Definition: Oil absorption value refers to the volume (in milliliters) of liquid required per 100 grams of powder material to absorb a specific liquid (commonly linseed oil or castor oil) to achieve a specific viscosity (such as forming a uniform agglomerate or paste). The unit is usually mL/100g.
This indicator is mainly measured manually or by instrument. In standard methods (such as GB/T 5211.15 or ASTM D281), the operator adds the liquid dropwise while stirring until the powder and liquid are completely mixed to form a non-dispersed, non-sticky, uniform agglomerate.
Significance in Inorganic Powder Materials:
Oil absorption value directly affects the application performance of inorganic powders. It mainly reflects the following key characteristics:
Specific Surface Area and Pore Structure
The oil absorption value is closely related to the specific surface area and porosity of the powder. The larger the specific surface area and the more developed the pores (especially open-pore structures), the higher the oil absorption value usually is.
For example: Nanoscale powders (such as nano-calcium carbonate) have much higher oil absorption values than powders of ordinary particle size.
Particle Morphology and Structure
Shape: Irregular, multi-faceted particles have higher oil absorption values than spherical particles.
Structure: Powders with porous or hollow structures (such as precipitated silica and some porous silica) have higher oil absorption values than dense, solid particles.
Agglomeration State: Loose, fluffy aggregates increase oil absorption values.
Surface Properties
Surface energy, polarity, and whether or not surface treatment has been performed significantly affect oil absorption values. For example, surface-modified calcium carbonate (e.g., treated with stearic acid) will have a significantly lower oil absorption value because its surface changes from hydrophilic to hydrophobic.
Importance in Practical Applications
Oil absorption value is a key parameter in downstream formulation design and production processes, directly affecting:
Processing and properties of composite materials (such as plastics and rubber):
High oil absorption value means that more resin or polymer is needed to wet and coat the powder; otherwise, it will lead to increased system viscosity, poor flowability, increased processing energy consumption, and may affect the mechanical properties of the final product (such as decreased toughness).
Powders with low oil absorption values are easier to disperse, reducing resin usage, lowering costs, and improving processing flowability.
Coatings and Ink Industry:
Affects the critical pigment volume concentration (CPVC), gloss, flowability, hiding power, and durability of coatings. Excessively high oil absorption values can lead to overly viscous coatings and poor color development.
Cost Control:
Oil absorption value is directly related to the amount of matrix materials (resin, oil, etc.) used in the formulation, and is a significant factor affecting material costs.
Evaluation of Surface Modification Effects:
Changes in oil absorption value are one of the important indicators for evaluating the surface modification effect of powders. Successful surface modification usually reduces the oil absorption value.
Summary:
Oil absorption value is a comprehensive "physical fingerprint" of inorganic powder materials. It is not just a simple adsorption amount data, but a comprehensive reflection of the powder's particle size distribution, specific surface area, particle morphology, pore structure, and surface properties. When selecting inorganic powders, it is essential to consider the processing technology of downstream applications and the performance requirements of the final product, combining oil absorption value with other indicators to achieve optimal formulation design and cost control. Simply put, the lower the oil absorption value, the less liquid (resin, oil, etc.) the powder needs in the matrix, resulting in better processing fluidity and easier achievement of high filling and low cost.
