**4. Sodium hydroxide treatment of lyocell woven fabrics in continuous process**

The key area in this part will be to examine the effect of aqueous sodium hydroxide treatment (alkalisation) of cellulosic natural-based polymer, in particular lyocell fabric, which are of cellulose II crystalline structure. The alkali treatment or NaOH uptake of cellulose is a long-lasting issue, regarding cotton and other cellulose materials. Sufficient information of alkali pad-batch process (no tension applied) to cellulose substrates is available with its effect onto cellulose fabrics. For example, the maximum NaOH uptake/swelling is between 2.0 – 2.5 mol dm-3 for fabric, high shrinkage force is present during treatment causing strong dimensional changes (shrinkage) to treated material, effect on crystallinity and dye sorption was reported. While numerous publications concerning NaOH treatment of cotton have been published, a gap in alkalisation knowledge of lyocell fabrics exists. Limited information is available on the continuous treatment process which constitutes important part of commercial operations. Therefore, a pilot-scale pre-treatment with NaOH was performed with a washer, a special semi-scale apparatus simulating a real alkali process to undertake a comprehensive study of various process parameters on lyocell woven fabric and its physico-chemical and sorption properties. Herein, the influence of NaOH treatment concentration, treatment temperature, tension applied to fabric and their effects to treated substrates will be discussed. Also, an influence of fabric structure/geometry (plain-, twill-, sateen-woven fabrics) on NaOH release (wash-off) from woven lyocell fabrics will be considered.

Before considering the relationship between the structure of cellulose substrates and their physical and chemical properties it is appropriate briefly summarise alkalisation process in textiles. Swelling is a special feature of porous substrate causing its expansion at different levels, *e.g.* fibre, yarn, or fabric. Particularly, this expansion results in close contact of fibres and yarns which in turn, reduces yarns mobility and increases swelling restriction. Therefore, the deformity or irregularity in the fibre cross-sectional area of, for example, lyocell fabric rises with increasing NaOH concentration (0-6 mol dm-3) as observed recently(Goswami et al., 2009) and porosity decreases. Swelling reduction induces restricted

9% (2.25 mol dm-3 NaOH) and temperature of 4°C and below. It is generally accepted that the immersion of ramie or cotton fibres into 12-16% (w/v) NaOH (3.0 to 4.0 mol dm-3 NaOH) yields *Na-cellulose I*, whereas the use of more concentrated alkali, typically 20-30% (w/v) NaOH (5.0 to 7.5 mol dm-3 NaOH), gives another allomorph: *Na-cellulose II*. The conversion of *Na-cellulose I* into *Na-cellulose III* is obtained by vacuum drying *Na-cellulose I*, whereas washing *Na-cellulose I* and *Na-cellulose II* until neutrality, yields the sodium-free *Nacellulose IV*, which in its turn will give *cellulose II* upon drying. As Porro *et al.*(2007) stated, the analysis of the X-ray data alone may not be sufficient to give a clear picture of the interaction of the Na+ ions with the cellulose molecules. Therefore, Porro suggested a thorough analysis of 13C solid-state NMR data of the various Na-cellulose complexes due to the low spectral resolution of X-ray which did not lead to a clear assignment of the resonances belonging to the various complexes. These authors proposed a phase diagram, based on the occurrence of *Na-cellulose I* and *Na-cellulose II* together with the *Q region* where cellulose is essentially soluble. It defines six regions, two of them being border zones where

**4. Sodium hydroxide treatment of lyocell woven fabrics in continuous** 

The key area in this part will be to examine the effect of aqueous sodium hydroxide treatment (alkalisation) of cellulosic natural-based polymer, in particular lyocell fabric, which are of cellulose II crystalline structure. The alkali treatment or NaOH uptake of cellulose is a long-lasting issue, regarding cotton and other cellulose materials. Sufficient information of alkali pad-batch process (no tension applied) to cellulose substrates is available with its effect onto cellulose fabrics. For example, the maximum NaOH uptake/swelling is between 2.0 – 2.5 mol dm-3 for fabric, high shrinkage force is present during treatment causing strong dimensional changes (shrinkage) to treated material, effect on crystallinity and dye sorption was reported. While numerous publications concerning NaOH treatment of cotton have been published, a gap in alkalisation knowledge of lyocell fabrics exists. Limited information is available on the continuous treatment process which constitutes important part of commercial operations. Therefore, a pilot-scale pre-treatment with NaOH was performed with a washer, a special semi-scale apparatus simulating a real alkali process to undertake a comprehensive study of various process parameters on lyocell woven fabric and its physico-chemical and sorption properties. Herein, the influence of NaOH treatment concentration, treatment temperature, tension applied to fabric and their effects to treated substrates will be discussed. Also, an influence of fabric structure/geometry (plain-, twill-, sateen-woven fabrics) on NaOH release (wash-off) from

Before considering the relationship between the structure of cellulose substrates and their physical and chemical properties it is appropriate briefly summarise alkalisation process in textiles. Swelling is a special feature of porous substrate causing its expansion at different levels, *e.g.* fibre, yarn, or fabric. Particularly, this expansion results in close contact of fibres and yarns which in turn, reduces yarns mobility and increases swelling restriction. Therefore, the deformity or irregularity in the fibre cross-sectional area of, for example, lyocell fabric rises with increasing NaOH concentration (0-6 mol dm-3) as observed recently(Goswami et al., 2009) and porosity decreases. Swelling reduction induces restricted

two phases are present at the same time.

woven lyocell fabrics will be considered.

**process** 

effect of chemicals to be swollen and hence, the accessibility of fabric decreases significantly. This effect can be seen in wash-off or alkali release from alkali treated lyocell fabrics which is discussed and shown in recent publication(Široký et al., 2011a). On the level of fabric, the fabric construction has a crucial effect as the swelling and wet pick-up differs for various fabric constructions (*e.g.* plain-, twill- or sateen-woven lyocell fabrics).

Fig. 10. Picture of apparatus used in continuous alkali pre-treatment process.

The continuing process of alkali pre-treatment was done with a washer simulating real alkali process which is given in Fig. 10. It was divided into four stages (A, B, C, D), each with two sub-compartments (1 and 2) that could be heated independently; the four stages were alkali treatment (A2), stabilisation treatment (B2), washing (C1 and C2), neutralisation (D1), and final washing (D2). The fabric was passed through the apparatus over a series of rollers including tension compensators (T) and pressurised squeeze rollers (P). The fabric after passing through the last compartment (D) was wound on a take-up roller (R). In treatment stage, the NaOH concentration, applied tension and temperature varied. Due to changes in the concentration in the treatment stage (caused by process), the "effective" concentration of alkali was established at 0.0, 2.53, 3.33, 4.48, 4.65 and 7.15 mol dm-3 for treatment bath and 0.0, 0.73, 1.08, 1.18, 1.48 and 2.15 mol dm-3 for stabilization bath. Residence time was adjusted at 75±2 s and 71±3 s in treatment bath and stabilization bath respectively. Tension in treatment compartments was applied either at 49 N m-1 or 147 N m-1, tension in stabilisation compartment was applied at 147 N m-1, and tension in washing and neutralization compartments was applied at 49 N m-1. During the alkali treatment stage the temperature of the solution was set at 25 °C or 40 °C, and in the stabilization stage the temperature was 60°C. The speed of passage of fabric through the system was set at 2 m min-1. Entire process and its all adjustments during the process are described in detail in our previous work.(Široký et al., 2009)
