Summary: Of prime importance in reactions involving insoluble cellulosic fibers is the sorption of reagents, which is governed by their degrees of accessibility in substrates. Swelling treatments of cellulosics in alkali solutions alter substrate accessibility leading to changes in their reactivity. In this paper, the first of a two-part series, we collate and examine the results from various studies involving different techniques to characterize modifications in cellulosic fibers after swelling treatments in alkali solutions. Results from measurements of structure and accessibility in fibers with techniques such as water retention, inverse size exclusion chromatography (ISEC), iodine sorption, fiber diameters, and fiber-splitting propensities indicate that the influence of swelling treatments on fiber structure/accessibility is differs with alkali type. The results show that a non-uniform rather than uniform distribution of reagents within structures is a more accurate representation of reactions involving swollen cellulosic fibers. Hence, the observed changes in cellulose-fiber reactivity are governed by the degrees of fiber swelling, and reagent sorption and accessibility during swelling treatments.
Bi-functional reactive dyes have been used for reducing the fibrillation of lyocell fibres. The sole influence of CI Reactive Black 5 dye on the fibrillation tendency of lyocell single jersey knitted fabrics was investigated by dyeing with different concentrations (35 g/L for medium shade and 70 g/L for dark shade), dyeing without dyestuff and by decolouration process after each dyeing. The fibrillation tendency of lyocell fibres was accessed by means of fibre wet abrasion resistance and fibrillation number. Nitrogen content was used as indication of the amount of reactive dye in fabrics during dyeing and decolouration processes. The correlation between fibre fibrillation tendency and colour values of fabrics was found. Due to the fibrillation reduction, pilling formation in dyed lyocell fabrics was improved. As colour values can estimate the dye fixation and reduction in fabrics, reactive dye can be used as a visible marker for crosslinking effect on lyocell fabrics.
As pilling in textiles originates from many factors, the kinetic of pilling formation play an important role in the investigation and approaches of pilling. The single jersey-knitted lyocell fabrics were treated with different alkaline solution concentrations and submitted to Rapid Pilling Test-a wet-state Martindale test for cellulosic fabrics performed with increasing abrasion cycles. After each type of cycles, the pilling density was microscopically counted, and then pilling was visually rated. The changes in fiber properties were followed by water retention values (WRV), fibers swelling, fiber wet abrasion resistance (NSF), and fibers tenacity/elongation in wet and in dry states. The kinetics of pill formation-quantified by pills/cm 2 -occurred in the following steps: pills are promptly formed at first abrasion cycles, reached the pill plateau cycles, and are self-removed from the fabric surface. The untreated and alkali-treated lyocell fabrics followed a similar trend of pill formation. However, the pilling propensity is distinct depending on the concentrations. The changes in the swollen state of fiber properties and fiber-fiber friction mainly determined the pill kinetics in lyocell fabrics. The kinetic model aims to figure out the pilling mechanism and the appropriate treatment for pilling resistance.
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