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United States Department of Agriculture

Agricultural Research Service

Research Project: NEW AND EFFICIENT PROCESSES FOR MAKING QUALITY LEATHER
2007 Annual Report


1a.Objectives (from AD-416)
Develop new technology for preparing hides for tanning. Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. Hide Preparation: The additional funding will be used to expand the scope of hide preparation research by investigating ways to impart efficiencies to short-term hide preservation (brine-curing).


1b.Approach (from AD-416)
Oxidative chemicals will be evaluated for dehairing activity. Following dehairing, fleshing and splitting, the grain split will be further dehaired if necessary to remove remaining hair stubble. Further processing would complete the conversion of hide to crust leather. Enzymes (keratinases, dispase, acidic or alkaline proteases, and type IV collagenases will be evaluated as alternatives to chemical dehairing. Processes will be developed for partial or total removal, from limed hides, of proteoglycans (such as decorin) and glycans (such as dermatan sulfate) by first 'opening-up' the hides thoroughly to the entrance of chemicals and then treating the hides in the presence of concentrated salts with chymotrypsin, trypsin, pancreatic bate, halophile protease and/or glycanases (during bating). Both the decorin core-protein and the sulfated glycan content will be measured before and after application of the novel treatment, and mechanical and physical changes in the resultant leather will be evaluated. The effect of treatments on the physical and mechanical properties of leather ultimately made from the treated hides will be assessed. A mathematical, predictive drying model for chrome-free leather will be established and compared to the earlier one developed for chrome-tanned leather. Based on the new model, the optimal drying conditions for chrome-free leather will be identified. A finishing process will be developed that will improve the UV- and heat resistance of automobile upholstery leather. Alpha-tocopherol (Vitamin E) will be added during wet processing or added to the finishes and applied to the grain layer of the leather during the finishing process. In-line nondestructive testing technology by acoustic emission (AE) will be developed to assess the mechanical properties of leather following drying, staking, buffing, drum milling, and finishing. The additional funding will be used to evaluate processes for expediting the diffusion of salt into the hide. The ability of acoustic/mechanical energy or alternative salt formulations to shorten the time of brining and possibly decrease the salt requirement will be assessed.


3.Progress Report
CWU scientists had developed a rapid unhairing process for use in a packing plant on carcasses prior to flaying and evisceration. The 1st-generation ARS system had relied on toxic sodium sulfide as depilatory, but a 2nd-generation version used a benign oxidative system. A meat packer and CRADA partner evaluated the new method as part of a broader study on pathogen reduction, but then decided not to pursue rapid oxidative unhairing at this time. A hide buyer has expressed interest, however, in using such a process to remove manure from brine-cured hides. Optimization of the process is ongoing. (NP306, Component 1, Quality Characterization, Preservation, Enhancement; Pbm. Area c, Factors and Processes that Affect Quality)

Likewise, alternatives are needed to use of sodium sulfide to unhair hides in the tannery. A CRADA is being negotiated with a commercial tannery to scale up an ERRC oxidative process (using sodium percarbonate). Studies were also performed to determine the efficacy of the oxidative agents to remove undesired noncollagenous proteins from hides; analysis of oxidative unhairing waste streams has been initiated. (NP306; Comp. 1, Quality Characterization, Preservation, Enhancement; Pbm. Area c, Factors and Processes that Affect Quality; and Comp. 2, New Processes, New Uses, and Value-Added Foods & Biobased Products; Pbm. Area c, New and Improved Processes and Feedstocks)

Decorin, a proteoglycan, is a minor but persistent component in hides as they are tanned to leather. CWU scientists hypothesized that thorough removal of decorin would lead to softer leather. The have observed that different sections of raw hides differ significantly in their initial decorin content. However, after subjecting each hide part to the same tanning treatments, no differences in residual decorin content were found. Techniques for decorin analysis were refined to eliminate inconsistencies of results; modified SDS-PAGE and Western blotting were added to the prior-applied ELISA technique for greater specificity and sensitivity. The improved techniques for decorin analysis will enable studies to correlate decorin content with leather softness. (NP306; Comp. 1, Quality Characterization, Preservation, Enhancement; Pbm. Area b, Methods to Evaluate and Predict Quality, and c, Factors and Processes that Affect Quality)

Production and application of unhairing enzyme: CWU scientists have been investigating the production of unhairing enzymes made by a common bacteria, B. subtilis. The production of both a gelatinase and a keratinase was achieved and unhairing experiments performed. The gelatinase was ineffective in hair removal. The keratinase worked very well and mixing it with an alkaline protease improved unhairing. Use of enzymes offers the potential to eliminate toxic sodium sulfide as a depilatory. (NP306; Comp. 1, Quality Characterization, Preservation, Enhancement; Pbm. Area c, Factors and Processes that Affect Quality; and Comp. 2, New Processes, New Uses, and Value-Added Foods & Biobased Products; Pbm. Area c, New and Improved Processes and Feedstocks)

Progress in other areas is reported below.


4.Accomplishments
Viscoelasticity of chrome-free leather: In some respects, the quality of chrome-free leather, demanded by European automotive leather markets, is inferior to that of traditional chrome-tanned leather, for example in lower UV resistance and hydrothermal stability. Scientists at Eastern Regional Research Center, Wyndmoor, PA, designed a test method to gain insight into the structural difference between chrome-tanned and chrome-free leather, in order to be able to adjust the leather-making processes to achieve the properties of chrome-tanned leather. Chrome-free leather was found to be not as elastic as chrome-tanned leather in terms of recovery from deformation, and relatively stiffer. The results indicate that when making chrome-free leather, more lubricants may be needed in the fibers. For improving elasticity, filler may be added to improve the leather’s density. Results will enable American tanneries to offer superior chrome-free leather to those global markets that are demanding this product over traditional chrome-tanned leather. (NP306, Quality and Utilization of Agricultural Products; Action Plan Component 1, Quality Characterization, Preservation, and Enhancement: Problem Area 1c, Factors and Processes that Affect Quality)

Brine Curing: Salt must be removed from brine-cured hides at the tannery before they are converted to leather, and disposal of that salt is a major environmental problem. A one-dimensional model of brine curing developed and tested by ARS scientists indicated that both the brine curing time and the amount of salt used in the brining solution could be reduced. Salt diffusion into the hide was shown to occur strictly from the flesh side. The findings support reductions in curing times by packers and hide dealers. (NP306, Quality and Utilization of Agricultural Products; Action Plan Component 1, Quality Characterization, Preservation, and Enhancement; Problem Area 1d. Preservation and/or Enhancement of Quality and Marketability; and Action Plan Component 2, New Processes, New Uses, and Value-Added Foods and Biobased Products; Problem Area 2c, New and Improved Processes and Feedstocks)

Airborne ultrasonic techniques: Under a CRADA, ARS scientists collaborated with industry to investigate a new acoustic emission (AE) method based on airborne ultrasonic techniques for inspecting and testing leather surface defects and mechanical properties. As this is a non-contact technique, it could also be an ideal inspection method for large raw hides with the hair on. Scientists at Eastern Regional Research Center, Wyndmoor, PA, have developed an airborne ultrasonic scanning technique to reveal the presence of defects in the leather created by healed wounds, insect bites, knife cuts or any other physical discontinuity that could affect the leather quality. Data also indicated a close relationship between the maximum tensile strength and the intensity of an AE signal measured from testing. This study will promote the development of an airborne ultrasonic inspection system for evaluating the quality of leather and hides. (NP306, Quality and Utilization of Agricultural Products; Action Plan Component 1, Quality Characterization, Preservation, and Enhancement; Problem Area 1b, Methods to Evaluate and Predict Quality, and Problem Area 1c, Factors and Processes that Affect Quality)

Antioxidants for UV and heat protection: ARS scientists have investigated an environmentally friendly finishing process that may improve the UV- and heat resistance of automobile upholstery leather. They added 1 to 5% of the natural antioxidants alpha-tocopherol and mixed tocopherol to the grain layer finishes of chrome-free leather. The treated samples were exposed to artificial sunlight at high temperature and then evaluated for the efficacy of UV and heat resistance and by mechanical property testing for strength and stiffness. Tests showed a significant improvement in color fading resistance against UV radiation and heat. This research will benefit the leather industry in the production of high quality, durable leather with improved UV and heat resistance. (NP306, Quality and Utilization of Agricultural Products; Action Plan Component 1, Quality Characterization, Preservation, and Enhancement; Problem Area 1c, Factors and Processes that Affect Quality)

Effects of milling on leather following drying operation: Leather is mechanically tumbled (milled) to soften it to adequate stiffness and feel. There is no report, however, regarding the effects of milling on the structural change and physical properties of leather. Scientists at Eastern Regional Research Center, Wyndmoor, PA, showed that milling caused a significant decrease in stiffness, but brought very little change in mechanical strength and toughness. Microscopy showed that the fibers of milled leather are well separated from each other, whereas the fibers of non-milled samples are still stuck together. The results of this research will benefit leather producers to gain a better understanding of the effects of milling on leather softness and justify development of tools to monitor these effects. (NP306, Quality and Utilization of Agricultural Products; Action Plan Component 1, Quality Characterization, Preservation, and Enhancement; Problem Area 1c, Factors and Processes that Affect Quality)


5.Significant Activities that Support Special Target Populations
None.


6.Technology Transfer

Number of web sites managed1
Number of non-peer reviewed presentations and proceedings17
Number of newspaper articles and other presentations for non-science audiences2

Review Publications
Anandan, D., Marmer, W.N., Dudley, R.L. 2007. High-level cellular protease production by aspergillus tamarii NRRL 20818 using solid-state fermentation. Journal of Industrial Microbiology and Biotechnology. 34:339-347.

Liu, C., Latona, N.P., Ashby, R.D., Ding, K. 2006. Environmental Effects on Chrome-free Leather. Journal of American Leather Chemists Association. 101(10):368-375.

Liu, C., Latona, N.P., Cooke, P.H. 2007. Effects of drying processes and fatliquoring on resiliency of leather. Journal of American Leather Chemists Association. 102(2):68-74.

Liu, C., Latona, N.P., Dimaio, G.L., Cooke, P.H. 2007. Milling Effects on Mechanical Behaviors of Leather. Journal of American Leather Chemists Association. 102(6):191-197.

Liu, C., Latona, N.P., Dimaio, G.L., Cooke, P.H. 2007. Viscoelasticity Studies for Chrome-Free Leather. Journal of Materials Science. 42:8509-8516.

Last Modified: 4/20/2014
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