Comparing hair tensile testing in the wet and the dry state: Possibilities and limitations for detecting changes of hair properties due to chemical and physical treatments

Abstract

Objectives: This investigation focuses, first, on the question to which extent wet and dry tensile tests on human hair may be considered as leading to independent results. Second, we try to assess the sensitivities of wet and dry-testing to detect changes of mechanical properties. Specifically, we were interested in separating changes, which were induced by a combination of a chemical (oxidation/bleach) and a physical treatment (heat). Methods:The basis for our study are data for the tensile properties (wet and dry) of a set of untreated and bleached hair tresses, which were submitted to the same schedule of thermal treatments. As characteristic tensile parameters, we chose modulus (E), break extension (BE), and break stress (BS). First, parameters were analysed across treatments for the correlations between wet and dry data.Second, we applied two-factor analysis of variance to assess the effects of the factors and their potential interaction.Results: Correlations for the dry versus wet data show only a weak relationship for E, while coefficients of determination (R 2 ) are quite high for BE and BS.Two-factor ANOVA enables to quantify the various contributions to the Total Sum-of-Squares for all three parameters. We show that the parameters respond quite differently to the chemical and the thermal treatments as well as to testing conditions (wet or dry). It is of interest to note that the interaction between the chemical and the physical treatment is generally quite weak. For the interpretation of the results, we use the concept of the humidity-dependent as well as strain-induced glass transition of the amorphous matrix. Conclusions:The independence hypothesis for dry and wet tensile measurements only applies for modulus. Overall, we consider modulus (wet) as the best tensile measure of fibre damage when assessing chemical and/or physical treatments. Under ambient conditions (dry), break stress is shown to be a feasible alternative measure.Conclusions: L'hypothèse d'indépendance pour les mesures de traction sec et humide ne s'applique qu'au module. Dans l'ensemble, nous considérons le module (humide) comme la meilleure mesure de traction des dommages des fibres, lors de l'évaluation des traitements chimiques et/ou physiques. Dans des conditions ambiantes (sèches), le stress de rupture est une mesure alternative réalisable.

Multifunctional Hair Dyeing with Curcumin via Thiol-Michael Click Reaction

“…After testing, all data were collected and SPSS software (version 13.0, Chicago, USA) was used to calculate the above mechanical properties. t test was performed to compare the means of data and considered statistically significant at p < 0.05. , …”

“…t test was performed to compare the means of data and considered statistically significant at p < 0.05. 27,28 2.3.5. Keratin Solubilization Test.…”

Reconnection of cysteine in reduced hair with alkylene dimaleates via thiol‐Michael click chemistry

“…The above mechanical properties were calculated based on the average of 30 hair single fibres and statistical analysis was carried out using SPSS software. A T ‐test was performed on the data of each group and the control group, and the p value were calculated [24].…”

A consumer cross‐over trial suggests that there are significant seasonal changes of the tensile properties (wet) of human hair

“…The stress-strain curve of a hair fibre provides potentially a rather large number of stress-related parameters [1]. We decided to test the fibres in the wet stage, since this provides the highest sensitivity to detect changes of hair properties [11].…”

“…To analyse the data for each variable, we conducted a 'fixed-factor analysis of variance' as implemented in the Statistica software [13]. Since we consider two nominal factors (#1 Phase/Season, #2 Treatment), we will refer to the statistical approach as 2F-ANOVA [11]. Each combination of factor levels is referred to as a 'cell' (see Table 1).…”