Effect of equilibrium pH on the structure and properties of bleach‐damaged human hair fibers

Abstract

Hair proteins are significantly affected by environmental pH. This impact tends to increase with prior hair damage. To understand how pH affects bleached hair properties, we utilized a number of techniques allowing for the determination of hair thermal properties, swelling and water sorption, and dry and wet tensile properties. At pH 5, hair proteins had the best structural integrity, as determined by differential scanning calorimetry and the highest tensile modulus. At pH 10, protein cross-linking density decreased, water content and hair cross-sectional diameter increased. Alkaline treatment, when compared with pH 5, did not reduce intermediate filament conditions (evaluated via enthalpy measurement) nor mechanical property performance in the wet state. In contrast to alkaline-treated hair, bleached hair equilibrated at pH 3 behaved very differently: it contained two different crosslink density zones, was the least stiff in dry and stiffest in wet conditions. Additionally, it absorbed less water and had the lowest diameter because of reduced water binding by protonated carboxyl groups. The pH 3 to 10 did not affect the mechanical strength of bleached hair in dry or wet conditions.

Proteins as Hair Styling Agents

“…The higher contribution of the proteins at this pH could be explained by the low perming efficiency obtained for the hair treated only with the ethanolic formulation at pH 7. Solutions with pH values close to 7 seem to influence the ratio between the number of salt bridges and hydrogen bonds, which are described to be involved in the shape of the hair fibers [33]. In this way, the low perming efficiency observed for the control at pH 7 highlights the effect of the proteins in the shaping of the hair fibers.…”

Lawsone and Indigo-Loaded Sepiolite Nanofibers for Hair Coloring with Sustained Release

“…An aqueous dispersion (50 mg/mL) of sepiolite-lawsone was prepared at pH 4.5, and at pH 5, hair proteins were reported to have the best structural integrity. 40 One gram of each type of hair was exposed to 4 mL of the dye-nanoclay dispersion, hand-massaged for 3 min, and allowed to rest for 30 min. Then, the sample was rinsed with water and dried with a hairdryer.…”

“…All the hair samples were kept in closed ziplock bags at 24 °C and a humidity of 32%. An aqueous dispersion (50 mg/mL) of sepiolite-lawsone was prepared at pH 4.5, and at pH 5, hair proteins were reported to have the best structural integrity . One gram of each type of hair was exposed to 4 mL of the dye-nanoclay dispersion, hand-massaged for 3 min, and allowed to rest for 30 min.…”

Comparing hair tensile testing in the wet and the dry state: Possibilities and limitations for detecting changes of hair properties due to chemical and physical treatments

“…Tensile testing of keratin fibres, including human hair, is of academic as well as of practical (textile, cosmetic industries) importance. Concentrating for the current context on human hair, tensile tests may in practice be conducted either in water (wet) or under ambient, defined, or standard conditions 1–10 . The choice of conditions may on the one hand be a matter of convenience.…”

“…Concentrating for the current context on human hair, tensile tests may in practice be conducted either in water (wet) or under ambient, defined, or standard conditions. [1][2][3][4][5][6][7][8][9][10] The choice of conditions may on the one hand be a matter of convenience. On the other hand, investigators may decide to employ both conditions, assuming that sets of data are essentially independent and reflect different aspects of hair properties.…”