Skip to main content
ARS Home » Research » Publications at this Location » Publication #142086


item Marmer, William
item Dudley, Robert
item Gehring, Andrew

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2003
Publication Date: 9/20/2003

Interpretive Summary: The first step in the conversion of bovine hides into leather is the removal of hair from the hide. Unhairing typically is done in the tannery over several hours, usually by treatment with sodium sulfide, lime, and soda ash. A rapid unhairing of the hide while still on the carcass in the slaughterhouse is an attractive alternative, because such a process could be part of a pathogen reduction program targeting the safety of the meat. Resultant unhaired hides offer advantages to their users, too. Rapidity is crucial to keep pace with the movement of the carcass through the meat packing operations. We have collaborated in the past with the packing industry to develop such a rapid unhairing process, but its major drawback is its continuing reliance on sodium sulfide, which if carelessly handled can create a dangerous, toxic environment for unhairing personnel and the downstream ecosystem. We now have investigated an alternative to sodium sulfide, namely caustic hydrogen peroxide. We found initially that high concentrations of caustic were required, which damaged the hide's grain layer and thereby lowered the quality and value of the resultant leather. We later found, however, that the concentration of caustic could be reduced without compromising the rapidity of unhairing; this was done by incorporating either lime or potassium cyanate in the unhairing formulation. Use of these formulations preserved the integrity of the hide, led to leather of a quality better than leather produced by the traditional unhairing of the tanning industry, and used agents regarded as toxicologically and environmentally benign. The new processes offer the hides and leather industries viable alternatives to currently used technology and potentially can revolutionize leathermaking and its impact on product quality and cost as well as the environment and workers' safety.

Technical Abstract: Hair can be rapidly removed from a bovine hide with caustic sodium sulfide. A rapid unhairing of the hide while still on the carcass in the slaughterhouse is an attractive alternative, because such a process could be part of a pathogen reduction program targeting the safety of the meat. The major drawbacks to the procedure are the high concentrations of base required for the unhairing, the potential of generating toxic hydrogen sulfide and the disposal of the spent unhairing solutions. We have studied the use of caustic hydrogen peroxide as a potential rapid oxidative unhairing agent to replace sodium sulfide. High concentrations of sodium hydroxide were required for the hydrogen peroxide to be an effective rapid unhairing agent. At these high base concentrations damage to the grain was observed. We were able to reduce the amount of sodium hydroxide and still carry out an effective rapid unhairing by the addition of lime or KOCN to the reaction mixture. An added advantage of using lime or KOCN was the elimination of grain damage. Shrink temperatures and physical test data of the wet blue and crust leather produced from hides that had been unhaired with alkaline hydrogen peroxide were compared to the results obtained from wet blue and crust leather produced from hide unhaired with sodium sulfide/lime/soda ash. The wet blue produced from hides that had undergone the four unhairing protocols had identical shrink temperatures. The shrink temperatures did not correlate to the chromium content of the wet blue. The physical testing data were also identical for all four samples except for the tensile strength and toughness index. The crust leather made from hides unhaired by sodium sulfide/lime/soda ash had significantly lower values. As with the shrink temperatures there was not a correlation between the physical testing results and chromium content.