Application of a tensile-strength test method to the evaluation of hydrating hair products.
The usual methods applied to studying the hydration state of hair (e.g. gravimetry, microscopy, evaporimetry) are mostly concerned with a limited area of the fibre. Consequently, the results obtained do not reflect the variability of the physicochemical properties of the whole fibre. Moreover, there are not many experimental methods to evaluate the hydrating power of hair care products in the literature. This study proposes a new method to measure the hydration state of treated or untreated hair by using a tensile strength test. A graphic analysis of tensile strength variation as a function of relative humidity after hair treatment allows the calculation of three hydration indexes: protection index, instant hydration index and permanent hydration index. This technique can give useful information on the behaviour of hair versus relative humidity and on the different hydrating mechanisms exhibited by hair care products.
Mercelot
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Laboratories EUGENE PERMA, 6 rued'Athènes, Paris, France.