From the desire to preserve the cosmetic value of hair to the real treatment of spoiled hair, hair care plays a very important part in both processes.
The growth of this market results mainly from the growing exposure of hair to various types of damage such as chemical treatments (permanents, bleaching) or mechanical stresses like styling and repeated drying1. Environmental factors – notably UV radiation – are particularly harmful, also making hair fragile. The most visible effect of UV radiation is bleaching2, but there is also cuticle damage and a reduction of intercellular adhesion. The morphologic changes induce an increase in the coefficient of friction as well as the fragility of the cuticle and the porosity of the fiber3. Subjected to these stresses, hair becomes dry, dull and rough due to the opening of the scales. It has more static electricity and thus becomes brittle and difficult to style.
To recover or preserve the hair surface properties – responsible for maintaining its structure and its aesthetic qualities – the cosmetics industry has produced coating hair care products. The coating property of a product is characterized by a substantive effect – i.e its ability to bind to the hair, and by its film-forming effect, its capacity to spread on the hair surface.
Normal hair coating products are composed of polymers such as silicone derivatives4, gum and starch5 as well as cellulose derivatives6. These products are the best among lipids, vitamins and protein derivatives because they provide excellent coating properties. However, these traditional polymers have the disadvantage of being sticky and are difficult to remove, which makes the hair heavy5.
Because of its experience in the area of protein polymers in developing its tensor products, SILAB has produced a high molecular weight polymer from quaternized soy proteins. This polymer is capable of binding to the hair and forming a cohesive film on the hair surface at the same time. Developing this active ingredient requires two steps. Step one is the quaternization of soy monomeric proteins of perfectly defined size, structure and solubility, selected and controlled by an enzymatic hydrolysis of native soy proteins. Step two consists of obtaining a 3-dimensional protein network of high molecular weight using an original and patented technology of protein polymerization to improve the substantive effect of quaternized peptides.
Material and methods
Study of the substantive effect of the quaternized soy peptides
Locks of natural blond hair (SECHER-FESNOUX, France) were soaked for 10 minutes in 50 cm3 of a solution containing 2% of soy peptides or 2% of quaternized soy peptides. The locks were rinsed under running water for 1 minute. The substantive effect of soy peptides towards locks of natural blond hair was evaluated using the modified Rubine test. Locks of hair previously treated with soy peptides were soaked for 20 minutes in a 0.5% solution of RED 80 (Ref 36554-8, SIGMA) adjusted to pH 3.5 with sulfuric acid. The locks were rinsed under water for 1 minute, dried using a hair dryer and then placed in a 60 °C incubator for 1 hour. Colorant elution was realized from 150 mg hair taken from each lock in 10 cm3 of a solution containing 2% of SDS for 15 minutes. Color intensity was measured with a spectrophotometer at 528 nm. Substantivity of the tested products towards locks of hair was measured (mg of bound colorant per g of hair) and then expressed as a % of fixed colorant compared to the control.
Study of the substantive effect of the quaternized soy polymer
Locks of natural blond hair (SECHER-FESNOUX, France) were soaked for 10 minutes in 50 cm3 of a solution containing 2% of quaternized soy peptides or 2% of quaternized soy polymer. The locks were rinsed under running water for 1 minute. The substantive effect of soy molecules towards locks of natural blond hair was carried out using the modified Rubine test described above.
Study of the build-up effect of the quaternized soy polymer
Locks of natural blond hair (SECHER-FESNOUX, France) underwent three different treatments, control was not treated and rinsed, positive control was quaternized cellulose (Rita Polyquat-400, RITA).
a) Locks of natural blond hair were soaked for 10 minutes in 50 cm3 of a solution containing 2% of quaternized soy polymer or 2% of quaternized cellulose (125 g/l). The locks were rinsed under running water for 1 minute.
b) Same treatment as a) but the rinsing step was repeated five times.
c) Same treatment as a) but the two steps of treatment and rinse were repeated five times.
The substantive effect of peptides towards locks of natural blond hair was carried out with the modified Rubine test described above.
Study by interference microscopy of the coating efficacy of the quaternized soy polymer
Treatment of locks of hair
A lock of dry and damaged hair about 20 cm long was divided into four equal parts which were treated as follows.
a) Lock 1 was untreated, not rinsed control, then dried using a hair dryer at low temperature.
b) Lock 2 was a test sample treated with 50 cm3 of a 2% solution of quaternized soy polymer, not rinsed and dried using a hair dryer at low temperature.
c) Lock 3 was untreated, rinsed (under running water for 1 minute) control, then dried using a hair dryer at low temperature.
d) Lock 4 was a test sample treated with 50 cm3 of a 2% solution of quaternized soy polymer, rinsed under running water for 1 minute and dried using a hair dryer at low temperature.
The surface topography of the hair was measured by interference microscopy.
Measurement of the surface topography of the hair by interference microscopy
Hair surface topography measurements were carried out with an interference microscope Phoenix (Eotech, France) and a 10X objective. This method enables the 3-dimensional acquisition of the surface topography image of hair, as well as nanometric measurements of its softness or roughness. Ten hair shafts per treatment were analyzed and three zones per hair were acquired. Three parameters were calculated to determine the state of hair scales along the shaft axis.
a) Gap thickness, corresponding to the ratio of scale opening over the mean differences between peaks and valleys.
b) Length, corresponding to the length of the scales.
c) Roughness, corresponding to the surface state of the hair.
Statistical processing of data
Standard statistical methods were employed to analyze the results. Student's test for non-paired data was used for statistical analysis.
Results
Evaluation of the substantive effect of the quaternized soy peptides
The substantive effect was evaluated by measuring the quantity of colorant fixed on the locks of hair. To determine the benefit of the quaternization technology, the substantive effect of soy peptides, quaternized or not, was carried out on natural blond hair with the modified Rubine test (Figure 1). Tested at 2% and compared to the control, the soy peptides had an affinity of 118% towards natural blond hair. Quaternization of the soy peptides increased the substantive effect by 45% in comparison with the non-quaternized soy peptides.
Evaluation of the substantive effect of the quaternized soy polymer
The film-forming effect of the quaternized polymer, tested at 2%, was studied with the Rubine test and compared to that of the quaternized soy peptides (Figure 2). The substantive effects of quaternized peptides and quaternized polymer, tested at 2%, were 163% and 196% respectively. Thus, the quaternization step increased by 33% the substantive effect of the polymer towards locks of natural blond hair. This 3-dimensional protein network of high molecular weight, obtained by cross-linking of monomeric soy proteins, is able to spread on the surface hair and to form a cohesive film providing elevated elasticity and flexibility properties.
Evaluation of the build-up effect of the quaternized soy polymer
The build-up effect was determined using the Rubine colorimetric method after several applications of the active ingredient, tested at 2% in solution on locks of natural blond hair. This effect was compared to that of a solution of quaternized cellulose at 2% (Figure 3).
After a single application and a single rinse, the rate of colorant deposited on locks treated with 2% of quaternized cellulose (103%) was close to that of locks treated with 2% quaternized soy polymer (96%). After one application and five rinses, the deposit of colorant on locks was significantly higher after the quaternized cellulose treatment (136%) than after the quaternized polymer treatment (74%). Finally, after one application and one rinse repeated five times, there was a significant difference in the level of fixed colorant on locks between the treatment with quaternized cellulose (134%) and quaternized polymer (89%).
Thus, our active ingredient was significantly easier to eliminate than quaternized cellulose. Moreover, repeated applications of the quaternized soy polymer did not lead to a deposit effect on the surface of the hair.
Evaluation of the coating efficacy of the quaternized soy polymer
Interference microscopy analysis of spoiled hair, treated with quaternized polymer at 2% in solution and not rinsed, resulted in a significant decrease in the roughness of hair by 9.8% (Figure 4). Moreover, the treatment also induced a significant reduction, by 8.7%, in the length of hair scales and tended to decrease scale gap. On the other hand, the quaternized polymer tested at 2% and then rinsed also showed a significant effect on the smoothing of the hair surface, also visualized by 3-dimensional iconography (Figure 5). The roughness as well as the scale opening of the hair was significantly reduced – by 7.5% and 8.4% respectively. Finally, the pronounced smoothing of scales and consequently the smoothing of the hair microrelief tended to decrease the hair scale length by 13.1%.
Conclusion
During this study we have shown that quaternized peptides obtained from natural soy proteins increased the substantive effect of the monomeric molecules towards locks of natural blond hair. Moreover, the film-forming effect of these peptides was optimized by using an innovative technology of protein polymerization. Because of its elevated substantive and film-forming properties, this 3-dimensional protein network improves the hair surface coating properties. It has the advantages of normal polymers without presenting a build-up effect, the major drawback of some coating products like quaternized cellulose, also tested in this study. Despite its high molecular weight, this active ingredient is easy to formulate because it is soluble in water solutions and in diluted alcoholic solutions.
The capacity of quaternized soy polymer to spread on hair with a protective film and thus to improve styling was confirmed with a sensorial test by a trained hair stylist on 20 volunteers having unspoiled natural hair (no perms, no coloring, no bleaching). Tested at 2% in solution and compared to the placebo, the active ingredient significantly increased the ease of styling, the hair shine and the coating effect by 15%, 17% and 15% respectively. That is why the coating ingredient could be used in hair care products, rinsed or not, because of its capacity to form a cohesive film on the hair fiber with important elasticity and flexibility properties.
According to published data, cationic products are more efficient when hair is spoiled. Thus they are able to induce a self-regulation of hair repair. In future, it will be interesting to evaluate the quaternized soy polymer on spoiled hair to study thoroughly all its properties.
References
1. C. Zviak, The science of hair care. Editions Masson, Paris, 1987.
2. A.C. Santos Nogueira and I. Joekes, Hair color changes and protein damage caused by ultraviolet radiation. J. Photochem. Photobiol. B, 2004, 27(74), 109-17.
3. V. Signori, Review of the current understanding of the effect of UV and visible irradiation on hair structure and option for photoprotection. J. Cosmet. Sci., 2004, 55(1), 95-113
4. H.I. Leidreiter and J.K Jorbandt, Comparative evaluation of modern conditionning agents by tests on hair tresses. SÖFW-Journal, 1994, 120, 14.
5. A.L. Syed, W.W Habib and A.M. Kuhajda. Water soluble polymers in hair care, prevention and repair of damage during hair relaxing. Water soluble polymer, 1998.
6. R.T. Jones and C.A. Brown. The behavior of cationic cellulose derivatives containing fatty quat groups. Int. J. Cosmet. Sci., 1988, 10, 219-229.