Silicones are used in barrier creams, body washes, shampoos, hair conditioners and fixative products. cosmeticsbusiness.com looks at a variety of silicones – including cyclotetrasiloxane and cyclopentasiloxane – plus alternatives for natural, organic and free from products.
Silicones have become a hugely useful ingredient in cosmetic products. But they have their critics and there is now a wide range of alternatives that seek to fit the same bill. John Woodruff examines the options
When silicones were first offered as ingredients for cosmetic products they were the inert dimethicones or so-called silicone oils. Their principal function was as replacement materials for hydrocarbon oils and for imparting water-resistance to barrier creams. Their molecular weight is controlled by the number of O-Si groups in the molecule, and their viscosity ranges from 0.65 cst to 1,000,000 cst. The higher molecular weight dimethicones are often mixed with cyclomethicones to form so-called silicone gums, which have wide applications in hair care.
Silicones are polymers that include silicon together with carbon, hydrogen, oxygen and sometimes other chemical elements. By a process termed hydrosilylation it is possible to form an Si-H bond, which can then be reacted with a terminal double bond, resulting in a stable Si-C bond. This gives rise to important groups of silicone compounds including alkyl silicones, fluoro silicones, PEG/PPG products and copolymer resins by a process known as functionalisation. These materials may then be derivatised to provide esters, phosphate esters sulfosuccinates, sorbitan esters, sulphates and carboxylates.
Modified silicones include the addition of perfuoro groups to increase spreading properties and of alkyl groups to improve substantivity and wet combing and to impart a velvety feel in skin creams. Aryl and phenyl groups give added gloss to hair and improve organic compatibility and polyether and glucoside groups provide emulsifiers, conditioning properties and foam boosting activity.
Silicone waxes are of interest to formulators. Their melting point depends on their molecular structure and varies from a soft gel to a high melting point wax. When incorporated into emulsions they lower the surface tension of the oil phase and thus improve its spreading properties and they can also be added to shampoos to add conditioning properties.
Silicones are driving innovation in personal care and allowing product differentiation based on performance. That statement was made by Claudius Schwarzwalder, Centre Européen des Silicones, at in-cosmetics 2006 and it is hard to imagine cosmetic compositions without them.
Current developments in silicone technology include combining basic silicone structures with organic moieties to create new hybrid materials. This is providing silicone resin gels and powders, new hyper-branched structures and materials such as silicone-polyethers for thermal protection of hair and thermoplastic silicone elastomers as film formers and fixatives. Future developments are expected to provide silicone-based delivery systems for bioactive compounds for controlled release, biologically active silicone compounds and enzymatic silicon-carbon bond formation.
One group of silicone compounds that found widespread acceptance were the cyclomethicones with D4, cyclotetrasiloxane and D5 or cyclopentasiloxane proving the most useful. Because cyclomethicones are volatile they require careful handling but once incorporated in an emulsion they improve its spreading properties, eliminate soaping and give a dry, silky skin feel. Unfortunately the use of cyclomethicones was queried by Canadian authorities and then under REACH and there was a real risk that its use in cosmetic products would be banned.
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