Smooth closer: The latest in silicones and silicone alternatives

Arguably silicones and silicone derivatives are the most useful and versatile of all existing groups of cosmetic ingredients. They range in viscosity from volatile liquids to solid pastes and are used as emollients that provide unique sensorial properties, hair conditioning agents, emulsifiers and for the surface treatment of pigments.

Unfortunately, for a variety of reasons, there is now a movement away from silicone materials and alternatives are being developed by many ingredient suppliers.

This feature will look at those silicones that still play a major part in cosmetic formulations and at alternatives to those that are falling out of favour.

Silicone lowdown

The cyclosiloxanes commonly known as cyclotetrasiloxane (D4) and cyclopentasiloxane (D5) are used for their anti-static, emollient, humectant, solvent, viscosity-controlling and hair conditioning properties in cosmetic products.

However, concerns have been raised about their toxicity and effects on the environment, and now it is recognised that cyclotetrasiloxane (D4) is toxic to human reproduction systems.

It also accumulates in the environment with unpredictable long term effects.

Cyclopentasiloxane (D5) can also be harmful to the environment and in January 2018 the EU commission published an update amending Annex XVII to Regulation (EC) No 1907/2006 of REACH.

After 31 January 2020, the concentration of D4/D5 in cosmetic products placed on the market that are rinsed off after application should be less than 0.1% by weight of either substance. This has now been amended to include cyclohexasiloxane (D6) and it is expected that this restriction will be extended to include leave-on products.

Because of these restrictions most silicone alternatives have been designed to replace D4/D5. It is not necessary to exclude silicone products and Innospec suggests that Volasil 8100 (INCI: Dimethicone, trisiloxane) provides the right combination of volatility, lubricity and spreadability to impart a dry, smooth application to hair and skin products.

It has a similar volatility to D4, and is recommended for antiperspirants and hair sprays requiring a fast drying time. Volasil DM-1.5 is a dimethicone that is slightly more volatile than D5; it imparts a dry, smooth application to hair and skin products.

Dimethisil DM-5 and Dimethisil DM-6 from Innospec are suggested as replacements for D6 in hair and skin products, and as a solvent for active ingredients, as well as a diluent for silicone gums and elastomers.

These and other possibilities were described at length in the presentation ‘Cyclic-free formulating’ given at in-cosmetics Global 2019 by Tony Gough. BRB claims that its BRB DM 55 is a low viscosity dimethicone with a similar sensory profile to D5 and may be used as a direct replacement.

Due to its similar sensory profile, BRB DM 66 can be used as a direct alternative to D5 or D6. A&E Connock offers low viscosity dimethicones of 5, 10, 20 and 50cs, and a mixture of C13-C14 isoparaffin with low viscosity dimethicone that can be considered as replacements for cyclomethicones.

Smooth closer: The latest in silicones and silicone alternatives

In response to increasing consumer interest in silicone-free products and tighter regulatory restrictions on silicones, Inolex has published a guide to silicone alternatives[1].

It identifies the principal properties of the silicones used in each product category and suggests suitable replacements from its extensive portfolio of cosmetic ingredients.

Cyclomethicones are principally used because of their volatility and fast spreading properties, and Inolex suggests suitable substitutes are LexFeel WOW (INCI: Triheptanoin, C13-C16 isoparaffin); LexFeel WOW DT (INCI: C13-C16 isoparaffin, heptyl undecylenate); LexFeel D4 (INCI: Neopentyl glycol diheptanoate, isododecane); and LexFeel D5 (INCI: Neopentyl glycol diheptanoate, isododecane).

Emollient function

A prime function of silicones in cosmetics is as emollients. They provide a protective layer to the skin and keep it moisturised. They solubilise lipophilic active ingredients and crystalline UV filters and disperse pigments.

Emollients play an important role in determining the right skin feel of a cosmetic product and each emollient has its own skin sensory behaviour enabling it to deliver a unique skin feel[2].

From BASF we have Cetiol C5 (INCI: Coco caprylate), which has a similar skin feel to cyclomethicone, supports the incorporation of powders, enhances the solubility of crystalline UV filters and promotes oil deposition from body wash to skin.

Cetiol CC (INCI: Dicapryl carbonate) is described as a multifunctional dry emollient with good pH stability and perfume and propellant solubility, making it suitable for antiperspirant and deodorant applications.

Cetiol Ultimate (INCI: Undecane, tridecane) from BASF is described as an ultra-light, non-polar and volatile hydrocarbon alternative to cyclomethicone with a positive effect on the performance and stability of sun care formulations when compared with cyclomethicone.

Seppic markets a range of alkanes as replacements for volatile silicone oils under its Emosmart and Emogreen trade names, which were described at in-cosmetics Global 2019[3].

They are readily biodegradable, inert and non-polar, and are not sensitive to oxidation, pH change or oxidising and reducing media. As texturising agents, they have different sensory effects depending on the grades: Emosmart L15 presents a fresh sensory and a ‘nude skin’ after-feel; Emosmart C28 provides a comfortable and nourishing finish; and Emogreen is characterised by its longer playtime associated with a powdery after-feel.

A prime function of silicones in cosmetics is as emollients; they provide a protective layer to the skin and keep it moisturised

A presentation by Croda[4] suggests alternatives to silicones across a wide spectrum of uses. Crodamol STS (INCI: PPG-3 benzyl ether myristate) is a readily biodegradable emollient.

Its molecular structure is responsible for its perceived benefits with alkoxylation improving dispersibility; methyl branching promoting fluidity; ether linkages increasing polarity and improving compatibility with pigments; and the benzyl moiety confering better compatibility with sunscreens, sterols and fragrances.

BergaCare FG Olive from Berg + Schmidt is a blend of hydrogenated ethylhexyl olivate and hydrogenated olive oil unsaponifiables offered as a new silicone alternative based on 100% olive as a source. It is said to mimic the sensory of cyclopentasiloxane, and can be used as an emollient in skin and hair care formulations.

It is compatible with all the usual cosmetic ingredients and is an ideal silicone-free emollient without compromise on texture.

Silicone derivatives are frequently used in cosmetic formulations to achieve appealing textures and a lightweight skin feel. With the growing demand for more natural and sustainable cosmetics, alternative solutions should provide a silicone-like texture with less environmental impact.

Symrise claims to have met these requirements with SymMollient PDCC (INCI: Propanediol dicaprylate/caprate) and SymMollient S green (INCI: Cetearyl nonanoate). In combination they can mimic the sensory profile of complex silicone derivatives.

Symrise tested this concept by sensory assessments conducted by a trained expert panel on formulations where different silicone derivatives were replaced by a combination of SymMollient S green and SymMollient PDCC without a significant difference in sensory profiles.

Getting glossy

Silicones and their derivatives are much used in hair care for their conditioning properties, colour protection and to impart gloss and shine. Biosil Basics Amino DL-30 from Biosil Technologies is a complex of dimethiconol with panthenol that is claimed to spread evenly on the hair, forming a smooth film on the surface of the cuticle.

It provides slip and detangling properties, aids in moisture retention and enhances hair volume. It is also shown to provide significant colour protection benefits in shampoo systems.

BioPlex Cetylsil S-PF combines the quaternary conditioning properties of cetrimonium chloride with a carboxylated silicone, cetyl triethylmonium dimethicone PEG-8 succinate. It can be added to hair care formulations to provide thermal protection, improve wet combability, and enhance manageability and conditioning.

It can also be used in skin care to provide the silky feel of cationics without increasing the irritation potential.

BioPlex Cetylsil Olive CE from Biosil is a substantive complex based on cetrimonium chloride with a water-soluble silicone (INCI: Cetrimonium dimethicone PEG-8 olivate/succinate), which provides hair care benefits for leave-in type formulations such as a conditioner, mousse, hairspray and pomade.

It is compatible with surfactant systems and is excellent for 2-in-1 shampoos and conditioning body washes. BRB 5446 is a clear, non-ionic microemulsion of a quaternary ammonium functional silicone (INCI: Silicone quaternium-17, trideceth-7, trideceth-5).

It may be added to hair shampoos, conditioners and hair styling products to provide wet and dry detangling, softness and healthy-looking hair. It enhances hair strength and elasticity, and gives heat protection by reducing moisture loss during thermal treatments.

ClariSilk from Inolex is polyester-37 that reduces static charge, improves combing and detangling effects and adds shine to hair when added to silicone-free conditioning shampoos. Crodamol SFX from Croda is PPG-3 benzyl ether ethylhexanoate, which adds lubricity and conditioning to hair.

Decorative cosmetics owe much to the versatility of silicones; they are used in the surface treatments of powders, pigments and particulate UV filters

Olive oil is the source of the squalane, which is combined with hydrogenated castor oil and hydrogenated olive oil to give Sollivia-FX by Sollice Biotech. It is described as a high-performance texturiser with emollient properties, and is recommended for use in anti-frizz hair care products and skin hydration formulations as a silicone and mineral oil replacement.

Lipex Shealight from AAK comprises shea butter ethyl esters as an eco-designed shea butter ester with excellent spreadability and a non-greasy feel. AAK suggests its use in hair care formulations to maintain volume and deliver a silky soft feel with improved shine and hydration.

When incorporated in serums it offers protection against environmental stress and improved control over split ends and frizzy hair. In skin care formulations it gives a light skin feel and a good sustainability profile.

It also has pigment wetting properties making it a suitable ingredient for sun care and make-up.

Make-up compatible

Decorative cosmetics owe much to the versatility of silicones. They are used in the surface treatments of powders, pigments and particulate UV filters.

ShinEtsu recently introduced a new series of silicone/alkyl surface-treated pigments that feature high hydrophobicity and dispersing performance in a wide range of oils to improve the quality of colour cosmetics. Various colours are available with the prefix KTP and they share the common INCI listing of iron oxides and triethoxysilylethyl polydimethylsiloxyethyl hexyl dimethicone.

KSG-016F (INCI: Dimethicone, dimethicone/vinyl dimethicone crosspolymer) from ShinEtsu is a non-emulsifying silicone gel containing 20-30% particles of a crosslinked silicone with a three-dimensional network structure in dimethicone with a refractive index of 1.398. KSG-016F combines a soft-focus effect with a very dry, non-oily feel due to the rolling effect of particles within the gel.

Silicones are used to provide transfer resistance to make-up and lipsticks. BRB TMS 501 is a solution of trimethylsiloxysilicate in isododecane that is compatible with most silicones, esters, hydrocarbons and organic sunscreens and pigments.

Due to the high volatility of isododecane, it quickly evaporates, leaving behind a non-tacky and water insoluble highly durable film of trimethylsiloxysilicate, providing wash-off and rub-off resistance.

Inolex suggests its cyclomethicone replacements are suitable for dispersing pigments, and for providing long wear and transfer resistance. Its alternatives to silicone elastomers used in pigmented products are Lexorez 100 (INCI: Adipic acid/diglycol crosspolymer), Lexorez 200 (INCI: Trimethylpentanediol/adipic acid/glycerin crosspolymer) and LexFeel Vibrant (INCI: Palm acid/adipic acid/pentaerythritol crosspolymer).

Finally, one objection to silicones is the high use of energy in their manufacturing processes. Belsil is now producing dimethicones of various viscosities using methanol obtained from biomass instead of fossil fuels.

References

1. Silicone Alternatives Guide by Inolex.
2. https://www.carecreations.basf.com/concepts-trends/concepts/silicone-alternatives/.
3. https://www.seppic.com/what-if-you-could-replace-silicones.
4. Alternatives to Silicones, a Tool Box. published by Croda.