Aug. 23, 2001 A textile scientist at North Carolina State University is developing a more efficient method of dyeing cotton that is not only less harmful to the environment, but also uses significantly smaller amounts of energy, water and salt in the dyeing process.
The key to the new process, called cationic fiber modification, is treating the cotton with a chemical that gives it a positive charge that attracts negatively charged dyes.
"The new process is much more efficient and saves about half of the time normally required to dye cotton. It uses one-third of the energy and only 20 percent of the water used in traditional methods, and no salt," said Dr. Peter Hauser, associate professor of textile engineering, chemistry and science.
Traditionally, cotton is dyed using water-soluble dyes, but these compounds don't naturally adhere well to cotton, so large amounts of salt must also be added to the mix to make the dye less soluble and better at adhering. The amount of salt needed sometimes approaches ratios of 1-to-1 by weight of the fabric. Large amounts of water are also needed -- it takes eight gallons of water to dye one pound of fabric.
In cationic fiber modification, a chemical called N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride is applied to the cotton before it is dyed. The chemical gives the cotton fiber a permanent positive electrical charge, which strongly attracts the negatively charged dyes. All cotton dyes have negative electrical charges.
As a result of the electrical attraction, less dye is needed, Hauser says, and the colors in the fabric appear to be more vivid. There is no noticeable change in the texture of the cotton fiber.
Another benefit of the new process, he says, is that it can be done using standard dyeing and finishing machines, so manufacturers don't have to retool their operations.
Hauser is now focusing his research on how to streamline the new process even further. Currently, he says, one drawback is that the fabric has to be taken out of the manufacturing line to have the chemical applied. Then it must be given time to react with the chemical. This extra step significantly slows the process of dyeing and finishing, which are best completed as one uninterrupted process.
Hauser is working to overcome that problem, but the biggest hurdle may be convincing industry to embrace the new process.
"The textile industry is very slow to adopt change, (especially on) something like this that mainly reduces pollution and energy consumption. There's been some interest in this, but so far commercialization has been slow," Hauser said. "This is going to be driven by the people who need to reduce pollution from their plant, or want to save energy or double their production capacity without buying more equipment."
Hauser's research is sponsored, in part, by Dow Chemical Co., the manufacturer of the chemical that gives the cotton a positive charge.
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