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United States Department of Agriculture

Agricultural Research Service

Research Project: NEW AND EFFICIENT PROCESSES FOR MAKING QUALITY LEATHER
2009 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
Worked with a major domestic tannery under a CRADA to scale up ERRC's oxidative unhairing process. Scientists conducted production scale oxidative dehairing trials at collaborator’s subsidiary. The activities have focused on optimizing the concentration of dehairing chemical and treatment temperature and duration. The work has attracted two additional companies seeking CRADA’s for an oxidative hair save process and an oxidative hair burn process for use in a gelatin plant.

Removal of minor constituents such as decorin, a proteoglycan of the skin, was observed by CWU scientists to take place in tanning processes that convert hides to leather. Further removal of decorin was explored to study its effects on the quality of leather, such as softness, strength and stretchability. Scientists correlated the amount of decorin to the mechanical properties of leather such as tensile strength, elongation, toughness and Young’s modulus. A new technology adapting sulfide-free dehairing and the addition of alkaline protease in the relime stage with presence of pepsin in the pickling stage of pretanning hides to leather was pursued to improve the removal of decorin.

Investigated a two-step drying process: vacuum dry and then toggle dry. During the second step drying, the leather with enough moisture was able to be stretched 5 to 20% more than the original length to increase area yield. A statistical experimental design was used to arrange drying and stretch variables to formulate a drying model for this system. The mechanical property and area yield are being measured to compare the one step drying process (vacuum and stretch simultaneously in a vacuum dryer). Worked on the development of a finishing process using environmentally friendly antioxidants that improve the UV and heat resistance of leather. Mixed tocopherols were added to the coatings of leather that had been tanned with an organic tannage without using chromium salts. Mixed tocopherols are abundantly available in nature and are produced through a renewable source such as soy beans. Following exposure to artificial sunlight, treated samples were evaluated for colorfastness and mechanical properties for the efficacy of UV- and heat resistance. Observation showed that leather treated with mixed tocopherols resulted in significant improvement in mechanical strength and color fading resistance against UV radiation and heat. Collaborated with the American Institute for Goat Research of Langston University (AIGR) to establish a pilot tannery for the production of goatskin leather using ERRC’s expertise. Some of ERRC’s developed technologies will be transferred to AIGR, such as oxidative dehairing, composite drying methods, finishing with natural antioxidants, and nondestructive testing. Results from this collaboration could positively impact U.S. tanneries and goat producers, who are mainly small farmers of minority and underserved populations, by increasing the use of U.S. goatskins domestically and increasing revenue for the goat and leather industries. Note: this project expired and is replaced by project 1935-41440-016-00D.


4.Accomplishments
1. Identified degreasers that may lower salt penetration when used for the preservation of hides: Sodium chloride is the most common preserving agent for raw hides and skins. An understanding of salt diffusion and the role that surfactants may play are necessary to make the preservation process more rapid and thereby less costly. Scientists’ experiments showed that salt entered the hide mainly from the flesh (bottom) side. Observations showed that one of the tested commercial degreasers and the biodegradable surfactant significantly removed fatty matter from the hide as well as enhanced the uptake of salt. Acceleration of salt penetration into the hide, should lead to a reduction in salt usage and turn-around times in hide preservation, thus significantly decreasing harmful environmental impacts and industry regulatory issues.

2. Decorin removal for improving quality of leather: It has been postulated that further removal of décorin could improve the softness of the leather product. Scientists developed a novel system for further removal of decorin, where alkaline protease is incorporated during the relime stage of pre-tanning, and pepsin is added in the pickling stage. Results confirmed that in general, the lower the décorin content, the better the quality of leather. Scientists demonstrated further improvement in the mechanical properties of the resultant leather if hides were oxidatively dehaired, which is a more environmentally friendly process than the traditional sulfide dehairing process. The results of this research have paved the way for the production of high-quality leather using an environmentally friendly dehairing process.

3. Leather finishing with natural antioxidants for enhancing leather durability: Durability of automotive leather is compromised by exposure to ultra-violet (UV) light and heat. 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 mixtures of humectants and tocopherols (Vitamin E) to the grain layer of chrome-free leather. Leather treated with glycerol/tocopherol mixtures resulted in significant improvement in strength retention and color fading resistance against UV radiation and heat. This research program strengthens the competitiveness of the U.S. hides and leather industries by encouraging environmentally friendly production, while imparting better quality to the finished product.

4. Better Understanding of effects of leather looseness on leather properties: Looseness is a very troublesome issue to tanners and results in the downgrading of leather to be used in lower end products. CWU scientists’ investigation resulted in a better understanding of the looseness effects on the fibrous structure and mechanical properties of concern to the leather industry. Scientists demonstrated that a separation gap exists between the interstitial layer (middle layer) and the corium layer (flesh side) in the loose leather, and the grain (hair side) appeared to be separated into sheet like structures. Mechanical property studies showed looseness led to a decrease in toughness. The results from this study have illustrated the loose structure and its resulting properties and provided the tanneries the insight on why they need to develop measures to correct this defect such as fine tuning the leather making processes, lowering the degree of fiber opening and adding fillers to the leather.


6.Technology Transfer

Number of Active CRADAs1
Number of Other Technology Transfer2

Review Publications
Anandan, D., Marmer, W.N., Dudley, R.L. 2008. Enzymatic Dehairing of Cattlehide with an Alkaline Protease Isolated from Aspergillus tamarii. Journal of American Leather Chemists Association. 103(10):338-344.

Ramos, M., Latona, R.J., Fortis, L.L., Marmer, W.N. 2008. Identification of Decorin and other Proteins in Bovine Hide during its Processing into Leather. Journal of American Leather Chemists Association. 103(10):324-329.

Liu, C., Liu, L.S., Latona, N.P., Goldberg, N.M., Cooke, P.H. 2009. Composite Drying with Simultaneous Vacuum and Toggling. Journal of American Leather Chemists Association. 104(4):131-138.

Liu, C., Ramos, M., Latona, N.P., Latona, R.J. 2009. Leather Coated with Mixtures of Humectant and Antioxidants to Improve UV and Heat Resistance. Journal of American Leather Chemists Association. 104(5):161-168.

Hernandez Balada, E., Marmer, W.N., Cooke, P.H., Phillips, J.G. 2009. Evaluation of Degreasers as Brine Curing Additives. Journal of American Leather Chemists Association. 104(5):169-176.

Last Modified: 4/21/2014
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