Carbon black modification & its application in rubber

Carbon black is a loose, light, extremely fine, black powdery amorphous carbon. It is the most important reinforcing filler in the rubber industry and is widely used in printing and dyeing, rubber, plastic processing, and transportation industries. Studies have shown that chemical modification of carbon black can greatly improve various properties of carbon black, which is also a hot topic in the current research on carbon black.

In order to meet the special requirements for the performance of carbon black in some applications, the purpose of modification can be achieved by post-processing the carbon black. Starting from the element composition and surface functional groups of carbon black, there are three ways to enhance the hydrophilic modification of carbon black: oxidation modification, graft modification, and coating modification.

Graft modification

Graft modification is one of the most widely studied methods of rubber modification. Graft modification is to graft polymer chains or low-molecular compounds on the surface of carbon black and bond them firmly to the surface of carbon black to prevent aggregation between particles to achieve the purpose of dispersion.

1.  Grafting of carbon black and low molecular weight

AO-80 (an organic antioxidant) decomposes under high temperature conditions to generate small molecular free radicals. In supercritical CO₂ fluid, small organic molecules (AO-80) are used to graft carbon black on the surface to prepare small organic molecules Grafted nano carbon black particles. The analysis of the particle size map after grafting AO-80 molecules onto the surface of carbon black draws the conclusion that the particle size of the modified carbon black aggregates is smaller and narrower.

2.  Grafting of activated carbon black and polymer

Utilizing the characteristics of a large number of end groups of hyperbranched polymers, and modifying carbon black with light end hyperbranched polymers can weaken the aggregation of modified carbon black particles. Hyperbranched polymer graft modified carbon black: the carbon black is first methylated, and then AB₃ type hyperbranched poly(amide ethyl) is grafted onto the surface of the carbon black.

3. Grafting to capture free radicals on the surface of carbon black

Sodium polystyrene sulfonate (PSS) is a water-soluble polymer with good interfacial activity. In an ultrasonic environment, the monomer sodium styrene sulfonate undergoes free radical polymerization, and the generated polymer long-chain free radicals are captured by the surface of the carbon black to prepare polymer grafted carbon black.

Oxidation modification

Carbon black particles are oxidized by an oxidant to undergo modification. The oxidation treatment of carbon black can change the specific surface area, porosity and conductivity of carbon black.

Surface oxidation treatment (gas phase oxidation and liquid phase oxidation) increases the type and number of oxygen-containing functional groups on the surface of carbon black, which can increase the volatile content of carbon black, reduce pH, and improve surface activity and polarity.

1. Gas phase method

Gas-phase modification of carbon black is a traditional modification method. Oxygen, ozone, dry air, and atomic oxygen or humid air are the main oxidants. The inert gas is introduced under closed conditions, and then the temperature is raised to the reaction temperature, and then the oxidant is introduced to carry out the modification reaction. After the reaction, inert gas is introduced. The experimental results show that as the test time increases and the reaction temperature increases, the more oxygen-containing groups on the carbon black surface, the better the dispersibility in the rubber matrix.

2. Liquid phase method

Liquid phase method, also known as chemical oxidation method, is a modification method in which an oxidant reacts with carbon black to generate a few radicals, carboxyl radicals and light radicals on the surface of the carbon black. The Cabot Elastomer Composite (CEC) researched by Wang Mengjiao and others is the first NR filler masterbatch produced by a continuous liquid phase mixing process. This technology makes it possible for environmental protection, low energy consumption, simple process, and low labor consumption. Compared with dry rubber compounding, this material can significantly improve the properties of vulcanized rubber, including reducing hysteresis loss, improving cutting resistance and flexing resistance, and increasing the wear resistance of vulcanized rubber when the amount of filler is increased.

Coating modification

Mix carbon black with water-dispersed white carbon black to make a slurry, add a proper amount of methanol, methyl triethoxy silane, sodium silicate and other dispersants to make the white carbon black coat the surface of the carbon black, and the resulting modified carbon black is filled In tires, conveyor belts and rubber rollers, it can give vulcanized rubber excellent physical properties such as high wear resistance, high grip and low rolling resistance.

Application of modified carbon black in rubber

In the rubber industry, carbon black is widely used as a reinforcing agent, and 90% of global carbon black production is used in the rubber industry.

• Application in NR (Natural Rubber)

The carbon black modified by the pyrolysis gas is used as a reinforcing agent and added to the rubber with HAF. As the amount of modified carbon black increases, the 300% tensile stress of the vulcanized compound increases, the elongation decreases, and the compression set decreases. The tear strength has been reduced.

The effect of pyrolysis gas modification-I and HAF on the performance of NR

• Application in EPDM (ethylene propylene diene monomer rubber)

EPDM rubber (EPDM) has excellent ozone resistance and aging resistance. It is often filled with carbon black modified by glycidyl methacrylate (GMA) monomer grafting to improve its processing and mechanical properties.

Carbon black was modified with unsaturated light fatty acid to enhance the vulcanization and physical and mechanical properties of EPDM rubber. It was found that the addition of unsaturated fatty acid significantly improved the tearing performance and flexing performance of the vulcanized rubber while maintaining relatively high performance. Good thermal oxygen aging performance can be well applied to shock-absorbing rubber products.

• Application in SBRL (vulcanized styrene butadiene rubber)

Styrene butadiene rubber is a commonly used industrial latex, which has the advantages of low cost and wide sources. Sodium styrene sulfonate is used to modify carbon black to prepare nano-dispersed carbon black suspension, and then the carbon black suspension is mixed with SBRL to prepare modified carbon black reinforced SBRL, which is applied to tire repair fluid.

• Application in polyurethane sealant

In the presence of the initiator benzoyl peroxide, the surface of ordinary carbon black is organically modified with styrene.

Performance comparison of carbon black added to sealant before and after modification

The sealant made of modified carbon black compound has good tensile strength, hardness, elongation and shear strength, and reduces the cost, and is widely used in sealing fields such as construction and automobiles.