Silica - the strongest filler in tyres and rubber

Silica is a kind of reinforced filling material with large specific surface area, high structure and high activity. Because of its special surface structure, particle morphology and physical and chemical properties, silica is widely used.

According to different preparation methods, white carbon black can be divided into gas phase white carbon black and precipitation white carbon black. Gaseous white carbon black has a ball-chain structure with large external specific surface area and less hydroxyl group on the surface, as shown in Figure 1. Precipitated silica is a low structure spherical material with high porosity, large internal and external specific surface area and more hydroxyl groups on the surface. Precipitated silica is mainly made of quartz sand, soda ash, industrial hydrochloric acid, sulfuric acid, nitric acid or carbon dioxide as raw materials. The raw materials are cheap and easy to obtain, the production process and equipment are simple, and the product price is low. At present, it occupies a dominant position in the market, and its output accounts for about 85% of the output of silica, as shown in Figure 2.

1, silica modification

There is a large amount of hydroxyl group on the surface of white carbon black, which leads to its easy agglomeration. White carbon black usually needs to be modified to improve its dispersion during use. The modification methods of silica mainly include physical modification and chemical modification. Silica dispersing agents mainly include mixture of fatty acid ester and zinc soap surfactant, alcohols and alcohols amines, fatty acid zinc soap, ester alcohol complex and silane coupling agent, among which coupling agent Si69 is the earliest and best modified silica. The action mechanism of the modifier is as follows:

2, white carbon black application

Adding proper amount of white carbon black into the traditional compound formula of bias tire can further improve the bonding properties of curtain rubber and tear resistance of tread rubber without affecting the reinforcing effect of carbon black, especially the wear resistance of the compound, and has no obvious effect on the curing time. Add white carbon black in meridian tyre rubber formula, can make the tyre has the high wet resistance and good drawing performance, thus improving automobile braking effect and improve the safety of driving, reduce the tire rolling resistance, save fuel consumption, reduce pollution, improve the strength of the overall structure of the tire and tire wear resistance, reduce the rate of blasting, increase mileage.

Yu Xiaobo et al. made silica and three kinds of carbon black (N330, N550, N660) into composite fillers, which were used to reinforce SSBR /BR and glue, and studied the curing properties, physical properties, compression heat generation, cutting resistance, wear resistance, wet slip resistance and dynamic mechanical properties of the composite. The results show that compared with the silica reinforced compound, the coke burning time of silica reinforced compound is shortened, the structure of filler network is enhanced, the physical properties are improved, the heat generation and rolling resistance are increased, the glass transition temperature is decreased, and the cutting resistance and wet slip resistance are decreased. With the increase of carbon black particle size, the coking time of the compound is shortened, the heat generation and rolling resistance are reduced, and the wear resistance and skid resistance are decreased.

Zhao Mingming et al. used silica to reinforce isoprene rubber (IR) and NR to study the effect of silica on the curing properties, physical properties, thermal aging properties and dynamic mechanical properties of the compound. The results show that the curing speed of IR is faster than that of NR, the coking time is shorter than that of NR, the crosslinking density is close to that of NR, and the physical properties of NR are better than that of IR. The aging resistance of IR was improved with the increase of the amount of silica, and the aging resistance of NR was the best when the amount of silica was 20. At 0℃, the loss factor of IR is greater than NR, and at 60℃, the loss factor of IR is smaller than NR.

Hao Min et al. used rubber processing analyzer to study the dynamic mechanical properties of phenyl silicone rubber with different dosage and different kinds of silica under different strain and temperature. The results show that the elastic modulus of the silicone rubber decreases and the loss factor increases with the increase of the strain under different strains. Under the same strain, the elastic modulus and loss factor of phenyl silicone rubber increase with the amount of silica. At different temperatures, the elastic modulus and loss factor of phenyl silicone rubber with different amount of silica do not change significantly in the range of 70 ~ 170℃. With the decrease of silica particle size, the elastic modulus and loss factor of phenyl silicone rubber increase, and the reinforcing effect of fine silica particle size is better than that of coarse silica particle size.

Xie Fei et al. modified the nitrile butadiene rubber (NBR)/white carbon black blend system by UV light crosslinking, and investigated the photocrosslinking characteristics of the compound and the effect of the amount of white carbon black on the properties of the compound. The RESULTS SHOWED THAT WITH THE INCREASE OF SILICA CONTENT, THE TENSILE STRENGTH INCREASED SIGNIFICANTLY, THE ELONGATION AT break DECREASED, AND THE GEL CONTENT INCREASED FIRST AND THEN DECREASED, REACHING the MAXIMUM VALUE AT 50.

Ren Jiaxai et al. studied the effect of silica/carbon black ratio on NR performance under the condition that the total amount of silica and carbon black was fixed. The results showed that the vulcanization rate of the compound decreased with the increase of silica content. Adding 20~25 parts of white carbon black is the most effective way to improve the slippery resistance and reduce the rolling resistance of the compound.

Rattanasom N et al. used carbon black Hisil233 and carbon black N330 to prepare composite filler and studied the effect of the ratio of carbon black to carbon black on the physical properties of NR. The RESULTS SHOW THAT WHEN 50 PARTS SILICA/CARBON BLACK COMPOSITE FILLER IS FILLED, THE COMPOUNDS WITH 20 PARTS SILICA AND 30 PARTS SILICA HAVE BETTER PHYSICAL PROPERTIES, BETTER DISPERSION AND LOWER NETWORK STRUCTURE.

Zhang Jin et al. investigated the thermal aging and oil resistance properties of NBR reinforced with carbon black N220, N550 and ST1120 and highly dispersed silica. The results show that carbon black N220 and ST1120 have significant effects on the aging properties of NBR. The appropriate dosage of carbon black N220 and ST1120 is 10 and 20 respectively. Carbon black N550 has little effect on the aging property of rubber and can be added in large amount to strengthen the rubber. High dispersion silica can significantly reduce the positive curing time and coke burning time of the compound.

Liang Peng et al. synthesized five-coordinated silicon compound by ultrasonic heating method, and synthesized styrene four-coordinated silicon compound with the obtained five-coordinated silicon compound as raw material, and used it to modify the surface of precipitated silica, and tested the tensile strength of the reinforced rubber. The results show that the yield of five-coordinated silicon compounds can reach 84.5% after 10min of ultrasonic radiation. The water contact Angle of modified silica increases with the increase of the amount of styrene tetra-coordinated silicon. When the amount of tetra-coordinated silicon is 10% of the mass of silica, the tensile strength of vulcanized silicone rubber reinforced by tetra-coordinated silicon reaches the maximum of 6.71MPa. After modification, the agglomeration of silica was improved obviously, the particle size distribution was narrowed, and the average particle size of silica was significantly reduced.

3, summarize

White carbon black due to the unique structure and excellent performance, as an important reinforcing agent has important application in the field of rubber, especially with the eu REACH regulation and the tyre label rules of implementation, green environmental protection, energy saving, green tire performance will be the development direction of the future, it provides the development of white carbon black is more broad application prospects.

With the adjustment of industrial structure, the enhancement of environmental protection consciousness and the change of energy structure, it is inevitable that white carbon black will gradually replace carbon black or use it with carbon black as the main reinforcing material of rubber. However, the problems such as easy agglomeration and poor binding force between silica and rubber have not been completely solved. Therefore, the future research should focus on the interface properties and modification of silica, so as to further exploit the advantages of silica as reinforcing filler.