38 SKIN CARE
Figure 7: Interaction of salt on the skin with typical biopolymers (e.g. xanthan gum) and microgels. A: Salt on the skin increases the viscosity, resulting in slow penetration of the cream into the skin. B: Salt on the skin results in the collapsing of the gel network and thus in a rapid penetration of the low viscous formulation into the skin
it possible to reduce or completely remove emulsifiers from a formulation. This gives formulators the possibility to make challenging formulations or try out completely new formats. Use of Aristoflex AVC, however, means
compromise on the use of a biodegradable polymer. Here, the tara gum rheology modifier demonstrates its relevance. It can stabilize up to 12 wt.% of oil matching the performance of carbomer. To the authors’ knowledge, it is the first biodegradable rheology modifier that can stabilize considerable amounts of oil, while maintaining an appealing texture. The tara gum rheology modifier was used to
create a serum without any use of emulsifiers. The formulation shown in Table 2 contains
■ Aristoflex Eco T ■ Carbomer Silicone % Greasy % Waxy % Oily %
Amount of residue Thickness of residue
Slipperiness
Figure 8: Spider diagram of a formulation with Aristoflex Eco T compared against same formulation with carbomer
PERSONAL CARE June 2023
various oil with a total concentration of almost 8 wt.% hydrophobic compound, while using only 0.8% of the naturally derived rheology modifier. The formulation is stable for at least three months at 0°C, 20°C and 40°C and has a viscosity of 8400 mPas.
Skin feel The skin feel of a formulation is affected by many factors, such as temperature, humidity, the end consumer and the ingredients used. Emulsifiers and emollients have a very strong influence on the perception of a cosmetic product. While there are still many petrochemical
sourced ingredients available, the industry is increasingly using natural emulsifiers, oils and
Wetness Spreadability Thickness Oil Wax Grease Stickiness
100 80 60 40 20 0
butters as there are numerous alternatives already available in the market. For rheology modifiers the situation is not
as easy, as natural biopolymers tend to deliver undesired skin feel and texture. Due to their structure, biopolymers tend to increase their viscosity or at least maintain their viscosity level in the presence of salt. This can be beneficial for formulations with high salt content, but on the other hand it is unwanted for the skin feel. The penetration of a skincare product into the skin is strongly influenced by the viscosity of the product. All typically used thickeners have shear thinning properties, which result in a decrease in viscosity upon application and thus an easier penetration into the porous skin. However, once on the surface and entering
the pores, shear forces decrease and the formulation becomes thicker again, resulting in an effect that works against a faster penetration into the skin. Figure 4 shows that xanthan gum increases viscosity in the presence of salt. As humans have salt on the skin, the
penetration of such biopolymers can take a long time and lead to a somewhat slimy and undesirable skin feel (Figure 7A). For rheology modifiers, which thicken via microgels, the effect is contrary. The microgel particles collapse in the
presence of salt, thus resulting in a low viscous product on the surface, which penetrates faster into the skin (Figure 7B). The tara gum rheology modifier thickens via microgel formation and as shown in Figure 4, has an initial drop in viscosity in the presence of salt, which can be perceived as an appealing fresh
www.personalcaremagazine.com
Skin
Cosmetic product
Skin
Cosmetic product
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80
