Formaldehyde and Non-formaldehyde Cross-linkers to Restructure Hair

Speaker: Crisan Popescu, PhD, Senior Research Scientist, German Wool Institute (DWI), and Professor, University Aurel Vlaicu

Thursday, June 26 10:45–11:30am

Shaping or changing the shape of the hair is an ever-growing cosmetic business since its incipience in the dawn of the 20th century. Chemical treatments designed to impart certain desirable shapes while preserving as much of the physical and chemical properties of hair as possible rely on the use of cross-linkers and involve reactions with poly-functional compounds for introducing new bonds into the protein structure. There are also procedures involving mono-functional reactants and inducing “self-crosslinking.”

The cross-linking operation is evaluated by measuring the cross-linking degree and the level of imparted effect. This paper discusses several of the methods for testing the level of cross-linking and ponders their advantages and weaknesses as related to the envisaged end-result of using the cross-linking.

Any talk on the cross-linkers of hair begins, inherently, with formaldehyde—the smallest molecule that succeeds in producing the best cross-linking results. Today, toxicological concerns push it away from commercial application, but it is still the most interesting product and serves as a model for other developments. It also offers the first glimpses into the way the keratin cross-linkers perform. More details are revealed by investigating how other compounds act as cross-linkers, and a mechanism able to describe most of the facts will be discussed.

This presentation also describes the effect of heat used either for assisting the cross-linking reactions of various chemicals or for inducing the “self-crosslinking” of hair during styling. A mechanism is proposed accounting for the way heat induces cross-linking, and this mechanism is compared with those suggested for chemically induced cross-linking with the aim to underline potential synergies.

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