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Fabric To Dye For
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Samples of wool/cotton crosswoven blends dyed
in a single dye bath. The solid-color swatches were pretreated
so that both the wool and cotton yarns would pick up the dye evenly.
In the untreated fabrics, the cotton stayed largely undyed.
(K9139-1)
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Cotton may soon be afforded the same
upscale recognition as wool, thanks to new technology.
ARS chemists Jeanette M. Cardamone and
William N. Marmer have found a way to make cotton more chemically similar to
its high-end counterpart—wool—so that a fabric blend of the two can
be easily dyed.
Dyeing a cotton/wool blend is difficult because the two fibers have different
chemical makeups. Wool, which is sheep hair, is made of animal proteins, while
cotton is made of plant cellulose—the main part of a plant's cell wall.
Normally, when wool and cotton are blended together, two separate dye baths are
required because the wool takes up most of the dye.
"The process we developed is a new single-bath dyeing procedure called
union dyeing," says Cardamone. She and Marmer are with the Hides, Lipids,
and Wool Research Unit at ARS' Eastern Regional Research Center (ERRC), in
Wyndmoor, Pennsylvania. "This process helps textile manufacturers overcome
a major technological barrier: dyeing all-natural blends to the same depth of
shade in one step." |
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Technician Chet Sutton studies colorfastness of
a union-dyed wool/cotton blend.
(K9143-1)
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In the conventional procedure,
Cardamone explains, cotton is dyed first and wool second. Wool is dyed in an
acidic environment at high temperatures, and cotton is dyed in a nonacidic
environment at lower temperatures. This difference requires that the wool and
cotton be dyed either separately, or sequentially in one bath in which the pH
and temperature levels are changed. "Our improved method uses
pretreatments to make the cotton as receptive to dye uptake as the wool,"
she says.
Opposites Attract
Cardamone and Marmer's simple approach is to reverse the chemical charge of
cotton from negative to positive before dyeing; wool is already positive. To do
this, they use cationic fixatives—positively charged ions—which are
typically used after cotton is dyed to help it keep its color. Applying the
fixatives before dyeing gives both fiber components of the fabric a positive
charge. Since the dye is negatively charged—and opposites attract—the
cotton and wool dye to a uniform shade because the dye is attracted equally to
both fibers. This union-dyeing process uses one dye in one bath, under one set
of conditions. |
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Chemists Jeanette Cardamone and William Marmer
study records of the effect of dyeing regimen on dye uptake.
(K9137-3)
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Cotton industry officials are excited about the new process. "This
technology is easy to adopt," 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 no satisfactory method for cotton
mills to dye blends. This technology could potentially increase the use of
cotton." Cotton Incorporated wants to expand the use of cotton and make it
more profitable for cotton farmers and the textile industry.
"This process gives cotton an upscale market. A cotton/wool blend 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.
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Technician Kimberly Baxendale dyes samples of
a wool/cotton blend fabric.
(K9140-1)
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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 union-dyeing 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 blends. In sweaters, for example, the blend's 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, Agricultural Research Service Information Staff.
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-ARSEastern 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. |
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"Fabric To Dye For" was published in the
November 2000
issue of Agricultural Research magazine.
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