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United States Department of Agriculture

Agricultural Research Service

Research Project: NEW AND EFFICIENT PROCESSES FOR MAKING QUALITY LEATHER
2005 Annual Report


1.What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter?
Hides are the most important byproduct of the meat packing industry; about 70% of the 35 million hides that America produces annually are exported, generating over a billion dollars in foreign trade. The remainder is tanned into leather domestically, quadrupling the value of the raw material. Hides undergo several chemical and physical treatments to convert them into their primary product leather. The research contributes directly to National Program #306, "Quality, and Utilization of Agricultural Products." The project specifically contributes to Program Components "New Processes, New Uses, and Value-Added Foods and Biobased Products" and "Quality Characterization, Preservation, and Enhancement."

The concentrations of natural minority constituents in a hide may affect the quality of the resulting leather. The main structural components of the hide are two fibrous collagens. One of the minority constituents, the proteoglycan decorin, is part of the fibrous collagen framework. The development of the fibrous collagen framework in skin and other tissues is controlled by minority constituents, proteoglycans (including decorin) and glycoproteins, that are part protein and part carbohydrate. Although these are present in much smaller amounts than collagen, a genetic lack of some of them (e.g., decorin, the proteoglycan lumican, or the glycoprotein thrombospondin-2) during development gives rise to an abnormal collagen framework and a fragile skin. ARS researchers in a predecessor project had determined that, though much of the glycan (carbohydrate) part of the proteoglycan decorin is removed during the wet chemical processing of hides into leather, the protein part of the molecule persists, unlike other minor proteins of skin that they investigated. Researchers in the current project seek to determine the effects of the persistence of decorin core-protein and glycan contents of the hide during processing on the physical properties of leather produced from the hide. Utilizing this information, they will determine the possible benefit of deliberately reducing the decorin core-protein and glycan (carbohydrate) content during an early stage of leather manufacture. One possible result may be a process for the controlled removal of decorin, in particular its core-protein; this has the potential benefit of yielding a softer leather. Decorin, however, is not the only minority component investigated in this manner, nor is it the only one considered by the CWU team.

There is a need to establish nondestructive methods for characterizing the properties of leather, to model the drying process taking fatliquoring (application of oils and surfactants) into consideration, and to improve the UV and heat resistance of leather by the use of naturally occurring antioxidants. Currently there is no adequate method to measure the softness of the leather after the fatliquoring process. Without a proper characterization method, the tanner has great difficulty in optimizing that process.

Drying, by which leather acquires its final texture, consistency and flexibility, is one of the most important and expensive operations in leather manufacture. A mathematical model is needed that relates the factors associated with drying -- concentration of fatliquor, time, temperature, water content in the starting material -- to leather quality indicators -- tensile strength, stiffness, resiliency, toughness -- and to area yield. The drying model will allow the leather industry to achieve higher drying efficiency, improved quality leather, and increased area yield, thereby producing stronger leather at a reduced cost.

The current commercial UV and heat protective agents such as phenols and amine derivatives are not effective for the growing market for aniline grade or lightly finished automotive leather. These important inadequacies need to be studied to determine why they occur and how they may be eliminated. UV and heat can have a detrimental effect on the durability of leather, especially for instrument panels and consoles, where temperatures reach well over 100 degrees C. Researchers in this project are developing a finishing process using environmentally friendly antioxidants that will improve the UV- and heat resistance of automotive leather. This research will expand the demand for domestic production of high quality, durable leather, thereby contributing to the viability of the domestic tanning industry.

The testing of leather at all stages of its production is an expensive and destructive process. Research in the current and predecessor projects has shown the potential for acoustic emission (AE) analysis to serve as an efficient, reliable, and nondestructive alternative. Collaboration with industry will develop AE technology into a realizable means for testing in the tannery, which in turn will allow the optimization of the leather-making process.


2.List the milestones (indicators of progress) from your Project Plan.
FY 2005

Objective 1: Hide preparation: Develop new technology for preparing hides for tanning 1a: Dehairing of hides using oxidative chemicals: Initiate with the meat packing industry an evaluation of rapid dehairing using oxidative chemicals. Establish bench-scale process on a (non-rapid) sulfide-free dehairing protocol for use in the tannery beamhouse. 1b: Enzymatic dehairing of hides: Demonstrate the effectiveness of A. tamarii protease for cattlehide dehairing at bench scale. Optimize growth conditions of A. tamarii. Complete preliminary scale-up experiments. 1c and d: Reduction or removal of decorin core protein and/or residual sulfated glycan from limed hides by treating hides with selected proteases and/or glycanases: Treat hides sequentially with two proteases, an alkaline protease (AP) and a pancreatic protease (PP), the latter in the presence of 4M NaCl. Measure residual decorin core-protein content immunochemically. Initiate evaluation of physical characteristics of leather product correlated with decorin core-protein content.

Objective 2: Leather quality and durability: Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. 2a: Drying experiments for glutaraldehyde-tanned leather: Formulate relationship between drying conditions and physical properties of leather. 2b: Finishing process for improved UV- and heat-resistance of leather: Complete studies on the effects of UV radiation on the physical properties of leather. 2c: Nondestructive acoustic emission (AE) testing of leather properties: Establish a mathematical model for the correlation between AE quantities and the physical properties of leather.

FY2006, from milestone chart for project 1935-41440-013-00D, 27 months:

Objective 1: Hide preparation - Develop new technology for preparing hides for tanning 1a: Dehairing of hides using oxidative chemicals: Continue working with the meat packing industry to evaluate rapid oxidative dehairing. Identify barriers to commercial implementation. Establish pilot-scale process (in-house) for a sulfide-free dehairing protocol. Initiate working with industry to optimize the dehairing conditions on a commercial scale. 1b: Enzymatic dehairing of hides: Establish optimal bench-scale parameters for A. tamarii-induced dehairing. If necessary, identify a suitable “sharpening” agent (chemical depilatory) to supplement the enzymic system to increase the rate and effectiveness of enzymatic dehairing. Establish at the bench-scale the potential of commercial gelatinase for dehairing hides. 1c and d: Reduction or removal of decorin core protein and/or residual sulfated glycan from limed hides by treating hides with selected proteases and/or glycanases: Treat (bate) hides with pepsin (at pH.
2)as a replacement for PP, after treating (reliming) them in the presence of AP. Continue to evaluate hides for their content of sulfated glycan and decorin core-protein. Make leather from treated hides and evaluate its physical characteristics. Correlate the results of the two sets of tests.

Objective 2: Leather quality and durability: Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. 2a, Drying experiments for glutaraldehyde-tanned leather: Establish a mathematical model of the rate of drying. 2b, Finishing process for improved UV- and heat-resistance of leather: Complete studies on the effects of UV radiation on the fine structure of leather fibers. 2c, Nondestructive acoustic emission (AE) testing of leather properties: Develop a portable AE tester that can be applied in-line and non-destructively measure leather strength and stiffness.

FY2007, from milestone chart for project 1935-41440-013-00D, 39 months:

Objective 1: Hide preparation - Develop new technology for preparing hides for tanning 1a: Dehairing of hides using oxidative chemicals: Modify rapid dehairing process to overcome identified barriers. Continue working with tanning industry on sulfide-free dehairing. Identify barriers to commercial implementation. 1b: Enzymatic dehairing of hides: Establish pilot-scale parameters for dehairing using an A. tamarii protease system. Establish at the bench-scale the potential for hair removal by specific enzymes known to attack the basement membrane of the hair follicle. 1c and d: Reduction or removal of decorin core protein and/or residual sulfated glycan from limed hides by treating hides with selected proteases and/or glycanases: Apply dual protease treatment to hides as per 15 months, but vary the duration of each treatment and the concentrations of the two proteases. Evaluate the effect of the treatments on the leather product as per 27 months, and thereby determine the conditions that provide the best softness and flexibility without significant adverse effect on the other physical characteristics, e.g., strength.

Objective 2: Leather quality and durability: Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. 2a, Drying experiments for glutaraldehyde-tanned leather: Complete studies on the effects of toggling on the physical properties and dimensional stability of leather. 2b, Finishing process for improved UV- and heat-resistance of leather: Identify the finishing conditions that yield the best UV and heat resistance of leather. 2c, Nondestructive acoustic emission (AE) testing of leather properties: Initiate field testing of the nondestructive AE tester. FY2008, from milestone chart for project 1935-41440-013-00D, 51 months:

Objective 1: Hide preparation - Develop new technology for preparing hides for tanning 1a: Dehairing of hides using oxidative chemicals: Modify sulfide-free dehairing process to overcome identified barriers. 1b: Enzymatic dehairing of hides: Transfer A. tamarii technology to the tanning industry for commercial scale implementation. Working with enzyme company, establish pilot-scale parameters for dehairing using the best of the studied enzyme systems. 1c and d: Reduction or removal of decorin core protein and/or residual sulfated glycan from limed hides by treating hides with selected proteases and/or glycanases: Treat hides with AP (during reliming) and with pepsin (as the bate) as per 27 months, the latter in the presence of 4M NaCl and/or a detergent. Evaluate the effect of the treatments of 1c above on the leather product as per 27 months, and thereby determine the conditions that provide the best softness and flexibility without significant adverse effect on the other physical characteristics, e.g., strength.

Objective 2: Leather quality and durability: Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. 2a, Drying experiments for glutaraldehyde-tanned leather: Optimize the drying conditions that give the best physical properties of leather. 2b, Finishing process for improved UV- and heat-resistance of leather: Optimize parameters. 2c, Nondestructive AE testing of leather properties: Complete field testing of the nondestructive AE tester, and modify the tester if is necessary.

FY2009, from milestone chart for project 1935-41440-013-00D, 60 months:

Objective 1: Hide preparation - Develop new technology for preparing hides for tanning 1b: Enzymatic dehairing of hides: Determine most effective commercial approach for enzymatic dehairing and transfer the technology. 1c and d: Reduction or removal of decorin core protein and/or residual sulfated glycan from limed hides by treating hides with selected proteases and/or glycanases:After reliming in the presence of AP, treat hides with a glycanase and then (bate) with a PP or pepsin in the presence of 4M NaCl and/or a detergent. Vary the duration and enzyme concentration during the glycanase treatment. Evaluate the effect of the treatments of 1c above on the leather product as per 27 months, and thereby determine the conditions that provide the best softness and flexibility without significant adverse effect on the other physical characteristics, e.g., strength.

Objective 2: Leather quality and durability: Establish drying and finishing processes and develop in-line nondestructive tests for improving the quality and durability of leather. 2a, Drying experiments for glutaraldehyde-tanned leather: Finish studies, transfer technology. 2b, Finishing process for improved UV- and heat-resistance of leather: Finish studies, transfer technology. 2c, Nondestructive AE testing of leather properties: Finish studies, transfer technology.


4a.What was the single most significant accomplishment this past year?
Drying studies for chrome-free leather: In the leathermaking process, the conditions applied during drying will influence the properties, quality, and area yield of the final product. Vacuum drying allows a lower drying temperature, resulting in improved mechanical properties. Stretching leather during vacuum drying may improve area yield. CWU researchers explored this stretching/drying method and investigated how drying variables affect the drying rate and mechanical properties of chrome-free leather tanned with glutaraldehyde. Using a statistical experimental design, a second order polynomial equation was derived to precisely describe the relationship between the drying rate and three major independent variables: drying temperature, stretch %, and drying time. Drying rate models derived from this investigation provide a clear understanding of the vacuum drying process for chrome-free leather. These models enable the leather industry to estimate the right drying parameters to dry leather without trial and error. CWU researchers discovered that stretch % during vacuum drying is the most significant variable affecting stiffness and area retention of leather. The leather manufacturer may use this information to increase the area yield and softness of leather. (NP306, Component II; Milestone: Objective 2a)


4b.List other significant accomplishments, if any.
Oxidative Dehairing in the Tannery: Alternatives are needed to use of toxic sodium sulfide to dehair hides in the tannery. The optimization of the alkaline sodium percarbonate dehairing formulation developed under this project yielded a new set of dehairing conditions. By simply changing the temperature of the dehairing reaction the tanner can reduce the amount of dehairing chemicals and reduce the amount of water used for dehairing. The reduction in the amount of chemicals results in a cost savings to the tanner. Likewise the reduction in water use results in less tannery wastes that need to undergo remediation at the tannery. The findings should promote the use of oxidative dehairing agents by the tanning industry. (NP306, Components I and II. Milestones: Objective 1a)

Application of humectants to prevent over drying: Moisture loss due to humidity decreases in the surrounding environment can result in area shrinkage, and therefore area yield. In addition, adequate moisture content is essential to the physical properties of leather, such as softness and mechanical strength. One of the problems, however, associated with leather quality is that traditional lubricants ("fatliquors," consisting of oils and surfactants) do not promote the retention of essential moisture, making the leather fibers prone to over-drying. CWU researchers have developed a formulation of lubricants that consists of a mixture of oils and low molecular weight polyethylene glycol (PEG). Leather treated with PEG mixtures showed increased moisture retention and tensile strength. Moreover, after the treated leather samples were heated at an elevated temperature, such as 90 ¿C, observations showed that the tensile strength retention of treated leather increases with PEG concentration in the fatliquoring bath. This implies that PEG increases the heat resistance of leather. These results suggest that adding humectants to traditional fatliquors improve the quality of leather. (NP306, Components I and II. Milestone: Objective 2a)

Nondestructive evaluation of leather: Current testing methods for quality control and quality assurance are time consuming and often subjective depending on the operator and the test being performed. Samples must be cut out of the leather and destructively tested, which consumes some of the profit since leather is sold by the square foot. Therefore there is a great incentive to develop a nondestructive test that will save time and materials as well as be less subjective than some of the current test methods. Under a collaborative research and development agreement, researchers developed the acoustic emission (AE) technique to dynamically and nondestructively measure the mechanical properties of leather. The developed tester measures acoustic emission, ultrasonic sound waves emitted by the leather when it is deformed. Test results showed an excellent correlation between the softness of leather and certain acoustic activities as well as correlated with a standard testing method. CWU researchers also found that this method was able to characterize the grain wrinkle pattern of leather, which is a visual and often subjective measurement, by measuring certain acoustic quantities. CWU researchers also established a mathematical model for the correlation between AE quantities and the physical properties of leather. This model is needed for a nondestructive AE tester to be applied in the manufacturing site and provide the industry with a nondestructive way to monitor the quality of their product without damaging the product. Therefore poor quality leather will be detected earlier and possibly reprocessed before it is carried all the way through the expensive tanning process. (NP306, Components I and II. Milestone: Objective 2c)


4c.List any significant activities that support special target populations.
None.


5.Describe the major accomplishments over the life of the project, including their predicted or actual impact.
Dehairing of hides: Alternatives are needed to the traditional use of sodium sulfide to dehair hides. Researchers demonstrated the effectiveness of oxidative agents commonly used in laundry products, namely percarbonate and perborate, as dehairing agents in tannery applications. Likewise, they optimized an oxidative chemical system, namely peroxide/cyanate, for rapid dehairing applications in the abattoir. They initiated research to show the applicability for cattlehide dehairing of an enzymatic system that had been reported effective for goatskin dehairing. Oxidative and enzymatic systems overcome the environmental and toxic drawbacks of the use of sodium sulfide for dehairing. (NP306, Components I and II. Milestones: Objectives 1a, 1b)

Decorin analysis: Decorin, a persistent though minor constituent of hides, has eluded methodology to track its presence or disappearance during the conversion of hides into leather. Its presence or absence may contribute to leather's softness or weakness. CWU researchers proposed the use of colorimetric methods to track the decorin molecule quantitatively by analyzing for its protein and carbohydrate (glycan) handles. For the protein handle, they developed three immunohistochemical procedures. For decorin's carbohydrate handle, they developed a colorimetric method based on precipitation and redissolution of a colored dye complex. They applied the methods to samples taken during the various stages of the processing of a hide into leather, and they altered conventional treatments of hides in the leathermaking process to allow conditions most favorable to the removal of decorin. Such removal was anticipated to lead to softer leather and enhanced 'opening-up' of the hide structure to the action of processing chemicals. The researchers showed that a hide treated sequentially with two protein-digesting enzymes under conditions that were chosen to favor the removal of decorin did indeed lead to very soft leather and a two-thirds reduction in decorin content. Determination of the decorin core- protein and glycan contents of in-process hides will permit the researchers to determine the impact of the levels of these components on the ultimate properties of the product leather. (NP306, Components I and II. Milestones: Objectives 1c and 1d)

Nondestructive testing of leather: Currently, the physical testing of leather is a wasteful, destructive process, wherein cutouts are removed from the leather and sent from the tannery floor for testing. CWU researchers developed a nondestructive testing method for improving quality control, based on the processing of ultrasonic sound patterns (acoustic emission; AE). Recent tests showed that the tear strength and softness of leather can be nondestructively measured by rolling a rotational acoustic emission (AE) sensor over a leather sample. Based on the results of this investigation, CWU researchers are collaborating with industry (CRADA #58-3K95-M-978) to design an automated in-line nondestructive AE tester to be applied at the manufacturing site. Production of an in-line AE instrument will provide the industry with a nondestructive way to monitor the quality of their product at each intermediate leather-making stage. (NP306, Components I and II. Milestone: Objective 2c)

Drying of chrome-free leather: The drying process is one of the key steps governing leather quality. To make quality leather, it is imperative to understand the effects of the different drying methods on the physical characteristics of leather. Although CWU researchers had studied the drying of typical chrome-tanned leather in prior years, the growing demand for chrome-free leather for auto upholstery highlights the need for studying its drying characteristics. To that end, CWU researchers carried out leather drying experiments focusing on the effects of the drying method. Results showed that the method applied in a drying operation significantly affects the physical properties of leather, particularly area retention and softness. Observations indicated that toggle drying produces higher area yield; it may, however, result in stiffer leather. Vacuum drying without toggling yields better toughness and softness. The ratio of strength to stiffness showed a strong correlation with the resultant area retention, which agrees with our previous finding for chrome-tanned leather. The information derived from this investigation will be used by leather manufacturers to select the right drying methods to meet quality demands. (NP306, Components I and II. Milestone: Objectives 2a)

Protection of leather from sunlight damage: Durability of automotive leather is compromised by exposure to ultra-violet (UV) light and heat. The fast growth in the domestic production of automotive leather to meet the demands of automakers magnifies the significance of this quality. CWU researchers developed an environmentally friendly finishing process to counteract UV and heat degradation and significantly increase the UV and heat resistance of leather. The process involves application of tocopherol (Vitamin E) to the grain layer of chrome-free, glutaraldehyde-tanned leather. The treated samples were exposed to artificial sunlight at high temperature and then evaluated for the efficacy of UV and heat resistance by testing for strength and stiffness. Leather treated with tocopherol resulted in significant improvement in strength retention and color fading resistance against UV radiation and heat. This research program will strengthen the competitiveness of the U.S. hides and leather industries by encouraging environmentally friendly production, while imparting better quality to the finished product. (NP306, Components I and II. Milestones: Objective 2b)


6.What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end-user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products?
Under CRADA # 58-3K95-M-1033, CWU researchers continue drying studies with a major domestic leather manufacturer to identify the optimal drying conditions that will produce improved quality and durability of non-chrome-tanned (chrome-free) leather.

Under a CRADA # 58-3K95-M-978, CWU researchers are working with industry to design a portable AE instrument to dynamically and nondestructively measure the softness of leather. The significance of this project is profound, especially as a quality control/quality assurance method for manufacturing and the potential for being a standard testing method. The collaboration is allowing the correlation of AE testing of commercial leather with subjective and other physical methods of testing, and the initial stages in developing commercial instrumentation for in-line application of AE testing.


7.List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below).
Reports on all phases of this project were presented before the annual meeting of the Research Liaison Committee of the American Leather Chemists Association, ERRC, Wyndmoor, PA, April 2005. (Industry, academic, government representatives of the hides, leather and tannery supplier industries.)


Review Publications
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.

Marmer, W.N., Dudley, R.L. 2005. Rapid oxidative dehairing using alkaline hydrogen peroxide and potassium cyanate: reuse of the dehairing reagents. Journal of American Leather Chemists Association. 100(5):165-173.

Liu, C., Latona, N.P., Lee, J. 2005. A drying study for glutaraldehyde-tanned leather. Journal of American Leather Chemists Association. 100(1):8-15.

Liu, C., Latona, N.P., Lee, J. 2005. Glutaraldehyde-tanned leather treated with tocopherol. Journal of American Leather Chemists Association. 100(3):102-110.

Liu, C. 2004. The application of acoustic emission to characterize the lubrication of a fibrous collagen material: leather [abstract]. Fiber Society Fall Technical Conference, A Symposium on Advanced Materials and Processes. p. 13-14.

Liu, C., Latona, N.P. 2005. Lubrication of leather with mixtures of polyethylene glycol and oil [abstract]. American Leather Chemists Association Meeting. Paper No. 10.

Liu, C., Latona, N.P. 2005. Characterization of polymeric coatings using acoustic emission techniques. American Chemical Society, Division of Polymeric Materials: Science and Engineering. PMSE Preprints. 97:905-906.

Last Modified: 4/18/2014
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