|Bailey, David - FORMER ARS EMPLOYEE|
Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 2002
Publication Date: May 20, 2003
Citation: GEHRING, A.G., BAILEY, D.G., DIMAIO, G.L., DUDLEY, R.L., MARMER, W.N., MAZENKO, C.E. RAPID OXIDATIVE UNHAIRING WITH ALKALINE CALCIUM PEROXIDE. JOURNAL OF AMERICAN LEATHER CHEMISTS ASSOCIATION. VOL. 98, 2003. p. 216-223. Interpretive Summary: Tanneries use sodium sulfide to remove and dissolve hair from animal hides. Sodium sulfide, however, is an environmental pollutant and forms a toxic substance if accidentally exposed to acids. Thus, the tanning industry desires a replacement for sodium sulfide. We have successfully demonstrated that several alternative chemicals may be used to rapidly remove hair from cattle hides. In particular, we achieved the most succes with calcium peroxide. An added advantage was that hair removed by calcium peroxide was still intact; as opposed to dissolved hair, intact hair has less environmental impact since it can be readily removed from waste streams. Thus, calcium peroxide may be used in tanneries as an alternative to sodium sulfide for hair removal. The rapidity of the process also lends itself to the removal of dirty hair from animal carcasses in meat packing plants; such removal promotes food safety while allowing an immediate grading of hides for quality, and downstream in the tanneries, less processing chemicals are needed for the conversion of the hides into leather.
Technical Abstract: Sodium sulfide is chiefly used to remove hair from animal hides during tanning operations. However, since sodium sulfide is an environmental pollutant that is quickly converted to highly toxic hydrogen sulfide gas if accidentally exposed to acid, an alternative unhairing agent is desired. We have observed that calcium peroxide may be used to rapidly unhair hides with efficiency comparable to that of sodium sulfide. Under alkaline conditions, 5% calcium peroxide mixture applied in two back-to-back applications, afforded either complete or nearly complete unhairing within 5-10 minutes. Although most of the hair was essentially dissolved in this rapid oxidative hairburn process, the hair could be removed virtually intact if only a single application of the calcium peroxide solution (with solids removed) was used followed by rapid adjustment of the hair solids to an approximately neutral pH. Laboratory-scale and pilot-scale matched sides studies of the calcium peroxide hairburn and hairsave processes were conducted and compared to hairburn with sodium sulfide. The studies revealed that shrinkage temperature, physical testing, dye shading, dye levelness and grain appearance were comparable. In addition, several commercially available non-sulfide sharpening agents were demonstrated to remove residual hair stubble during reliming.