ABSTRACT

In this study, we investigated the effect of the treatment of cotton fibers with N-methylolamide crosslinking agent, hydroxyalkylamine or quaternary ammonium salt additive, and polyethylene glycol on the mechanical processing of fibers into yarn and knitted fabric. We also investigated the dyeing properties of the resulting smooth drying fabric with anionic dyes of several dye classes.

Cotton fibers (average staple length = 1.09 inches) were treated in both the picker lap and carded sliver form by padding with solutions composed of 5-6% dimethylol- dihydroxyethyleneurea (DMDHEU) crosslinking agent, 1.8% magnesium chloride hexahydrate or magnesium chloride hexahydrate/citric acid mixed catalyst system (20:1 ratio), 5-6% triethanolamine hydrochloride (TEAHC1) or tetrakis (2-hydroxyethyl) ammonium chloride (THEAC), and 5- 6% polyethylene glycol (PEG) with molecular weights of 400 or 600. The treated fibers were dried, opened, carded, spun into 22/1 yarns, and then knitted into 3.5 inch circular plain jersey knit fabrics on a Lawson- Hemphill fiber analysis knitter. Afterwards, the knit fabrics were cured at 160EC for 3 minutes in a forced-draft laboratory type oven to insolubilize the chemical agents and produce a smooth drying fabric with dimensional stability.

Although the nitrogenous agents might be expected to increase fiber friction, the polyethylene glycol would be expected to lubricate the fibers and promote efficient mechanical processing after the fibers were treated and dried. Accordingly, in this study the fibers were processed without difficulty. Yarn analysis revealed that the number of neps for the treated picker lap cotton was greater than that for the control yarn, and the nep count was higher for fiber treated with TEAHCL and PEG than with THEAC and PEG. The nep count was also higher for fiber treated with nitrogenous additive and PEG 400 than for the same additive and PEG 600. However, the nep count on yarn from treated carded fibers was less than that for the control yarn. This is because the yarn from the treated carded sliver is composed of fibers that were carded twice, both before and after treatment with the chemical formulation. With respect to thick and thin sections of the yarns, ratios of thick to thin components for treated yarns were comparable to that of the control yarn. The best overall properties were attained on yarn from fibers treated with THEAC and PEG 600.

After the crosslinking operation at elevated temperature, the knitted fabrics were dyeable with anionic dyes such as acid, direct, and reactive dye classes. Usually, cotton is not dyeable after crosslinking because of restricted fiber swelling. Nevertheless, the nitrogenous additives are instrumental in increasing the affinity of the crosslinked substrate for various classes of anionic dyes. Some of these dyes, such as acid and reactive dyes, normally have no affinity for cotton under the conditions employed. The finished fabrics were dyed by using conventional dyeing techniques, except that the pH of the dye solutions were adjusted to 3 with acetic acid. However, fabric containing quaternary ammonium salt additive is dyeable over a wider pH range (pH 3-6). Surface appearance of the dyed knitted material was very good. Excessive amounts of chemicals were avoided not only because of potential processing problems of the fibers, but also because of fiber strength losses which result from crosslinking of cellulose at elevated temperatures.

Some of the concerns associated with dyeable, crosslinked cottons are evenness and uniformity of the dyeings. These properties are influenced by the total finishing process. Any unevenness in the application of the of crosslinking agent and reactive additive invariably results in uneven dyeing.

Additionally, migration of reactants within the fiber during the drying process also influences dyeing uniformity. The reason for this is that dye sites are limited to the location of the amine hydrochloride or quaternary ammonium salt additive which is affixed to the cellulosic substrate through the crosslinking agent. Treatment of cotton in the fiber form should alleviate some of the these problems because of random distribution of chemical agents within the fibers prior to fixation in fabric form. Analysis of fiber cross-sections reveals that dye distribution is good even with relatively large size dyes, especially considering that the fibers are crosslinked. Although these treatments and processes were conducted on a very small scale, the operation demonstrates that fiber treatment and subsequent processing into yarn and fabric for specialty effects of the finished product is feasible if suitable finishing techniques and processing procedures are utilized.