Natural or sustainable products are a staple of the personal care market. As consumers exhibit a strong desire for “greener” personal care products, it is a challenge for the formulator to create systems that meet their desire for increased sustainability as well as their demand for high performance. The growing demand for greener goods has led to advancements in the development of biopolymers for personal care that provide a more natural and sustainable alternative to synthetic polymeric rheology control agents. Nonionic derivatives of cellulose, notably hydroxyethyl cellulose (HEC), have long been used as thickeners and rheology modifiers in personal care products. Modification of cellulose has enabled the development of a class of cellulose derivatives for personal care that provide new and unique benefits to a variety of personal care formulations.
A new family of water-soluble cellulose derivatives developed by AkzoNobel Global Personal Care provides more sustainable rheology control as well as improved efficiency in formulation. These ingredients also serve to modify the aesthetics of personal care formulations, delivering beneficial properties and enabling the formulation of differentiated consumer products. They are suitable for personal care products including shampoos, conditioners, styling products, personal cleansers and skin care products. AkzoNobel Global Personal Care promotes these derivatives under the Structure Cel trade name.
The new family includes ethyl hydroxy- ethyl cellulose (EHEC), methyl hydroxy-ethyl cellulose (MEHEC) and hydropho- bically modified ethyl hydroxyethyl cellulose (HM-EHEC). These naturally based polymers, derived from sources including wood and cotton linter, are not only effective thickeners and rheology modifiers but also display high surface activity in comparison to HEC, leading to additional benefits in formulation.
EHEC, MEHEC and HM-EHEC are readily dissolvable powders that exhibit stronger surface active properties than conventional HEC. Figure 1 shows the surface tension of different cellulosic derivatives in aqueous systems. Low surface tension allows stronger interaction with surfactants in shampoos and personal wash formulations that will result in enhanced foam and cleansing performance.
Variables and Mechanism
The key structural variables of these ingredients include molecular weight of the polymer, degree of ethoxylation, degree of alkylation and alkyl group size. Chain entanglement is the main thickening mechanism of EHEC and MEHEC. The viscosity of EHEC or MEHEC solutions depends principally on the chain length of the polymer molecules, degree of polymerization and the molecular weight. The thickening mechanism of HM-EHEC contains contributions from both chain entanglements and hydrophobic interactions. In an aqueous solution, the hydrophobic groups of HM-EHEC along the water-soluble EHEC backbone attempt to minimize contact with water and associate to each other. The association of the hydrophobic groups is very similar to self-association of surfactants into micelles. The surface of the micelle is covered by the hydrophilic EHEC backbone.
Rheological properties are of great importance in personal care formulations such as shampoos, conditioners and hair gels where flow behavior is a critical performance factor. Because EHEC, MEHEC and HM-EHEC solutions are non-Newtonian, there is a non-linear correlation between the viscosity and the mechanical stress applied to the liquid. Similar to most polymers in a solution, the viscosity relates to the shear rate in a shear-thinning way. Rheology profile measurements performed using cone and plate on a Rheometric Scientific rheometer have demonstrated that EHEC, MEHEC and HM-EHEC in solution offer a wider range of viscosity-building capabilities and shear thinning rheology than HEC, as illustrated in Figure 2.
Since EHEC, MEHEC and HM-EHEC are nonionic polymers, they have considerable tolerance to salts—as much as 6% salt in aqueous systems. This benefit can be utilized in a variety of personal care applications. They also show efficient thickening capabilities over a broad pH range.
In shampoos and cleansers, EHEC and MEHEC increase viscosity, modify rheology and enhance foam creaminess and richness. These benefits can be seen even when using low surfactant levels (5-6% active) to create mild systems with improved economics. Thickening and stabilizing sulfate-free systems is typically a significant challenge for the formulating chemist. As shown in Figure 3a, MEHEC provides superior capabilities for building viscosity and improving the rheology profile of a simple sulfate-free system that is based on sodium C14-16 alpha olefin sulfonate/cocamidopropyl betaine, compared with a similar system thickened with sodium chloride. As shown in Figure 3b, MEHEC is a more efficient thickener for a sulfate-free shampoo system than HEC.EHEC and MEHEC provide additional improvements in aesthetics and foam quality, yielding creamy, rich and more luxurious foam compared with sulfate-free systems thickened with salt or other polymeric thickeners.
EHEC and MEHEC also exhibit a great positive impact on the foam characteristics of shampoo formulations by increasing the elasticity of the foam membrane and preventing drainage. This is attributed to their interaction with the surfactants typically used in such formulations. As shown in the performance graph in Figure 4 and depicted in the photos of Figure 5, MEHEC provides dramatic enhancement of foam stability and creaminess compared with systems thickened with salt or HEC, even when used at lower levels. Foam evaluation was performed on a 1% MEHEC solution using a Waring blender for 30 seconds, which was then poured into a graduated cylinder. Liquid drainage time was the time taken to drain half of the solution. In conditioner formulations, EHEC, MEHEC and HM-EHEC exhibit shear-thinning rheology. Figure 6 displays the efficiency of the EHEC as a rheology modifier compared to HEC. EHEC and MEHEC can be used at lower levels to provide equal or better attributes on hair when compared to a traditional conditioner system thickened with HEC. As shown in Figure 7, the conditioner system formulated with EHEC demonstrates improved wet combing, wet feel, and dry combing properties while providing the formulator with improved economics as a result of the lower polymer use level.
The nonionic nature of these products allows for excellent compatibility with a wide range of raw materials and it has been identified to be useful in a variety of other personal care applications other than rinse-off systems. A small percentage of EHEC or MEHEC to a traditional styling mousse formulation creates rich, luxurious foams and enhances the texturizing properties, allowing for products that provide lasting height and volume. In skin care applications, EHEC, MEHEC and HM-EHEC provide thickening and texture to formulations and leave the user with smooth application, excellent rub-in properties, reduced tack and a conditioned after-feel.
EHEC, MEHEC and HM-EHEC are naturally derived multifunctional polymers with unique properties, including high surface activity, wide molecular weight range and various degrees of ethoxylation and alkylation, and alkyl group size. They offer efficient thickening, enhanced performance and unique sensory benefits in a wide range of personal care product types. These new ingredients can be easily formulated into a wide variety of products such as:
• Traditional (sulfate containing) shampoos;
• Sulfate-free shampoos;
• Hair conditioners and treatments;
• Skin care emulsions;
• Body washes, shower gels and facial cleansers; and
• Hair mousses, styling crèmes and lotions.
The use of EHEC, MEHEC and HM-EHEC allows formulators to improve thickening efficacy, enhance performance and aesthetics, and meet the growing consumer demand for personal care products containing more naturally derived and sustainable ingredients.
Sulfate Free Shampoo(2346-70H.1)
Ingredients: % Wt.
Deionized water (aqua) 83.00
Witconate AOS (39% active) 7.50
(Sodium C14-16 olefin sulfonate)
Crodateric CAB 30 (30% active) 7.50
(Croda) (Cocamidopropyl betaine)
Structure Cel 8000 M 1.50
Glydant Plus liquid (Lonza) 0.50
[DMDM hydantoin (and)
Charge water, Witconate AOS and Crodateric CAB 30 into an appropriately sized vessel and begin mixing, using an overhead mixer, making sure to pull a vortex. Slowly sift Structure Cel 8000 M into the side of the vortex and begin heating to 40ºC. Mix until fully hydrated, then cool to room temperature and add remaining ingredients.
Simply Sensible Shampoo(2346-68K.A)
Ingredients: % Wt.
Deionized water (Aqua) 78.50
Standapol ES-2 (25% active) 15.00
(Cognis, Care Chemicals)
(Sodium laureth sulfate)
Crodateric CAB 30 5.00
(30% active) (Croda)
Structure Cel 8000 M 1.00
Glydant Plus liquid (Lonza) 0.50
[DMDM hydantoin (and)
Charge water, Standapol ES-2 and Crodateric CAB 30 into an appropriately sized vessel. Mix using an overhead mixer, making sure to pull a vortex. Slowly sift Structure Cel 8000 M into the side of the vortex, heat to 45ºC and mix until fully hydrated. Cool to room temperature. Add Glydant Plus. Adjust pH if necessary to 6.0-7.0.
Silky Creamy Conditioner(2346-71A.1)
Crodacol C95-NF (Croda) 1.50
Crodacol CS-50 (Croda) 1.50
Incroquat Behenyl TMC-85 1.27
chloride (and) isopropyl alcohol)
Deionized water 90.54
Structure Cel 4400 E 1.00
Arquad PC 16-29 (29% active) 3.45
Dissolvine NA2-P chelate 0.25
(AkzoNobel GPC) (Disodium
Glydant Plus liquid (Lonza) 0.50
(DMDM hydantoin (and)
Citric acid 20% solutionq.s. to pH 4.5-5.0
[Citric acid (and) water]
Add ingredients of phase A into a vessel and heat to 80°C with moderate mixing (hot water bath is good for this type of heating). Add ingredients of phase B into a separate vessel and mix Structure Cel 4400 E in water at 25°C; then begin heating to 80°C and add Arquad PC 16-29 once the 4400 E is completely hydrated. Once at 80°C, add phase B to phase A. Mix at about 400 rpm for 10 minutes at 80°C, then begin cooling to room temperature. Switch to a sweep blade once temperature drops below 50°C and mix at about 200 rpm and add remaining ingredients. Adjust pH if necessary to 4.0-4.5 with phase D.
About the Author
Ra’eda Asad is the hair care project leader for AkzoNobel Global Personal Care. More info: 888-331-6212. Or visit www.akzonobel.com/personalcare