Factors Influencing the Conductivity of Carbon Black

Carbon black is widely used as a conductive filler in various industries, including rubber, plastics, and coatings. Its conductivity is a critical property that significantly impacts the performance of the final products. Several factors influence the conductivity of carbon black, which are discussed below:

1. Particle Size of Carbon Black

Theoretically, the smaller the particle size of carbon black, the greater the number of particles per unit volume, which is beneficial for enhancing conductivity. This is generally true for conductive rubber products. However, in conductive plastic applications, excessively small carbon black particles can lead to poor dispersion due to reduced shear forces after plasticization. As a result, carbon black may aggregate into small clusters within the matrix, diminishing the mechanical properties of the conductive plastic and rendering it impractical. Therefore, controlling the particle size within a specific range ensures good dispersion in plastics, maximizes the number of particles per unit volume, and enhances conductivity without significantly compromising the original mechanical properties.

2. Structure of Carbon Black

The DBP (dibutyl phthalate) absorption value indicates the structure level of carbon black aggregates. Generally, a higher DBP value suggests a chain-like or branched structure, which is conducive to conductivity. However, some carbon blacks derived from heavy oil gasification by-products exhibit high DBP values but are found to have hollow shell-like microstructures under electron microscopy, indicating that their structure may not be as high as suggested. Their high conductivity could be attributed to their larger volume per unit mass and the creation of numerous new particles due to shear forces during processing. To achieve good conductivity in plastics, carbon black should have a relatively larger particle size and a moderate structure, preferably linear, to facilitate dispersion and the formation of conductive networks, thereby achieving antistatic properties with minimal carbon black content.

3. Roughness of Carbon Black

A certain degree of roughness is essential for carbon black to form conductive pathways. This is achieved by maintaining a significant difference between the nitrogen adsorption surface area and the CTAB (cetyltrimethylammonium bromide) surface area of carbon black.

4. Surface Volatiles

Surface volatiles on carbon black, primarily composed of organic groups and incompletely cracked oil films, form an insulating layer that increases the potential barrier between carbon black particles, severely affecting conductivity. Therefore, it is crucial to control the volatile content to a minimum.

5. Ash and Moisture Content

High ash and moisture content in carbon black effectively reduce the carbon black content, negatively impacting conductivity. During production, it is essential to control the ash and moisture content. For instance, Ketjen Black EC and acetylene black have carbon contents of approximately 99.8%, while general carbon blacks typically have less than 98%. Moisture content should generally be controlled below 2.5% to prevent the formation of bubbles that could compromise the mechanical properties of the final products.

In conclusion, understanding and optimizing these factors are crucial for achieving the desired conductivity in carbon black and ensuring the performance of the end products in various applications.