Eco-Friendly, Vegetable-Based Esterquat from Evonik
Evonik researchers detail the benefits of an eco-friendly and vegetable-based esterquat for hair conditioning and skin care applications.
Brian Yang, Anna Howe, Angela Paez and Murat Quadir
Evonik Goldschmidt Corporation
(804) 452-5672 or www.evonik.com/personal-care
Quaternary alkyl ammoniumsalts have traditionally been the “workhorse” in the hair care industry.Materials such as cetrimonium chloride (CTAC), behentrimonium chloride (BTAC) and distearyldimonium chloride (DSDC) have strong substantivity to the hair surface and provide the desired conditioning properties. In addition, the use of DSDC, including palmitamidopropyltrimonium chloride (PATC), was further extended to skin care. They can act as cationic emulsifiers for oil-in-water lotions as well as creams providing a typical powdery, smooth and dry skin feel. In sun care formulations, these cationic materials offer the benefits of low tackiness, high water resistance and excellent sand repellency. They are economical and cost effective. However, these materials have poor biodegradability. In recent years, these negatives were further compounded by the growing public awareness concerning the sustainable use of natural resources.Formulators are looking for greener solutions for their performance needs in hair and skin applications. Consumers are also looking for eco-friendly and sustainable products.Hence the need is emerging for creative technologies that are naturally derived, biodegradable, eco-friendly and sustainable while maintaining good performance in hair conditioning as well as skin care properties.
To fulfill market needs, Evonik Goldschmidt GmbH has developed a new esterquat, distearoylethyl dimonium chloride (DSEDC), as an alternative for alkyl quats with improved biodegradability and eco-toxicity.
Sustainable and Easy to Handle
DSEDC is a vegetable-based quaternary ammonium compound having two C18 fatty acid chains with two readily hydrolyzable ester linkages, representing a novel class of hair conditioning agents and oil-in-water skin care emulsifiers. The inclusion of ester linkages into the aliphatic chains has significantly improved the kinetics of biodegradation of the cationic surfactants, lowering the environmental exposure levels.
The biodegradation of DSEDC was investigated over a 28-day period in a Manometric Respirometry Test according to the guideline OECD 301 F. At a test concentration of 25mg/L, the biodegradation of the product was above the official criteria of 60% within a 10-day window and is classified as readily biodegradable. On the contrary, the alkyl quats have very poor biodegradability as demonstrated by CTAC in Figure 2.
The esterquat is typically prepared through reacting a (mono-, di- or tertiary) alkanolamine with fatty acids, followed by reaction with an alkylating agent to the corresponding quaternary. The esterification is
carried out in the presence of a catalyst, the raw materials are heated
|Fig. 2: DSEDC is readily biodegradable
consumes less energy and generates less waste and is therefore more sustainable.
|Fig. 3: Synthesis process of esterquat compared to alkylquat
This novel esterquat, DSEDC, is substantive to both hair and skin. It improves the detangling and wet combing of hair fiber while exhibiting superior dry combing and dry feel of hair. In comparison to the market standard, cetrimonium chloride (CTAC), it forms a very dense and rich appearance of the final conditioner formula. It also acts as an oil-in-water cationic emulsifier imparting a powdery, smooth and dry skin feel after application even in high lipophilic loadings. Additional special advantages in sun care are low tackiness, high water resistance and sand repellency.
Human hair is composed of keratinous material. Its surface has isoelectric point (IEP) around 3.7 and therefore, in normal condition, where the pH is above the IEP, bears a net negative charge with excess anionic groups. The negative charge density on the hair surface increases when it is further damaged; e.g., by bleaching, or dying via the oxidization of cystine linkage, forming mainly cysteic acid, resulting in a high number of anionic groups.When hair is treated with cationic ingredients, the electro-static interaction drives these ingredients to the hair surface. Esterquat DSEDC is highly substantive to hair providing the desired conditioning benefits such as improvement of wet and dry combing and feel, and antistatic properties.
Esterquat DSEDC&CA can be dispersed in water at approximately 80-85°C. Addition of nonionic emulsifiers such as Ceteareth-20 would improve the processability of DSEDC&CA in water, but is not mandatory. The formula below is an example of a simple but very efficient eco-friendly and PEG-free conditioner formula without an additional emulsifier.
Varisoft EQ 65 (Evonik)3.1
chloride (and) cetearyl alcohol)
DSEDC shows good stability at lower pH. We have found that DSEDC as a single ingredient is sensitive to neutral-alkaline pH. However, it is more stable in formulations. We recommend to formulate a cream rinse conditioner formulation with a typical pH between 4 and 5, preferably below 4.5.
|Fig. 4a: Half head test results–comparison between Esterquat (Varisoft EQ 65) and cetrimonium chloride (CTAC)|
Figure 4a shows that for most proved parameters esterquat DSEDC&CA clearly outperformed the market standard cetrimonium chloride.
Figure 4b shows that the conditioning properties of the esterquat DSEDC &CA are very similar to the highly efficient behentrimonium
|Fig. F4b: Half head test results with 10 panelists–comparing Esterquat (Varisoft EQ 65) and behentrimonium chloride (BTAC).
Skin Care Effects
In hair care formulations, cationic moieties have typically been associated with conditioning. In this application, they impart lubricity, antistatic properties and smoothness to the hair fibers. These properties, plus excellent emulsifying properties, substantivity to the skin, renewable raw materials and good cost/performance ratio are increasing the interest in these well known ingredients for skin care applications (Figure 5).
Sun Care and Sand Repellency
|Fig. 5: Increasing number of cationic skin care products|
Although an oily feel is acceptable for the beach, it is not desirable for daily wear. The challenge for formulators is to develop high SPF formulas that protect the skin and wear well, but do not have the classic sunscreen feel. The esterquat (DSEDC&CA) offers cosmetic chemists a novel biodegradable cationic emulsifier for their formulas to achieve the aesthetics along with the additional benefit of water resistance and sand repellency at low usage concentrations.
The sand repellency study was carried out by applying 0.3g of the emulsion to the dry, inner forearm of a panelist. After one minute the forearm is sprinkled with 30mL of fine aquarium sand. The panelist then claps his hands three times to remove the sand. Sand that is left on the forearm is rinsed off, dried and weighed.
The results of the test indicate that cationic emulsifiers, specifically esterquat (DSEDC&CA) and distearyldimonium chloride provided the best sand repellency (Figure 6). The excellent sand repellency reduces the discomfort resulting from the sand sticking on the skin, thus enhancing the fun experience of beach playing, especially for kids or adults who play beach sports.
|Fig. 6: A strong sand-repellent formula (left) vs. a weak sand-repellent formula (right).
Cationic Sun Care Lotion I, Sand-Repellent SPF* 8
Distearoylethyl dimonium 6.00
chloride (and) cetearyl alcohol
Mineral oil (30 mPas)1.50
SPF* (in-vivo): 8; Star Rating: 3; Water Resistance**: 50%
*(COLIPA Method, panel of 5 persons)
**(Spa Pool Method Colipa Europe)
Cationic Sun Care Lotion II, Sand-Repellent SPF* 8
Distearoylethyl dimonium 5.00
chloride (and) cetearyl alcohol
SPF* (in-vitro): 8; Star Rating: 3; Water Resistance**: 92%
*(Optometrics SPF analyzer 290S; 1 mg/cm2; on PMMA slide)
**(Internal in-vitro method)
Esterquats represent a novel class of cationic product providing formulators with a new tool to develop products that meet consumer demands.