New Technology for Animal Hides, Wool, and Cotton

by William N. Marmer, Research Leader, Hides, Leather, and Wool Research Unit, Eastern Regional Research Center, ARS, USDA, Philadelphia, PA, and Noelie R. Bertoniere, Research Leader, Textile Finishing Chemistry Research Unit, Southern Regional Research Center, ARS, USDA, New Orleans, LA.

When we think of nonfood agricultural commodities produced in this country, cotton surely comes to mind as a source of fiber for clothes. Nevertheless, two major byproducts of the meat industry are also major sources of nonfood products for apparel: sheep give us wool, and the hides of sheep, pigs, and cattle give us leather.

You might guess correctly that cotton is overwhelmingly the most significant natural fiber crop in this country. We meet all our national needs for the raw fiber from the domestic crop. Even when cotton in finished products is included, we are a net exporter as well. The scope of USDA-ARS cotton research covers the full breadth of the cotton industry, including such diverse areas as cotton growth, ginning, marketing, spinning and weaving, and textile finishing. Much of the program has been centered at the Southern Regional Research Center (SRRC) of the Agricultural Research Service (ARS) in New Orleans.

In terms of wool, we meet a third of our needs for raw wool fiber from the domestic clip, but when wool in imported garments is factored in, that figure drops to 13 percent. Australia and New Zealand, the world's major exporters of wool, raise their sheep primarily for fiber. American wool, on the other hand, is truly a byproduct of the lamb industry. The current ARS program in wool research is a small one, functioning out of the ARS Eastern Regional Research Center (ERRC) in Philadelphia. The aim of the current program is to add value to the domestic wool clip, which suffers in its market return relative to its foreign counterparts.

Regarding hides and leather, the United States produces more animal hides than its tanning industry can convert to leather, so our hide export market is a $2 billion-a-year industry. We are also net exporters of unfabricated leather, but when shoes and other fabricated products are factored in, we are overwhelmed by imports. ARS research in hides and leather is also centered at ERRC and focuses on all aspects of research, from hide quality and preservation through tanning and finishing.

This chapter concentrates on some new technological developments from all of these ARS programs. Research is directed toward making quality products, making the domestic products more competitive with their foreign counterparts, making our products more durable and easy to care for, and assisting the producers and users of these commodities in working within increasingly stringent environmental controls.

Wool: Bleaching Stained Fibers and Black Hairs

Raw wool carries with it such a tremendous amount of extraneous material that the true wool yield may be only half the original weight of the fleece. Most of the contaminants, such as grease, are washed out during "scouring." However, two contaminants particularly problematic in some domestic wools are stubbornly persistent heavily stained fibers and black hairs. Stained fibers give wool a yellow cast that is particularly noticeable when the end product is a white or pastel-dyed garment. As for black hair, just a few enmeshed in the thousands of white fibers in a piece of fabric are amazingly conspicuous.

Stained fibers are traditionally bleached with hydrogen peroxide, an oxidative bleach. Once oxidative bleaching is done, it may be followed with reductive bleaching (another class of bleaching agent) to achieve the whitest products. Such combined or "full" bleaching is an expensive process because it involves the preparation and heating of two separate bleach baths and the rinsing of the product in between. In general, full bleaching is not practiced.

ARS scientists in Philadelphia looked at full bleaching and discovered that the two processes could be combined into one sequential procedure in the same bath. In the new process, the two parts are accomplished in a clever way by chemical manipulation of the peroxide left over after the initial oxidative bleaching. Instead of discarding that bath, the peroxide is chemically converted to a reductive bleach by addition of thiourea to the bath. The result is extra whiteness.

Bleaching black hairs and stained fibers simultaneously is particularly difficult. The textile industry uses a variation of peroxide bleaching that requires specifically for the black hairs treatment of the wool with iron salts. When the new ARS process is coupled with the iron-salt method, the elimination of the rusty discoloration that sometimes results from residual iron is an added benefit.

Followup work is now permitting the single-bath full-bleaching concept to be extended to allow subsequent dyeing in the same bath. ARS scientists have been granted four patents to cover the bleaching process in all its variations. These scientists have worked to transfer this technology to the private sector by assisting woolen mills in experimenting with the system in their plants. One license has already been granted, a partially exclusive license for one niche of the woolen market.

Chemist Frank Scholnik (left) and research associate James Chen examine the results of experimental treatments for leather. The Agricultural Research Service has designed an environmentally friendly way to sterilize hides with electron-beam irradiation rather than salt brine curing.

Scott Bauer/USDA 92BW0839

Hides and Leather

Hide Preservation. When a hide comes out of the packing plant, it usually has to be preserved for a long period during shipping to and storage at the tannery. Almost all hides are preserved through curing in a concentrated salt brine. Needless to say, this is a large generator of salt pollution. ARS scientists in Philadelphia have looked at an unconventional way of preserving hides without using salt.

Irradiation by a beam of electrons is currently used to sterilize small items such as surgical bandages and scalpels. It is very effective so long as the item is enclosed in sterilized packaging. In 1986, a number of hides were sealed in plastic with a small amount of bactericide, then irradiated with an electron beam. Some of those hides were soon tanned to leather, and the properties of the resulting leather were compared to those of leather from brine-cured hides. Differences were inconsequential. More impressive, however, was recent experimentation on the remaining hides in which tanning was delayed; 5 years later, samples were removed from their packaging and tanned to leather of excellent quality. The private sector is showing renewed interest in such preservation, and new research is under way.

Recycling of Solid Tannery Waste. Tanneries generate a tremendous amount of solid waste during the multistep conversion of hides into leather. Much of this waste is chrome-containing solid waste from the 90 percent of hides that are chrome tanned. This waste, mostly destined for landfills, amounted to over 50,000 metric tons in the United States in 1988 alone.

The tanning industry appealed to ARS scientists in Philadelphia to look into chrome waste. Landfill expenses were skyrocketing, and environmental concerns were rising over potential hazards from this waste. Although the chrome in this waste is not the toxic variety and is legal in landfills, questions have been voiced over the longterm fate of the waste in landfills.

ARS responded by developing a process that allows the chrome to be separated from the waste. The recovered chrome can be recycled back into the tanning operations, and the balance of the material, now chrome-free, can be used for fertilizer or as an additive for cosmetic products or animal feed. The ARS process has been patented, and worldwide interest has led to initial licensing activity.

Computer Modeling of Hide Protein (Collagen). Why would such a theoretical item as collagen modeling be included in a chapter on new technology? The computerized molecular model of collagen is being developed and refined, and new changes to the model are continually made available to the world's research community through the Protein Data Bank of the Brookhaven National Laboratory. This ARS model is of immense value, not only for leather research but also for diverse studies of collagen's role in human skin and bone tissue.

A lot of tanning technology has been developed from experience or observation, with no real understanding of why it works. This is particularly true for chrome tanning. Why is chrome tanning so effective? It is because chrome (or its substitutes) interacts with collagen, the backbone molecule for hide tissue. Collagen is a complex molecule that forms bundles seen under the microscope as fibers.

The computer model, a detailed map of every atom of these fibers, will be used to learn how chemicals such as chrome neatly fit into the molecular structure of collagen during tanning. In response to increasing pressure for investigation of "environment-friendly" chrome alternatives, the model will be used to test the ability of chrome substitutes to "dock" with collagen. Followup studies in the lab and tannery will be used to confirm the effectiveness of these chrome alternatives as tanning agents.