Carbon Black and Recycled Carbon Black

What is Carbon Black?

Carbon black is an amorphous black solid of carbon with a large surface area and a relative density of 1.8–2.1 g/cm³. It sublimes at 3652–3697 °C, has a boiling point of 4827 °C, and is insoluble in water, acids, and alkalis. It can be prepared by the thermal decomposition or incomplete combustion of gaseous hydrocarbons, or by conversion from carbon dioxide.

Hydrocarbons are black, powdery substances produced by incomplete combustion or pyrolysis in the gas phase under strictly controlled process conditions. Their main component is elemental carbon, with small amounts of oxygen, hydrogen, and sulfur. Many particles often dissolve or aggregate into three-dimensional dendritic or fibrous aggregates. In rubber processing, they are added to rubber through compounding as a reinforcing agent and filler, especially in tire manufacturing; they are also used in plastics, inks, and coatings, and are one of the oldest industrial products.

What is Recycled Carbon Black?

Recycled carbon black (rCB) refers to carbon black materials obtained from waste tires, waste rubber, waste plastics, and other waste materials through pyrolysis or other chemical treatments. Recycled carbon black possesses advantages such as extremely high specific surface area, good dispersibility, excellent conductivity, and environmental friendliness, making it a promising material for numerous applications in the rubber industry, plastics processing, road engineering, battery manufacturing, coatings, and inks. However, its composition is complex, often containing additives from rubber products (such as sulfur, hydrogen peroxide, and titanium dioxide) and organic impurities generated during pyrolysis (such as asphaltenes and polycyclic aromatic hydrocarbons (PAHs)). These impurities can lead to particle agglomeration, reducing its effective specific surface area and performance.

The core difference between carbon black and recycled carbon black (rCB) lies in their production processes. Carbon black is a high-purity virgin material produced using fossil fuels, boasting excellent performance but also high cost and significant carbon emissions. Recycled carbon black, on the other hand, is an environmentally friendly material recovered through pyrolysis from waste materials such as used tires. While it contains minor impurities and has slightly inferior performance, it offers high cost-effectiveness and is low-carbon and environmentally friendly. Currently, carbon black dominates high-performance fields such as high-end tires, while recycled carbon black, thanks to policy support and technological advancements, is accelerating its "waste-to-treasure" recycling in plastics, coatings, and non-critical rubber products.

Specific Uses of Recycled Carbon Black

Tire Manufacturing Industry

In the tire manufacturing industry, the application strategy for recycled carbon black depends on its purity and surface activity level.

Mid-to-low-end replacement applications: In non-tread components such as the airtight layer and tread trim, general-purpose and recycled carbon black, after magnetic separation and pulverization, can partially replace N600 and N700 series reinforcing carbon black in equal quantities. These applications have relatively lower requirements for wear resistance, primarily utilizing their inherent durability and cost advantages, while simultaneously reducing the overall carbon footprint of tire products.

Exploration of high-performance alternatives: High-quality recycled carbon black, through deep deashing (controlling ash content below 1.5%) and surface activation treatment, has achieved a reinforcing index approaching the ASTM N300 series standard. Currently, some research institutions and tire companies are applying it to the tread base compound formulation of commercial truck tires to balance rolling resistance and cut resistance. However, there are still technical bottlenecks in fully meeting the requirements for high abrasion-resistant carbon black for tire surfaces (such as the N100 series).

Non-tire Rubber Products

Compared to tires, general rubber products have less stringent requirements for dynamic fatigue performance, making them the largest end-market for recycled carbon black at present.

Industrial transmission and sealing components: Recycled carbon black is often used as the main reinforcing filler in conveyor belt covers, industrial hoses, gaskets, and shock absorber supports, with an addition ratio of 20% to 40%. Its semi-reinforcing properties are sufficient to meet the basic mechanical properties of the products, and it can significantly reduce raw material costs.

Building and civil products: such as rubber floor tiles, paving materials, and sports tracks, recycled carbon black mainly serves to provide coloring and UV aging resistance, while also imparting a certain tensile strength to the products.

Functional Materials and Emerging High-Value Pathways

Beyond the traditional category of fillers, recycled carbon black, due to its residual mineral components and nanoscale carbonaceous skeleton, is being developed for more value-added applications.

Industrial Pigments and Coatings: Some steel companies have established application standards for recycled carbon black as a black inorganic pigment, used in the production of back coatings for color-coated steel sheets. The requirements are not focused on reinforcing properties, but rather on blackness (reflectivity) and dispersion fineness. This opens up a waste rubber consumption channel for low-grade recycled carbon black.

Wastewater treatment adsorption medium: Regenerated carbon black modified by sulfonation or oxidation has its specific surface area reconstructed, exhibiting adsorption capacity for azo dyes and heavy metal ions in dyeing and printing wastewater. This application is based on the circular economy logic of treating waste with waste, but attention needs to be paid to the secondary disposal of the waste after adsorption saturation.

Performance Limitations and Selection Principles

In engineering practice, the selection of recycled carbon black requires balancing the impact of its ash content on the sulfidation rate and the interference of its particle size distribution on the surface finish of the product. It is generally recommended to pre-adjust its volatile matter and pH value during formulation design to avoid adverse reactions with accelerators.