Temperature dependence of the mechanical properties of human hair in relation to structure

Synopsis--The mechanical properties in tension of human hair were examined as a function of temperature in a buffer solution at pH 7.0 both in the presence and absence of a sulfhydryl group blocking agent. Untreatcd hair as well as hair that had been partially reduced to in-crease the free SH content was investigated. It was found that the elastic modulus, post-yield modulus, and fiber strength decrease with increasing temperature while extensibility increased. The turnover point between the yield and post-yield regions was observed to undergo a transition at a characteristic temperature of 85.5øC. This transition temperature was decreased to 66.0øC for the partially reduced hair. The presence of the SH-blocking agent tended to decrease extensibility and increase the post-yield modulus but had no effect on the elastic modulus and strength. The results are explained in terms of a sulfhydryl-disulfide interchange mechanism whereby stressed disulfidc bonds are relieved and trans-formed into stress free positions. The transition te•nperature is associated with the stability of the disulfide bond and the onset of the SH catalyzed disulfide interchange