RAPID OXIDATIVE DEHAIRING: DEGRADATION OF HAIR, KERATIN, AND CYSTINE

Authors: Marmer, William; Dudley, Robert

Submitted to: American Leather Chemists Association Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2005
Publication Date: 6/1/2005
Citation: Marmer, W.N., Dudley, R.L. 2005. Rapid oxidative dehairing: degradation of hair, keratin, and cystine [abstract]. American Leather Chemists Association Meeting. Paper No. 3.

Interpretive Summary:

Technical Abstract: Last year we presented a paper on the reuse of the dehairing reagents in a rapid oxidative dehairing process. Since then, we have conducted further studies to understand the effect of the oxidizing reagents on hair and its proteins. In these recent studies, we investigated two rapid oxidative systems--hydrogen peroxide/NaOH and hydrogen peroxide/NaOH/KOCN--and compared the results with those from either NaOH hydrolysis or 4-h dehairing using sodium perborate/NaOH. One of our concerns was that, at high base concentrations, immunization of the hair might occur, thus reducing the efficacy of the dehairing mixture. Dilute (4%) NaOH solutions can cause immunization, as manifest by the subsequent inability of sulfide to remove the hair. Nevertheless, the rapid oxidative dehairing formulations readily removed such immunized hair. Thus, if any immunization of the hair did occur during the rapid oxidative dehairing, due to the high concentrations of base, it did not affect the removal of the hair by the oxidative chemicals. Next we used cystine as a model compound to study by NMR the oxidative cleavage of the disulfide linkage. Both the concentration of base (1N NaOH) and the concentration of the oxidative chemicals in the cystine studies were lower than what is used in the rapid oxidative dehairing formulation (5N NaOH). We found that a 10-fold molar excess of the oxidative chemical to cystine effectively cleaved the disulfide linkage and converted the sulfide to the corresponding sulfonate within 1 h at 25ºC. In the final set of experiments, we applied oxidative dehairing formulations to hair (both wool and bovine) and then determined the molecular weight (MW) of resultant solubilized keratin. The solubilized protein isolated from the rapid (4-min) oxidative dehairing solutions had a higher MW than the protein isolated from a 4-h dehairing using sodium perborate/base. More protein, of a lower molecular weight, was solubilized if the rapid oxidative dehairing reaction was allowed to run for a longer period of time (up to 4 h). It is likely that in rapid dehairing, solubilized protein depletes the dehairing agent and thereby lowers the efficiency of dehairing as such protein builds up in solution during repetitive runs. Thus, in a rapid dehairing process, insolubles-including hair and hair pulp-should be removed from the reagent during its recycling.