CROSS-LINKING STRUCTURE OF KERATIN .3. RUBBER-LIKE ELASTICITY ORIGINATING FROM NONUNIFORM STRUCTURES OF THE SWOLLEN HAIR AND WOOL FIBERS

Hair and wool fibers treated with an 11 M LiBr solution containing N-ethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8 M LiBr and diethylene glycol monobutyl ether. Stress-strain relations of the swollen fibers were treated with a two-phase structural model: a mechanically stable phase of higher crosslinked domains and a rubbery phase with lower crosslink density. Stress-strain curves were analyzed by applying non-Gaussian chain statistics to the swollen keratin network, including microdomains, which act as reinforcing filler particles in rubber. Swollen hair showed about 2.3 times higher modulus than wool. It has been suggested that: (1) the difference in the modulus between the two keratins is attributable to the difference in the volume fraction of domains, and (2) the crosslink density of rubbery phase in hair is virtually identical to that in wool.