Sustainability should not be defined by its separate factors such as renewable resources, carbon emissions, toxicity to the environment or human health, but it should be considered as the whole. More than a collection of technical challenges, it is a responsible approach that global companies are trying to define and implement in multiple and complementary areas such as corporate social responsibility, manufacturing, product profiling and sourcing.
In personal care, ingredients such as synthetic polymers, silicones, ethoxylated surfactants and preservatives are commonly used, proposing a challenge for raw material manufacturers to create ingredients that are sustainable with equal performance.
The aspect of sustainability that perhaps is most perceivable for the consumer is the emergence of resource-oriented raw materials with a better green profile such as those of vegetable origin rather than animal or petrochemical origin. Although designing such raw materials with a more sustainable profile will be successful in a limited number of cases, a new origin for petrochemical- or animal-derived ingredients (non-renewable origins) is of value, specifically when the ingredient widely is used around the globe. Sodium laureth sulfate (SLES) is an example of a widely used ingredient in the personal care industry. Its frequent use justifies the review and redesign of its production process and petrochemical origin (non-renewable).
Some manufacturers of sustainable personal care products utilize the claim ethylene oxide (EO)-free, which often is associated with sulfate-free products. This claim is challenging for formulators, as it involves the total replacement of EO-based surfactants like SLES. The substitutes must maintain the formulation ease of using SLES (body wash, shampoo) while providing the level of performance expected by the consumer (foam, cleansing, mildness, conditioning). Recent surfactant structures and additives have been created that are free of EO and/or of natural origin, can offer pleasant cleansing, and perform according to the consumer’s needs. When certain raw materials cannot be easily replaced due to their unique properties (i.e., silicones for their silky feel), finding ingredients that make formulations more efficient remains one of the main challenges for formulators.
Table 1 lists the raw material families discussed in this article to address different approaches of sustainability from top to bottom. These raw materials include: an anionic, plant-based SLESa as a replacement for the conventional petro-based gradeb; an EO-free and sulfate-free surfactant concentratec, as a replacement for the conventional SLES/ cocamidopropyl betaine (CAPB) system; amphoterics, either hydroxysultainesd or amphoacetatese as replacements for CAPBf; naturally derived polymers, either nonionic guarsg, h or xanthani to provide adequate viscosity and/or ability to suspend in these surfactant media, or cationic guarsj with less impact on the environment yet still providing conditioning to hair.
The table also gives the formulator important information regarding the use of these materials such as the computed percentages of renewable molecular weight; the computed percentages of renewable carbon index; the biodegradability; the impact on the environment according to the European Commission criteria; the absence of several chemicals (i.e., dioxane, preservatives, formaldehyde, paraben, EDTA and sulfates; and the classification with respect to different recognized standards, i.e., Ecocert, Whole Foods and the Natural Products Association (NPA)).
Materials and Methods
Shampoos were made with combinations of the ingredients from Table 1 to illustrate the design of more sustainable cleansing products. These shampoos were compared to shampoo formulations containing the conventional surfactant systems SLES and CAPB in different proportions. A silicone (noncommercial dimethicone emulsion with 65% w/w active) oil was often added to the sustainable shampoo formulation to provide conditioning. When necessary, sodium chloride (NaCl) was added to adjust the viscosity of the formulation to the desired level, as measured with a viscometerk (spindle 5, 10 rpm).
Table 2 provides six examples of sustainable formulations, each formulated to fulfill a different need. Included is a shampoo formulation based on plant-sourced and petro-sourced SLES (Formulation A); a sulfate-free formulation texturized with mixtures of naturally derived polymers (Formulation B); a formulation with enhanced deposition of silicone oil using naturally derived guars compared to other polymers (Formulation C); a formulation with an EO-free and sulfate-free concentrate (Formulation D); a formulation with enhanced deposition of silicone oil using amphoacetates rather than conventional CAPB (Formulation E); and a formulation with the synergistic combination of amphoacetate and coco glucoside (Formulation F).
In-house evaluations1 (i.e., dimethicone depositions, combing benefitsm, sensorial assessments) were conducted by applying 1 g shampoo on 5 g hair tresses (i.e., 20% w/w dose), either virgin or damaged, by single- or double-bleach procedures. In the particular case of SLES, either petro- or plant-sourced, life cycle assessments were performed according to the International Organization for Standardization 14040–14044 standards (ISO 14040–14044) and reviewed by an independent expert.
Replacing SLES in Sustainable Formulations
SLES is a widely used anionic surfactant in personal care, as more than 70%n of all cleansing products (mostly in the personal care market) launched by 2011 were based on this ingredient. SLES is difficult to replace with raw materials of a different chemistry because of its unique foaming, cleansing and structuring properties.
Replacing SLES with a more eco-friendly version is not always sufficient. The EO-free trend specifically aims for the total replacement of conventional EO-based surfactants like SLES to obtain formulas with the associated claim. Such a replacement of the whole surfactant system with an EO-free and often a sulfate-free alternative presents challenges for the formulator, such as achieving mildness for the consumer while maintaining the expected thickness and foaming. Totally replacing SLES often results in reconsidering the whole formulation and its performance.
Formula benefits: Because SLES is difficult to replace with raw materials of a different chemistry, it is necessary to replace it with an innovative grade of SLES that is as efficient as the existing ones yet with a more sustainable profile. Figure 1 illustrates how a vegetable-based SLES grade compares to its petro-derived equivalent by plotting the viscosity and salt concentrations of petro- (orange) and bio-sourced (green) SLES, when 14% w/w solids are combined with 2% w/w cocamidopropyl betaine (squares) or 2% sodium cocoamphoacetate (circles).
The minor shifts existing between the curves originate from a difference in the buffers used for the two SLES grades (i.e., citric acid (and) phosphate vs. citric acid). Both ingredients show the same viscosity profiles, whether formulated with a CAPB or sodium cocoamphoacetate. Overall, the two grades seem to formulate the same.
Petro- vs. bio-sourcing of SLES: The classical petrochemical route used to synthesize conventional SLES, as shown in Figure 2, is based on naphta steam cracking, which dilutes a hydrocarbon feed (such as naphta or ethane) in gas or liquid forms with steam and heats the mixture in a furnace without the presence of oxygen. It results in breaking large saturated hydrocarbons into smaller ones (often unsaturated), effectively producing olefins such as ethylene and propylene. This process produces the ethylene necessary to form the ethylene oxides that are grafted onto lauryl alcohol to produce the lauryl alcohol ethoxylate that becomes a sulfate.
On the other hand, the bio-based sourcing of SLES illustrated in Figure 2 utilizes a renewable resource (sugar cane) and an eco-friendly reaction (fermentation), which benefits from the use of sugar cane by-products (bagasse) to generate the energy that will be used during fermentation. The method effectively produces bio-ethanol, bioethylene and bio-EO.
As both the petro-derived and the bio-derived SLES have the same performance and behavior during application, a comparative life cycle assessment should be conducted that considers the production steps and the end of life (destruction by total oxidation). While the performance of a chemical (here SLES) is directly proportional to the dose in the formulation, the production and destruction of that chemical are characteristic of the ingredient’s chemistry.
Environmental impact of production: Plant- and petro-based SLES (based on 100% active) were compared for their carbon dioxide footprint and the consumption of non-renewable resources, as shown in Figure 3. The life cycle assessment accounts for the production and destruction of the two products, which have equivalent applicative performances.
As shown in the figure, the carbon dioxide footprint and the consumption of non-renewable resources were both reduced by about 20% when one goes from a conventional petro-based SLES to a sugar cane-based SLES. With its 86% vegetal origin, its 100% renewable carbon and a production process designed to benefit from its wastes to generate energy, this SLES grade is an example of how the sourcing and production of a raw material can be revisited to meet sustainability requirements.
Naturally Derived Thickening Polymers
From a formulation standpoint, the thickening of sulfate-free and/or EO-free formulations can be rather difficult, since traditional solutions used by formulators (salt) often fail at building viscosity in these media. The use of a mixture of naturally derived polymers, such as modified guars and xanthan gum, can provide a thickening solution. With a 70–87% vegetable origin and 63–83% renewable carbon for HP guars and a 100% vegetable origin and 100% renewable carbon of the xanthan gum, the use of this blend of natural polymers allows for the formulation of natural, mild and sulfate-free cleansing products.
Guar gum is a polysaccharide extracted from the guar beans seeds. It is a vegetable and renewable resource. Hydroxypropyl modification (HP) of the material improves the speed of hydration, compatibility with surfactant and transparency. The use of HP guar alone as a rheology modifier in surfactant systems will provide an efficient thickening, moderate shear-thinning rheology and no yield stress, hence no particle suspension.
On the other hand, xanthan gum is an anionic polysaccharide obtained from fermentation of carbon hydrates by xanthomonastype microorganisms. As a rheology modifier in surfactant systems, xanthan gum provides a high shear-thinning rheology and strong suspension properties. However, used at a high level in a formulation, the latter becomes jelly, a clear negative for the consumer.
These two naturally derived polymers are well-known to have a genuine synergistic association, which takes place between the double-helix of the xanthan gum and the mannan segment of guar.2 Therefore, the formulator can benefit from the best of both, obtaining formulations with a shear-thinning behavior that allow for easy extraction from the packaging and ease of application for the consumer and a yield stress sufficient to disperse and stabilize different actives like exfoliating particles, emollient capsules or oil droplets. When put in a sulfate-free surfactant system, a mixture of HP guar and xanthan gum can provide an optimum thickening efficiency, combined with a high clarity and a tunable yield stress through an adequate choice of the ratio between the two polymers.3
Figure 4 shows how different ratios of xanthan gum vs. hydroxypropyl guar at a total solid concentration of 1.0% w/w change the properties of a surfactant system made of 9.2% w/w disodium laureth sulfosuccinate and 1.8% w/w cocamidopropyl hydroxysultaine as milder replacements for an SLES/CAPB combination. Also shown are images of the same formulations containing dispersed beads stabilized with the yield stress provided by polymers. It can be concluded that this polymer combination allows the formulator to fine tune the yield and transmittance without compromising the viscosity.
When alone, the hydoxypropyl guar provides only moderate viscosity, no yield stress but high transparency. On the other hand, xanthan gum alone provides high yield stress with a reduced transmittance. The mixture of both offers a compromise between these three parameters, important for the formulator and the consumer.
Surfactant Systems Without Sulfates or EO
From an application standpoint, replacing SLES with sulfate-free and/or EO-free ingredients is not without consequences. Not only is the thickening of the formulations more challenging, but the flocculation mechanism that makes formulations work on skin or hair, can be greatly affected. Most shampoos rely on the association that occurs upon use and dilution between surfactant micelles, mostly anionic, and cationic polymers usually are added to provide conditioning benefits such as improved combing, hair and skin softness, etc.
Once the whole surfactant system is changed, the interaction with the cationic polymer is significantly impacted and the performance is impacted as a result. However, sulfate-free surfactant systems do exist that are easy to thicken and provide a pleasant cleansing experience with excellent application performances. Indeed, smart mixtures of several surfactants based on disodium laurylsulfosuccinate and sodium lauroamphohydroxypropyl sulfonate have been recently developed.
Figure 5 shows that it is possible to build viscosity in a formulation based on a blend of sulfate-free surfactants by adjusting the pH. In the absence of a silicone oil, a conditioning shampoo formulated with this blend of surfactantsc combined with 0.3–0.5% w/w guar hydroxypropyltrimonium chloridep not only provides the sensorial experience of a rich, dense foam that is generated during lathering, but also excellent conditioning performances in bleached hair.
To illustrate the improvement in combing force, Caucasian hair tresses were washed with a shampoo formulated with 16% w/w surfactants, either 14% SLES and 2% CAPB or 39% of the surfactant blend (16% active) and 0.4% guar hydroxypropyltrimonium chloride. Sensorial attributes were tested with the same combinations of surfactants but with 0.3% guar hydroxypropyltrimonium chloride.
The combing improvement in bleached hair with the EO- and sulfate-free shampoo is better than the combing achieved with a conventional combination of 14% SLES and 2% CAPB, one at the same concentration of surfactants in the formulation. Thus, high performing cleansing products based on an EO-free and sulfate-free system that are easy to formulate and thicken can be designed.
Reducing Silicone Content
Silicone oils frequently are used in personal care formulations. For now, replacement technologies cannot match the benefits of silicones such as the silky feel resulting from a silicone-based shampoo. However, some manufacturers are formulating silicone-free or silicone-reduced solutions with solutions able to boost the delivery of oils, whether natural or silicones.
Structured surfactants: A recent paper discussed how structuring a surfactant system into multilamellar vesicles can either reduce the amount of silicone in formulations by increasing their delivery or help natural oils deposit.4 The yield provided by these closely packed, water-swollen surfactant assemblies effectively helps stabilize natural oils, such as sunflower oil, without pre-emulsifying them. Their delivery on hair effectively leads to shampoos free of silicones, yet with sensorial profiles equivalent to a well-known dimethicone-containing leading international brand.
Once the formulator learns to use existing surfactants by structuring them into multilamellar vesicles instead of just conventional micellar systems, it is possible to design a silicone-free formulation that will satisfy the consumer. Obtaining the same with a conventional micellar system would require a pre-emulsification of the natural oil (implying additional surfactants and energy) and the addition of a rheological active able to provide yield (like acrylates copolymers) to durably stabilize the emulsion in the shampoo bottle. A structured medium is simply able to do both at the same time.
The total replacement of silicones is not always possible. In this case, being able to deposit silicone in a much more efficient way is also of great importance to help reduce the use of this nonrenewable resource. Multilamellar vesicles are effective at boosting the silicone deposition, as they can help multiply the deposition by a factor from 2 to 10 compared to a conventional micellar formulation. Therefore, a formulator could use structured surfactants rather than micellar ones to achieve a better deposition and reduce the silicone content of a formulation. However, other technologies such as polymers, can help obtain the same result from conventional SLES-based micellar formulations with a nice twist—a better green profile.
Guar deposition aids: Guar polymers are known silicone deposition aids. Once guar gum has been cationically modified to enhance its affinity for hair, the final modified guar contains more than 90% vegetable material, with up to an 83% renewable carbon index. It is usually produced as a 100% solids powder, requiring less volume shipped and stored, and does not require the use of preservatives. In a silicone-containing formulation, such cationic guarsq, r are more efficient than modified celluloses (polyquaternium-10s) or the popular synthetic cationic polymer (polyquaternium-7t).
Deposition of 1% dimethicone was compared among the cationic guarsq, r, polyquaternium-10 and polquaternium-7, all at 0.2% w/w in a surfactant system of 14% SLES, 2% CAPB and 1.5% sodium chloride. It was concluded that the cationic guars resulted in higher silicone deposition, with 43%q and 53%r silicone deposition compared to 13.6% silicone deposition for polyquaternium-7 and 4.9% silicone deposition for polyquaternium-10.
The synergy of cationic guars5 with amphoacetates (ingredient suitable for Ecocert and Whole Foods formulations) allows modified guars to help reduce the consumption of silicones without compromising on the benefit for the consumer. The deposition of 2% dimethicone was compared in three shampoo formulations that were all formulated with 0.3% hydroxypropyl guar hydroxypropyltrimonium chloride: one formulated with 10% SLES and 3% cocoamphoacetate, one formulated with 10% SLES and 3% lauroamphoacetate and one formulated with 10% SLES and CAPB.
Sodium chloride was added to adjust the viscosities to 7000 cP (10 rpm) in formulations of pH 5.5. While the combinations of cocoamphoacetate and lauroamphoacetate with the cationic guar deposited 21.4% and 19.7% of the silicone, respectively, the formulation with CAPB and cationic guar deposited 8.3% of the silicone. This shows how formulators can benefit from combining the naturally derived polymer with amphoacetates to improve silicone deposition. Interestingly, combining amphoacetates with alkyl polyglucosidesu in the presence of a conventional cationic guar increases the silicone oil deposition on hair tresses more.
This was tested by comparing the distribution of 2% w/w dimethicone in three different shampoos, all formulated with 12% SLES, 0.2% guar hydroxypropyltrimonium chloride and 1% sodium chloride: one formulated with 2% sodium cocoamphoacetate, one formulated with 2% coco glucoside and one formulated with both. The combination of amphoacetates with alky polyglucosides produced a 36.2% silicone deposition yield, whereas the sodium cocoamphoacetate and coco glucoside produced a 25.2% and 22.8% silicone deposition yield, respectively. This use of surfactant synergy helps reduce the amounts of silicone wasted and paves the way for the development of silicone-reduced, yet high-delivering conditioning shampoos.
Considering the complexity and number of ingredients in today’s personal care formulations, a 100% sustainable formulation is a challenging task. As illustrated by this article, progress has been made to develop sustainable formulations with ingredients that have less impact on human health (EO-free, sulfate-free solutions like smart surfactant systems), reduced consumption of non-renewal resources (by going from a petrochemical to a natural sourcing), less impact on climate change (improved production processes with less carbon dioxide-equivalent emissions), lower ecotoxicity (with readily or 100% biodegradable products such as guar or xanthan gums) and reduction of water consumption for the production of all these ingredients. This additional aspect of the problem, rarely spoken of, will probably constitute one of the major challenges that manufacturers will face in the future, as drinking water will become a resource important to protect.
Indexes, such as the Dow Jones Sustainability Index, now award those manufacturers that are the most active in the area of social and environmental responsibility. For now, only 250 companies have been granted this index, among which only nine chemical companies have been repeatedly awarded throughout the years. The development of such recognition will hopefully push manufacturers to improve their production processes and develop new environmentally and user-friendly products. The life cycle assessment employed in this study is a valuable tool to quantitatively assess the impact on the environment of the entire life cycle of a product. It not only demonstrates benefits provided by new products brought to the market by innovation, but it also highlights remaining impacts that have to be diminished.
Acknowledgment: Rhodia’s Consumer Care Laboratory in France and personal care team in Chicago contributed to the experimental work presented in this article. The authors are thankful to H Lannibois, V Bienaymé, I Le-Fur and S Catarino for fruitful discussions.
1. C Mabille, Novel conditioning and volumising guar polymer, Personal Care magazine, Sept (2009) www.personalcaremagazine.com/Story. aspx?Story=5516 (Accessed Jun 3, 2011)
2. RL Davidson, Handbook of Water-Soluble Gums and Resins, McGraw-Hill Book Co., NewYork (1980)
3. M Adamy, Efficient rheology control for cleansing formulations, presentation at In-Cosmetics Milan, April 2011
4. D Bendejacq, C Mabille, V Picquet and E Gates, Structured surfactant systems for high performance shampoos, Cosm & Toil, 125(11) 22–29 (2010)
5. WO1999036054 (ordered as EP1049456B1), Use in cosmetic compositions of amphoteric surface-active agents for precipitating cationic polymers in the dilute state, JM Ricca, assigned to Rhodia (July 1999)