Submitted to: Wool International Conference Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/1995
Publication Date: N/A
Citation: Interpretive Summary: When attempting to dye fabric cross-woven with wool and cotton yarns, union shades (same color on wool and on cotton) are difficult to achieve because there is preferential dye uptake by wool. Current dyeing procedures require first dyeing cotton, then wool, and finally, adding more dye for final shade correction. We developed two methods for pretreating wool/cotton fabrics and subsequently dyeing the fabrics with one dye in one dyebath. Method 1 involves pretreating wool/cotton with the conventional resins used for durable press cotton in the presence of the chemical choline chloride. Method 1 is specific for dyeing with all dye classes from acidic dyebaths. Method 2 involves pretreatment with these same resins in the presence of a different chemical, monoethanolamine. Method 2 is specific for dyeing with "reactive dyes" for exceptional colorfastness. Results show that both methods yield true union shades, high take-up of dye from the dyebaths, and perfect colorfastness to light exposure and to the normal conditions of consumer wear and care, all without damaging wool.
Technical Abstract: A major difficulty in the production of wool/cotton fabric blends is the dyeing of union shades. Lengthy procedures often require multiple baths and multiple dye classes. For example, cotton may be dyed first, using a reactive dye at high pH, followed by the dyeing of wool with either an acid or direct dye at low pH and higher temperatures. These processes are cumbersome and require large additions of salt. Damage to wool is possible, and sometimes there is a need for final shade correction. We have developed two methods for the union dyeing of wool/cotton. They involve pad/dry/cure pretreatments with glyoxal crosslinking resins followed by simple one-bath dyeing procedures, single dye class, little or no salt, and favorable wool conditions. Method 1 is specific for dyeing with anionic dyes (acid, direct, and reactive dye classes) by ionic attraction and involves prefinishing with dimethyloldihydroxyethyleneurea (DMDHEU) and choline chloride. Method 2 is directed to reactive dyes for covalent bonding and involves prefinishing with glycolated- or methylated-DMDHEU and primary amines. Results show true union shades of 0.1% to 3.0% on weight of fabric, high exhaustion with levelness within 20 minutes, and >87% dye fixation. Colorfastness ratings were 5 (perfect) with acceptable strength retained. These methods overcome the problem of differential dye uptake of wool and they provide unprecedented ease of processing wool/cotton shades.