Dynamic hairspray analysis. III. Theoretical considerations.
Model mechanical calculations were carried out to simulate the properties of hair fiber assemblies operating in the bending mode. It was assumed that the fibers were in omega-loop configuration (as in experimental work), and the theory of deformation of thin rings provided a fundamental relationship between stress and strain. A dependence on the stiffness of multi-fiber assembly was derived and verified empirically. Theoretical bending stiffness for fixative-treated hair was calculated for various model fiber distributions by calculating their area moment of inertia according to the parallel axis theorem. General equations for stiffness of fiber assemblies were derived for cross sections placed on cubic and hexagonal lattices. The results suggest a good agreement between the theoretical and experimental data.
Dynamic hairspray analysis. I. Instrumentation and preliminary results
A new method, termed dynamic hairspray analysis, was developed to study the mechanical behavior of pre-set hair tresses, untreated and modified by hairspray resins, under a wide range of bending deformations. The technique includes a vertically acting tensile meter designed to measure the force in both compression and extension modes. The instrument, including a sample holder and spraying devices, was housed in an environmental chamber equipped with a humidity controller. The drying of a hairspray was investigated by (a) applying low intermittent deformations to a preformed hair tress in order to determine the properties of untreated hair, (b) treating the fibers with a hairspray, and (c) measuring the changes both in adhesive properties of a hairspray solution on the surface and in mechanical stiffness of the fiber assembly as a function of drying time. This approach allows the simultaneous determination of parameters such as stiffness of untreated and resin-modified hair, duration of tack, maximum value of tack force, and time of drying. In addition to this, the data collected during the experiment provide information about changes in geometrical dimensions of hair after the application of hairspray and after subsequent drying. In order to test the resistance of fixative resins to high humidity, the kinetic measurements of stiffness and tackiness were also performed at 90% RH.
Some Observations on the Hair Cuticle
Synopsis--Some PHYSICO-CHEMICAL PROPERTIES of CUTICLE are described and correlated to the function of the latter in the overall STRUCTURE of HAIR. Chemical analysis of the cuticular layer revealed significant differences in the amino acid composition of the cuticle and the cortex of the hair KERATIN. The cuticle is extensively crosslinked by cystine, is more hydrophobic than the cortex, and contains large quantities of serine, glycine, and proline. All this satisfactorily accounts for the function of the cuticle as a molecular sieve and a chemical barrier.