Methicone is a polymethylhydrogen siloxane, which absorb traces of water from pigment surface and converts Si - H bond to Si - OH with liberation of small amount of hydrogen gas and upon curing form covalent Si - 0 pigment chemical bonds. The coating formed is highly hydrophobic and not solubilised by common solvents. The pigments wet well in oils particularly silicone oils. Skin feel is somewhat dry with enhanced slip and spreadability. It is preferred for pressed powder formulations.
When incorporating methicone treated materials in to system containing water, care must be taken to utilize an 'emulsion grade' of treatment, in which the hydrolysis reaction is driven as far as possible to completion.
If unreacted hydrogen remains within the system then on prolonged contact with water hydrolysis of the residual hydrogen occurs and hydrogen gas is released from the finished cosmetics.
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