74 CLEAN BEAUTY Hardness (force in gram to penetrate 5 mm) ■ Flexibility (mm)■ 6
4.5 3
1.5 0
Stick 1 Without Bentone Gel®
Stick 1 With
Bentone Gel® PTIS v
Stick 2 Without Bentone Gel®
Figure 7: Hardness vs. flexibility in stick formulas with various Bentone Gels
resilient than the one from waxes, thus the Bentone Gel can help to stop the stick system from melting upon high temperature. The stability test shows that the Moisture Boost
Serum Stick (F-1012-01) with 10% Bentone Gel LC V (INCI: C9-12 Alkane (and) Disteardimonium Hectorite (and) Triethyl Citrate) did not melt when stored at 40°C, while the benchmark formula without Bentone Gel partially melted. The prototypes have also been stored in the
oven at 50°C, and the results shows that the one without Bentone Gel partially melted in an uneven way (Figure 6). Another important aspect of stick application is the firmness. It describes the interaction between the oils and waxes within the formulation and can be controlled by altering the oils or waxes used. Within a formulation, formulators need to carefully select the paste-like materials that can be used to create micro-crystalline or gel-like structure to ensure more ‘elasticity’ and are less prone to potential breakage. On the other hand, if the stick texture is too
hard, it will impact another key attribute – the pay-off. Pay-off is a measure of the amount of product deposited on the skin when applying, and is directly related to the formulation’s wax structure. Pay-off is important to ensure even and
thorough covering of area with product, and can be inversely proportional to firmness i.e. the
softer formulations provide increased payoff and vice versa. This relationship creates a challenge for
formulators – balancing the need for a firm formulation while maintaining a good pay-off, the two fundamental attributes where good performance is expected by the customer. Hectorite-based organoclay gels make the stick structure more elastic, and the hydrogen bonding network structure will be fully formed when the product is in the container. When shear is applied, the platelets align flat on the skin, giving a beautiful application. Generally, Bentone Gel will make a stick softer, so that a better payoff on application can be achieved. At the same time, it will give a stick more flexibility, so that it is less prone to breakage. Current beauty sticks have gone beyond skin
moisturisation only, and more diversified multi- purpose sticks are emerging in the market, such as clay mask stick, sun care stick, highlighter stick, foundation stick etc. The variety of applications brings more insoluble ingredients like sunscreens, particles, pigments, clays and some actives into the stick, causing more challenges to the formula system. The Bentone Gel series offers an unique
rheological performance in both single oil systems and the oil phase of an emulsion. The honeycomb like network formed by a Bentone Gel, or often referred to as a house of cards, can help the oil
droplets, pigments and other particles to be evenly suspended and stabilised in the system in a much finer texture. The extraordinary suspension performance of
Bentone Gel leads to a much more uniform and stable stick, and ensures replication of the formula performance from batch to batch. Particularly during the moulding process in
production, when oils and waxes are still liquid, sedimentation of the particles is of concern. Figure 9 depicts glitter in a stick base, that was put into the mould at 80°C, and without organoclay gel (10% Bentone Gel GTCC V), all the glitter sedimented. It is clearly shown that the incorporation of Bentone Gel into the stick system will help improve the suspension performance at large. One extra benefit brought by Bentone Gel is the smooth and velvet sensory. Most stick formulas are wax-based, which often leave a greasy feeling when applied to the whole face instead of lips only. Hectorite clay is treated with quaternary ammonium compounds, which cover the hydrophilic surface structure of the clay with organophilic (hydrophobic) material to facilitate the clay to build the network in the oil phase of a system.
These so-called organoclays demonstrate
enhanced skin-feel by masking greasy or tacky components and impart a pleasant residual silkiness to the skin.
PC Stick 2 With Bentone Gel® LIP V
Stick 3 Without Bentone Gel®
Stick 3
With Bentone GEl® PTM V
Stick Formula Without Bentone Gel
Figure 8: Idealised two-dimensional representation of the network formed by a Bentone Gel for stabilising actives and particles
PERSONAL CARE September 2022
Stick Formula With Bentone Gel
Figure 9: Bentone Gel helps to improve the particle suspension in a stick formula
www.personalcaremagazine.com
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