A process to make cotton more chemically similar to wool, so the two fibers can be combined into an easily dyed fabric blend, has been developed by Agricultural Research Service chemists.

Scientists, at ARS' Eastern Regional Research Center, in Wyndmoor, PA, developed the new single-bath dyeing procedure, called union dyeing, for wool-cotton blends. Normally, when wool and cotton are blended together, two separate dye baths are required.

Before the new process was developed, dyeing a cotton-wool blend was difficult, because the two fibers have different chemical makeups, leading to uneven coloring. Wool takes up most of the dye, while the cotton is left mostly undyed.

ARS' simple approach is to reverse the chemical charge of cotton, from negative to positive, before dyeing, so that both fabrics are positively charged. Wool is positive. The scientists use positively charged compounds called cationic fixatives, which typically are applied after cotton is dyed to help it retain color.

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 one-step union-dyeing process can be done with one dye, in one bath, under one set of conditions.

Experimental textile treatments like this one may broaden the market for cool-weather garments made of wool and cotton blends. This technology could cut textile dyeing costs, savings that can be passed to consumers seeking versatile garments for the spring and fall months.

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