Submitted to: International Union of Leather Technologists and Chemists Societies
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2002
Publication Date: 1/1/2003
Citation: Gehring, A.G., Bailey, D.G., Crowther, J.C., Dimaio, G.L., Dudley, R.L., Marmer, W.N. 2003. Improved hide quality and rapid unhairing. Proceedings of the 27th Congress of the International Union of Leather Technologists and Chemists Societies. p. 66-88.
Technical Abstract: The quality of hides suffers from their treatment by the packing industry as a byproduct, at best, of meat production. A meat packing company had changed this mentality by developing a vertically integrated cattle operation in which the hide is a product in its own right. A key component of that innovative operation was the rapid unhairing of stunned cattle carcasses prior to flaying in the slaughterhouse. Since it removes hair-associated manure, dirt, and microorganisms, rapid unhairing greatly reduces the cross-contamination of microorganisms on the hide to the meat. A consequence, however, is the allowance for the rapid hide grading, splitting in the raw, and cost savings in downstream tanning operations. Under a cooperative agreement, we worked with that company to develop an effective rapid unhairing process. Optimal conditions included 6.2% sodium sulfide at 35°C applied as a pressurized spray (in two applications) to warmed hide piece samples; an additional spray application of the sodium sulfide was used to remove the partially dissolved hair from the samples and subsequent neutralization of residual sulfide (still on the sample pieces) with 3% hydrogen peroxide was brought about in less than 5 min of total reaction time. The process sufficiently removed hair and hide-associated manure balls, allowing for splitting of green hide. The process was further developed to incorporate the recycling of the unhairing agent (sodium sulfide) and recovery of removed hair. Analysis of the recycled unhairing solution over 16 cycles showed a linear consumption of ca. 20% sulfide with a linear gain of ca. 1% nitrogen (proportional to dissolved hair protein content). More recently we have targeted the replacement of sulfide by systems that are safer to handle and yet preserve the integrity of the grain layer of the hide. Most successful, in terms of rapidity and extent of unhairing, were several formulations consisting of dilute alkaline peroxides and other substances (including potassium cyanate and lime). Results, including physical tests are presented for these alternative, oxidative unhairing treatments. These unhairing systems may be adapted for use in the tannery.