50 SUN CARE unprotected skin without sunscreen.5 In order
to achieve a high SPF rating, the UV filters must have a high absorption in the UVA and UVB spectrum to achieve a well-balanced UV shield. Moreover, it is equally as important to
ensure the UV filters are well distributed in the formulation and that the product can efficiently adhere to the skin as the homogeneity of the sunscreen and film-formation play an important role with respect to SPF as demonstrated in Figure 1.6
Finally, the sunscreen formulation
must be stable and be able to provide good dispersion of the UV filters throughout the shelf life of the product.7 As a formulator, achieving a high SPF rating
with good stability is not the only challenge. In order to create a sunscreen with high SPF of 50 or above, it needs to contain at least 25-30% UV filters. Such high dosage levels of UV filters result in tacky, hard-to-spread formulations, which can often leave a white coating on the skin.7
The role of SPF boosters SPF boosters are frequently used to reduce the amount of UV filters required to achieve a certain SPF rating, while maintaining the same level of protection. This, in turn, creates a more appealing skin-feel. SPF boosters work by either increasing the homogeneity of the UV filters in the sunscreen formulation or by increasing the film thickness on the skin.5 SPF boosters can be polymeric solutions/
dispersions/powders or waxes and emollients. Majority of the polymeric SPF boosters available on the market are synthetic polymers based on acrylic acid or polyurethane.8 With the recent proposal by ECHA to ban
microplastics in all cosmetic formulations and an increase in demand for more natural products by consumers, formulators are looking for alternative solutions.9
Valida S+, hereafter
known as the fibrillated cellulose, (INCI: Cellulose/Cellulose Gum), made by Sappi, is a 99.9% natural (ISO 16128) cellulose material that can boost the SPF and UVA PF of mineral, and a combination of both mineral and chemical, UV filters.
Fibrillated cellulose as alternative to polymers and plastics The fibrillated cellulose is a renewable material that delivers multiple functionalities to cosmetic and everyday products. Unlike conventional cellulose materials, the fibrillated cellulose is not chemically modified, nor does it use any chemicals, such as solvents, in its processing. Instead, it is fabricated by mechanically
processing cellulose fibres into cellulose fibrils (Figure 2). The raw material used, wood pulp, is sourced from sustainably managed forests and it is PEFC and FSC certified. The mechanical fibrillation process results in a strong 3D network structure (Figure 3), which is one of the fundamental properties of the fibrillated cellulose together with its high specific surface area and water retention. As it is manufactured from a purely
mechanical process, the fibrillated cellulose is fully biodegradable in marine under TUV OK certification (pending OECD 301f) and has a
PERSONAL CARE October 2023
Figure 3: The 3D network is formed through the hydrogen bonding and mechanical entanglement of the cellulose fibrils
naturality of 0.99 according to ISO 16128. The 3D network structure enables
stabilisation of sunscreen formulations by uniformly distributing the UV filter particles, keeping them in suspension, which results in SPF boosting and UVA-PF boosting (Figures 4 and 5). The results from in vitro testing of oil-in-water sunscreens show that Valida S+ can boost the SPF of the formulation by 25% at concentrations of 0.4-0.5%, based on solid content.
Dispersion, suspension and stabilisation properties The powerful dispersion and suspension properties of the fibrillated cellulose can further be accounted for by its storage modulus. As seen in Figure 6, the storage modulus the fibrillated cellulose is significantly higher than the other natural rheology modifiers, which
suggests that more energy is required in order to deform the elastic fibre network of the fibrillated cellulose compared to the other raw materials. In terms of stabilisation capacity, a higher
storage modulus indicates that the fibrillated cellulose is capable of stabilising high density particles, such as titanium dioxide and zinc oxide, at lower concentrations (1% active) compared to xanthan gum and other cellulose materials. The fibrillated cellulose can stabilise up to 40% zinc oxide powder, implying the possibility to stabilise mineral sunscreens with a high SPF.
The fibrillated cellulose can suspend
both lightweight and dense particles, such as encapsulated fragrances and titanium dioxide, respectively. It does so with a minimal impact on the final viscosity of the formulation, therefore it can be said that Valida S+ conveys
www.personalcaremagazine.com
Figure 2: The cellulose fibrils acquired through the mechanical fibrillation process of cellulose fibres to create the fibrillated cellulose
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