardens the rubber and generates great heat during mixing. In order to obtain good dispersion, it is required to maintain the highest possible shear force during initial mixing, so that these aggregate particles of silica can be destroyed as much as possible without causing too much mechanical degradation of rubber molecular chain. Therefore, white carbon black should be added in small amounts in batches to reduce heat generation. Properly raising the mixing temperature is conducive to removing some moisture absorbed on the surface of silica, reducing the cohesion between particles, and facilitating the dispersion of silica in the rubber compound.

(2) Structure control of silica reinforced silicone rubber compound
Silica, especially fumed silica, is the best reinforcing agent for silicone rubber, but there is a problem that hardens the compound, commonly known as "structural effect". Its structure increases with the prolongation of rubber storage time, even to the extent that it can not be returned for refining or scrapping. There are two explanations for this. One is that the end group of silicone rubber is condensed with the hydroxyl group on the surface of silica; On the other hand, it is believed that the silicone rubber siloxane links form hydrogen bonds with the surface hydroxyl groups of silica. There are two ways to prevent structurization. One is to add some substances that can react with the hydroxyl groups on the surface of silica during mixing, such as hydroxy silicone oil, diphenyl silicone glycol, silazane, etc. When diphenylsilanediol is used, it shall be treated for 0.5~1h at 160~200 ℃ after mixing. This can prevent the structure of silica filled silicone rubber. Another way is to modify the surface of silica in advance, first remove some surface hydroxyl, and fundamentally eliminate the structure.

(3) Mooney viscosity of rubber compound
The ability of silica to generate gel is comparable to that of carbon black. Therefore, when mixing silica, the Mooney viscosity of the rubber compound is increased, which worsens the processing performance. Therefore, the selection and amount of softener in the rubber compound formula containing silica are very important. Paraffin hydrocarbons, naphthenic hydrocarbons and aromatic hydrocarbons are often added to IIR, and the amount varies depending on the amount of silica and Mooney viscosity, generally up to 15-30%. Among NR, plant softeners such as pine oil and tall oil have the best softening effect, while synthetic softeners have little effect, while mineral oil has the lowest softening effect.

(4) Curing speed of rubber compound
There are a large number of micropores on the surface of silica particles, which have a strong adsorption effect on the vulcanization accelerator, so the vulcanization is obviously delayed. In order to avoid this phenomenon, on the one hand, the dosage of accelerator can be appropriately increased; On the other hand, active agent can be used to make the active agent preferentially adsorb on the surface of silica, thus reducing its adsorption of accelerator.

The active agent is generally low molecular compound of amine, alcohol and alcohol amine containing nitrogen or oxygen. Amines are more suitable for NR, such as diethanolamine, triethanolamine, butylamine, hexamethylene tetramine, etc. For SBR, alcohols are more suitable, such as hexyl alcohol, diethylene glycol, glycerol, polyethylene glycol, etc. The amount of active agent shall be determined according to the amount of silica, PH value and rubber type, and the general amount is 1~3% of silica.

Online QQ Service, Click here

QQ Service

Wechat Service