Source: http://www.agclassroom.org


Cotton may soon beafforded the same upscale recognition as wool, thanks to new technology. ARSchemists Jeanette M. Cardamone and William N. Marmer have found a way to makecotton more chemically similar to its high-end counterpart-wool-so that afabric blend of the two can be easily dyed.



Samples of wool/cottoncrosswoven blends dyed in a single dye bath. The solid-color swatches werepretreated so that both the wool and cotton yarns would pick up the dye evenly.In the untreated fabrics, the cotton stayed largely undyed.


Peggy Greb (K9139-1)


Dyeing a cotton/woolblend is difficult because the two fibers have different chemical makeups.Wool, which is sheep hair, is made of animal proteins, while cotton is made ofplant cellulose-the main part of a plant's cell wall. Normally, when wool andcotton are blended together, two separate dye baths are required because thewool takes up most of the dye.


"The process wedeveloped is a new single-bath dyeing procedure called union dyeing," saysCardamone. She and Marmer are with the Hides, Lipids, and Wool Research Unit atARS' Eastern Regional Research Center (ERRC), in Wyndmoor, Pennsylvania. "Thisprocess helps textile manufacturers overcome a major technological barrier:dyeing all-natural blends to the same depth of shade in one step."


In the conventionalprocedure, Cardamone explains, cotton is dyed first and wool second. Wool isdyed in an acidic environment at high temperatures, and cotton is dyed in anonacidic environment at lower temperatures. This difference requires that thewool and cotton be dyed either separately or sequentially in one bath in whichthe pH and temperature levels are changed. "Our improved method usespretreatments to make the cotton as receptive to dye uptake as the wool," shesays.


Opposites Attract


Cardamone and Marmer's simpleapproach is to reverse the chemical charge of cotton from negative to positivebefore dyeing; wool is already positive. To do this, they use cationicfixatives- positively charged ions-which are typically used after cotton isdyed to help it keep its color. Applying the fixatives before dyeing givesboth fiber components of the fabric a positive charge. Since the dye isnegatively charged-and opposites attract-the cotton and wool dye to a uniformshade because the dye is attracted equally to both fibers. This union-dyeingprocess uses one dye in one bath, under one set of conditions. Cotton industryofficials are excited about the new process. "This technology is easy toadopt," says John Turner, a senior chemist with Cotton Incorporated in Cary, North Carolina. It doesn't require elaborate equipment or expense.


In the past, there was nosatisfactory method for cotton mills to dye blends. This technology couldpotentially increase the use of cotton. "Cotton Incorporated wants to expandthe use of cotton and make it more profitable for cotton farmers and thetextile industry. "This process gives cotton an upscale market. A cotton/woolblend would have greater value than a 100-percent cotton item,"

 

Turner says. "And depending on the blend level, it could be cleaned in the washing machine". Cotton Incorporated has a research partnership with the ERRC scientists. The wool industry also finds the concept appealing because it creates a new market for wool. Approximately 66,800 sheep producers raise 7.2 million sheep and lambs, producing about 49.2 million pounds of wool in the United States. Even so, the country still imports wool from Australia and New Zealand. This technology could help open more markets for American wool by increasing demand.




Keeping Colors Colorful


The ERRC scientists also use another method that helps make dyeing wool/cotton blends possible-a durable-press finishing resin. The resin treatment was originally developed by chemists at the ARS Southern Regional Research Center (SRRC) in New Orleans, Louisiana, to prevent wrinkling in 100-percent cotton. SRRC scientists further developed the technology to increase cotton's dyeability. SRRC chemist Eugene Blanchard collaborated with ERRC scientists on using the durable-press finishing resin treatment for cotton/wool blends. Cardamone says resin treatments, which are alternatives to cationic fixatives, are important for good colorfastness in laundering. Colorfastness is a textile industry standard that determines how stable the color is in a garment. Good colorfastness means the garment won't fade after one washing. Resin pretreatment is best for garments that require excellent colorfastness. Cationic fixatives could be used for outerwear garments where colorfastness to washing is moderate but colorfastness to dry cleaning is high, notes Cardamone."Both pretreatment systems will effectively lead to uniondyeing of wool/cotton blends, but the treatment should be selected to accommodate the anticipated end use. A wool/cotton-blend fabric is ideal for multiseason apparel because wool provides inherent resiliency and warmth while cotton contributes comfort and coolness," says Cardamone. "These experimental textile treatments may broaden the market for cool-weather garments made of cotton/wool blend's. In sweaters, for example, the blends wool component retains body heat and imparts thickness, while cotton makes it comfortable to wear. Both natural fibers are great at wicking away moisture, too." Through a cooperative research and development agreement between ERRC researchers and chemical specialties manufacturer Hercules, Incorporated, other pretreatment systems are being investigated. Applied commercially, these technologies may cut textile dyeing costs-savings that can be passed on to consumers seeking versatile garments for spring and fall.-By Tara

 

Weaver-Missick, ARS.


This research is part of New Uses, Quality, and Marketability of Plant and Animal Products, an ARS National Program (#306) described on the World Wide Web at http://www.nps.ars.usda.gov .

William N. Marmer and Jeanette M. Cardamone are with the USDA-ARS Eastern Regional Research Center, Hides, Lipids, and Wool Research Unit, 600 East Mermaid Lane, Wyndmoor, PA 19038; phone (215) 233- 6585 [Marmer], (215) 233-6680 [Cardamone], fax (215) 233-6795, e-mail wmarmer@arserrc.gov and jcardamone@arserrc.gov.




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