Permanent waving reduction

Microemulsions have also been investigated for the use in chemical hair treatment [14]. Permanent wave products are based on the reduction of hair keratine cystine, which weakens the protein structure and allows a manipulation of the hair shape. Savelli et al. compared the cystine reduction obtained by thioglycolic acid in water with that obtained by a microemulsion. The microemulsion is based on the anionic surfactant sodium dode-cylsulphate, the co-surfactant pentanol and dodecane as the unpolar oil component. The cysteine formation is evaluated over a time period of 5 min. The experimental data are... 

Analytical procedures involving reduction and determination of mercaptan are not accurate determinations of cystine in permanent-waved hair or in hair treated with mercaptan because mixed disulfide is reduced to mercaptan during analysis adsorbed mercaptan can also interfere in the determination. Procedures that do not involve reduction of hair such as ninhydrin detection (alpha-amino group) or dinitrofluorobenzene (DNFB) reaction followed by chromatographic separation [1, 58] discriminate between mercaptans and, therefore, should be better analytical procedures for detecting the different types of mercaptans and disulfides actually present in permanent-waved hair. 

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. 

In spite of the fact that research on permanent waving has decreased over the past several decades, significant findings have been made within the past 10 years. For example, Wortmann and Kure [1,2] have developed a model and recently extended it to show that the bending stiffness of reduced and oxidized fibers controls the permanent waving behavior of human hair and that the cuticle plays a role in permanent waving. Further, they have shown not only that the cuticle functions as a barrier to reduction but also that its stiffness may contribute to fiber set. 

One purpose of these studies was to try to achieve essentially complete reduction of a smaller cross section of the hber and to determine if effective permanent-waving could still be achieved. A potential advantage to this type of process is to lessen cortical reduction and thereby to lessen cortical damage to the hair (the region primarily responsible for tensile properties) during the permanent-wave process. 

Undoubtedly, the condition of the hair also plays a role in the rate of reduction, especially under conditions where diffusion is rate-limiting. Permanent-waving [31] and bleaching [32] produce alterations to hair that result in increased swelling in solvents. One might also anticipate more rapid rates of reduction for hbers that have been previously bleached or... 

An initiation time for the reduction reaction was found by Weigmann [22] in his kinetic study of the reduction of wool fiber. Weigmann attributed the initiation time to the epicuticle, this initial barrier to reduction is eliminated after only a short reduction time. Weigmann suggested that the epicuticle is substantially altered during permanent-waving. As a consequence, hair that has been permanent-waved or has undergone alterations to the epicuticle should provide no initiation time in subsequent reductions or reactions. 

Fiber diameter determined in the wet or swollen state is sensitive to detect changes produced by damaging treatments like permanent waves or bleaches. The swelling action of permanent-waved hair [30] and in bleached fibers [32] is greater than in unaltered hair and has been used to estimate the relative extent of alteration produced by reduction and reoxidation [31]. For additional discussion on hair swelling, see Chapters 1 and 8. 

The chemistry of the reactions of permanent waves with human hair involves reduction of disulfide cross-links and molecular shifting by stressing the hair on rollers followed by reoxidation. These reactions produce extensive changes to the tensile properties of the fibers, both during reduction and even after reoxidation. 

This amount of tensile damage appears to be typical for a normal permanent-wave treatment, where approximately 20% of the disulfide bonds are ruptured during the reduction step [42],... 

Shansky [114] developed a special microscopic cell to follow hair swelhng and used this system for studying permanent-wave reactions with hair. With this system, he found that the reduction step produces an increase in... 

FIGURE 1 5.18 Permanent waving, a chemical oxidation-reduction process. 

In this strategy reminiscent of the reduction-oxidation steps in producing curls in hair by a permanent wave , the calcium ions play the role of the curlers-they reorganize the available carboxylate groups in an optimal geomehy, subsequently immobilized by reoxidation of the mercapto cross-linkers. This reduction-oxidation treatment results in a significant increase in the affinity for calcium ions. In contrast, when the gel was reoxidized in the absence of the calcium template, affinities for calcium dropped. 

Figure 27 Proposed mechanism for covalent substantivity of exogenous protein to hair by sulfide-disulfide interchange in permanent waving treatment. The formation of new —SS—bonds between the two species can occur by nucleophilic attack of thiol groups of reduced hair on disulfide bonds of unreduced protein (a), or via contemporaneous reduction of hair and protein derivative (b). A third possible route (not shown) is based on a separate activation of the protein derivative by sulfitolysis with Na2S03 at a concentration sufficient to reduce soluble peptides, but having neghgi-ble effects on the hair.

Formulating Considerations Do not heat above 40°C. Should be added between reduction and oxidation steps when used in permanent waves Form Supplied Clear amber liquid Microbial Considerations Standard for proteins... 

The reagent most frequently used for the reduction of hair is thioglycolic acid [68-11-1]. Although a variety of other mercaptans have been screened (51), none has been able to match the unique combination of efficacy, safety, and low cost that is a hallmark of thioglycolic acid. The use of microemulsions and their effectiveness on cystine reduction obtained by thioglycolic acid as compared to water has been investigated. An anionic surfactant, sodium dodecylsulfate, has shown to be less effective than that of water for permanent wave formulations. However, surfactants based on nonionic surfactants are less irritating (52). 

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