Effect of Equilibrium pH on the Structure and Properties of Bleach-Damaged Human Hair Fibers

The study examined the effects of pH on bleach-damaged human hair fibers, revealing that pH significantly influences hair's structural integrity, mechanical properties, and water interaction. At pH 5, hair proteins had the best structural integrity and highest tensile modulus, while pH 10 led to decreased protein cross-linking, increased water content, and larger hair diameter, but did not reduce mechanical properties in wet conditions. Hair at pH 3 was less stiff in dry conditions but stiffer in wet conditions, absorbed less water, and had a smaller diameter. The study found that the pH range of 3 to 10 did not affect the mechanical strength of bleached hair in dry or wet conditions. Additionally, hair at pH 3 absorbed fewer water molecules, while alkaline conditions increased ion absorption and destabilized the hair matrix. The study also noted that hair swelled more at higher pH levels, with finer hair showing more swelling than thicker hair. The research concluded that pH impacts bleached hair's thermal, tensile, water sorption, and swelling properties, and these effects could potentially be manipulated using other compounds. The study was supported by Lonza and TRI Princeton, with no competing interests reported.