1a. Objectives (from AD-416):
1. Develop commercially viable hide preparation and leather processing methods that are environmentally friendly while maintaining and improving the quality and/or value of hide products. 1A: Develop computational and laboratory models for predicting the effectiveness of new chrome-free tanning agents. 1B: Develop improved environmentally friendly processes for hide preparation. 2. Create commercially viable hide-quality sensing technologies that are more rapid, accurate, precise, nondestructive, and cost-effective than current systems. 3. Develop technologies that enable new products from hides such as green composites (reinforced with hide fibers), nonwoven fabric filters, and new fillers and coatings for leather. 3A: Develop green composites and fibrous materials from hides. 3B: Develop new applications for tanning waste.
1b. Approach (from AD-416):
To develop a basis for designing or selecting effective chrome-free tanning agents, the results of studies of the interactions between collagen and current or proposed tanning processes will be integrated to give the best overall evaluation. The ERRC computational molecular model of collagen will be used to predict how the secondary or tertiary structure of collagen might be affected by a proposed modification. The model can predict if the modifier will fit into the structure, and how likely is the modifier to attach to telopeptide residues or form bonds with sidechains in the end-to-end gap between triple helices. Bench scale experimental model systems using collagen at different stages of molecular complexity (soluble collagen, milled collagen or powdered hide) will be used to evaluate by physical, chemical and biochemical methods the effect of these modifications on collagen. The development of effective and eco-friendly methods for removal of manure and other organic contaminants from animal hides will build on the incorporation of glycerol or biosurfactants or combination of both. Methods to enhance hide preservation using less salt or salt-free alternatives will also be developed. Environmental and economic concerns in terms of obtaining better quality hides and higher returns are the major criteria for developing and accepting new and alternative cleansing and preserving techniques. The goal is to not completely remove all of the manure prior to processing but to achieve a state where the manure/hair adhesion can be broken by a mechanical removal process without removing the hair at the root or tearing the grain. The advanced evaluation technology for the detection of hide defects and the evaluation of hide quality will be developed by incorporating airborne ultrasonic (AU) technology. Green composites will be designed and prepared with gelatin as the matrix reinforced with collagen fiber networks. Both components will be derived from hides. In addition, new fibrous products such as filters having a nonwoven fibrous structure will be prepared from fine diameter collagen fibers (fibrils). Collagen fiber networks will be obtained from split hides that have been processed to remove the noncollagenous materials. The use of chemical and biochemical techniques for enhancing the properties of tanning byproducts will proceed concurrently with the work on tanning. To demonstrate a potential role for protein recovered from leather waste, used alone or in conjunction with other renewable agricultural resources, model systems will be developed, in which these renewable resources will be treated with known chemoenzymatic crosslinking agents to determine functional properties. Effects then will be made to establish if these products would be appropriate to be used in leather processing, for example as potential fillers, coatings and encapsulating agents. Aqueous gelatin will also be combined with fibrous protein waste products, such as chrome shavings, buffing dust, feathers, and meat & bone meal, and then the mixture will be modified with enzyme to prepare products, such as films, with unique functional properties.
3. Progress Report:
For the development of models to predict the effectiveness of chrome-free tannages (Objective 1a), powdered hide prepared from hides that had been dehaired by traditional and more eco-friendly methods was carried through the steps to produce vegetable tanned leather. The effectiveness of vegetable tannages on hides dehaired by different methods were evaluated to assist the tanner in modifying later stage processes. Computational methods were used in the development of a fundamental understanding of tanning mechanisms. Methods were developed for including hide processing steps, and water, an essential component of leather, in the computational model. In the development of environmentally friendly processes for hide preparation (Objective 1b), a low salt hide preservation process was evaluated and obtained by incorporating crude glycerol and sodium carbonate with low concentration of various molecular weights of polyethylene glycol (PEG). The alternative preservation brining solution with low molecular weight PEGs showed promising improvement in water removal efficiency even at lower salt concentration. Because the presence of crude glycerol in the presoaking formulation that can remove adobe type manure generated better quality leather, its incorporation could help in counteracting the fast drying effect of PEG and also avoid longer rehydration process of the preserved hides. For the creation of commercially viable hide-quality sensing technologies (Objective 2), project scientists used airborne ultrasonic (AU) transducers with low resonant frequencies to evaluate the quality of hides and leather. The use of low resonant frequencies enables an effective transmission of ultrasound waves through hides or leather. Results showed the moisture content of the test sample is an important factor affecting scanning results in addition to the sample’s thickness and elasticity. In the development of technologies for new products (Objective 3a), pieces of limed hides were neutralized, completely dried and then ground in a Wiley Mill using a 1 mm, 2 mm or 4 mm screen size. Non-woven sheets were prepared using paper-making technology. They were then used as reinforced components to make composites that use gelatin as the matrix. Mechanical properties were evaluated for the resultant composites with various fiber contents. In the development of new applications for tanning waste (Objective 3b), studies were continued on the application of fillers from polyphenol-modified gelatin on wet blue and wet white leather; these studies resulted in leather being produced with enhanced properties. In cooperative research for oxidative dehairing of cattle hides, ARS scientists completed CRADA and demonstrated the potential of oxidative dehairing as well as the optimal parameters required to have an effective process. Further processing adjustments down line were identified and these, along with a better understanding as to whether the chemistry of the hide has been altered by this treatment, are areas that currently are being addressed.
1. Developed an eco-friendly and effective low salt brining process to preserve bovine hides. Raw hides are traditionally preserved with high amount of salt before they are stored and shipped to tanneries to be processed into leather. Thus, a large volume of water with high salinity adds more to the cost of waste water treatment causing the need for low salt or salt free preservation alternatives. ARS researchers at Wyndmoor, Pennsylvania have developed promising alternative low-salt hide preservation formulations that have a lower impact to the environment. The physical properties of preserved hides using low salt but incorporated with crude glycerol and low molecular weight polyethylene glycols were comparable to the control hides traditionally preserved using high salt (brine) solutions. In addition, the leathers obtained from hides preserved with the newly developed alternative process showed significant improvements in mechanical properties. The leather samples obtained were generally softer, more stretchable, and stronger compared to the control samples.
2. Better-quality leather products from hides treated with renewable vegetable tannin-modified gelatin fillers. The production of leather from cattle hides generates significant amounts of inedible gelatin. ARS researchers at Wyndmoor, Pennsylvania modified gelatin with the vegetable tannin, tara (caesalpinia spinosa) a gallotannin to produce products that could be used effectively as a filler in leather processing. Tara modified gelatin is almost colorless, an advantage in production of light colored leather; it also imparts light-fastness to leather. The treated leathers, both chrome tanned and chrome free, when processed using tara modified gelatin, demonstrated significant improvement in subjective properties (e.g. softness and fullness); there were no significant differences in the mechanical properties. Thus a byproduct (gelatin) from leather-making process, modified with a common renewable polyphenolic tanning agent (tara), can be employed to make finishing products for the leather-making process.
3. Fiber-reinforced composites developed from tannery solid wastes. The hides and leather industries are facing a serious challenge in the disposal of solid wastes, such as trimmings and splits generated in various manufacturing processes. Most of these wastes are transported out of processing plants for landfills, not only incurring the expense of transportation but also creating environmental issues. ARS researchers at Wyndmoor, Pennsylvania have solved this problem by developing the methods to convert these wastes into useful products such as fiber-reinforced composites (FRC). Potential applications of FRC include landscaping timbers, park benches, window and door frames, and indoor furniture. Research was done to process the solid wastes into collagen fibrous networks, which were then mixed with gelatin and molded into fiber-reinforced composites. A major domestic tannery has shown great interest in a collaboration to evaluate the commercial potential.
Liu, C., Latona, N.P., Taylor, M.M., Latona, R.J. 2013. Effects of bating, pickling and crosslinking treatments on the characteristics of fibrous networks from un-tanned hides. Journal of American Leather Chemists Association. 108(3):79-85.