Hair Structure

Hair is composed of an outer cuticle layer, an inner cortex, and the medulla, which serves as the hair's core.

Multiple repeating layers make up the outer cuticle, and the surface of the cuticle is arranged with the fatty acid 18-methyleicosanoic acid (18-MEA). The F-layer, this fatty acid layer, is what gives the hair surface its hydrophobic properties. The hair’s texture, including how smooth it feels to the touch, is also influenced by the F-layer.

Damaged Hair and Conditioners

UV radiation, hair coloring and routine hair care procedures like washing, brushing and using a hair dryer are all capable of damaging hair.³⁾ In addition to breakage, damaged hair lacks elasticity and bounce and becomes dry and brittle. The bottom layer of hair becomes visible due to damage to the F-layer on the hair surface. Furthermore, cuticles become loose and separate from the cortex as a result of these damaging conditions.

The most common conditioning agents are cationic surfactants. Through ionic bonding with anionic surfaces, cationic surfactants adsorb in damaged hair; however, they cannot selectively adhere to non-anionic surfaces. Consequently, we can conclude that cationic surfactants alone are unable to sufficiently treat damaged hair.

LEOGARD DGG

LEOGARD DGG consists of diglucosyl gallic acid; glucose and gallic acid. LEOGARD DGG contains carbonyl groups that act as spacers and establish ionic bonds with cationic surfactants, as well as many OH groups that adsorb to the hair surface.
LEOGARD DGG, due to its structure, has the following three effects on damaged hair:

1. Enhancing hydrophobicity of hair surface
   
2. Strengthening effect
3. Boosting elasticity

Enhancing Hydrophobicity of Hair Surface

Water contact angles, referring to the angles created by water droplets making contact with untreated damaged hair, hair treated with only a cationic surfactant (LQT800) and hair treated with both LQT800 and LEOGARD DGG, were measured. The higher the degree of the contact angle the lower the adhesion rate, indicating a high hydrophobicity.
Contact angles of damaged hair treated with only LQT800 saw a slight improvement over less hydrophobic untreated damaged hair. Damaged hair treated with DGG + LQT800, however, saw the highest degree of contact angles, indicating a marked increase in hydrophobicity.

* LQT800 (LIPOQUAD T-800): Steartrimonium Chloride

Strengthening Effect

Tensile strength, the maximum amount of force that can be applied to hair before it breaks, was measured with the aid of a tensile tester. Damaged hair had a lower tensile strength than undamaged hair. No difference was recorded between the tensile strength of damaged hair and hair treated with only LQT800. Damaged hair treated with DGG + LQT800 had a higher tensile strength than both damaged hair and damaged hair treated with only LQT800, putting it on par with undamaged hair.

Boosting Elasticity

The flexural modulus of the hair was determined using the equilibrium fiber method.⁴⁾ The flexural modulus of damaged hair drastically decreased in comparison to the flexural modulus of undamaged hair. Damaged hair treated with only LQT800 had a flexural modulus value equal to that of damaged hair. The flexural modulus of hair treated with DGG + LQT800 was the greatest and was similar to that of undamaged hair.

Analysis of the Effects of LEOGARD DGG and LQT800 on Hair and Modes of Action ⁵⁾

Time Of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) method was utilized to investigate the mode of action of LQT800 on the hair surface. While damaged hair surfaces treated with LQT800 alone demonstrated uneven LQT800 activity and a lower detected intensity higher intensity suggests higher adsorption on hair. On the other hand, damaged hair surfaces treated with DGG + LQT800 showed that LQT800 acted uniformly over the entire surface and that its detected intensity was higher.

Because LEOGARD DGG’s structure contains numerous OH groups that are formed from glucosyl groups, we believe that it adsorbs by creating numerous hydrogen bonds with hair proteins exposed on the damaged hair surface. In addition, the DGA structure’s carboxy group, which is generated from gallic acid, demonstrates anionic characteristics via acid dissociation, establishing an ion complex with the cationic surfactant LQT800. We have found that LEOGARD DGG has elevated the concentration of LQT800 that interacts with the hair, therefore significantly increasing the hydrophobicity of the hair surface.

Further analysis of LQT800’s effect on a cross-section of hair using ToF-SIMS revealed that LQT800 affects not only the hair surface, but also the entire lower cuticle layer. In addition, when compared to damaged hair treated with only LQT800, much more LQT800 was detected in damaged hair treated with LEOGARD DGG + LQT800, making it clear that LEOGARD DGG increases the amount of LQT800 in the hair’s cross-section as well as on its surface.

Using scanning electron microscopy (SEM), the damaged, undamaged, LQT800-treated, and LEOGARD DGG + LQT800-treated damaged hairs were examined. While the cuticle of damaged hair treated with LQT800 was observed to be partially detached, it was still more intact than the cuticle of untreated, damaged hair, which was shown to be missing and detached. In the cuticle tip, damaged hair treated with LEOGARD DGG + LQT800 was found to be neat and flat, with no cuticle tips lifted.

According to the action analysis above, LEOGARD DGG operates in regions where LQT800 is unable to act, increasing the quantity of LQT800 that acts on the hair surface by serving as a spacer. Additionally, the hair surface’s hydrophobicity was significantly enhanced. Furthermore, we believe that LQT800 operates more on the cuticle surface and throughout the cuticle layer, aligning the cuticle as a whole and enhancing mechanical qualities including strength and elasticity. Therefore, we anticipate that using LEOGARD DGG will enhance the feel of hair, reduce breakage and split ends, and increase bounce and firmness.

References

1. 大門一夫, 毛髪科学入門, 理美容教育出版 (1973)
2. A.P.Negri, Textile Res. J., 63(2), 109 (1993)
3. 西田勇一, 細川 稔, 伊藤武利, 青野 恵, フレグランスジャーナル, 30(8), 33-41 (2002)
4. G.V.Scott, C.R.Robins, A convenient method for measuring fiber stiffness, textil.res.j, 39, 975-976 (1969)
5. Arisa Masuda, Hiroshi Konta, Masao Ishiguro, Norio Tobori J. Soc. Cosmet. Chem. Jpn. 54(4): 358-363