Oil Absorption of Titanium Dioxide
The oil absorption of pigment refers to the minimum mass of oil needed to achieve complete wetting for every 100g of pigment, and the oil absorption is often expressed as a percentage. Oil absorption is also one of the important pigment properties of titanium dioxide, because it relates to the filling state of titanium dioxide in the spreading agent, and can indicate its dispersion performance in the medium.
There are more factors affecting the oil absorption, for example, when the particles are small, the specific surface area is large, the oil covered by the surface of the particles, the oil absorption is high; when the particles of coalescence and flocculation are large, the gap between the particles is large, the gap needs to be filled with more oil, the oil absorption is also high; for flaky particles, in the pinch is parallel arrangement, the pores are small, the oil absorption is low; needle-shaped or irregularly shaped particles, due to the larger pores, the oil absorption is high; And close to the spherical particles, theoretically the oil absorption is about 40%.
Since the operation of oil absorption is manual and the end point is observed by the naked eye and the sense of touch, it carries a little qualitative nature. At present, the more common method of measuring oil absorption is the end point when the pigment is wetted by oil (generally linseed oil) into a putty like paste that does not break, does not disperse and can be scraped up by a scraper. This end point can be understood as the end point when the surface of the pigment particles are covered with oil and the pores between the particles are filled with oil.
Another method is the Gardner-Coleman method, which is the end point when the oil is wetted to the point of flow, equivalent to the Flowpoint, but of course the results measured by this method are on the high side.
There is a test to prove, the two particle size difference between the larger pigment, according to a certain ratio mixed together, the pores between the large particles are filled by the small particles, the measured oil absorption than the original two particles measured oil absorption is lower, but two particle size comparable pigment mixed together without this phenomenon.
