TESTING
feeling to the touch.12 18-MEA can be easily removed from the
hair surface due to different damaging agents, therefore, the degree of 18-MEA degradation can be used to gauge damage to hair fibres. Taking this into consideration, ToF-SIMS is a valuable tool to substantiate claims, as it is possible to infer the efficacy of hair care products on damage repair or damage protection, when analyses on the 18-MEA degradation are performed.
Optical profilometry to evaluate the hair damage Optical profilometry is a rapid, non-destructive and noncontact surface metrology technique. Optical profilometry quantifies and qualifies the relative contribution of different characteristics of a samples’ surface, such as structure, waviness, roughness, volume, and others, by the production of a detailed three-dimensional surface map of a test surface. Therefore, this technique not only allows
to obtain high resolution images of the samples’ surface, but also quantifies various topographical characteristics.13
The damage
induced by heat and by discoloration can be analysed with this technique (Figure 2) since if the hair suffers damage, the hair surface becomes more irregular and causes an increase of the surface roughness.
Split ends evaluation through Brightfield microscope and clinical score Split ends develop when the structure of the hair weakens from injury, particularly mechanical and chemical damage, causing the longitudinal rupture of the hair shaft.14 Due to being a result of an excessive and continuous damage, hair tresses are submitted to a thermal/mechanical stress prior to the performing of the tests, in order to induce the formation of split ends. Therefore, a thermal/mechanical apparatus (Figure 3) is established. This apparatus consists
Figure 3: Thermal/mechanical apparatus
of one plastic brush attached to a cylindrical arm that has an engine and is made to rotate at 60 rpm through the hair tress in a horizontal position. Simultaneously, the hair tress is exposed
to the hot air of a blow dryer during rotation, which is positioned to keep the hair against the brush. The hair tress is exposed to this thermal/ mechanical stress for two hours at 60 rpm - this treatment corresponds to approximately 3,600 brush strokes per hour and simulates what a consumer does during the styling process. The hair split ends evaluation is assessed by
one expert in standardised lighting and position conditions, in previously damaged hair tresses, by the assignment of a visual score, taking into account the tress split ends cover area observed, using a visual score scale. After visual score assignment, hair fibres
are collected and the split ends area is visualized with a Brightfield microscope in order to visualize the extension of the damage, and photographs are captured so that representative images (Figure 4) of the assigned score are obtained. When a claim substantiation on a hair care
product is sought, split ends are analysed after products’ application (Figure 5) in order to assess on the mending effect of the product.
Hair strength evaluation with texturometer As previously referred, the hair is easily damaged by a variety of agents, such as exposure to chemicals, colouring and environment or daily hair drying that weaken the hair by increasing inter-fibre friction, leading to breakage.
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Figure 4: Images obtained with a Brightfield microscope of split ends of a damaged hair tress before product application
Figure 5: Images obtained with a Brightfield microscope of mended split ends of a damaged hair tress after a single product application
www.personalcaremagazine.com October 2022 PERSONAL CARE
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