Keith R. Beck

NIR Characterization and Measurement of the Cotton Content of Dyed Blend Fabrics

Near infrared (NIR) techniques for the measurement of cotton-polyester (PET) blend content have concentrated on yarn slivers and greige fabrics rather than the more difficult application to dyed or printed fabrics. The need for a robust and rapid measurement of the fiber content in dyed cotton-PET fabrics has been expressed by several organizations. Investigations were initiated to develop NIR techniques to measure the cotton content of dyed blend fabrics. NIR measurements were made on dyed or pigmented cotton-PET fabrics that comprised a wide range of cotton content, fabric parameters, and patterns/colors. The samples were analyzed on two NIR instruments at two locations with various reflectance NIR sampling systems. Significant spectral differences were observed for 100% cotton and 100% PET samples, and these spectral differences carried over to the dyed cotton-PET samples with changing cotton content. The impacts of significant differences in baseline were minimized with the use of advanced chemometric normalization techniques. Rapid (less than 5 minutes) and accurate NIR measurements of the blend content in dyed cotton-PET fabrics were developed, with a NIRlaboratory method agreement normally within ± 3.0% cotton for nearly 90% and higher of the validation samples.

Effect of Different Catalysts on the DMDHEU-Cotton Cellulose Reaction

The utility of alkaline hydrolysis as a method for removal of DMDHEU crosslinks from cotton is illustrated in this paper. The method was applied to fabric treated with DMDHEU/MgCl 2 and DMDHEU/MgCl2/citric acid mixed catalyst systems. Removal of the finish was complete as verified by nitrogen and formaldehyde analyses and by wrinkle recovery measurements. Losses in breaking strength and flex abrasion resistance produced in the cotton fabric upon treatment with DMDHEU were almost completely restored by the resin stripping. The DMDHEU/MgCl 2 treatment reduced the dpv (degree of polymerization by viscosity) of cotton by about 24% and DMDHEU/mixed catalyst treatment reduced it by about 18%. The quantity and chemical nature of the catalyst affect the ethyl acetate solubility of cellulose nitrate formed after stripping and nitration of crosslinked samples. Neither of the catalysts alone imparted ethyl acetate insolubility, but each catalyst by itself decreased the degree of polymerization of the cotton cellulose to a significantly greater extent than in the presence of DMDHEU. Fabrics treated with high concentrations of both catalyst systems could not be completely stripped of nitrogen and formaldehyde, and were not soluble in ethyl acetate (after nitration).

A New and Effective Method for Removing DMDHEU Crosslinks from Cotton 1

A new and relatively simple method for removing zinc nitrate-cured DMDHEU crosslinks from cotton cellulose is reported. The method entails boiling the finished fabric in 23% NaOH for 10 minutes. Removal of the finish was verified by nitrogen and formaldehyde analyses and by wrinkle recovery measurements. Little change in viscometric degree of polymerization (dpv), copper number, carboxyl content, breaking strength, and abrasion resistance of an untreated control fabric subjected to alkaline hydrolysis indicated that the stripping method was nondegradative. Losses in breaking strength and flex abrasion resistance produced in the cotton fabric upon treatment with DMDHEU were almost completely restored by resin stripping. Relatively small increases in reducing groups and carboxyl content and a dp loss of only about 13% (500 out of 3700) indicated that treatment of cotton with the DMDHEU/zinc nitrate system produced little chemical damage in the cellulose.

Reagent Residues of DMEU on Cotton Fabric as a Function of Pad-Bath pH and Storage Period of the Treated Fabric

The effect of pad-bath pH and storage of padded fabric on the stability of DMEU was investigated. In addition to the expected demethylolation products, MMEU and EU, other oligomeric/polymeric materials were generated. Since the latter were not quantifiable by liquid chromatography, they were measured by nitrogen analysis. Some of the oligomeric residues were water soluble and were extracted along with the DMEU, MMEU, and EU, while others were water insoluble and remained on the fabric. When padded from a bath of pH 6-10, DMEU was stable on the fabric for about two days. As pH was decreased from 6 to 3, formation of water-soluble oligomers and water-insoluble polymers increased significantly. At pH 10, even after 15 days, no oligomer/polymer was observed as the total residue was accounted for by the DMEU, MMEU, and EU. Differences between DMEU and DMDHEU under similar pH and storage conditions are discussed.

The Effect of Pad-Bath pH and Storage Period on the Hydrolysis of DMDHEU

The effect of pad-bath pH and storage of padded fabric on hydrolysis of DMDHEU has been investigated using aqueous liquid chromatography. The study showed that hydrolysis of DMDHEU during storage of the padded fabric is dependent more on the pH of the pad-bath than on the storage period. The hydrolysis of DMDHEU to MMDHEU is accelerated above pH 6, and at pH 9 subsequent hydrolysis of MMDHEU to DHEU occurs. At pH 10 the rate of hydrolysis of DMDHEU and MMDHEU is very high, relative to the rales at lower pH values, and even DHEU decomposes to unidentified products at this high pH. At pH 3-6 little hydrolysis of DMDHEU on padded fabric is detected, even after 55 days.

Stability of DMDHEU and Alkylated Crosslinking Finishes Towards Acidic and Alkaline Hydrolysis

Cotton fabrics treated with various alkylated derivatives of DMDHEU were subjected to hydrolysis by urea-phosphoric acid, hot 23% sodium hydroxide, and urea-phosphoric acid followed by sodium hydroxide. Sequential treatment with acid and base removed more nitrogen and formaldehyde than the alkaline treatment, which removed more nitrogen and formaldehyde than the acid treatment. Stability of the crosslinks generated by these resins depended on both the degree of alkylation of DMDHEU and the nature of the alkyl cap. This stability was reflected in greater amounts of residual nitrogen and formaldehyde after hydrolysis. Those residues, in turn, affected the residual break ing strength, flex abrasion resistance, and wrinkle recovery of the hydrolyzed fabrics. The stability of the crosslinks also correlated well with formaldehyde release data for the treated fabrics.

Reply to "Comments on 'A New and Effective Method for Removing DMDHEU Crosslinks from Cotton'"

The removal of a DMDHEU finish from a cellulosic fabric by base-catalyzed hydrolysis is expected to occur by chemical mechanisms similar to those suggested for the alkaline hydrolysis of alkoxymethylureas [8] and for the formation and ring opening under alkaline conditions of 4,5-dihydroxyethyleneureas [ 12]. Reactions in basic media of this sort are generally initiated by removing a proton from either the urea nitrogen or the hydroxyl oxygen [10]. Eventually the ring opens and the product yields the starting materials or other products. If DMDHEU acts as a tetrafunctional agent and both kinds of protons are absent, then no hydrolysis of the finish would be expected unless conditions