Formulating sustainable hair oils: COSSMA

Consumers are increasingly looking for personal care products that allow them to feel their best while also making a positive impact on the planet. Cindy Delvallé and her co-authors show the benefits of silicone gum blends in hair care products.

Silicone gum blends have a proven track record of success in personal care applications thanks to their benefits such as hair conditioning, hair shine, heat protection, frizz control and sensorial attributes.

New gum blends were successfully designed from the same silicone gum historically used in blends to help maintain performance in application. In addition, they leverage a natural positioning with the use of alternative carriers, including bio-processed materials from renewable sources to meet the demands of eco-conscious consumers.

Each of the new gum blends uses a different carrier, specifically chosen to create a new sensorial experience and be complementary to one another. For example, the C13-15 Alkane is a bioderived, inherently primary biodegradable carrier obtained from a renewable source. Table 1 provides a summary of the corresponding key features.

table 1: New silicone gum blends overview. table: Dow

High performing blends

The use of the same dimethiconol gum as in the historical cyclopentasiloxane-based blend enables a similar level of dry combing performance. However, other performance aspects such as shine, sensory or heat protection, are impacted by carrier characteristics, making it vital to choose the appropriate blend (or combination of blends).

Figure 1 shows the dry combing performance achieved (as for all subsequent testing unless mentioned otherwise) on slightly bleached hair. Data was generated using a Diastron device and applying 0.1g/g of hair of a blend diluted to 9% gum active.

Shine is typically impacted by carrier refractive index and volatility. With relatively high refractive index, these carriers have the potential to provide shine. As figure 2 shows, blends based on carriers with low volatility provided the highest level of shine. Data was generated using the previous preparation protocol and shine was measured with a Bossa Nova device.

Carrier nature and volatility also impact sensory performance. The carrier volatility range in the new set of blends allows an array of sensory properties on hair or skin from the final formulations. For example, the 2cSt dimethicone-based blend was shown to deliver the same sensory profile as the cyclopentasiloxane-based equivalent.

figure 2: Shine performance of new gum blends (statistical comparison to the cyclopentasiloxane-based blend). figures: Dow

Heat protection continues to be a demand from consumers and is one of the benefits demonstrated with all new gum blends, to various degrees of intensity depending on the carrier nature. Figure 3 shows the corresponding details in systems obtained by diluting each blend in cyclopentasiloxane down to a 4% gum active level. The hair was treated with the blends then heat-damaged in an oven heated at 230°C following a standard procedure and finally repeatedly combed. The amount of resulting broken hair was used as a predictor for heat protection performance.

Overall, the gum blends provide flexibility on multiple formulation and application benefits criteria, including volatility, manufacturing process, and sustainability profile. Altogether, they offer a carrier toolbox approach built around the same dimethiconol gum. Combining these blends offers more options to formulators, allowing them to fine-tune accordingly to obtain specific sets of desired formulation properties and benefits.

figure 3: Heat protection performance. figures: Dow

Formulating with gum blends

Like cyclic-based silicone gum blends, this new generation of  products can also be used to formulate hair oils. For example, a formula can use the 2cSt dimethicone-based blend, further diluted in a combination of two volatile linear siloxanes with respective viscosities of 1.5cSt and 2cSt. Additionally, a hair oil can contain an antioxidant, a colorant, natural oils such as sweet almond oil for benefits like hair strengthening and repair, and moringa oil to provide shine and protection against hair breakage.

In hair oils, gum blends are typically used to provide the required viscosity-building properties. However, in many cases, when replacing cyclic-containing silicone gum blends with low cyclic versions, a decrease in viscosity can be observed in final formulations, especially in hair oils. This phenomenon can already be observed at the product viscosity stage, i.e., prior to formulating as previously shown in table 1.

Figure 4 exemplifies this further through the study of gum blend dilutions systems used as simplified representations of hair oils. The viscosity of silicone gum blends diluted down to an 11.1% gum active level in their own carrier has been measured with Brookfield DVII T (spindle 4, 100rpm) at 20°C.

Two hypotheses are currently considered to explain this:

1. The lower density of carriers translates into a much higher volume fraction in the blend. This would lead to thinner final viscosities when formulated into hair oils compared to the cyclic-containing gum blend.

2. The PDMS chain/carrier interaction is different due to differences in compatibility. This would lead to a lower chain extension in the new blends, resulting in lower viscosity.

figure 4: Impact of the use of low cyclic silicone gum blends on final hair oil viscosity. figures: Dow

To overcome this and maintain hair oils aesthetics, the hydroxy-terminated polydimethylsiloxane with an 80,000 cSt viscosity (INCI: dimethiconol) can be leveraged. Adding 10% of this thickening aid to a silicone gum blend-based anhydrous system has been shown to increase viscosity by roughly 290%, thus allowing to reach the same viscosity range as what would be obtained with a cyclic- containing silicone gum blend.

Figure 5 comparatively discloses the viscosities of ternary systems  composed of a gum blend with  11.1% silicone gum active, a thickening aid, and a solvent1. Viscosity was measured with Brookfield DVII T (spindle 4, 100rpm) at 20°C.

Depending on the silicone gum blend and oil nature (anhydrous system composition) it is recommended to use between 5% and 20% of this hydroxy-terminated polydimethylsiloxane. Beyond its thickening efficiency, it also maintains hair  oil transparency while keeping the hair looking conditioned yet natural with sensorial benefits. This new thickening aid can be used globally as it is listed in the China Catalogue of Cosmetic Ingredients. Its fluid nature and compatibility with either cold or hot processes make it easy to handle and provide flexible solutions to formulators.

figure 5: Thickening effect of the OH-PDMS medium viscosity. figures: Dow

Conclusion

Silicone gum blends have been used for decades in hair care to provide versatile benefits, like enhanced hair conditioning and sensorial attributes. New options are now available to formulators, allowing them to continue creating unique leave-on hair and skin care products with features such as enhanced shine and smoothness, easier wet and dry combing, frizz control, or heat protection.

To follow regulatory guidance, they can be formulated globally with the INCI names listed in the China Catalogue of Cosmetic Ingredients. Built around the same performance-proven silicone gum, these silicone gum blends offer a product toolbox approach, enabling formulators to combine them and optimise final formulation properties whether it be for cosmetic performance, formulation, or manufacturing process.