74 SILICONES
Structured gels with organic oils and alkyl dimethicone
n Tony O’Lenick – Siltech LLC, US
David Zhang PhD - Siltech Corporation, Canada Abstract
Butters are very commonly used in personal care formulations. Butters are divided into two classes, those that exist in nature, including shea butter,1 butter3
cocoa butter2 , lilpe butter4 , mango
Butters are structured gels that provide not only a unique skin-feel but also have a great rheology thinning under pressure.5
and several others or those that are man-made such as olive butter. There are only a handful of butters in nature, many
US Patent 7,875,2637 describes structured
gels that are produced by heating the oil together with the proper alkyl silicone to above the melt point of the alkyl silicone and adding the oil to produce a butter with unique skin spreadability properties. This provides combinations of particular value as a carrier in antiperspirants, pigmented products, skin care products, sun care and the like since they spread rapidly and efficiently on the skin from a gel providing emmoliency. Additionally, there are a host of oil soluble additives including sun screen actives, hydroxy acids, antioxidants, flavonoids, tocopherol, vitamins and the like that can be incorporated into the formulation. These gels are very cosmetically appealing having a dry feel on the skin and provide a lubricious property which improve the aesthetics of skin creams, skin care lotions, moisturisers, facial treatments such as acne or wrinkle removers, personal and facial cleansers, liquid soaps, bath oils, perfumes, colognes, sachets, sunscreens, pre-shave and after- shave lotions, shaving soaps, and shaving lathers. It can be used in hair shampoos, hair conditioners, hair sprays, mousses, permanents, depilatories, and cuticle coats, to enhance cosmetic elegance. The oil phases that are of most interest are glyceryl esters (triglycerides including natural oils), trimethylolpropane esters, and pentaerythritol esters. The two key ingredients in the blend
determine the properties of the final gel. The first is the selection of the alkyl dimethicone and the second is the ester to which it is added.
PERSONAL CARE EUROPE
of the rest are made by partial hydrogenation of the oil. Another approach to make structured gels that avoid partial hydrogenation is addition of alkyl dimethicone compounds to natural oils and esters. These compositions offer the formulator the ability to make a wide variety of structured oil formulations offering a variety that of formulations that not only have a great initial feel and playtime on the skin, but a variety of tunable final aesthetics after rub in. This article will address the basic technology used to make these materials.6
Figure 1: Alkyl Dimethicone Structure CH3 CH3 CH3
CH3–Si–O– (–Si– O)a– (–Si–O)b CH3
CH3
R is –(CH2 x is 17–31
Alkyl silicone
Alkyl dimethicone polymers have the structure shown in Figure 1.
A: Alkyl chain length (‘x’)
The ‘x’ value is the most important factor in determination of the melt point of the alkyl dimethicone. Figure 2 shows the melt point data for a series of dimethicone polymers. Gels made with melt points below 40ºC
)x –CH3
will have a refreshing feel on the skin melting at body temperature.
B: Percentage alkyl by weight If the percentage of alkyl by weight is above 80 per cent, the resulting gel will crack rather than flow when pressure is applied. The lower the percentage of the alkyl component, the softer the gel will become. Controlling the “a” to “b” ratio is key to the softness of the gel.
November 2018 R CH3
–Si– CH3 CH3
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