In many industrial production fields—especially in the rubber, plastics, and coatings industries—pyrolysis carbon black is a key material, and its performance plays a decisive role in the quality of the final product.
The performance of pyrolysis carbon black is defined by a series of specific indicators. Conducting an in-depth analysis of how these indicators impact product performance is crucial for optimizing production processes and improving overall product quality.
1. Particle Size and Specific Surface Area
The particle size and specific surface area of pyrolysis carbon black are closely related and significantly affect product performance. Smaller particle sizes result in larger specific surface areas. In rubber products, pyrolysis carbon black with a small particle size and high specific surface area can form more contact points with rubber molecules, enhancing the interaction between the two and providing strong reinforcement. This greatly improves the tensile strength, tear resistance, and wear resistance of rubber products. For example, in tire manufacturing, these properties can effectively extend tire service life and reduce wear.
However, an excessively small particle size and excessively large surface area may have negative effects. During the mixing process, the viscosity of the rubber increases, resulting in more difficult processing and higher energy consumption. Additionally, due to its high surface activity, the carbon black is prone to agglomeration. If not evenly dispersed, this can reduce the performance of the final rubber product.
2. Structural Degree
The structural degree reflects the complexity of pyrolysis carbon black aggregates.
Carbon black with a high structural degree has branched or chain-like aggregates with more voids. In rubber processing, this structure improves dispersion in the rubber matrix, forming an effective network structure that enhances the processing performance of the rubber. For example, during mixing, highly structured carbon black can improve rubber fluidity, facilitating molding operations.
In terms of final product performance, high-structure pyrolysis carbon black increases the tensile strength and hardness of rubber products while having little effect on elasticity, thereby preserving the rubber’s resilience. On the other hand, while low-structure pyrolysis carbon black may reduce rubber viscosity in some cases, it offers relatively weak reinforcement and less processing stability.
3. Ash Content
Ash is the non-flammable inorganic residue in pyrolysis carbon black. Its content has a significant impact on product performance.
In rubber products, an appropriate amount of ash can act as a filler, increasing the hardness and modulus of the product. However, excessive ash becomes a defect point in the rubber network structure, reducing tensile strength and tear resistance. For example, when the ash content is too high, tires made from the carbon black are more prone to cracking during use, thereby shortening their service life.
In the coatings and plastics industries, ash also affects product performance. A high ash content can reduce coating gloss, deteriorate stability, and cause surface granularity. In plastics, ash has poor compatibility with the plastic matrix, which can reduce mechanical properties and compromise appearance quality.
4. Volatile Content
Volatile content refers to the substances released when pyrolysis carbon black is heated to a specific temperature, primarily including water, carbon dioxide, and some organic compounds.
The volatile content reflects the chemical activity and polarity of the carbon black surface. An appropriate amount of volatiles helps enhance the affinity between pyrolysis carbon black and matrix materials such as rubber, improving dispersion.
However, if the volatile content is too high, the surface activity of the carbon black may become excessive, leading to premature vulcanization or scorching. This can severely affect rubber processing and may also produce unpleasant odors during mixing. In coatings, excessive volatiles can cause defects such as bubbles and pinholes during the drying process, compromising both the quality and appearance of the finished coating.
5. pH Value
The pH value of pyrolysis carbon black reflects its surface chemical characteristics.
Acidic pyrolysis carbon black contains more acidic functional groups on its surface, which can affect its interaction with matrix materials like rubber. In rubber processing, an acidic pH may slow down vulcanization and reduce vulcanization efficiency.
On the other hand, pyrolysis carbon black with an alkaline pH value typically results in a faster vulcanization rate. However, if the alkalinity is too high, it may cause degradation of the rubber molecular chains, negatively impacting the final product’s performance. Therefore, controlling an appropriate pH level is essential to ensure good processing behavior and final product quality.
6. Tensile Strength
In tire manufacturing, high tensile strength is a key indicator of the durability of pyrolysis carbon black.
When a vehicle is in motion, tires constantly experience friction with the road surface and bear the weight of the vehicle along with various dynamic stresses. Pyrolysis carbon black with high tensile strength enhances the intermolecular forces in rubber, making the tire less prone to tearing or damage from sharp objects or impacts with stones. This significantly extends tire life.
In industrial conveyor belts, tensile strength is directly related to operational stability. Pyrolysis carbon black enhances the rubber’s tensile strength, enabling conveyor belts to withstand heavy loads without breaking under tension.
7. 300% Elongation Stress
For automotive shock-absorbing rubber components, 300% elongation stress is a critical performance indicator.
When a vehicle travels over rough terrain, the shock-absorbing rubber deforms. Pyrolysis carbon black with suitable 300% elongation properties enables the rubber to stretch to three times its original length and then quickly and effectively return to its original shape.
This ensures that, during vibration, the shock-absorbing rubber continues to provide cushioning, offering a smooth and comfortable ride for passengers while also protecting the vehicle’s chassis and components from excessive vibration-related damage.
In rubber seals, 300% elongation determines sealing reliability. For example, in engine gaskets, high temperatures and pressures can cause deformation. The excellent elongation properties of pyrolysis carbon black allow the gasket to retain sufficient resilience after deformation, maintaining a tight seal to prevent leaks of engine oil, coolant, and other fluids—ensuring the engine’s normal operation and the system’s overall stability and reliability.
8. Oil Absorption Value
The oil absorption value directly reflects the structural complexity of pyrolysis carbon black.
A high oil absorption value indicates that the carbon black aggregate structure is more developed, with more voids and branches. In rubber products, this high-structure carbon black provides more anchoring points for rubber molecules, forming a tighter and more complex network. Like building a sturdy bridge, more connection points create a more stable structure, thereby significantly improving the tensile stress and hardness of rubber products.
From a processing standpoint, the oil absorption value directly affects the viscosity of the rubber compound. Pyrolysis carbon black with a high oil absorption value absorbs more rubber oil during mixing, resulting in increased viscosity. However, carbon black with an appropriately high oil absorption value offers advantages in enhancing the stiffness and shape retention of the rubber compound. For instance, in manufacturing rubber soles, pyrolysis carbon black with a suitable oil absorption value helps the sole maintain its shape better during molding, improving production efficiency and product quality.
9. Iodine Absorption Value
The iodine absorption value is an important indicator of the surface activity of pyrolysis carbon black.
A higher iodine absorption value indicates that the carbon black surface has more active sites, capable of forming strong physical or chemical interactions with rubber molecules. For example, in tire manufacturing, highly active pyrolysis carbon black forms stronger bonds with rubber, enhancing the interfacial adhesion between rubber and carbon black. As a result, when the tire is subjected to external forces, stress is more effectively transferred between the rubber and the carbon black, avoiding localized stress concentration and significantly improving the tire’s tensile strength and wear resistance.
The iodine absorption value is closely related to the reinforcing ability of pyrolysis carbon black. In rubber products, carbon black with a high iodine absorption value can provide better reinforcement by filling the gaps between rubber molecular chains, restricting their relative movement, and increasing the rubber’s modulus. In practical applications, rubber products such as conveyor belts and seals—which require high strength and wear resistance—can benefit significantly from using pyrolysis carbon black with a suitable iodine absorption value. This not only enhances performance and prolongs service life but also reduces maintenance costs.
10. Blackness
In the rubber industry, blackness is a key factor influencing product appearance.
For example, in cable sheaths, high-blackness pyrolysis carbon black gives the cable a deep, rich black color. This not only enhances the visual appeal but also conveys a strong and durable impression. The visual effect created by deep blackness elevates the perceived quality and strengthens brand image.
In plastic products, the impact of blackness is equally important. High-blackness pyrolysis carbon black can give plastic shells an ink-like richness, adding a sense of advanced technology and high-end appeal. The strong visual impact of this deep black helps products stand out among competitors. Furthermore, uniform and consistent blackness distribution improves the overall appearance of plastic products, eliminating issues such as color inconsistencies and ensuring a refined and professional finish.
11. Tinting Strength
In the field of coatings, the tinting strength of pyrolysis carbon black is crucial for achieving precise color matching.
Whether it is dark paint for building exteriors or high-saturation black masterbatch products, pyrolysis carbon black with high tinting strength can achieve rich and vivid color effects with only a small dosage. This not only ensures deep and pure colors but also helps control production costs effectively.
In the ink printing industry, the tinting strength of pyrolysis carbon black directly affects the clarity and accuracy of printed colors. During the printing process, carbon black with high tinting strength ensures that the ink produces sharp, full black lines and patterns on paper. Both text and image printing benefit from high contrast and fine layering, contributing to a high-quality printed result.
12. Heating Loss
The heating loss of pyrolysis carbon black mainly comes from the moisture and volatile organic matter it contains.
Upon heating, moisture evaporates first. A high heating loss value indicates that the carbon black contains a significant amount of moisture. This moisture hinders the dispersion of pyrolysis carbon black within the matrix material, leading to weak points in the rubber structure—similar to how unevenly distributed sand can compromise the strength of concrete.
High heating loss requires additional energy and time to evaporate moisture and achieve proper dispersion. During the mixing process, excessive moisture alters the viscosity of the rubber compound, increasing equipment load and wear, and potentially affecting equipment performance. Furthermore, during vulcanization, residual moisture turns into vapor. If not released in time, it can form bubbles or pores inside the rubber product. Although heating loss may seem like a minor indicator, it has significant implications for dispersion quality, processing efficiency, and final product performance.
13. Elongation at Break
In rubber products, the elongation at break of pyrolysis carbon black is directly related to product flexibility.
For example, in tires, pyrolysis carbon black with a higher elongation at break allows the tire rubber to undergo deformation under various driving stresses without cracking, improving tire durability and reducing the risk of blowouts.
In plastic products, such as pipes, elongation at break affects plasticity. A higher value allows the material to stretch more easily during processing and molding, facilitating the production of complex-shaped products. Overall, elongation at break influences flexibility, durability, plasticity, and impact resistance, making it a critical performance factor across a wide range of applications.
14. Toluene Transmittance
Toluene transmittance is a direct indicator of impurity content in pyrolysis carbon black.
Higher transmittance indicates fewer impurities and higher purity, and it also indirectly reflects particle size and dispersion quality. Carbon black with uniform particle size and good dispersibility tends to have stable toluene transmittance values.
In the rubber industry, such carbon black can be uniformly dispersed throughout the rubber matrix, enhancing its mechanical properties. In the plastic industry, high toluene transmittance contributes to a smoother, more uniform appearance of plastic products, eliminating visual defects such as granularity or uneven coloration.
15. Screen Residue
Screen residue refers to particles in pyrolysis carbon black that fail to pass through a specific mesh size.
If the screen residue content is too high, these larger particles are difficult to disperse uniformly when blended with other materials. For example, in paint production, they can severely affect the surface smoothness and appearance quality of the paint. In plastic processing, excessive screen residue can disrupt extrusion and injection molding processes, leading to inconsistent product quality.
Although screen residue may seem like a minor index, it plays a significant role in product performance by influencing dispersion uniformity, mechanical properties, and processing behavior. Therefore, strict control of screen residue is essential to ensure the high quality of the final product.
16. Shore Hardness
Low Shore hardness indicates that pyrolysis carbon black particles are relatively soft in texture.
When mixed with matrix materials such as rubber or plastic, these softer particles are more likely to deform under external forces like stirring and blending. This deformation allows the particles to conform more effectively to the flow of the surrounding matrix—similar to how a soft sponge can flexibly fill gaps.
As a result, softer carbon black particles disperse more evenly in the matrix material, promoting improved uniformity and performance of the composite product.
17. Specific Gravity
The specific gravity of pyrolysis carbon black typically ranges from 1.8 to 2.1 g/cm³.
However, it may vary depending on the production process, raw material sources, and the microstructure of the final product. Specific gravity impacts various performance characteristics across different applications:
Rubber products: Specific gravity affects the overall density of the rubber compound, influencing both material cost and product weight. Higher specific gravity increases the weight of a product for the same volume, potentially raising material consumption and costs. It may also negatively impact mechanical properties such as elasticity and flexibility.
Plastic products: A mismatch in specific gravity between carbon black and the plastic matrix can hinder uniform dispersion, leading to particle agglomeration, compromised appearance, and reduced mechanical strength and weather resistance.
Coatings and inks: Specific gravity influences sedimentation stability. A higher specific gravity may cause carbon black to settle during storage, resulting in inconsistent coloration and reduced hiding power.
18. Particle Crushing Strength
The particle crushing strength of pyrolysis carbon black refers to its ability to resist mechanical damage under external force.
Typically expressed as the maximum pressure per unit area (e.g., N/m²), this parameter is a key indicator of material quality and robustness.
Impact on production and processing:
Equipment wear: Production efficiency: If carbon black particles crush too easily during mixing, dispersion becomes uneven, which may reduce productivity and lead to unstable product quality.
Impact on product performance:
Rubber products: In the rubber industry, carbon black serves as both a reinforcing agent and filler. Particles with high crushing strength can better withstand stretching and compression during use, enhancing the tensile strength, abrasion resistance, and tear resistance of the final product.
Plastic products: In plastics, carbon black with adequate crushing strength forms a stable filler network, improving hardness, rigidity, and heat resistance. If particles break too easily, this structure is compromised, reducing overall product performance.
19. Pour Density
The pour density of pyrolysis carbon black refers to the mass per unit volume when the material is freely poured into a container under specified conditions, typically expressed in grams per cubic centimeter (g/cm³).
It impacts both production processes and final product performance in the following ways:
Impact on production and processing
Measuring accuracy: Pour density directly affects the precision of carbon black dosing. If the pour density is inconsistent, volume-based dosing may lead to inaccurate mass additions, resulting in formulation errors and compromising product quality.
Transportation and storage: Pyrolysis carbon black with a higher pour density has greater mass per unit volume, which places more stress on conveying systems. This necessitates careful selection of appropriate transport methods and equipment. Additionally, higher pour density requires storage containers with sufficient load-bearing capacity and optimized spatial planning.
Impact on product performance
Measuring accuracy: Pour density directly affects the precision of carbon black dosing. If the pour density is inconsistent, volume-based dosing may lead to inaccurate mass additions, resulting in formulation errors and compromising product quality.
Transportation and storage: Pyrolysis carbon black with a higher pour density has greater mass per unit volume, which places more stress on conveying systems. This necessitates careful selection of appropriate transport methods and equipment. Additionally, higher pour density requires storage containers with sufficient load-bearing capacity and optimized spatial planning.
Impact on product performance
Rubber products: A higher pour density allows more carbon black to be incorporated into a given volume, potentially enhancing the hardness, tensile strength, and wear resistance of rubber. However, if the density is too high, it may hinder uniform dispersion, negatively affecting the performance of the rubber compound.
Plastic products: In plastics, a suitable pour density helps achieve uniform dispersion of carbon black within the matrix, improving mechanical strength, UV resistance, and durability. Conversely, an unsuitable density may lead to agglomeration, poor appearance, and reduced performance.
Conclusion
The various performance indicators of pyrolysis carbon black—such as tinting strength, heating loss, elongation at break, toluene transmittance, screen residue, Shore hardness, specific gravity, particle crushing strength, and pour density—are interrelated and collectively determine its effectiveness across different applications.
In practical manufacturing scenarios, both producers and users must have a deep understanding of how these parameters influence product quality. Only by precisely selecting and controlling the appropriate properties of pyrolysis carbon black based on specific product requirements can manufacturers optimize performance, ensure production stability, and enhance product competitiveness in the market.
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