Sorption of dyes on cellulose II: effect of alkali treatment of fibre and dye structure

Abstract

Cellulose is a linear 1,4-b-glucan polymer where the units are able to form highly ordered structures, as a result of extensive interaction through intra-and intermolecular hydrogen bonding of the three hydroxyl groups in each cellulose unit. Alkali has a substantial influence on morphological, molecular and supramolecular properties of cellulose II polymer fibres causing changes in crystallinity. Lyocell fibres pre-treated with 0.0, 2.0, and 4.0 mol dm -3 aqueous NaOH solution were dyed with hydrolyzed reactive dyes that had different molecular shapes and sizes. Overall exhaustion (q e ), value of K, and -DG increased for lyocell samples pre-treated with aqueous NaOH solution in the following order: 2.0 [ 4.0 [ 0.0 mol dm -3 NaOH. The same trends were observed for colour strength (K/S) values of the dyeings. Pretreatment of lyocell with 2.0 mol dm -3 NaOH creates the substrate that achieves the most thermodynamically favourable system for sorption of hydrolyzed reactive dyes, as at this concentration crystallinity decreases (with respect to 0.0 mol dm -3 NaOH treated lyocell) to afford higher sorption; however, at higher alkali concentrations the macro-sorbent forms a compacted unit that limits diffusion within the sorbent interior. Molecular size of the sorbate dye has a significant effect on the sorption process: for the largest dye structure the sorption isotherm is most closely correlated to a Langmuir isotherm; as the size of the dye decreases correlation to a Langmuir isotherm is observed, but with good correlation to the Freundlich isotherm; as the size of the dye is decreased further sorption is more typical of a Freundlich isotherm.

Limitations of Cellulose Dissolution and Fiber Spinning in the Lyocell Process Using [mTBDH][OAc] and [DBNH][OAc] Solvents

“…Thereafter, the fabric was washed to remove dirt. A cold mercerization using NaOH 20⁰ Bé was performed to improve dye uptake (Goswami et al 2011). Finally, the fabric was wash cleaned with cellulase enzyme (Morgado, Cavaco-Paulo & Rousselle 2000;Carrillo et al 2003) before final drying.…”

From hybrid fibers to microfibers: The characteristics of polyamide 6/polypropylene blend via one‐step twin‐screw melt extrusion

“…Moreover, the PP dissolved in the toluene can be used again to produce PP micro/nanofibres using electrospinning method . Recycling of solvents in fiber production is well known and is used commercially by fiber producers .…”

Controlling fibrillation – experiences of the dyeing and finishing of lyocell fibres

“…Treatment of the lyocell fabrics in NaOH has a wide range of effects on fabric behaviour. These changes affect the fine structure of the fibre as well as affecting dyeing behaviour . It is also worth noting that caustic soda treatment in preparation will help to increase the easy care rating of lyocell fabrics.…”