Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 2: Accessibility and Reactivity

Abstract

The reorganization of cellulose fibers by swelling treatments in alkali solutions results in numerous changes to fiber structure, causing changes of chemical reactivity in the fiber‐solution heterogeneous system. An important part of the change in chemical reactivity is the change of fiber accessibility because it results in exclusion of chemicals such as reagents or catalysts from the fiber. In the second of a two‐part series of papers, we examine the influence of changes in fiber accessibility and/or reactivity due to treatment in swelling solutions on the performance or behavior of substrates during and after chemical finishing treatments. Changes in fiber accessibility due to alkali treatments are visualized with fluorescence microscopy. The effect of alkali treatments on enzymatic hydrolysis and pad‐dry‐cure crosslinking treatments of cellulose substrates are discussed as representative examples to demonstrate the effects of swelling processes on fiber reactivity and accessibility. Model calculations indicate that a considerable redistribution of chemicals in substrates occurs during dry‐cure operations resulting from molecule‐specific exclusion effects. Pilling tests on lyocell knit‐fabrics show the impact of preceding alkali processes on the final physical performance of textile fabric highlighting the importance of correct selection of alkali processes to achieve desired behavior.

Dyeing behaviour of lyocell fabric: effect of NaOH pre-treatment

“…5 Optical crosssections of lyocell filaments in a yarn dyed with 2% omf Cibacron Brilliant Red 4G-E following pretreatment with: a 0.0 mol dm -3 NaOH; b 1.5 mol dm -3 NaOH, c 2.0 mol dm -3 NaOH, d 5.0 mol dm -3 NaOH, and e 7.0 mol dm -3 NaOH. Scale bar is 20 lm Cellulose (2009) 16:481-489 485 this finding is in agreement with the findings of Bui et al (2008), where they reported an increase in porosity and accessibility in lyocell fibres after treatment with NaOH solution. The increase in %E, %F, and K/S from concentrations of 0.0-2.0 is attributed to a decrease in density and crystallinity of lyocell fibre with increasing concentration of NaOH in the pre-treatment bath (Goswami et al 2009); as adsorption and diffusion of dyes only occurs in the amorphous regions of a fibre this decrease in crystallinity affords the corresponding increase in dye sorption.…”

Mechanical pretreatment improving hemicelluloses removal from cellulosic fibers during cold caustic extraction

“…A lower than the optimum NaOH concentration will lead to a decreased fiber swelling, thus reducing the pore size/porosity, which negatively affects the hemicelluloses diffusion through the fiber wall, thus, the overall hemicelluloses removal. Bui et al (2008) investigated the effect of alkaline treatment on the reactivity of regenerated cellulosic fibers, and the results indicated that the alkaline treatment can increase the porosity of the fiber wall and accessibility of fibers to NaOH.…”

Alkali pretreatment and resin finishing of lyocell: Effect of sodium hydroxide pretreatments

“…1,2 However, the strong swelling propensity of lyocell fibers in alkali solutions 3 changes substrate properties and may lead to alterations in the accessibility and reactivity of lyocell for chemicals and reagents and influence its performance in subsequent treatments. 4,5 In earlier work, 6,7 we examined the influence of alkali pretreatments on the performance of lyocell fabrics in subsequent resin finishing treatments. Fabric samples were pretreated with sodium hydroxide (NaOH; 120 g/L) or KOH (250 g/L) and resinfinished with a dimethyloldihydroxyethylene urea (DMDHEU) based product.…”