Hair relaxation after shaping - A kinetic approach

Area of Science:

• Materials Science
• Physical Chemistry
• Hair Science

Background:

• Hair fibers can be shaped using thermal or chemical treatments.
• Understanding the recovery process kinetics is crucial for hair science applications.
• Previous research has not fully elucidated the rate-controlling mechanism of hair recovery post-shaping.

Purpose of the Study:

• To evaluate the time-relaxation transients of thermally and chemically shaped hair fibers.
• To kinetically model the recovery process to determine the rate-controlling mechanism.
• To compare the activation energy of relaxation for different shaping methods.

Main Methods:

• Hair fibers were shaped thermally between heated plates and chemically in water.
• Relaxation transients were measured under controlled environmental conditions.
• Kinetic modeling using exponential and logarithmic laws, with residual sum of squares for model fitting.

Main Results:

• Shaping and recovery were modeled as successive quasi-chemical reactions.
• Thermally shaped fibers followed an exponential law (first-order process).
• Chemically shaped fibers followed a logarithmic law (percolation theory-based relaxation).
• Calculated activation energies were similar for both thermal and chemical shaping methods.

Conclusions:

• The rate-controlling mechanism for hair fiber recovery is consistent across different shaping methods.
• This mechanism is proposed to be the reformation of thiol-disulphide bonds within hair proteins.
• Kinetic analysis provides insights into the molecular processes governing hair shape recovery.