SILICONES
different textures, have made silicone crosspolymers more popular. Silicone elastomers can give unique sensory profiles. They can give a silky touch during application. Also they can provide a non-tacky velvety sensation, improve transfer resistance, durability and modify viscosity profiles of formulations. They can also act as a binder and facilitate spreading. When formulated with a non-volatile carrier, reduced cracking over time of powder cosmetics can be achieved. Crosspolymers may be used in various colour cosmetics like lipsticks and foundations. Examples of generic formulations can be found in Table 1.
Hair care
Crosspolymers are also used in hair care formulations. Their non-glossy appearance and non-tackiness can be used. They do, however, not have good adhesion to hair, which has to be overcome by using other silicones such as amodimethicones.
Chemistry
Silicone crosspolymer gels are commonly blends of silicone elastomer in silicone fluid, which acts as diluent. The silicone fluid used often is a low viscosity dimethicone (e.g. dimethicone 5 cSt) or cyclopentasiloxane.
The common production method used to produce these materials is depicted in Figure 1.
The production of silicone crosspolymers as shown in Figure 1 consists of two different steps. The first step consists
Spreadability
After-feel intensity
100 75 50 25 0
affect appearance, feel and aesthetics of the final formulation. This means proper control of particle size (distribution) is key for many applications, which logically means the importance of using the right method of production.
Properties See Table 2 for an overview of several critical silicone crosspolymers properties and the relation to their chemical composition.
Figure 4: 1% TiO2 disperions in 33% crosspolymer solutions, showing difference in stability.
of an additional cured reaction of an SiH functional siloxane with a vinyl functional siloxane. The reaction is carried out in solvent (typically cyclopentasiloxane or dimethicone), and a soft solid, gel-like, 3D crosslinked structure is formed. The creation of connections between linear polymers convert a liquid linear polymer such as a dimethicone into a solid silicone crosspolymer gel.
During a second step, shear processing and additional dilution are used to obtain the typical gel-like structure common for most silicone crosspolymers. This, and the chemical composition determine the properties of the silicone crosspolymer gels.
Crosspolymer properties are completely different compared to linear dimethicones. The crosslinking density determines the properties, the higher the crosslinking density, the higher the hardness of the crosspolymer will be. Particle size and particle size distribution of the silicone crosspolymer
Because of their ability to swell when combined with solvents, silicone crosspolymers are effective oil phase thickeners. Figure 2 depicts the rheological behaviour of typical undiluted crosspolymers. The thickening effect is caused by interactions between swollen gel particles. For more explanation on the rheology of crosspolymers, please see the section about thickening profiles.
Differences between the various crosspolymers types and chemistry The INCI name or the specification is of little value to determine the equivalency of crosspolymers or the suitability of a crosspolymer in a formulation. Within the INCI name of the active ingredient: Vinyldimethicone/Dimethicone Crosspolymer there is a lot of freedom to influence the properties of a crosspolymer. The degree of crosslinking, elastomer structure, gel content, carrier fluid and shear process used to create the crosspolymer blend all greatly influence the appearance and properties of a product. Therefore it is crucial to test crosspolymers in the formulation and for the application.
Spreadability Wetness
After-feel intensity
100 75 50 25 0
Firmness Stickiness
■ BRB SG 106 ■ BRB SG 116 ■ BRB SG 117 ■ BRB SG 506 ■ BRB SG 516 ■ BRB SG 517
Figure 5: Radar chart showing a comparison between various sensory attributes of BRB SG crosspolymer series.
Wetness
Firmness
Smoothness
Figure 6: Sensory characteristics of a body gel formulation containing 20% of three different BRB crosspolymers.
April 2012 PERSONAL CARE 117
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