82 TESTING The hair strength evaluation is assessed
through the measurement of the force required to break the hair fibres with a TA.XT texturometer. In this test, the hair fibres are placed in tensile grips are stretched to the breaking point (Figure 6). The rupture force (N) that is obtained by correspondence of the maximum force in the force versus distance graph. As breaking stress evaluates fibre integrity,
mechanical strength/resistance of the hair is measured many times to evaluate the damage degree of a hair fibre and/or the efficacy of hair care products.15
Hair styling/enhancement products On the aim to substantiate hair products claims related to hair appearance and/or malleability, several evaluations can be performed as below.
Anti-frizz evaluation Although the definition of frizz is not straightforward, frizz can be defined as a very high degree of fibres misalignment.16
The most obvious reason for frizzy
hair is the natural shape of the hair: in general the curlier the hair, the frizzier it will be. The exposure of the hair to high humidity environment will disturb the alignment of the hair and leads to frizz. This disturbance is often a result of high
environment conditions therefore, for this method, pictures of the hair tresses are taken before the exposure (Figure 7A), after six hours of exposure (Figure 7B) and after 24 hours of exposure (Figure 7C) to high humidity conditions. The angle, area and height of the tresses are
measured with an image processing and analysis programme at each time point, and the calculated differences determine the extent of the frizz. Thus, it is possible to make claims about a product’s anti-frizz effect when compared with a negative control, for example.
Combability evaluation with texturometer Combability is defined as the ease with which hair is combed.17
Keeping healthy and manageable
hair is important to the consumers, as hair and hairstyle contribute to a great extent to the overall facial image of a person. The loss in manageability can directly be attributed to an alteration of the hair surface.
A
Figure 6: Sample fixed in the tensile grips of the texturometer
Furthermore, the state of the cuticle is directly
connected to the frictional properties of hair fibres and determines how the hair feels to the touch, as well as how it combs. Combability can be evaluated by a texturometer with a hair-combing device (Figure 8) and is related to the resistance encountered as the comb is moved through the hair. Since damaged hair has a rougher surface than healthy hair, it directly leads to the need of higher forces to comb it. The force needed to comb the hair tress
(combing force) is recorded through a combability curve: force versus the distance travelled by the texturometer’s comb as also as force versus the time elapsed between the beginning and the end of each cycle. Texture analysis provides accurate,
quantifiable and repeatable data on the physical properties of hair care products. The use of a texturometer to analyse the hair combability will help to support claims that can be used
B
in hair products, such as makes the hair more manageable and easier to comb.
Anti-static efficacy Brushing or combing of the hair in low-humidity environments leads to static electricity in the hair. This effect happens due to electron migration from the hair to the brush/comb developing a positive charge on the hair strands. The repulsion between the strands with the same surface charge leads to disruptive static flyaway. The duration of the static flyaway effect is
highly dependent on the ease by which the charge can be dissipated, which is strongly dependent on the moisture content of the hair. Therefore, in low-humidity conditions, where the hair contains less water content, the charge dissipation is poorest and the static flyaway effect is more probable to occur.18 The anti-static charge efficacy of a hair care
product can be evaluated by an ex vivo method, through the determination of the ‘fly away effect’ (repel of hair fibres after being combed). To determine the fly away effect, the rest
angle of the hair tress (hanged on an extension clamp attached to a universal support in a vertical position) produced by the projection of the hair shadow on a 360° protractor is measured before and after combing the hair tress ten times with a plastic comb. The shadow is created by a 9W lamp positioned at a pre-defined distance from the protractor in a dark room. The fly away effect is calculated as the
difference between each hair tress’ rest angle after combing and the hair tress rest angle before combing. This assessment is conducted before product application and after one product/reference application. The angle was determined from both sides
(left and right) by a researcher positioned at 45° from the lamp and from the shadow. This methodology is easy to execute and allow reproducible results on a short period of time.
Final considerations Since present methodologies are typically used to research one particular characteristic, they can be complementary, as hair fibre has many different properties.
C
Figure 7: Hair tress after product application and before exposure to high-humidity (a); after six hours of high-humidity exposure (b); and after 24 hours of high-humidity exposure (c)
PERSONAL CARE October 2022
www.personalcaremagazine.com
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