3 Ways to Reduce the Oil Absorption Value of Calcium Carbonate
In practice, most fillers use the oil absorption value as an indicator to roughly predict the filler's demand for resin, i.e., the oil absorption value is an important guide for selecting fillers.
1、What is oil absorption value?
Oil absorption value, also known as resin adsorption amount, indicates that the filler on the resin absorption of a kind of index. Oil absorption value is usually expressed as the mass of linseed oil required for 100g of sample (% or mL/100g). This means that for every 100g of sample, the minimum amount of oil is required to achieve complete wetting.
Oil absorption value = the amount of linseed oil / 100g sample
The oil absorption value is related to the particle size distribution, particle shape, dispersion and cohesion, specific surface area and surface properties of the powder.
(1) The finer the particle size of the powder particles, the larger the specific surface area, the narrower the distribution, the higher the oil absorption value;
(2) The oil absorption value of different particle shapes: needle-like > flake-like > spherical. Needle-shaped particles due to the filling arrangement of crisscrossing, larger gaps, high oil absorption; flake particles mixed together in a parallel arrangement, the gap decreases, its oil absorption is low; neat arrangement of spherical particles, its free space is small, oil absorption is also small.
(3) The surface defects of crystals are less, the degree of perfection is high, its specific surface area is small, and the oil absorption is also low.
2、The "harm" of high oil absorption value of packing material
(1) filler oil absorption value is high, may "eat" several times or even dozens of times the price of its own resin, which will invariably increase the production cost;
(2) filler oil absorption value is high, the viscosity of the resin rises, which will seriously affect its impregnation of fibers, and even change the rheological properties of molded plastics, so that its molding process performance deterioration;
(3) In the coating industry, the oil absorption value is an important influencing factor affecting the coating film performance and coating viscosity. In the process of coating film drying, the resin not only has to be completely coated on the surface of the powder, but also has to fill in the inter-particle voids, when the oil absorption value of the powder is large, more resin is needed to fulfill these functions.
3、How to reduce the oil absorption value of calcium carbonate?
(1) Control particle morphology
For lightweight calcium carbonate (or nano lightweight calcium carbonate), its oil absorption value and the production process has a great relationship. In the absence of special requirements on particle morphology, a crystal control agent can be used to regulate the crystal shape and specific surface area of calcium carbonate, thus reducing its oil absorption value.
(2) Control fineness and particle size distribution
The fineness should be appropriate, not the finer the better, and the particle size distribution should also be determined according to the needs.
For general product applications, if the fineness of calcium carbonate and particle size distribution requirements are not high, you can choose the appropriate mix of products with a large gap in particle size distribution, so that the small particles will enter the large particles of the gap, the stacking is relatively tight, the oil absorption will also be reduced.
For high-quality product applications, calcium carbonate with high fineness and narrow particle size distribution helps to improve product performance, and then it is necessary to solve the problem of oil absorption value through surface modification.
(3) Surface modification
Surface modification is an important means to reduce the oil absorption value of the powder. Calcium carbonate after surface modification, the aggregation of particles to reduce, improve the dispersion, reduce the inter-particle voids, while the modified molecules on the surface of calcium carbonate to cover the particles within the gap is reduced, and this cover also changes the surface properties of calcium carbonate, so that the surface polarity weakened, the inter-particle friction becomes smaller, lubrication has become better, so the stacking of the more tightly packed, the density of stacking increased, the oil-absorption value is reduced.
