Seventeen commonly used reinforcing and filling agents for rubber

• 2024-05-29

The most commonly used material is carbon black, which has reinforcement and filling functions. There are also many materials that can be used for reinforcement while reducing costs as filling materials

1.1 Carbon Black

Carbon black is a widely used chemical product, which can be used in products such as rubber, resin, printing ink, coatings, wires and cables, batteries, paper, pencils, pigments, etc. The main use of carbon black is for manufacturing tires and various rubber products. About 70% of global carbon black is used for tires, 20% for other rubber products, and less than 10% for industries such as plastic additives, dyes, and printing inks. Half of the rubber products are used to manufacture automotive components such as V-belts and shock-absorbing rubber. Therefore, approximately 80% of carbon black is consumed in the automotive industry.

Overall, the global carbon black industry has entered a mature stage, and its production technology is mainly developing towards single furnace capacity/scale, carbon black product specialization, comprehensive energy conservation and consumption reduction, and environmental safety.

(1)High performance and low hysteresis loss carbon black

In order to adapt to the development of tire products, especially the demand for high-performance and green tires, major foreign carbon black companies have developed many new varieties of high-performance and low lag loss carbon black. The common characteristics of high-performance carbon black are small particle size, suitable structure, narrow aggregate distribution size, and high surface activity. The common characteristics of low hysteresis loss carbon black are high structure, wide aggregate size distribution, and high surface activity. Some of the earlier developed varieties, such as N134 and N358, have been included in the ASTMD1765 standard and have been widely adopted by tire manufacturers. In recent years, new varieties that have been researched and developed have not been included in ASTM standards, nor have their chemical indicators been disclosed. Only some products have descriptions of their application performance in the manufacturer's product catalog, and these new varieties are currently being promoted and applied.

(2)Nanostructured carbon black

Low lag loss carbon black is the focus of development, which is determined by the downstream industry of carbon black - the development trend of "green tires" in the tire industry. As long as carbon black enterprises and tire enterprises cooperate closely, low lag loss carbon black will enter the stage of large-scale application.

Nano carbon black is manufactured using an improved furnace process. Compared with traditional ASTM carbon black, nanoscale carbon black has higher surface roughness and greater surface activity. The higher surface activity is mainly related to the highly disordered cross-linked smaller crystalline particles. This type of crystalline particle has a large number of edges, making it an active field with particularly high surface energy. The active field generates strong mechanical/physicochemical interactions between carbon black and polymers. Improving the interaction between fillers and polymers can reduce hysteresis loss and heat generation under dynamic deformation. The natural rubber tread rubber of heavy-duty truck tires filled with 52 parts of ASTMN356 carbon black and corresponding E-1670 nanometer carbon black can significantly reduce hysteresis loss and heat generation, thereby reducing rolling resistance. Due to the low DBP value of nanoscale carbon black, the 300% tensile stress of the vulcanized rubber is slightly lower.

(3)Conductive carbon black

Due to the fact that conductivity/electrostatic properties are fundamental properties required for many rubber products, the development prospects of conductive carbon black cannot be ignored. The development of conductive carbon black mainly follows two series of directions: conductive carbon black for rubber and conductive carbon black for plastics.

1.2 White Carbon Black

White carbon black, also known as hydrated silica, activated silica, and precipitated silica, has a molecular formula of SiO2 · nH2O. It is a highly dispersed amorphous powder or flocculent powder, lightweight, with high electrical insulation, porosity, and water absorption. Its original particle size is less than 3 μ m, so it has a large surface area and good reinforcement and thickening effects, as well as good dispersion, suspension, and vibration liquefaction characteristics. It has been widely used in more than ten fields such as plastics, rubber, papermaking, coatings, dyes, and inks, especially in the rubber industry. White carbon black ranks first for its superior reinforcement and transparency. However, due to the presence of active silicon hydroxyl groups, adsorbed water, and acid zones on the surface of white carbon black caused by the preparation process, white carbon black is hydrophilic and difficult to infiltrate and disperse in organic phases. It cannot be well compatible with polymers in rubber vulcanization systems, thereby reducing vulcanization efficiency and reinforcement performance, making it unusable in certain special fields. The modified white carbon black has improved surface activity, dispersion and compatibility in organic phases, greatly expanding the application fields of the product and enhancing the high added value of white carbon black.

White carbon black can be divided into physical and chemical methods according to its method. The grade of white carbon black products prepared by physical methods is not high, while the white carbon black fillers required by the rubber industry are usually produced by chemical methods. Chemical method can be divided into dry pyrolysis method (including gas phase method and arc method) and wet method. Wet method can be divided into precipitation method (including sulfuric acid precipitation method, hydrochloric acid precipitation method, nitric acid precipitation method, carbon dioxide precipitation method and hydrothermal method) and gel method (including ordinary drying method and aerogel method) according to its generation characteristics. At present, there are two main production processes for white carbon black at home and abroad. One is the gas-phase method using silicon tetrachloride as raw material. The silicon tetrachloride gas is placed in a stream of hydrogen and oxygen, hydrolyzed under high temperature conditions, to produce smoke like silicon dioxide, which is then condensed into a flocculent state, separated and deacidification to obtain the product. White carbon black produced by gas-phase method is a high-quality product with high purity and small particle size, generally used as a fine filler. However, due to its high raw material prices, long reaction process, high energy consumption in the production process, and high product prices, it is limited. Another method is the acid precipitation method using water glass as raw material, which involves obtaining loose, finely dispersed, and flocculent Si2 powder through acidification of water glass. The preparation of white carbon black by acid precipitation method has a simple production process and low product cost, but the product particle size is large, the activity is low, and the product quality is low.

European tire manufacturers proposed the concept of green tires in 1992, so the development status of fillers began to change. By using special polymers and white carbon black/silane systems, high wet road traction performance and wet road braking performance can be achieved, and fuel consumption can be reduced by 5% by reducing rolling resistance. The white carbon black/silane filling system used in the formula of car tire tread rubber in the original equipment tire market (OEM) in Europe has reached over 80%. The significant improvement in the performance of modern winter tires mainly relies on the use of white carbon black/silane in the tread rubber.

In addition to using white carbon black as the main filler for car tire tread rubber, using white carbon black for tire body rubber can also further reduce heat generation and rolling resistance. By using specialized highly dispersed white carbon black, combined with high structured fine particle carbon black, the use of white carbon black can be expanded and applied to heavy-duty truck tires. By adopting this optimal filling system, the main performance requirements of heavy-duty truck tires can be met, which is to reduce tire hysteresis loss, thereby reducing rolling resistance while maintaining wear resistance.

1.3 Carbon Black White Carbon Black Biphasic Filler

The carbon black white carbon black biphasic filler is produced using a unique technology developed by Cabot Corporation. Traditional carbon black is composed of 90% -99% carbon element, with oxygen and hydrogen as the other main components, while this new type of filler is composed of carbon black phase and white carbon black phase dispersed in the carbon black phase. Its main feature is to enhance the interaction between rubber and fillers in hydrocarbon elastomers, while reducing the interaction between fillers. This filler can improve the performance of rubber materials, especially the relationship between hysteresis loss and temperature of tire tread rubber, greatly reducing rolling resistance and improving traction, but it does not reduce the wear resistance of traditional carbon black.

Carbon black white carbon black biphasic filler (CSDPF) has been sold in the market under the trade names ECOBLACKTM and CRXTM2XXX series, so there are also CSDPF2000 series and CSDPF4000 series products. The differences between CSDPF2000 and 4000 include the distribution of white carbon black, surface coverage of white carbon black, and silicon content. CSDPF4000 has a higher surface coverage and silicon content of white carbon black than CSDPF2000. This situation can be seen from the changes in silicon content and surface area during hydrofluoric acid (HF) extraction. During HF extraction, white carbon black is dissolved by the unchanged carbon black phase. The fact that a large amount of white carbon black still exists during HF extraction of CSDPF and the surface area increases sharply indicates that CSDPF2000 white carbon black is distributed throughout the aggregates. On the contrary, the surface area of CSDPF4000 did not change much, and almost no white carbon black was left after HF extraction. This indicates that CSDPF4000 aggregates. The white carbon black in only stays on the surface.

Compared with traditional carbon black and white carbon black, CSDPF2000 and 4000 both have higher filler polymer interactions and lower filler filler interactions when mixed with hydrocarbon polymers. For filling rubber materials, the elastic modulus decreases as the strain amplitude decreases, which is called the "Payne Effect". The Payne effect, mainly controlled by filler filler interactions, is commonly used as a method to measure the network structure of fillers. Although from the perspective of chemical composite materials, the performance of CSDPF2000 and 4000 is between that of carbon black and white carbon black, what is actually observed here is that both new fillers have the lowest Payne effect.

By using CSDPF2000, the friction coefficient between the tread of heavy-duty truck tires and the road surface can be increased, thereby improving the tire's wet road anti-skid performance. The high coverage of white carbon black in CRX4000 can reduce the micro elastic hydrodynamic lubrication, which is beneficial for improving the wet road anti-skid performance of car tires. Therefore, in order to improve the comprehensive performance of tire tread, CSDPF4000 can be used in the formula of car tire tread rubber, while CSDPF2000 can be used in the formula of truck tire tread rubber.

1.4 Other Fillers

(1)Modified kaolin

After special treatment, Shanxi Jinyang Calcined Kaolin Co., Ltd., a Sino foreign joint venture, increased the specific surface area of coal bearing kaolin and then carried out surface modification treatment, which can greatly improve the reinforcement effect of rubber. In the application of rubber products such as automotive tires and EPDM, the reinforcement performance can even exceed that of carbon black or white carbon black in some aspects.

(2)Fly ash type rubber reinforcing agent (XRF)

Fill glass microspheres separated from fly ash into polyvinyl chloride (PVC) to improve performance and reduce costs. A new type of rubber reinforcing agent (XRF) developed by Beijing University of Chemical Technology, mainly composed of fly ash, has been applied in Beijing Rubber Factory. Numerous experiments have shown that the application performance of the new rubber reinforcing agent (XRF) in natural rubber and synthetic rubber (such as styrene butadiene rubber, nitrile rubber, EPDM rubber, chloroprene rubber, etc.) has fully reached the level of equivalent substitution for semi reinforcing carbon black. This technology not only solves the environmental pollution caused by the accumulation of a large amount of fly ash, but also makes a significant contribution to resource conservation.

(3)Concave convex rod modified clay

The chemical composition of attapulgite is silicon and aluminum oxides, with small amounts of iron, calcium, and manganese oxides. White fibrous crystals are semi reinforcing fillers that can make the surface of extruded and rolled rubber materials smooth. The new high-quality rubber reinforcing agent, concave convex rod modified clay, can increase the tensile stress of rubber products by 300%, improve the elongation at break, have fast powder feeding speed, prevent dust from flying, and have the characteristics of high whiteness, high dispersibility, and high covering power. Adding this product to rubber products can not only improve their appearance quality and delay aging rate, but also resist acid and alkali corrosion, reduce costs, and is an excellent rubber reinforcing agent. It can be widely used in rubber transmission belts, automotive inner and outer tires, and other rubber products.

(4)Modified hard clay

Hard clay has a semi reinforcing effect in rubber and can improve the mechanical properties of vulcanized rubber. Soft clay has no reinforcing effect in rubber. Modification of clay with stearic acid, vinyl silane, hydrogen silane, and titanate coupling agent can increase its surface hydrophobicity, improve the tensile strength and tensile stress of the adhesive, reduce heat generation and compression permanent deformation, and its reinforcement performance is comparable to that of white carbon black, with good aging performance. The new reinforcing agent - ultrafine activated clay SFAC, has the same effect as semi reinforcing carbon black in the case of equivalent substitution.

(5)DSI rubber reinforcing agent

Ultra fine powder processed from rice husk as raw material, used as a rubber reinforcing agent through coupling activation, mainly suitable for glass, paint, paper, rubber and plastic products.

(6)Plastic based rubber reinforcing filler

Using polyolefin plastic as the base material, combined with heavy CaCO3 powder, calcium magnesium powder, and various high-performance surfactants, a high-performance plastic based rubber reinforcement filler is produced through multi-layer coating technology. This reinforcement filler has good flowability and can be applied to various rubber miscellaneous parts mainly composed of natural rubber at high filling amounts, such as rubber V-belts, rubber seals, rubber rollers, rubber pads, rubber pipes, rubber sheets, etc.

(7)Lignin type rubber reinforcing agent

Lignin is directly modified in papermaking pulp waste liquid, and a new rubber processing technology is used to achieve molecular level permeation and cross-linking between rubber and lignin, thereby making the alloy composed of rubber and natural polymer compounds (lignin) have excellent comprehensive properties. Its mechanical properties are comparable to those of high wear-resistant furnace carbon black, and its proportion in rubber can be twice as high as that of carbon black.

(8)ZnO

Nano zinc oxide is a fine white or slightly yellow powder that is easily dispersed in rubber and latex. It is a reinforcing agent, activator, and vulcanizing agent for natural rubber and synthetic rubber, as well as a coloring agent and filler for white rubber materials. After adding active zinc oxide to the rubber material, it can make the rubber have good wear resistance, tear resistance, and elasticity.

(9)Sepiolite rubber reinforcing agent

The chemical composition of sepiolite is a hydrate of silicon oxide and magnesium oxide, containing small amounts of aluminum and iron oxides. Used as a reinforcing agent in light colored rubber products, its performance is only inferior to that of white carbon black. Treating sepiolite powder with silane, its reinforcement performance is close to that of white carbon black, and its price is only half of white carbon black. It is resistant to acid and alkali, chemical corrosion, and has good dispersibility in rubber and plastic products, making it an ideal filling and reinforcing agent in rubber and plastic products. The use of natural rubber has better effects, can significantly reduce costs, improve product quality and economic benefits.

(10)Magnesium Carbonate

Magnesium carbonate is mainly used as a filler and reinforcing agent in rubber products, which can increase gloss, whiteness, and high temperature resistance. It is a thermal insulation material.

(11)Modified bentonite

Modified bentonite is formulated from natural bentonite, modifiers, and other additives, with strong adsorption and cation exchange capabilities. It is mainly used as a filler and reinforcing agent for various rubbers, which can improve the performance of rubber products, reduce the cost of rubber products, enhance the bonding strength between rubber and cord, and improve the processing performance of rubber materials.

(12)Zeolite

Zeolite powder is a non-metallic mineral that, due to its unique mineral structure, can be used as a filler and reinforcing agent for various rubbers, improving the performance of rubber products.

(13)High activity silica coupling agent 481 reinforcing agent

High activity silica coupling agent 481 reinforcing agent is a new type of rubber industrial material developed by Xinli Plastic Co., Ltd. in Haicheng City, Liaoning Province. It is non-toxic, odorless, and has a microscopic sheet-like structure. This product has a reinforcing effect and high activity, making it a good reinforcing auxiliary material for the rubber industry. Its product performance has strong hydrophobicity, stable chemical properties, heat resistance, and light resistance.

(14)Mica Powder

Sericite has a reinforcing effect and can replace some semi reinforcing carbon black. It can also be used as an isolation agent. Due to its monoclinic crystal system, its crystals are in thin flakes, which can improve the damping performance of rubber. It has good heat resistance, acid resistance, and electrical insulation properties, as well as the function of protecting against ultraviolet and radioactive radiation, and can be used for special rubber products.

(17)Coal gangue powder

The chemical composition of coal gangue is similar to kaolin, which is a mixture of alumina, silica, and magnesia. Its volatile component is as high as 27%, and it has a semi reinforcing effect, commonly known as silicon aluminum carbon black. Easy to mix into rubber, good dispersibility, can replace some carbon black as a reinforcing agent.