Abstract
A two-stage sequential pretreatment including caustic mercerization (CM) and liquid ammonia (LA) treatment was applied to investigate the influence on dyeing performance and handle of knit cotton fabric, and the relationship between dye size and dyeing properties. Various techniques were applied to characterize all the treated fabrics. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses of the treated fabrics confirmed that both sequential treatments decreased the crystallinity of cotton fabric more than only the CM or LA treatment. The pattern of cellulose I was transferred to a mixed configuration of cellulose II and cellulose III after the CM/LA or LA/CM treatment. Thermal performances measured by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) techniques showed that the thermal stability of the treated cotton only marginally decreased. The wicking height increased after the sequential CM/LA treatment, indicating that the hydrophilicity of the fabric increased. The dye absorption and color uniformity were better for the reactive dye with a smaller molecular weight (Reactive Red 2) compared with the one with a larger molecular weight (Reactive Red 195). The total dye fixation efficiency (T%) increased to 72.93% and 73.24% for Reactive Red 2 dyeings of CM/LA- and LA/CM-cotton fabric from 46.75% of the untreated fabric, respectively; the T% increased to 65.33% and 72.27% for Reactive Red 195 dyeings of CM/LA- and LA/CM-cotton fabric from 35.17% of the untreated fabric, respectively. The colorfastness and dye exhaustion and fixation percentages of the samples were enhanced after the treatments. Furthermore, compared to the single CM or LA treatment, the softness handle properties were further improved after the fabrics were sequentially treated by CM/LA. The developed pre-treatment of CM/LA can be used in the textile industry to promote the dyeability, handle, and mechanical properties of knit cotton fabrics.
Highlights
Mercerization pretreatment by caustic mercerization (CM) or liquid ammonia (LA) in the textile sector is often employed to improve several characteristics of cotton fabrics, including luster, tensile strength and dyeability [1,2]
It is known that mercerization by CM or LA decreases the crystallinity of cotton fiber, i.e., more amorphous regions in fiber are produced, but LA treatment is more effective than CM [10]
The CM/LA-treated and LA/CM-treated cotton fabrics dyed with Red 2 had the same E% values, because the Red 2 molecule was small enough to migrate through the small size pore of cotton fiber, which is consistent with the wicking results
Summary
Mercerization pretreatment by caustic mercerization (CM) or liquid ammonia (LA) in the textile sector is often employed to improve several characteristics of cotton fabrics, including luster, tensile strength and dyeability [1,2]. It is known that mercerization by CM or LA decreases the crystallinity of cotton fiber, i.e., more amorphous regions in fiber are produced, but LA treatment is more effective than CM [10]. The crystallinity of untreated cotton fiber was 65.7%, and it decreased to 61.4% and 58.6% by CM and LA treatment, respectively [6]. The dyeability of mercerized cotton fiber should increase based on the dyeing principle. The LA-treated cotton fiber only exhibits a poorer dyeability in using big reactive dyes [11]. The dyeing mechanism of cotton fiber with reactive dye differs from the direct dye. Without any dye fixation post-treatment, the reactive dyed cotton fiber shows a higher colorfastness to washing and rubbing, compared to direct dyed one. It is significant to investigate the dyeing performance and handle of CM, LA, CM/LA, and LA/CM pre-treated knit cotton fabric with reactive dye. Fabric softness was directly obtained with a WOOL HandleMeter instrument
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