Читать книгу Surface Science and Adhesion in Cosmetics - Группа авторов - Страница 42

The cooling rate will affect the nucleation, crystal growth and solidification of oil-wax systems. With high cooling rate, wax crystals are smaller and have high crystal density than at low cooling. At low cooling rate, the crystal growth rate is dominant over nucleation, resulting into larger crystals.

The crystal growth from rice bran wax in hexane (non-polar oil) was investigated by using a laser diffraction technique. Ghosh and Bandyopadhyay [31] found that a high cooling rate and low temperature induced formation of a large number of small nuclei and maximal crystal size was obtained in the temperature range of 10°C-15°C.

Hwang and coworkers showed that with an increase of cooling rate from 0.1°C/min to 4°C/min, the crystal sizes of 4% sunflower wax in soybean oil reduced and the firmness of the oil-wax gels increased due to high density of small crystal formation [29].

Therefore, the hardness or firmness of oil-wax system can be modulated by cooling rate at a fixed wax concentration. A fast cooling rate will have a large impact on the hardness of the oil-wax system when a high concentration of wax is used.