Sustainable stabilisation: COSSMA

If you want to manufacture products on a sustainable basis, you should also pay attention to microplastics in the formulations. To reduce the proportion of synthetic polymers that are difficult to degrade, other stabilisation systems, for example based on microcrystalline cellulose, can be used.

Microplastics are an omnipresent component of our rivers and oceans today and have already been detected in crustaceans, mussels, and fish. Since the environmental pollution by plastic particles gained publicity, microplastics in cosmetics became a muchdiscussed topic.

Solid microplastics have mostly been faced out in several countries by official bans and the rising pressure by the public discussion. Synthetic polymers are still allowed to be used to enhance the rheology, to stabilise or to provide a film-forming effect. Only in Germany, 23,700 t per year of dissolved polymers enter wastewater by cosmetic products alone. A large number of those water-insoluble synthetic polymers is only weakly biodegradable and we do not yet know well about their impact on the environment¹. Cellulose is one of the main components

of the plant cell walls and consists of several hundreds to thousands glucose monomers. Cellulose builds the scaffold of the plant, comparable to the steel framework of a house. Together, with the other main plant cell wall component lignin, the “concrete” within the house building, it provides stability and solidity to the whole plant. Microcrystalline cellulose is characterised by a dominating number of crystalline regions isolated from the amorphous parts of the cellulose polymer.

While powdered microcrystalline cellulose are porous particles of aggregated crystalline rods, non-dispersible and only effective as of its high binding capacities, colloidal microcrystalline cellulose is redispersible resulting in gel-like structures in aqueous suspensions. By activation at high shear force, the microcrystalline cellulose particles form a colloidal 3D network, optimal for stabilising effects without increasing the viscosity at a high rate.

figure 1: Results of the sensorial evaluation of a formulation with and without Sensocel stab. graphs: CFFx

Stabilisation of emulsifierreduced emulsions

An emulsion is defined as a dispersion of two or more liquids, usually oil and water, that are actually immiscible. When oil and water are mixed, the surface and energy of the system increase, resulting in a thermodynamic instability of the emulsion.

The small droplets tend to coalesce to compensate the energy level in the system and consequently its interfacial tension. Usually emulsifiers are used to stabilise an emulsion as they accumulate within the interface of water and oil and decrease the tension of the system.

Emulsifiers are characterised by amphiphily, enabling the connection to both phases. Emulsifiers do not only influence the emulsification process but also interact with the stratum corneum lipids. As a consequence, the protective barrier of our skin is weakened, and the permeability is expanding. Harmful or toxic substances are now able to enter the skin layers. Simultaneously the TEWL (transepidermal water loss) is increased which is used as an indicator of skin barrier function and health. With a special microplastic-free stabilising system based on colloidal microcrystalline cellulose²it is possible to reduce the

emulsifier concentration or even to reduce the emulsifier system to one single emulsifier. The stabilising power of this stabilising system at reduced amount of emulsifier leads to a stable, homogenous emulsion without any phase separation at a skin friendlier base. Beside the stabilisation effects it also positively influences the characteristics of a formulation with an emulsifier reduction by 3% and addition of another element of the stabilisation system3 at 1.5%.

Figure 1 shows that the stabilisation system leads to a less greasy, very soft formulation that is easier to spread and feels quickly absorbed by the skin.

Demonstrating the stabilisation

To demonstrate the stabilisation power in a Pickering emulsion, CFF used a simplified emulsion of only three components: water, oil and stabilising system. The stabilisation of the system alone was compared to the stabilisation in combination with an emulsifier (potassium cetyl phosphate) and to the stabilising effects of xanthan gum.

The emulsion was composed of 49% water, 49% vegetable plant oil and 2% of the stabiliser system (1% each in case of the combination of the stabilising system with the emulsifier). All ingredients were homogenised for two minutes at 10,000 rpm with an Ultra-Turrax T25 (Ika). A stability test at 4°C was absolved for three months and the viscosity was checked by a Brookfield viscometer with a S06 spindle.

Figure 2 shows the viscosity results of all three emulsions at the beginning of the stabilisation test and after a time of three months (99 days). The emulsion with the stabilisation system shows a constant viscosity, which means that the system is stable over a time of three months. No phase separation was observed. In addition, the stabilisation system with the emulsifier keeps it viscosity over the stability test. The system with xanthan gum suffers from a viscosity decrease over the testing time.

Properties for stable emulsions

This proved that the stabilisation system is a natural, microcrystalline cellulose based stabilising system that is free of microplastics. According to DIN EN 14851 microcrystalline cellulose shows a biodegradation rate of 85% after only 39 days under freshwater conditions, which perfectly represents a maritime environment. It occurs as a highly pure, white, odourless, and tasteless fine powder that requires an activation step at high shear force.

The activated stabiliser is pH-stable within the whole pH-range, showing a slower gelling below pH 4.5 and higher than pH 9. Temperature insensitivity is given from -26°C to 100°C. Free ions and electrolytes are also uncritical for the activated version.

Cosmos and Natrue conform types are available. Its thixotropic character makes it also the natural solution for the stabilisation of sprayable systems. It can be applied in skin care, hair care and oral care for plantbased stabilisation effects.

References

¹Bertling et al. 2018: Mikroplastik und synthetische Polymere in Kosmetikprodukten sowie Wasch-, Putz- und Reinigungsmitteln, Fraunhofer Institut für Umwelt-, Sicherheits- und Energietechnik UMSICHT.

²Sensocel stab

³ Sensocel stab 026