A nature-derived film forming polymer and dispersing agent was developed to enable more sustainable sun and color formulas. Its water resistance, SPF-boosting, pigment wetting and dispersion, and film-forming properties were evaluated as described here.
Film-forming polymers used in sunscreens and color cosmetics provide water resistance and long wear properties. Traditionally, they are fossil-derived and non-biodegradable but there is growing interest in the industry to move toward natural, sustainable ingredients to reduce negative environmental impacts.1, 2 To meet this market need, a technology was developed to functionalize a natural organic oil and polymerize it without the use of catalysts or initiators.
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A nature-derived film forming polymer and dispersing agent was developed to enable more sustainable sun and color formulas. Its water resistance, SPF-boosting, pigment wetting and dispersion, and film-forming properties were evaluated as described here.
Film-forming polymers used in sunscreens and color cosmetics provide water resistance and long wear properties. Traditionally, they are fossil-derived and non-biodegradable but there is growing interest in the industry to move toward natural, sustainable ingredients to reduce negative environmental impacts.1, 2 To meet this market need, a technology was developed to functionalize a natural organic oil and polymerize it without the use of catalysts or initiators.
More specifically, the technology enables the addition of hydrophobic or hydrophilic functionalities to natural oil, to influence the physical-chemical properties of its molecules and thereby change its performance characteristics. In this case, the aim was to create a hydrophobic film-forming polymer. To achieve such, naturally derived soybean oil was maleated as a first step, following which two naturally derived monomers – octyldodecanol and glycerin – were attached to the polymer.
The resulting ingredient is a polymer having the INCI name of: Maleated Soybean Oil Glyceryl/Octyldodecanol Estersa. In terms of naturality and sustainability, the polymer has a natural content of 82% according to ISO 16128-2:2017 and is inherently biodegradable following OECD 301F methodology. The starting soybean oil is certified organic and non-GMO, and the glycerin and octyldodecanol are both MB, RSPO-certified. The product is thus classified as a novel, nature-derived, non-GMO, vegan-suitable stable film former and SPF booster.
The natural polymer has demonstrated compatibility with organic and inorganic ingredients and offers color transfer resistance (not shown). In terms of performance, water resistance, SPF-boosting, pigment dispersion and film-forming properties were evaluated as described here.
Materials and Methods: SPF and Water Resistance
Test formulas: The maleated soybean oil glyceryl/octyldodecanol esters ingredient was formulated into several sunscreen emulsions. The first emulsion (see Formula 1, below) contained organic sunscreen actives while the second (see Formula 2, below) contained mineral UV filters. Control formulations without the natural polymer also were made for each emulsion.
Standard processes were used to prepare the emulsions, as follows.
- Emulsion 1: Phases A and B (see Formula 1, below) were heated separately. B was then added to A at 75-80°C with homogenization. After homogenizing for 10 min, the batch was neutralized with C and homogenized for an additional 5 min. The batch was then cooled while mixing on a sweep blade.
- Emulsion 2: Phases B and C were prepared (see Formula 2, below) by mixing vigorously with a homogenizer until completely dispersed. Phase A ingredients were placed in the main beaker and mixed with a paddle mixer. B was then added to A and with additional mixing. C was added to AB at RT under paddle mixing until uniform, then homogenized for an additional 10 min.
In-house stability protocol: The test formulas were screened in-house for stability over three months at 5°C, 25°C and 45°C with five freeze thaw cycles. Viscosity and pH measurements were recorded at 25°C every two weeks. The formulations’ stability was confirmed.
In vivo water resistance and SPF: The test formulas were assessed by a third-party lab that measures the SPF of over-the-counter (OTC) sunscreens according to FDA guidelines.3 Measurements were made for static SPF and SPF after 80 min immersion.
Dispersion, wetting and film formation tests: Pigments were wetted by adding the maleated soybean oil glyceryl/octyldodecanol esters polymer and mixing until uniform. Films were created by adding three drops of each formula between glass slides and pressing them by hand.
Results: In vivo SPF and Water Resistance
Emulsion 1: The static SPF and water resistance results for Emulsion 1 and its control are shown in Figure 1, below. The static SPF of the control formula was 35, whereas the test formula containing the natural polymer at 1% gave an SPF of 40. This suggests the polymer boosted the SPF of the formulation.
In comparing water resistance results for Emulsion 1, the control formula gave an SPF of 30 whereas the test formula gave an SPF of 38. This significant difference between SPFs after 80 min of immersion shows the natural polymer’s ability to boost SPF and improve water resistance.
Emulsion 2: An SPF boost was also demonstrated for the mineral-based Emulsion 2 (see Figure 2, below). In this case, the static SPF value for the test emulsion was 42 whereas the control only achieved an SPF of 30. This significant increase in SPF value can be attributed to the addition of the 2% maleated soybean oil glyceryl/octyldodecanol esters polymer. (Editor's note: Only SPF boosting was measured for Emulsion 2. Researchers note that as a w/si emulsion with mineral filters, it inherently has good water resistance.)
The higher SPF results for these two emulsions also demonstrated the natural polymer is compatible with both organic and inorganic UV filters. However, the extent of the natural polymer’s compatibility – or rather, synergy – became apparent upon closer examination of Emulsion 2.
Dispersion and Pigment Wetting Effects
The high SPF boost for the mineral formula suggested it was not only due to a polymeric film being formed, but also could be due to the interaction of the polymer with the inorganic sunscreens. To test this theory, several 50% titanium dioxide dispersions were made in a variety of esters, with and without 1% of the natural polymer, and the viscosities of the dispersions were measured. The results are presented in Figure 3, below.
Adding the new polymer to the dispersions reduced the viscosities significantly from 200,000 cps to negligible readings (almost zero). The ability to wet and disperse pigments in such a way is unusual. To capture this phenomenon visually, a picture was taken of the 50% titanium dioxide dispersion in isodecyl neopentanoate, with and without polymer (see Figure 4, below). Notably, the polymer was not very effective when dimethicone was used as the dispersing ester, since the polymer is not soluble in dimethicone.
Film-forming Performance
When the viscosity of a dispersion is lowered due to increased wetting, this allows for more efficient mixing and better dispersion, which in turn produces a more homogenous film. An example showing the film homogeneity from dispersed particles of titanium dioxide in castor oil is displayed in Figure 5, below.
In the present work, the industry benchmark, polyhydroxystearic acid, was compared with the maleated soybean oil glyceryl/octyldodecanol esters polymer using the formulas shown in Table 1, below. All dispersion blends with the natural polymer could be made at room temperature, whereas those with polyhydroxystearic acid had to be heated.
As noted above, a film for each dispersion was cast and assembled between two glass slides. The images in Figure 5, below, clearly show that the film made with the maleated soybean oil glyceryl/octyldodecanol esters polymer was smooth, with no cracks, whereas the film made with polyhydroxystearic acid had cracks around the edges.
Conclusions
The novel maleated soybean oil glyceryl/octyldodecanol esters polymer described here offers a solution to personal care manufacturers, enabling them to improve the naturality and sustainability of their formulations. As shown, the film former was successfully formulated without heating into stable emulsions containing both organic and inorganic sunscreens actives. Furthermore, in vivo, it demonstrated good water resistance and SPF-boosting capabilities.
The natural polymer also was used with various solvents to enhance the wetting of pigments and drastically reduced the viscosity of test dispersions. Finally, films cast from pigment dispersions containing the polymer were visibly more uniform. Taken together, the new natural polymer can enable the successful formulation of organic and inorganic sunscreen emulsions as well as color cosmetics that are more efficient and cost effective.
a Antaron Soja Glyceride is a product of Ashland.
References
1. Bom, S., Jorge, J., Ribeiro, H.M. and Marto, J. (2019). A step forward on sustainability in the cosmetics industry: A review. Journal of Cleaner Production, 225 270-290.
2. Ghazali, E., Soon, P.C., Mutum, D.S. and Nguyen, B. (2017) Health and cosmetics: Investigating consumers’ values for buying organic personal care products. Journal of Retailing and Consumer Services, 39 154-163.
3. U.S. Food and Drug Administration. (2011, Jun 17). Labeling and effectiveness testing: Sunscreen drug products for over-the-counter human use. Available at https://www.govinfo.gov/content/pkg/FR-2011-06-17/pdf/2011-14766.pdf
