Hair serums and oils are a key part of many consumers hair care routines and are relied upon for their glossing, anti-frizz, and heat protection performance. Having the appearance of clear oils such products have historically relied upon the use of volatile silicones such as Cyclopentasiloxane (D5). The use of Harmonie™ Soft fluid (C9-12 Alkane) and Harmonie™ GB-2301 blend (C9-12 Alkane and Dimethiconol) from Momentive Performance Materials brings to the market a new solution for reformulation of these popular products. Equivalent performance with a higher naturality index as defined by ISO 16128 can be achieved; allowing manufacturers to manage upcoming regulatory changes in Europe whilst maintaining consumer acceptance.

‍The hair care market

Hair care is a complex market, which varies from region to region and country to country depending upon hair types, hair treatment, environmental conditions, social standards,and fashion. However, dig under the surface and you will find that most market products are built upon a common chassis with a limited number of ingredients used routinely. Many formulations become commonplace because they work well and are cost efficient. Take hair serums and oils as an example, these are often based upon a combination of volatile Cyclopentasiloxane (D5) and a high molecular weight Dimethicone or Dimethiconol gum. These are fairly simple systems which perform well and have been staples of popular hair care brands for many years.

A changing market environment

It would take a major change in the market environment to drive a reformulation of such popular products, and this is what we see in Europe today. Restrictions on the use of volatile cyclic silicones have come into force in Europe over the last few years, first within wash off products for Cyclotetrasiloxane (D4) and Cyclopentasiloxane (D5) and now these will be extended. Following the publication of Annex XVII to the REACH regulation the level of D4, D5 and Cyclohexasilxone (D6) in consumer products will be restricted to a maximum of 1000ppm with compliance required for all cosmetic products by 6^thJune 2027.⁽¹⁾

These restrictions are specific to Europe. Countries such as Canada and Australia have not found reason to restrict the use of D4, D5 and D6 in cosmetic products.⁽²⁾ Cyclopentasiloxane based hair serums can continue to be sold in a wide range of other territories and suppliers of silicones world wide dispute the need for the EU restrictions.⁽³⁾

In addition to regulatory changes, we also see a change in consumer attitudes. Interest in the product’s composition has never been greater and concerns about sustainability are at a high. Today’s beauty consumers are described as “more informed, engaged and connected than ever before”⁽⁴⁾ Euromonitor International’s 2022 Voice of the Consumer: Beauty Survey, reported that 12.3%of US respondents were looking for “ingredient transparency” when they shop for hair care products, up from 11.1% in 2021.⁽⁵⁾

Hair serums sit within the treatment and masks category of hair care but could also be considered as hair styling products due to their multiple performance attributes. A survey of European retailer websites shows the breadth of claims associated with hair serums and oil across all aspects of conditioning and protection.

Different hair types

Hair can be classified into 4 different hair types, which each contain 3 subtypes, in a system developed by Andre Walker in the 1990s^(6).  The classification details hair types from very straight to tightly coiled and was originally designed to help market Walker’s line of hair care products.  

Hair serums and oils are well suited to thicker, coarser hair types, however anyone can and may want to use them for various reasons. When they first appeared on the market, the primary function was to tame frizz, however, the benefits of serums have expanded into many other areas such as protection from heat and enhancing shine. Hair serums must be carefully formulated for different hair types, as a serum for type 1 or 2 hair will not be suitable for type 3 or 4 and vice versa. The formulation must be adapted to suit the hair type, this could be by choosing a higher molecular weight silicone gum, a higher gum concentration,or by changing the carrier oil. Using a non-volatile carrier for instance offers heavier conditioning and is therefore suited to thicker hair types. Silicone gum blends are available based upon a natural C13-15 Alkane, also known as C13-16 Isoparaffin, as one potential solution for this.

Type 3 and 4 hair are prone to breakage due to the twists and turns along the varying diameter of the elliptical fibres. Hair serums are ideal treatments for textured hair, as they offer protection and moisturization to this very fragile hair type. Applying a serum to wet hair will aid in reducing tangles and ease of combing, which must be very carefully executed to avoid propagating further fibre breakage.⁽⁷⁾

Heat protection

One of the primary reasons to use a hair serum is heat protection. By their nature, silicones provide excellent heat resistance due to their low thermal conductivity.  A serum containing a silicone gum blend will not only offer protection from heat damage, allowing the hair to feel much smoother and softer, it will also help straightening irons to glide over the hair more easily.⁽⁸⁾

Formulating a hair serum

Traditionally hair serums are comprised of high molecular weight Dimethicone or Dimethiconol gum diluted in a volatile cyclic silicone oil such as Cyclopentasiloxane. The term silicone gum simply describes a Polydimethylsiloxane with a molecular weight and viscosity so high that it is too thick to pour. Dimethicone has a terminal methyl group which is replaced by a hydroxyl group in Dimethiconol, both gum types may be used in hair serums. The volatile carrier enables spreading of the highly viscous gum along the hair shaft, followed by evaporation of the diluent leaving the silicone gum behind to give long lasting performance.

Many silicone gum blends are commercially available, usually containing between 10 and 20 percent silicone gum in a carrier oil. Newer versions are available based upon low molecular weight volatile linear silicones in the form of Disiloxane, Trisiloxane and Dimethicone, naturally derived alkanes such as C9-12Alkane or C13-15 Alkane; or Isododecane.

To create the final formulation the gum blend is diluted with volatile cyclic silicone to reach either the desired gum content or a target formulation viscosity. The Dimethicone or Dimethiconol gum also performs the secondary function of viscosity modifier for the serum or oil, with  viscosity being  a key attribute driving the consumer experience. The final formulations may contain additional natural oils, frequently Argan oil, oil soluble vitamins or extracts in addition to fragrance to support marketing claims and product positioning.

A new solution for hair serums

A wide range of oils and emollients have been used in personal care for decades. From unmodified natural oils to esters, ethers, and more recently naturally derived alkanes, a range of chemistries have been used to provide different physical characteristics from melting point and viscosity, to refractive index or polarity.

A significant challenge for the industry has been replicating the properties of volatile solvents from naturally derived feedstocks. Cyclomethicone has unique attributes which enable the formulation of hair serums that are light enough to leave on the hair.

An optimised composition of C9-12 Alkane comprising both straight and branch chained alkanes that is 70% naturally derived (according to ISO 16128) has been found to be a potential solution. The specific ratio of branched to straight chain alkanes has been designed to provide the optimum alternative to volatile silicones such as Cyclopentasiloxane. The optimized blend of C9-12 Alkane also functions as an ideal solvent and carrier for high molecular weight silicone gum.

‍Proof of principle

Initial trials were conducted to check the use of C9-12 Alkane and Dimethiconol on hair swatches in leave on applications. Experimental formulations were created by combining C9-12 Alkane or Cyclopentasiloxane with high molecular weight Dimethiconol gum to both a specific formula viscosity and a specific active Dimethiconol level. This combination should be considered experimental only as the maximum use level of C9-12 Alkane in a market formulation is 60 percent.  

Swatches of virgin European frizzy hair were prepared by pre-washing with a non-conditioning shampoo (1.3 mL per tress), massaging for 30seconds and then rinsing for 30 seconds with 37°C tap water. The hair swatch was then combed 10 times on each side and dried overnight at 23°C and 65% relative humidity. To evaluate the hair serum, 0.1mL serum was applied to the hair tress and massaged into the hair for 2 minutes. The hair tress was combed 10 times on each side and assessed. The sensory parameters were evaluated by 5 panellists who evaluated the feel and appearance of tresses during application and after treatment.

Key performance parameters assessed during application of the serum to the hair swatch included ease of spreading, slip and smoothness,absorption into the hair and greasiness. After application important parameters included ease of combing, detangling, smoothness, and shine.

The tests systems based on C9-12 Alkane and Cyclopentasiloxane were found to be a close match on all parameters both during and after application, demonstrating that C9-12 Alkane is an ideal replacement for Cyclopentasiloxane in hair serums and oils.

Additional performance tests were carried out to further confirm the key performance attributes for hair serums and oils, that of gloss and frizz reduction. Hair serums must primarily smooth flyaway and de-frizz the hair, reducing the overall volume and providing a more uniform appearance; this can be evaluated by image analysis. In these trials the formulations were  matched by viscosity to approximately 500cPs.

0.2 ml of hair serum was applied to tresses of pre-washed virgin European frizzy hair with a gloved hand until no more product was transferred. Hair tresses were photographed before and immediately after application and then stored at 90% relative humidity for 24 hours. The swatches were photographed at regular intervals for 24 hours.

C9-12 Alkane and Dimethiconol was found to act as an effective anti-frizz agent with a visible effect being maintained for 24 hours at high humidity. Performance was comparable to the Cyclopentasiloxane based formulation of the same viscosity.

Shine enhancement is another attribute expected from these types of products and can also be measured using image analysis. Hair was placed on mounts and 0.5ml of ethanol applied to the centre of the virgin hair tress to facilitate spreading. 0.5ml of the test product was applied to the hair tress and spread with a clean finger cot. The tresses were photographed at T=0 and then after 30 mins, 3 hours and 24 hours.

As the images show, it is possible to generate a high level of shine from application of a hair serum based upon C9-12 Alkane and Dimethiconol comparable to Cyclopentasiloxane and Dimethiconol.

‍Formulation examples

C9-12 Alkane is recommended for use in cosmetic formulations up to a concentration of 60%. For this reason, example formulations were developed incorporating additional naturally derived oils, including esters and naturally derived alkanes. Performance evaluations were then completed.

In the anhydrous formulation Sleek and Shine Hair Serum (HC-003-23-SA-BNG) the C9-12 Alkane, Dimethiconol blend and C9-12 Alkane have been combined with C13-15 Alkane and Coco-Caprylate/ Caprate. A blend of natural oils has been added to support additional marketing claims and the overall formulation has a natural origin index of>70%. (ISO 16128)

A sensory panel rated the performance to be equal to that of a Cyclopentasiloxane and Dimethiconol based formula across all attributes including frizz control, softness, ease of combing, manageability, and overall likeability. This formulation can be used on wet or dry hair with only small quantities required to achieve a perceivable effect.

It was also found possible to use a C9-12 Alkane based hair oil as a pre-shampoo conditioning formulation,as demonstrated by Rescue and Repair Nourishing Hair Oil (HC-005-23-AK-BG).  The formulation was compared the same system with a Cyclopentasiloxane and Dimethiconol gum blend.

Rescue and Repair Nourishing Hair Oil was applied to pre-washed virgin Asian hair. 0.5ml was applied to each hair swatch and massaged into the hair for 30 seconds. The hair swatch was evaluated for sensory parameters including ease of combing,smoothness, softness, greasiness, and frizz reduction.  The swatch was then washed with a 15% SLES solution and dried overnight before reassessing.

As a pre-shampoo conditioning treatment, Rescue and Repair Nourishing Hair Oil was found to be beneficial across all parameters tested including ease of combing, smoothness, silky feel, and manageability.

Conclusion

Cosmetic products are dependent upon specific chemistries. When those chemistry types are no longer available or are no longer preferred, it can be difficult to achieve a product with the desired consumer characteristics. The use of Harmonie Soft fluid (C9-12 Alkane) and Harmonie GB-2301 blend (C9-12 Alkane and Dimethiconol) provides formulators of hair serums and oils with a solution to meet consumer needs, in particular those with dry, frizzy hair or those requiring shine or heat protection.

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Authors: Andrea Tomlinson; Roxanne Smith

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References

1)      ECHA - European Chemicals Agency. Restrictions on the manufacture, placing on the market and use of certain dangerous substances, mixtures and articles. Available at https://www.echa.europa.eu/documents/10162/0ac1f453-ad41-4010-e837-a68273b896ca

2)      CHTGermany Gmbh, Legal Conditions, D4,D5,D6 Siloxanes, (cited 31/10/2023)available at

cht-silicones.com/news/LegalConditions D4, D5 & D6 Siloxanes

3)    Global Silicones Council, Environment, (cited31/10/2023) available at Environment -Global Silicones Council

4)    KWolfe, 3 Ways to Empower and Engage with Today’s Informed + Connected BeautyConsumer, 04/04/2019, (cited 31/10/2023) available at 3Ways to Empower and Engage with Today’s Informed + Connected Beauty Consumer |Global Cosmetic Industry (gcimagazine.com)

5)    Euromonitor, Haircare in the US CountryReport, Euromonitor, May 2023

6)    99percentInvisible, The Hair Chart, 17/04/18, (cited 31/10/23) available at The Hair Chart - 99% Invisible (99percentinvisible.org)

7)    Camacho-Bragado, G. A., Balooch, G.,Dixon-Parks, F., Porter, C., and Bryant, H. (2015). Understanding breakage incurly hair. Brit J Dermatol 173 suppl 2 10-16.

8)    S Marchioretto et al, Heat Protection Getting Warmer,Cosmetics and Toiletries, 10/06/2016, available at Heat ProtectionGetting Warmer: Specialty Silicones for Hair | Cosmetics & Toiletries(cosmeticsandtoiletries.com)

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