HAIR TREATMENT 67
fatigue tensile measurement in controlled constant stress mode (applied force per averaged cross-sectional area). The constant stress unit is expressed in gmf/µm2
or Mpa. The computer records
the number of cycles at hair breakage and selected tensile load-extension curves, which allows one to monitor changes in the mechanical behaviour, such as modulus changes or permanent fibre deformation extension (% elongation). Data were analysed by Weibull statistical tools using Minitab software. The scale-value as well as characteristic life time is the number of cycles where 36.8% hair fibres are still survived. The higher this number of cycles is, the stronger the hair is. FT-IR spectroscopic imaging was accomplished using a Perkin Elmer Spotlight 400 imaging FT-IR microscope. Images were spatially resolved to 6.25 µm2 pixels. Spectra were obtained with 16 scans at 4 cm-1
resolution. The frozen hair cross-
sections were prepared on a Leica CM 3050S microtome at 5 µm thickness. The spectral maps were concatenated to each other before analysis, assuring equivalent data treatment between samples. Analysis was accomplished from the ratio of intensity of the carboxylate region of the spectra at nominally 1400 cm-1
amide I band at nominally 1650 cm-1
to the intensity of the .
Differential scanning calorimetry (DSC) was carried out using a TA Instruments Q2000. Studies were completed using a heating ramp rate of 2 °C/min in a nitrogen environment, employing a method in which the fibres were sealed with water in a high- pressure stainless steel pan during the experiment.2
Penetrating into the hair fibre during bleaching Infrared imaging was utilised to confirm the penteration of the hair protecting molecule
3x bleach control
3x bleached hair with FiberHance BM solution
0
10 20 30 40
0 20 40 60 Micrometers Figure 2: FT-IR image of hair bleached with FiberHance BM vs. control.
into the hair fibre. The intensity of the band at 1400 cm-1
by FT-IR spectroscopic
imaging was normalised against protein content (amide II band, 1540 cm-1
) in hair. It
is clear from Figure 2 that there is a substantial amount of the hair protecting molecule in the cuticle region of hair along with some penetration into the interior of the fibre (cortex). In the FT-IR image, red corresponds to the highest intensity, and hence highest concentration of the hair protecting molecule, while blue indicates lower concentrations of the molecule.
Protecting cuticle integrity from damage during bleaching Chemical treatments, such as bleaching, can severely damage the cuticle. As seen in Figure 3, the hair cuticle for control hair is severely damaged and cuticle layers are missing, leaving hair vulnerable to damage to the cortex as well.
Protecting the integrity of the cortex
Cyclic fatigue testing was used to test the durability of the hair fibre by utilising a dynamic oscillating procedure intended to mimic strains experienced by the fibre
during normal grooming procedures. Frequently, damage to the hair cuticle causes flaws or tiny cracks to appear in the hair fibre. When the hair fibre is exposed to repeated cycles of stress, these cracks propagate, and after a number of cycles, the hair fibre ultimately breaks. Cyclic fatigue testing is used to measure the change in the mechanical properties of hair after application of different treatments.1 As seen in Figure 4, addition of the hair
protecting molecule to the bleach formulation had a significant protective and strengthening effect on the hair fibre. It not only reduced cuticle damage, but it also had a protective effect on the cortex. When the hair protecting molecule was added to the bleach mixture, a significant increase in the survival probability of the hair fibres was observed compared to the control. The increase in survival probability indicates that the hair protecting molecule helps prevent and mitigate damage to the hair fiber during the bleaching process.
Reducing internal protein damage During the bleaching process, cystine is converted into cysteic acid. Cysteic acid levels increase with the amount of time hair
3x bleach with added HPgluconamide and HPammonium gluconate
80 100 120 -0.2
3x bleached hair Control
-0.4
-0.2
-0
Figure 3: SEM micrographs of hair fibres exposed to three bleaching cycles. June 2018 PERSONAL CARE EUROPE
Micrometers
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