Carbon Black Properties Terminology of the Morphological Properties
Particle size and its distribution play a particularly important role in carbon blacks used in polymers and are quite a complicated subject with different types of size being referred to. The main classification is into three size types: primary particle, aggregate, and agglomerate. Primary particle size refers to the basic building block particles formed before collision leads to sticking and growth. These primaries rarely exist as such in polymer-grade blacks, but are an important concept and largely determine the specific surface area. Aggregates are the main effective particle in polymers. These result from partial fusion of primary particles and from further overgrowth and are strong enough to remain as discrete particles, instead of breaking
Fig. 2 Primary particles, aggregates, and agglomerates
down to primaries even under the influence of high shear during dispersion. The largest level of size is due to agglomerates. These are collections of aggregates, but with no intergrowth and only physically held together, so that they are fairly easily separated. The main effect of these is on powder handling properties including bulk density, dustiness, and dispersion. The pyrolysis process naturally gives small, weak agglomerates with low bulk density and high dustiness, and various methods are used to increase agglomerate size and strength. These issues are illustrated in Fig. 2.
The complex arrangement of primary particles in the aggregates and agglomerates is called carbon black structure. Unfortunately, it is an ambiguous term as it implies chemical structure. To distinguish carbon black structure with the atomic arrangement of the carbon in the primary particles, the term microstructure was introduced for the latter.