The Effect of Treatments on the Shear Modulus of Human Hair Measured by the Single Fiber Torsion Pendulum

July 2007

Don Harper, Y. K. Kamath

shear modulus single fiber torsion pendulum cuticle layer bleaching Polyquaternium-10 cetyl trimethylammonium bromide humidity CETAB

TLDR Different treatments change the strength and flexibility of human hair.

The study investigated the effects of various treatments on the shear modulus of human hair using a single fiber torsion pendulum. Abrading the hair surface to remove the cuticle layer significantly reduced the shear modulus. Bleaching also softened the cuticle layer, reducing the shear modulus. Treatments with Polyquaternium-10 and cetyl trimethylammonium bromide (CETAB) were tested, with CETAB increasing the shear modulus more significantly due to its smaller molecular size, which allows it to penetrate the cuticle layer. Polyquaternium-10 had a slight increase in shear modulus. Additionally, an inverse relationship between humidity and shear modulus was observed, particularly pronounced in bleached hair fibers.

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9 citations, March 2005 in “International Journal of Cosmetic Science”

The torsional method effectively evaluates hair damage and the performance of hair care ingredients.