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Effect of equilibrium pH on the structure and properties of bleach‐damaged human hair fibers
Author(s) -
Malinauskyte Ernesta,
Cornwell Paul A.,
Reay Louise,
Shaw Neil,
Petkov Jordan
Publication year - 2020
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.23401
Subject(s) - chemistry , ultimate tensile strength , differential scanning calorimetry , swelling , protein filament , absorption of water , dehydration , sorption , enthalpy , protonation , biophysics , nuclear chemistry , chemical engineering , composite material , biochemistry , organic chemistry , ion , physics , materials science , adsorption , biology , engineering , thermodynamics , quantum mechanics
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.