Carbon blacks are obtained by cracking oil or gas organic feedstocks in a limited oxygen atmosphere. They can be obtained via several processes:
• Channel starting from gas, leading to acidic and slow curing carbon blacks. Specialty Carbon Black
• Furnace starting from oil. Most commonly used today for rubber reinforcement.
• Thermal starting from gas. The obtained carbon blacks are weakly or non-reinforcing.
• Acetylene starting from acetylene. These carbon blacks are used to make conductive polymers.
Physically, the carbon blacks are organized in three structural levels:
• Primary particles characterized by size ranging from 10 to 500 nm.
• Aggregates of particles characterized by size ranging from 40 to 600 nm.
• Agglomerates of aggregates.
The main properties of carbon blacks and their characterization.
The basic property is the particle size (10 to 500 nm) that can be measured by direct methods or indirectly by surface area measurement such as absorption of liquids or gases: CTAB,iodine, nitrogen. Each method leads to a different value. Contrary to the CTAB index, the nitrogen absorption measures both porosity (inaccessible for rubber) and external surface area. Current surface areas range from 10 m2/g to 150 m2/g.
The smallest particle sizes lead to the highest surface areas and the corresponding carbon blacks are the most reinforcing but also the most difficult to disperse.
The aggregate sizes (40 to 600 nm) and structures (voids, number of particles) are characterized by oil absorption, currently dibutylphthalate or DBP absorption with values ranging from 30 to 150 cm3/100 g.
The rubber that fills the voids does not share an active part in the mechanical performances: elasticity, elongation, compression set.