Human hair as alpha-keratin fiber exhibits a complex morphology, which for the context of this investigation is considered as a filament/matrix-composite, comprising the intermediate filaments (IF) and a variety of amorphous protein components as matrix. Differential scanning calorimetry (DSC) under aqueous conditions was used to analyze the denaturation of the alpha-helical material in the IFs and to assess the changes imparted by repeated, oxidative bleaching processes. The DSC curves were submitted to kinetic analysis by applying the Friedman method and assuming first order kinetics. It was found that the course of the denaturation process remains largely unchanged through oxidation, despite the fact that pronounced decreases of denaturation temperature as well as of enthalpy occur. In parallel, the reaction rate constant at the denaturation temperature, k(TD), increases with repeated treatments, that is with cumulative chemical modification. However, this effect is in fact small compared to the overall change of k(T) through the denaturation process. This leads to conclude that once the temperature rise in combination with the chemical change has induced a suitable drop of the viscosity of the matrix around the IFs, denaturation of the remaining helical material occurs along a pathway that is largely independent of temperature and of the pretreatment history. This emphasizes the kinetic control of the matrix over the denaturation process of the helical segments in the filament/matrix composite.
Although human hair as an alpha-keratinous fiber exhibits a complex morphology, it can be considered as a nano-structured filament/matrix composite for the context of thermal analysis. Using differential scanning calorimetry (DSC) in water, the denaturation performance of the alpha-helical protein fraction and the effects of reductive treatments were studied. The results are viewed in the context of a previous study for oxidative treatments. It was found that the course of the denaturation process remains generally unperturbed by the treatment, following an irreversible, one-step, first-order process. Arrhenius activation energies and pre-exponential factors were determined from the DSC-curves by applying the principles of the Friedman-method. Comparing activation energy values between reductive and oxidative processes shows the differences of the effects on the components of the composite. In contrast, the values of the rate constant at the denaturation temperature, though showing differences in their trends with cumulative treatments, are very similar. This further emphasizes the theory that the viscosity of the matrix affects strict kinetic control over the denaturation of the alpha-helical segments. Once the viscosity of the matrix has decreased enough for the denaturation process to occur, this follows a path that is largely independent of the temperature range and of the chemical pre-history.
SynopsisRemovability by shampoo and water is one of the criteria to be met by polymers used in hair sprays or setting lotions. To obtain quantitative measures for removabilities, ample laboratory testing is required. Gravimetry is one method which serves this purpose, with the disadvantage of being very time-consuming and depending on the individual handling of the materials. The new method to be presented in this paper is based on conductivity measurements of polymer-coated electrodes in electrolyte solutions. The effect of polymer blending and the degree of neutralization on removability can be assessed readily. Several polymers commonly used in hair sprays or setting lotions and polymer mixtures were tested. Comparison of the results shows good correlation between the two methods. The new method is especially useful in screening experiments. Changes in polymer properties as a function of composition can be detected rapidly. Rhum6Elimination au lavage est I'un des critkres que doivent poss6der les polymeres utilises dans les laques capillaires et les lotions coiffantes. Pour obtenir des mesures quantitatives quant B ce crittre, des tests approfondis sont necessaires. La gravimktrie est une mkthode qui permet d'atteindre cet objectif avec I'inconvenient d'&tre longue, fastidieuse et dependant de la manitre dont les individus manipulent les materiaux. La nouvelle methode prisentee dans cet article est basCe sur les mesures de conductivitk d'electrodes enduites de polymtres dans des solutions d'klectrolyte. I1 est alors aise d'analyser le degrC de neutralisation et d'tlimination des polymeres. On a ainsi teste plusieurs polymkres purs ou en melange frequemment utilises dans les laques capillaires ou lotions coiffantes. La comparaison des resultats montre une bonne correlation entre les deux mkthodes. La nouvelle mithode est particulikrement utile dans les experiences de criblage. Les changements de propriBtBs des polyrnkres peuvent 6tre rapidement detect&.
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