Cationic Surfactants

Can Cationic Surfactants Really Protect Hair from Damage? Introduction and Background Hair care represents a strongly growing market segment within the personal care industry. The products that best represent this market are hair conditioners, shampoos and hair dyes. Currently, there is an increasing trend toward formulating products that are safe for both people and the environment due to consumer perception and regulatory requirements. Additionally, as regulations in Europe become increasingly restrictive [1], interest is growing in products that are readily biodegradable in nature and do not harm the environment. In rinse-off hair care products, alkyl amidoamines properly neutralized with an acid represent a good alternative to commonly used monoalkyl quats such as Cetrimonium and Behentrimonium Chloride. [3] In general, alkyl amidoamines show better compatibility with anionic surfactants compared to monoalkyl quats and work together more easily. Furthermore, these molecules in cationic form exhibit greater structural similarity to hair than commonly used quats and impart a much more effective antistatic effect to hair. (Figure 1.) Today, most rinse-off hair products make claims beyond simply softening hair and easing combing. The increasingly preferred extended claim is "protection against damage." Hair can sustain damage from daily activities such as UV radiation exposure, brushing and heat treatments. Additionally, hair is regularly damaged by applications such as hydrogen peroxide-based hair bleaching, perming or hair coloring. Hair damage can be examined through methods that each reveal changes in the structure of the hair shaft. Contact angle measurements are extremely useful in determining hydrophobicity, and thus can establish how damaged the hair surface is. Scanning Electron Microscopy (SEM) helps visually confirm the extent of damage to the hair cuticle. On the other hand, techniques such as tensile strength testing help detect damage within the hair shaft (cortex). By employing all of the above techniques, it is possible to examine the benefits of alkyl amidoamines in protecting hair compared to linear monoalkyl quats, which is the primary objective of this study. [caption id="attachment_140204" align="aligncenter"] Figure 1. Chemical structures of linear monoalkyl quats (CTAC and BTAC) and alkyl amidoamines
(SAPDMA and BAPDMA (AMIDET® APA-22)).[/caption] Materials and Methods Materials Natural and bleached hair samples used in this study were supplied by Kerling GmbH. Cocamidopropyl Dimethylamine (CAPDMA) was synthesized at KAO Chemicals Europe and used without further purification. Stearamidopropyl Dimethylamine (SAPDMA) corresponds to AMIDET® APA-18, Behenamidopropyl Dimethylamine (BAPDMA) corresponds to AMIDET® APA-22. Cetrimonium Chloride (CTAC) is the active ingredient in QUARTAMIN® 60W25 (25% active, solvent: water). Behentrimonium Chloride (BTAC) is the active ingredient in QUARTAMIN® AB (85% active, solvent: isopropyl alcohol). Cetearyl alcohol corresponds to KALCOL® 6850P. All surfactants are part of the KAO Chemicals Europe portfolio. Bleaching (Oxidation) Process Hair samples were immersed in a 6% H2O2 solution at 30°C for 30 minutes. Subsequently, they were rinsed for 1 minute. Tensile Strength and Combing Force Measurements Two tests were performed using an Instron dynamometer (model 5543, 1 kilogram load cell). For tensile strength determination, approximately 30 hair samples with a diameter of 80 ± 10 μm were selected. Hair strands were extended at a rate of 100 mm/minute. Results were expressed as force during extension (average) and force at hair strand breaking [6-8]. For combing force measurement, approximately 20 g of hair sample was combed at a rate of 500 mm/minute. Force was recorded after applying a 1-minute treatment to the test sample, followed by 1-minute rinsing. The final combing force value was obtained by averaging 10 measurements [9]. Scanning Electron Microscopy (SEM) Hair strands with a diameter of 80 ± 10 μm were selected, mounted using carbon conductive tape and coated with gold/palladium. Analysis was performed using a JEOL JSM 6100 scanning electron microscope. Contact Angle A tensiometer (Krüss K12) was used to measure the contact angle between a single hair strand (φ = 70 μm) and water at 25°C. Dynamic advancing contact angle was measured from six sections of each hair strand. At least 5 different hair strands were used. Results were averaged. Cationic Adsorption A solution containing 6.67 × 10⁻⁴ meq/g cationic surfactant was prepared from test samples. Hair samples were immersed in 150 mL of this solution for one minute. Cationic active matter in the solution was analyzed by potentiometric titration with SLS at acidic pH before and after hair sample immersion. The difference between these values was assumed to represent cationic surfactant retained on hair [13]. Results and Discussion The examination of the protective effects of alkyl amidoamines on hair has been divided into three stages: preventing hair damage through pre-bleaching treatment with these products, minimizing hair damage by adding alkyl amidoamines as a gelling agent to hair dye bases, and finally providing conditioning effects with alkyl amidoamines as cationic surfactants in hair conditioners for damaged hair. Prevention of Hair Damage Prior to the oxidation process, Caucasian-type hair samples were treated with Cetrimonium Chloride (CTAC) or amidoamine solutions of different alkyl chain lengths (0.04 meq/g) and water (blank sample). This treatment was repeated 15 times. Following this treatment, the extent of damage to the hair strand was analyzed by measuring tensile strength determination and contact angle values. (Tables 1-2). When the products used in the pre-bleaching treatment contained long-chain alkyl amidoamine, BAPDMA (AMIDET® APA-22), it was observed that a higher force was required to break the hair strands. This result was supported by obtaining higher contact angle values compared to short-chain alkyl amidoamines and Cetrimonium Chloride. Higher contact angles indicate that the hair surface is less hydrophilic after bleaching and therefore sustains less damage. Despite the good performance of BAPDMA (AMIDET® APA-22), the effect is minor as the differences were not statistically significant. [caption id="attachment_140205" align="aligncenter"] Table 1. Tensile strength determination resulting from treatment of different hair samples with different solutions. CAPDMA: Cocamidopropyl Dimethylamine (C12-C14), SAPDMA: Stearamidopropyl Dimethylamine (C18), BAPDMA (AMIDET® APA-22): Behenamidopropyl Dimethylamine (C22).[/caption] [caption id="attachment_140206" align="aligncenter"] Table 2. Advancing contact angle results of hair samples treated with different solutions.[/caption] Minimizing Damage During Hair Coloring Alkyl amidoamines can be used as leveling agents and gelling agents in permanent color applications. When alkyl amidoamines are used as leveling or gelling agents, their performance is equal to or superior to market standards. In addition to these properties, alkyl chain length plays a role in minimizing hair damage during coloring. To examine this effect, different chain length amidoamines were used in a typical hair dye base (5% w/w concentration). Along with the results of this study, a patent application was filed [14]. This hair dye base was used in combination with an emulsion-type oxidation cream containing H2O2. Some hair damage is expected following hair coloring procedures due to the peroxide used. The amines used were Cocamidopropyl Dimethylamine (CAPDMA), Stearamidopropyl Dimethylamine (SAPDMA) and Behenamidopropyl Dimethylamine (BAPDMA (AMIDET® APA-22)). The contact angle value between the hair shaft and water depends on the structure of the hair. The more hydrophobic the hair surface, the higher the contact angle. As the level of damage in hair increases, the contact angle decreases. For bleached hair, contact angle values tend to be lower depending on the degree of damage in the hair (from 75° to 50°), while for untreated natural hair strand, the contact angle is approximately 90°. [caption id="attachment_140217" align="aligncenter"] Table 3. Advancing contact angles of untreated natural hair colored with formulas containing 5% amidoamines of different chain lengths.[/caption] [caption id="attachment_140219" align="aligncenter"] Figure 2. SEM photographs of hair treated with hair dye containing two different chain length amidoamines (C22 and C18)[/caption] As can be seen from the table above, the longer the alkyl chain, the more hydrophobic the hair surface becomes. This is confirmed by the SEM analysis shown in Figure 2. In the image on the right (BAPDMA (AMIDET® APA-22)), no damage is observed, while in the one on the left (SAPDMA), the cuticle scales are more separated. In conclusion, when long-chain amidoamines such as BAPDMA (AMIDET® APA-22) are used in hair coloring procedures, they not only increase surface hydrophobicity but also result in less damage compared to what is seen when short-chain amidoamines are used. Hair Damage Repair To examine the performance of alkyl amidoamines after damage has occurred, hair conditioners containing different cationic surfactants were prepared. To compare their adsorption on natural and damaged hair and the conditioning effect of the cationic surfactants shown in Figure 1 after bleaching, four different hair conditioners with equal cationic surfactant content were prepared. Both amidoamines were subjected to pre-neutralization with lactic acid. The pH of all formulas was adjusted to 4 with the same acid. The affinity of damaged hair for short and long-chain alkyl amidoamines was determined through analysis of cationic matter adsorbed on hair samples. For natural hair, the best result was achieved with BAPDMA (AMIDET® APA-22); for SAPDMA, a value close to nearly double the amount of cationic surfactant retained on hair was obtained. For damaged hair, C22 amidoamine (BAPDMA (AMIDET® APA-22)) adhered more to hair than C18 amidoamine (SAPDMA). Due to the high affinity of C22 amidoamine on damaged hair, this surfactant showed effective conditioning properties in this hair type, as seen in the combing ease measurements (Figure 3). Particularly good results were achieved with BAPDMA (AMIDET® APA-22) for dry combing ease of bleached hair samples. Conclusion Hair damage resulting from oxidation cannot be completely prevented by commonly used cationic surfactants such as Cetrimonium Chloride or alkyl amidoamines, since the hydrogen peroxide molecule can penetrate the surfactant layer adsorbed on the hair surface. However, long-chain amidoamines, particularly BAPDMA (AMIDET® APA-22), have a slight effect in preventing hair damage compared to short-chain amidoamines and CTAC. On the other hand, long-chain alkyl amidoamines (C22) play a role in minimizing damage that occurs during hair coloring procedures. Furthermore, long-chain amidoamines have been proven to effectively bind to damaged hair strands and therefore provide highly effective conditioning benefits to hair. In addition to their good performance on damaged hair, C22 amidoamine is biodegradable in nature without environmental harm and does not exhibit toxic effects on aquatic organisms, aligning with market trends. Different perspectives have emerged regarding alkyl amidoamines in protecting hair structure. Since large molecules such as hair dyes cannot penetrate the surfactant layer accumulating on the hair surface, long-chain alkyl amidoamines can be used in color-protective shampoos and hair conditioners. While AMIDET® APA-22 is used as a cationic surfactant in hair conditioners, it is used as a nonionic surfactant in 2-in-1 shampoos, serving as a conditioning and color-protective agent. In hair coloring products, it is used as a gelling and hair-protective agent. This multifunctional and high-performance product, compared to commonly used cationic surfactants, is an attractive, environmentally friendly alternative for the hair care product market due to its easy biodegradability and low toxicity to aquatic organisms.     Authors Maria Minguet, Neus Subirats, Pilar Castán KAO Chemicals Europe Translator and Compiler Serpil Tatlıdil Salman Technical Solutions Leader Organic Chemistry     References [1] Opinion on alkyl (C16, C18, C22) trimethylammonium chloride, non-preservative uses, SCCP Colipa No P72 [2] Minguet M, Subirats N, Castán P, Cosmetic Science and Technology, 2008; 179-186. [3] Kortemeier U et al, Cosmetics and Toiletries Manufacture Worldwide, 2000: 271-276. [4] Robbins C, Kamath Y, J. Cosmet. Sci, 2007, 58: 629-636. [5] Tate ML, Kamath Y, Ruetsch SB, J. Soc. Cosmet. Chem. 1993, 44: 347-371. [6] Woodruff J, Cosmetics & Toiletries, 2002, 117: 33. [7] Robbins CR, Crawford RJ, J. Soc. Cosmet. Chem. 1991, 42: 59-67. [8] Syed AN, Ayoub H, Cosmetics & Toiletries, 2002, 117: 57-64. [9] Garcia ML, Díaz BS, J. Soc. Cosmet. Chem., 1976, 27: 379-388. [10] Hössel P, Sander R, Schrepp W, Cosmetics & Toiletries, 1996, 111: 57. [11] Höcker H, Skin Pharmacol. Appl. Skin Physiol., 1999, 12: 158-165. [12] Rogasik S, Martin N, Ricca JM, Wielinga W, Anthony O, SÖFT-Journal, 1999: 32. [13] Watanabe H, Okumura T, Hayashi S, Kao Corporation Japan internal report. [14] EP1714677 (A1)