SILICONES
Table 3: Silicone crosspolymer process and application properties. Trade INCI
name BRB SG 106 Vinyldimethicone/
dimethicone crosspolymer (and) cyclopentasiloxane
BRB SG 116 Vinyldimethicone/
dimethicone crosspolymer (and) cyclopentasiloxane
BRB SG 117 Vinyldimethicone/
dimethicone crosspolymer (and) cyclopentasiloxane
BRB SG 506 Vinyldimethicone/
dimethicone crosspolymer (and) dimethicone
BRB SG 516 Vinyldimethicone/
dimethicone crosspolymer (and) dimethicone
BRB SG 517 Vinyldimethicone/
dimethicone crosspolymer (and) dimethicone
*Initial crosslinking density before dispersion, subject to further swell depending on solvent
Also viscosity figures are meaningless unless a specific shear rate is quoted at which the viscosity is determined. Viscosities always have to be compared at the same shear rates. Furthermore it is also very likely that crosspolymers with other INCI names such as Dimethicone Crosspolymer or Polysilicone is interchangeable with a crosspolymer with INCI Vinyldimethicone/Dimethicone Crosspolymer. This can only be tested in the end formulation.
Silicone crosspolymers typically exhibit shear thinning behavior which is most apparent when processing the pure crosspolymer. However, once formulated this distinct property becomes less apparent. The diluted crosspolymers often show a more Newtonian rheological profile, as can be seen in the graphs. Also the thickening power of products can differ greatly.
In Figure 3 a dilution of one part crosspolymer with two parts of the base solvent is displayed. The differences are clearly visible in the low shear rate range below 10s–1
. The advantage is that
when a crosspolymer is used for thickening, the low shear rheology is crucial for suspending solids. This difference is also observed when stability tests are done. This can be seen in Figure 4, where on the left the diluted SG 106 is displayed. On the right is a competitor product, diluted in the same way. Both mixtures contain 1% TiO2
,
which has clearly settled in the sample on the right on this picture. In other words, products with similar INCI/composition can be thickeners exhibiting very different performances.
118 PERSONAL CARE April 2012 Sensory profiles
The radar chart is a convenient way to distinguish the effect between the different crosspolymers on the sensory characteristics of the cosmetic formulation in which it will be used. Such evaluation can be used to compare and define the performance of cosmetic formulations to provide direction in product formulation nd research guidance.
Sensory characteristics can be defined by properties such as product pick-up, delivery rub-out and after-feel. There are, however, problems with such sensory evaluation. Sensory attributes are very personal so how do you objectively measure them?
How do you convey results to your audience?
ASTM E1490-03 provides a guideline for qualitatively and quantitatively comparing these various sensory attributes and their intensity (over time). Figure 5 depicts a comparison between the BRB SG crosspolymer series using a “radar chart”. Although all these products have the same INCI name, they show very different sensory characteristics that can be classified in 3 groups: Firm and intense after-feel. Wet, smooth and spreadable. Firm, intense after-feel and fairly smooth and spreadable.
Each group (SG1 and SG5 series) has a dimethicone and cyclomethicone version. This shows the sensory characteristics can be fine-tuned regardless of these carrier fluids. Table 3 gives an overview of the process
parameters and their application properties. It indicates that a higher crosslinking density tends to give a broader spectrum of sensory attributes. Also there is an optimum crosslinking density for obtaining maximum thickening power.
When formulating products based on crosspolymers, know-how about other formulation and process parameters that influence the application properties is essential.
According to BRB’s experience, cross- polymers which are diluted in formulations behave the same in terms of sensory characteristics in the final formulation. The effects are slightly levelled out though, as you can see in Figure 6. However, the thickening behaviour of a diluted crosspolymer is more difficult to predict based on its undiluted rheological properties (Fig. 5).
Conclusion
The unique benefits of silicone crosspolymer gels are the compatibility with silicones and lipophilic active ingredients, combined with a dry smoothness and a light silky, non-greasy skin feel. The complexity of the crosspolymer chemistry goes far beyond an INCI name and simple physicochemical characteristics. You can find on the market a versatile range in terms of sensory characteristics and rheology. A smart design between crosslinking density, solvent nature, shear process, particle size and distribution allows endless formula customisation of the sensory benefits and the thickening profile. Being rich of an long customising experience, BRB is offering an extremely versatile range of silicone crosspolymers.
PC Broad Low Non-volatile Medium Wet, smooth and spreadable Broad Low Non-volatile Narrow High Non-volatile
Very High Firm, intense after-feel and fairly smooth and spreadable
High Firm and intense after-feel Broad Low Volatile Medium Wet, smooth and spreadable Broad Low Volatile High
Particle size distribution
Narrow High
Crosslinking density*
Carrier fluid
Volatile
Thickening effect
Very high
Sensory characteristics
Firm, intense after-feel and fairly smooth and spreadable
Firm and intense after-feel
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