Set and Supercontraction

One might also anticipate greater cuticle contribution to a permanent wave in fine hair as compared to coarse hair because Wolfram and Linde-mann [114] have provided evidence for a greater ratio of cuticle to cortex in fine hair. This is because thin and coarse hair contain the same number of cuticle layers, with essentially the same thickness. Therefore, fine hair contains a greater proportion of cuticle to cortex than coarse hair. 

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Because reduction of the disulfide bond and its subsequent reactions is vital to several important cosmetic products, a large amount of research that is relevant to these chemical processes has been conducted. This chapter is concerned with reducing the disulfide bond in hair by mercaptans, sulfites, alkalis, and other reducing agents. Reactions of reduced hair are also considered, followed by a discussion of water setting, set and supercontraction, and swelling of hair, processes especially relevant to permanent waves, hair straighteners, and depilatories. 

Several other approaches have been used for studying the stretching properties of human hair. Among these approaches are vibrational methods [10, 11], stress relaxation [46], stretch rotation [65], set and supercontraction [19], fatiguing [66], and extension cycling [67]. 

Evidence, which favors this explanation of permanent set and supercontraction, is that lanthionine and lysinoalanine are found in hydrolysates of wool that has been treated in boiling water. The involvement of disulfide exchange in setting is also supported by experiments in which wool fibers have been set in solutions of reducing agents and by experiments... 

The extensive investigations by Astbury and Woods (1933) of the X-ray diffraction patterns of animal fibers before and after stretcihing, setting, or supercontraction (Section VI,5,2) have had a major influence on the models proposed to account for the load-extension properties. Astbury and Woods showed that when animal fibers are stretched, the characteristic a-pattern decreases in intensity with the simultaneous appearance of a d-pattern similar to that obtained from silk. The sharpness and intensity of the /3-pattern increases with sti ain, with temperature, and with time under strain. In the Hookean region the 5.1 A meridional spacing increases by up to 2 % (Astbury and Haggith, 1953). Astbury and Woods (1933) stated that virtually no /3-pattern appears until the fiber has been stret( hed by at least 20 %, and for 25 years this observation dominated the models proposed to explain the elastic properties of wool (Alexander and Hudson, 1954). 

This section is concerned primarily with the effects of chemical modifications of keratins on their physical properties—supercontraction, setting, swelling, load-extension characteristics, and other mechanical properties. Much of this work could be described by the term mechanochemical coined by Speakman (1947). The complexity of the cellular and sub-cellular structure of keratins necessitates the use of simplifying assumptions in the interpretation of mechanochemical experiments. 

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