36 SKIN CARE Aristoflex Eco T■ Xanthan Gum ■ Carbomer■ 100000 10000 10000 100 10 0.0 0.5 1.0 1.5 Polymer concentration (%)


Figure 2: Viscosity in deionized water against polymer concentration for Aristoflex Eco T, xanthan gum and carbomer (Brookfield lv2, 20 rpm, 20°C, pH = 5.5)


to the stabilization of oil droplets and solid particles. By adjusting the amount of thickener, formulators can define the viscosity level of their product and how it is placed on the market. Figure 2 shows that the tara gum rheology


modifier clearly builds higher viscosities compared to xanthan gum and approaches the performance of carbomer. Outstanding for a biodegradable rheology modifier is the feature that the tara gum rheology modifier already builds up viscosity at low concentrations (from 0.5%), allowing formulators to use less of the product to stabilize their cosmetic product. Although carbomer builds still higher


viscosities, for a leave-on application the tara gum rheology modifier has a good enough performance level to make all kinds of products, ranging from lightweight lotions to rich night creams. Many leave-on applications, such as facial creams or body lotions, are located around a pH of 5.5. However, depending on the application the pH may change, which ultimately can


100000 2.0 2.5 1000 0 2 4 6 pH


Figure 3: Viscosity versus pH of Aristoflex Eco T, xanthan gum and carbomer (Brookfield lv2, 20 rpm, 20°C). The polymer concentration is 1.0 wt.%


influence the viscosity-building properties of a rheology modifier and thus the cosmetic product appearance and stability. For instance, sunscreen usually has a pH level around 7, while chemical peels are most efficient when the pH is below 4. Other applications, especially in hair care need an alkaline pH of around 9-11 to be most efficient, for example hair coloration creams. It is thus essential that a rheology modifier


shows stable viscosity at different pH values to be a real allrounder. Yet there are more factors to consider.


Formulations are made to last for several months or years, depending on the type of formulation. However, throughout its lifecycle, the product may experience stresses such as temperature variations, sun exposure and so on, which may affect its shelf life. A first sign of destabilization is a decrease


in pH, often caused by oxidation or hydrolysis of an ingredient. Rheology modifiers with a stable viscosity throughout a wide pH range can absorb such changes while maintaining the


Xanthan Gum ■ Carbomer■ Aristoflex Eco T■


same viscosity level of the formulation. Figure 3 shows the viscosity dependence


of several rheology modifiers at different pH values. Just like carbomer, the tara gum rheology modifier possesses a very stable viscosity throughout the pH range. Even below pH 3.5, good viscosity levels can be attained, while the carbomer is seen to have low viscosity at this level. On the other hand, xanthan gum shows


a very unstable viscosity throughout the investigated pH range. At neutral pH, xanthan gum is a polyelectrolyte, while at very low pH, the carbonyl groups get protonated and thus the biopolymer behaves like a non-ionic thickener. The tara gum rheology modifier is also an electrolyte, but unlike xanthan gum, it remains charged between pH 3-11, which is the reason for its excellent pH stability.


Stability against electrolytes Besides pH, electrolytes may also influence the viscosity-building properties of rheology modifiers. Many actives or preservatives can possess a charge, but also unavoidable residual salts in cosmetic ingredients can increase the electrolyte load in a formulation. A certain stability against such ingredients is thus appreciated by many formulators. A simple test in assessing the electrolyte


10000 10000


stability of rheology modifiers is the addition of NaCl to an aqueous solution of 1.0 wt.% polymer, followed by the measurement of the viscosity. Results can be seen in Figure 4, where viscosity is shown against NaCl content. Just like carbomers, the viscosity of the tara gum rheology modifier drops in the presence of salt. However, for elevated electrolyte content


100 0.0 0.5 1.0 NaCI (%)


Figure 4: Viscosity of Aristoflex Eco T, xanthan gum and carbomer (Brookfield lv2, 20 rpm, 20°C) versus NaCl content. The polymer concentration of the aqueous solution is 1.0 wt.%


PERSONAL CARE June 2023 1.5 2.0 2.5


the viscosity remains at a higher level, while it continues to decrease for carbomer. In both cases, salt causes a screening effect on the anionic functional groups, which in turn results in the collapsing of the polymer network and thus is lower viscosities. Unlike for carbomer, where the viscosity


becomes almost water-like, the tara gum rheology modifier maintains a higher viscosity


www.personalcaremagazine.com 8 10 12 14 10000 100000 Aristoflex Eco T■ Xanthan Gum ■ Carbomer■


Viscosity (mPas) Viscosity (mPas)


Viscosity (mPas)

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