Oil Absorption Number analysis OAN of carbon black

The Oil Absorption Number, often abbreviated as OAN, is a key parameter for the performance of carbon black materials. Carbon black is a material that is either won from oil or man-made from the incomplete combustion of coal-like products such as coal tar. It has many applications such as in coatings and batteries. One of the properties of carbon black is the ability to absorb oil into its structure. If oil is constantly added to this mixture by titration, and with the help of some stirring, it turns from a free-flowing state into a semiplastic agglomerate.

The oil absorption number OAN is equal to this transition. This value is of interest in a lot of industries such as the cosmetic, pigment or rubber industry, where the latter is probably the most important. A tire manufacturer might want to know how much oil carbon black is able to absorb, indicated by a high oil absorption number, which means it has a great capacity for interaction with rubber compounds. This also improves the dispersion of carbon black in rubber matrices. A low oil absorption number is generally not favorable for tire manufacturers, as it indicates that the material is not able to absorb a lot of oil due to low pore volume of carbon black and leads to complications with optimal dispersion of carbon black in rubber matrices. However, it may offer better extrudability poperties during processing.

All kinds of carbon black can be analyzed for OAN. However, there exists carbon black with low bulk density on the market, also known as “fluffy” carbon black. Due to its low bulk density, it may cause issues for oil absorption analysis. This results in an underfilled chamber at the end of the analysis which causes inaccuracies in oil absorption analysis. We developed a method to measure the OAN for fluffy carbon black that avoids underfilling of the measurement chamber enabling accurate assessment of the OAN.

The oil absorption number analysis is performed on the Absorptometer C, which is equipped with a torque measuring system that records the amount of torque and oil titration volume. The standardized method according to ASTM D2414-17 is followed where non-fluffy carbon black is used for analysis. Our oil of choice is paraffin oil, compared to other oils such as DBP, paraffin oil is generally considered safe.