**2. Regenerated cellulose**

It is difficult to verify when cellulosic materials were used the first time for clothing, because of the biodegradability, but the oldest cotton textiles found go back to 5800 BC and were found in a cave in Tehuacän in ancient Mexico;(Abu-Rous, 2006) other important sources like flax, linen, hemp or wool were also used in early history. For instance, Babylonia was the first country to process and trade in wool (Babylonia = land of wool) and also, the proof of using leather of different skin in clothes and shoes by discovery of the oldest European mummy; Ötzi the Iceman – man who lived about 5,300 years ago, on the border between Austria and Italy. (Hollemeyer et al., 2008; Kutschera & Rom, 2000)

Regenerated cellulose fibres are the first artificial fibres ever made. Processes capable of dissolving the cellulose derived from wood or cotton linters were first discovered by Schnöbein (1845, nitrocellulose soluble in organic solvents), Schweizer (1857, cellulose in cuprammonium solution), Cross, Bevan and Beadle (1885, cellulose sulfidized in sodium hydroxide; 1894, cellulose triacetate in chloroform) followed by commercial production of acetate fibres started in 1919; in 1955 they were joined by triacetate. The introduction of modifiers by Cox in 1950 and the development of high-wet-strength fibres initiated by Tachikawa in 1951 again increased the variety of cellulosic man-mades. In the 1960s, high wet modulus type rayon fibres were developed to improve resistance to alkali and to increase wet fibre mechanical properties and dimensional stability of fabrics. In the 1970s, new kinds of rayon fibres were produced - Avtex Avril III (a multilobal fibre), Rayonier's Prima and Courtaulds' Viloft (a hollow fibre with high water-holding capacity). In the late 1970s due to increasing investment in pollution control, which became cost-determining, several companies (Courtaulds, Lenzing, Enka) started to examine the application of carbon disulfide-free, direct solution systems for cellulose. Several direct solvent systems, such as dimethylsulfoxide/para-formaldehyde, N-methylmorpholine-N-oxide (NMMO) and N,Ndimethylacetamide lithium chloride were investigated, but only NMMO became of practical importance. Lyocell fibre made from an NMMO-solution is today a newest class of manmade cellulosic with very promising properties.

Textile fibres can be divided into two main categories, natural and man-made, as it is depicted in Fig. 1; in addition, there is another category which lies in between, and shares some features of both categories – it is termed 'regenerated fibres' and includes regenerated cellulosic fibres, which are typically wood pulp converted into continuous filaments by

Cellulose fibres exhibit a unique position among the textile fibres, due to their hydrophilicity and their ability to change their dimension by swelling. Swelling occurs in water, polar solvents and in particular in aqueous alkali hydroxide solutions, which are widely applied in textile finishing processes of cotton and regenerated cellulose fibres. Due to their high swelling capability regenerated cellulose fibres are highly sensitive during the alkaline treatment, thus a careful selection of alkalisation conditions for such fabrics is required. This particular behavior of cellulose to swell extensively in alkaline solutions results in a different performance in comparison to synthetic fibres. Herein, the chapter is dedicated to detailed discussion of the fibre behavior and the resulting effects/impacts onto

It is difficult to verify when cellulosic materials were used the first time for clothing, because of the biodegradability, but the oldest cotton textiles found go back to 5800 BC and were found in a cave in Tehuacän in ancient Mexico;(Abu-Rous, 2006) other important sources like flax, linen, hemp or wool were also used in early history. For instance, Babylonia was the first country to process and trade in wool (Babylonia = land of wool) and also, the proof of using leather of different skin in clothes and shoes by discovery of the oldest European mummy; Ötzi the Iceman – man who lived about 5,300 years ago, on the border between

Regenerated cellulose fibres are the first artificial fibres ever made. Processes capable of dissolving the cellulose derived from wood or cotton linters were first discovered by Schnöbein (1845, nitrocellulose soluble in organic solvents), Schweizer (1857, cellulose in cuprammonium solution), Cross, Bevan and Beadle (1885, cellulose sulfidized in sodium hydroxide; 1894, cellulose triacetate in chloroform) followed by commercial production of acetate fibres started in 1919; in 1955 they were joined by triacetate. The introduction of modifiers by Cox in 1950 and the development of high-wet-strength fibres initiated by Tachikawa in 1951 again increased the variety of cellulosic man-mades. In the 1960s, high wet modulus type rayon fibres were developed to improve resistance to alkali and to increase wet fibre mechanical properties and dimensional stability of fabrics. In the 1970s, new kinds of rayon fibres were produced - Avtex Avril III (a multilobal fibre), Rayonier's Prima and Courtaulds' Viloft (a hollow fibre with high water-holding capacity). In the late 1970s due to increasing investment in pollution control, which became cost-determining, several companies (Courtaulds, Lenzing, Enka) started to examine the application of carbon disulfide-free, direct solution systems for cellulose. Several direct solvent systems, such as dimethylsulfoxide/para-formaldehyde, N-methylmorpholine-N-oxide (NMMO) and N,Ndimethylacetamide lithium chloride were investigated, but only NMMO became of practical importance. Lyocell fibre made from an NMMO-solution is today a newest class of man-

dissolving the wood in suitable solvents from which they can be regenerated.

regenerated man-made fabrics, for example lyocell fabric, during alkalisation.

Austria and Italy. (Hollemeyer et al., 2008; Kutschera & Rom, 2000)

made cellulosic with very promising properties.

**2. Regenerated cellulose** 

The main raw material from which regenerated cellulosic fibres are manufactured is purified wood pulp; mainly produced from wood and linters, but also from annual plants. For its conversion into textile fibres, it must be dissolved in a suitable solvent from which it can be regenerated as continuous filaments after the solution has been extruded through a fine orifice. At present, the following three methods are mostly used: the viscose process; the lyocell process; and the cuprammonium process.

Most of the world's man-made cellulose fibres are produced via the viscose process; these fibres are called 'rayons' because of the basic fibre-forming process, which involves cellulose regeneration from a cellulose xanthate, a chemical derivative of cellulose and carbon disulfide. The viscose process is characterized by high versatility, which is the result of various modifications that can be made at different stages of the process. The degree of polymerization of cellulose used, additives to modify the viscose solution, coagulation (controlled by coagulation bath additives, exerting an effect on the orientation and alignment of the cellulose molecules in the direction of the fibre axis), and stretching applied during fibre processing, can lead to a huge range of rayon forms and properties. These variations and their consequences on the end products are given in details in Morton and Hearle (1993).

With regard to the macrostructure of viscose fibres, regenerated cellulosics are different in their morphology to cotton as they have no lumen and are non-fibrillar (Fig. 2), which is directly due to the manufacturing process.

Fig. 2. Scanning electron microscope (SEM) micrographs of viscose fibres.

Lyocell is the generic name of a new generation of regenerated cellulosic fibres made by a solvent spinning process. The development of this fibre was driven by the desire for an environmentally friendly process to produce cellulosic fibres with an improved performance profile and cost compared to viscose rayon, utilizing renewable resources as raw materials.

This cellulosic fibre is derived from wood pulp (typically eucalyptus) produced from sustainably managed forests; the wood pulp (good quality, DP = 400-1000) is mixed at 70-90 °C with approximately 80% (v/v) *N*-methylmorpholine-*N*-oxide (NMMO) solution in water with a small quantity of degradation inhibitor. NMMO is capable of physically dissolving cellulose without any derivatisation, complexation or special activation, and it is able to break the inter- and intra-molecular hydrogen-bonds of cellulose.

Alkali Treatments of Woven Lyocell Fabrics 183

fibres have a microfibrillar structure because a portion of the molecular chains aggregate to form microcrystals while recrystallizing along the chains, whereas the remaining chains exist in the amorphous phase as links between these two phases.(Okano & Sarko, 1984) In the crystalline regions of cellulose II polymers, the layered structure is very regular, so the

Although, the physical properties of lyocell are unique among all kinds of rayons (Table 2) remarkably when wet, problems of lyocell properties occur as well.(Woodings, 1995) The weaker lateral links between crystallities are consequence of the highly crystalline lyocell structure and as a result of wet abrasion, at the surface of fibre the separation of fibrous elements known as *fibrillation* (Fig. 5) occurs. Basically, it is the longitudinal splitting of a single fibre filament into microfibers of 1-4 µm in diameter. It can also yield the 'peach skin' touch of fabrics, characteristic surface touch of lyocell fibre, but unwanted and uncontrolled fibrillation can worsen the fabric quality, for example, entanglement of microfibers causes a

Man-made cellulose fibres, such as viscose or lyocell, morphological structure can be described as a network of elementary fibrils and their more or less random associations; this is called a "fringe fibrillar" structure which is basically one of the macro-conformations of polymer chains depicted in Fig. 6. Schuster et al. (2003) used Ultra Small Angle Neutron Scattering (USANS) to yield information on lyocell fibres and their proposed structure at different dimensional levels is given in Fig. 7. In general, lyocell fibre is distinguished by its high crystallinity, high longitudinal orientation of crystallites, high amorphous orientation,

length of hydrogen bonds between molecules is the same.

Fig. 4. World production of cellulosic fibres in tonnes.

Fig. 5. Fibrillation of lyocell fibre. (Zhang, 2004)

serious problem of pilling.

In the ternary system, cellulose is dissolved in a narrow region and the solution is stabilised using suitable chemicals, *e.g.* isopropyl gallate. The homogenous solution (*dope*) with a minimum of undissolved pulp particles and air bubbles, is put into the evaporator vessel (evaporation of water) operated under vacuum to reduce temperature (ca 90-120 °C), due to the amine oxide solvent in solution degrading if it is overheated. Before spinning, the solution is passed through two stages of filtration. For spinning, the solution is supplied to each jet (a small *air gap* with thousands of tiny holes), and it is then extruded and spun through an air gap (*fibre* or *tow* is obtained) into a spin bath containing dilute amine oxide solution. The fibres are *drawn* or *stretched* in the air gap by the pull of *traction units* or *godets*. Afterwards, the fibres are washed and from the excess liquor and NMMO is recovered by filtration, purification and concentration. Lyocell fibre differs from viscose rayon in the fibre structure and morphology (Fig. 3).

Fig. 3. Lyocell fibre SEM micrograph.(Zhang, 2004)


Table 1. Comparison of the viscose and lyocell processes.(Harvey, 2007)

Production of fibres using this process has very little impact on the environment mainly in terms of chemical used and is a benign technology process. The manufacturing process recovers >99% of the solvent, additionally, the solvent itself is non-toxic and all the effluent produced is non-hazardous. The environmental impact of the viscose and lyocell processes are compared in Table 1. Lyocell is designed as a fully biodegradable cellulosic polymer with beneficial properties, which will be mentioned later. Despite all of these benefits, the production of lyocell was in 2002 only *ca*. 2.5% of the total regenerated cellulosic fibre production (total of 2.76 million tonnes), as shown in Fig. 4.(Abu-Rous, 2006)

The lyocell process is less flexible then the viscose process due to the high orientation of the obtained polymer after the air gap. However, there are other possibilities to influence the structure and properties of lyocell fibres using physical process parameters.

Lyocell fibres have the thinnest and longest crystallites, even the amorphous regions are oriented along the fibre axis, and its crystallinity is of high degree (up to 60-70%). These

In the ternary system, cellulose is dissolved in a narrow region and the solution is stabilised using suitable chemicals, *e.g.* isopropyl gallate. The homogenous solution (*dope*) with a minimum of undissolved pulp particles and air bubbles, is put into the evaporator vessel (evaporation of water) operated under vacuum to reduce temperature (ca 90-120 °C), due to the amine oxide solvent in solution degrading if it is overheated. Before spinning, the solution is passed through two stages of filtration. For spinning, the solution is supplied to each jet (a small *air gap* with thousands of tiny holes), and it is then extruded and spun through an air gap (*fibre* or *tow* is obtained) into a spin bath containing dilute amine oxide solution. The fibres are *drawn* or *stretched* in the air gap by the pull of *traction units* or *godets*. Afterwards, the fibres are washed and from the excess liquor and NMMO is recovered by filtration, purification and concentration. Lyocell fibre differs from viscose rayon in the fibre

**Viscose Process Lyocell Process**

Derivatisation CS2, NaOH ---- Solvent NaOH NMMO Toxicity Very toxic (CS2) Non-toxic Spinning Bath H2SO4, ZnSO4 H2O

Table 1. Comparison of the viscose and lyocell processes.(Harvey, 2007)

production (total of 2.76 million tonnes), as shown in Fig. 4.(Abu-Rous, 2006)

structure and properties of lyocell fibres using physical process parameters.

Pulps Small variety Large Variety Recovery Complex Simple

Production of fibres using this process has very little impact on the environment mainly in terms of chemical used and is a benign technology process. The manufacturing process recovers >99% of the solvent, additionally, the solvent itself is non-toxic and all the effluent produced is non-hazardous. The environmental impact of the viscose and lyocell processes are compared in Table 1. Lyocell is designed as a fully biodegradable cellulosic polymer with beneficial properties, which will be mentioned later. Despite all of these benefits, the production of lyocell was in 2002 only *ca*. 2.5% of the total regenerated cellulosic fibre

The lyocell process is less flexible then the viscose process due to the high orientation of the obtained polymer after the air gap. However, there are other possibilities to influence the

Lyocell fibres have the thinnest and longest crystallites, even the amorphous regions are oriented along the fibre axis, and its crystallinity is of high degree (up to 60-70%). These

structure and morphology (Fig. 3).

Fig. 3. Lyocell fibre SEM micrograph.(Zhang, 2004)

fibres have a microfibrillar structure because a portion of the molecular chains aggregate to form microcrystals while recrystallizing along the chains, whereas the remaining chains exist in the amorphous phase as links between these two phases.(Okano & Sarko, 1984) In the crystalline regions of cellulose II polymers, the layered structure is very regular, so the length of hydrogen bonds between molecules is the same.

Fig. 4. World production of cellulosic fibres in tonnes.

Although, the physical properties of lyocell are unique among all kinds of rayons (Table 2) remarkably when wet, problems of lyocell properties occur as well.(Woodings, 1995) The weaker lateral links between crystallities are consequence of the highly crystalline lyocell structure and as a result of wet abrasion, at the surface of fibre the separation of fibrous elements known as *fibrillation* (Fig. 5) occurs. Basically, it is the longitudinal splitting of a single fibre filament into microfibers of 1-4 µm in diameter. It can also yield the 'peach skin' touch of fabrics, characteristic surface touch of lyocell fibre, but unwanted and uncontrolled fibrillation can worsen the fabric quality, for example, entanglement of microfibers causes a serious problem of pilling.

Fig. 5. Fibrillation of lyocell fibre. (Zhang, 2004)

Man-made cellulose fibres, such as viscose or lyocell, morphological structure can be described as a network of elementary fibrils and their more or less random associations; this is called a "fringe fibrillar" structure which is basically one of the macro-conformations of polymer chains depicted in Fig. 6. Schuster et al. (2003) used Ultra Small Angle Neutron Scattering (USANS) to yield information on lyocell fibres and their proposed structure at different dimensional levels is given in Fig. 7. In general, lyocell fibre is distinguished by its high crystallinity, high longitudinal orientation of crystallites, high amorphous orientation,

Alkali Treatments of Woven Lyocell Fabrics 185

low lateral cohesion between fibrils, low extent of clustering and relatively large void (pore)

microfibril

**Macrofibril**

**Ø 0.5 - 1 µm**

macrofibril

**10-30 µm thick**

**Fiber (skin-core)**

volume in comparison to other cellulosic regenerated fibres.

**Fringed Micellar Cellulose II (Elemental Fibril)**

**Ø 5-20 nm**

higher crystal orientation at the skin.

**Elemental Fibril**

**A: crystallites B: amorphous regions C: interfibrillar tie molecules D: cluster formation E: void**

5.15 Å

**Cellulose II Crystallite**

elemental fibril

**Ø - 100 nm**

Fig. 7. Lyocell fibre structure at different dimensional levels.(based on Schuster et al. (2003))

There is a wide range of possibilities or processes to influence the fiber structure and its properties such as changing the parameters (*e.g.* type of pulp and molecular weight of polymer, dope composition, air gap length, l/d ratio of spinning nozzle, spinning speed, draw ratio, spinning bath composition, *etc.*) during the fibre formation. One of the processes for lyocell fibres mentioned herein is a "softer" precipitation, involving a two-stage precipitation in alcohol and water. By this process a decrease of crystallinity and orientation of lyocell fibers is obtained and, therefore, the fiber structure and core-shell structure is affected.(Klemm et al., 2005) It is also known that the structure and properties of regenerated fibers, like density, crystallite size, orientation, pore number and volume and therefore, skin-core structure as well, can be influenced with applied physical process (spinning) conditions. Recently, a skin-core model for lyocell fibers was proposed by Biganska(Biganska, 2002) where three-component system is presented. A system with compact fiber core, a porous middle zone and a semi-permeable fiber skin. However, Gindl et al. (2006) showed that only two different parts within lyocell fiber do exist, skin and core. They observed that studied fibers have uniform skin-core orientation, in contrast, Kong et al. (2007) obtained non-uniform skin-core orientation by X-ray diffraction as claimed due to the differences of used beam size (5 × 5 µm vs. 500 nm). This non-uniformity resulted in the higher average orientation of the fiber skin than of the core. Additionally, it was shown that the skin-core model of lyocell fibers is influenced by the increased shear forces on the outer region of the fiber during passing the spinning dope through the spinneret, which generates

**Microfibril**


aThe 'Y'-shaped rayon data are based on Courtaulds' Galaxy fibre;

bThe solvent-spun rayon data are based on Courtaulds' Tencel fibre

Table 2. Physical properties of selected commercially available rayon fibres.

Fig. 6. Illustration of the macro-conformations of polymer chains. A, amorphous; B, regular chain folding; C, chain-extended which represents the limiting cases, and the middle part D, fringe micelle represents the intermediate structure.

20-24 15-20 18-22 34-36 40-45 40-44

10-15 9-12 9-12 19-21 30-40 34-38

20-25 7-23 17-22 13-15 8-12 14-16

25-30 16-43 23-30 13-15 10-15 16-18

90-100 100 100-110 75-80 55-70 65-70

40-50 30-50 35-45 100-120 140-180 250-270

DP 250-350 450-550 250-350 300-500 550-700 550-600

Fig. 6. Illustration of the macro-conformations of polymer chains. A, amorphous; B, regular chain folding; C, chain-extended which represents the limiting cases, and the middle part D,

aThe 'Y'-shaped rayon data are based on Courtaulds' Galaxy fibre; bThe solvent-spun rayon data are based on Courtaulds' Tencel fibre

fringe micelle represents the intermediate structure.

Table 2. Physical properties of selected commercially available rayon fibres.

rayona Modal Polynosic Lyocell

fibre b

rayon Cuprammonium 'Y'-shaped

Property Regular

Fibre crosssection

Dry tenacity (cN/tex)

Wet tenacity (cN/tex)

Extension at break (%, dry)

Extension at break (%, wet)

Water imbibitions

Cellulose

Initial wet modulus (at 5 %)

(%)

low lateral cohesion between fibrils, low extent of clustering and relatively large void (pore) volume in comparison to other cellulosic regenerated fibres.

Fig. 7. Lyocell fibre structure at different dimensional levels.(based on Schuster et al. (2003))

There is a wide range of possibilities or processes to influence the fiber structure and its properties such as changing the parameters (*e.g.* type of pulp and molecular weight of polymer, dope composition, air gap length, l/d ratio of spinning nozzle, spinning speed, draw ratio, spinning bath composition, *etc.*) during the fibre formation. One of the processes for lyocell fibres mentioned herein is a "softer" precipitation, involving a two-stage precipitation in alcohol and water. By this process a decrease of crystallinity and orientation of lyocell fibers is obtained and, therefore, the fiber structure and core-shell structure is affected.(Klemm et al., 2005) It is also known that the structure and properties of regenerated fibers, like density, crystallite size, orientation, pore number and volume and therefore, skin-core structure as well, can be influenced with applied physical process (spinning) conditions. Recently, a skin-core model for lyocell fibers was proposed by Biganska(Biganska, 2002) where three-component system is presented. A system with compact fiber core, a porous middle zone and a semi-permeable fiber skin. However, Gindl et al. (2006) showed that only two different parts within lyocell fiber do exist, skin and core. They observed that studied fibers have uniform skin-core orientation, in contrast, Kong et al. (2007) obtained non-uniform skin-core orientation by X-ray diffraction as claimed due to the differences of used beam size (5 × 5 µm vs. 500 nm). This non-uniformity resulted in the higher average orientation of the fiber skin than of the core. Additionally, it was shown that the skin-core model of lyocell fibers is influenced by the increased shear forces on the outer region of the fiber during passing the spinning dope through the spinneret, which generates higher crystal orientation at the skin.

Alkali Treatments of Woven Lyocell Fabrics 187

interactions between lattice layers, leading to a widening of lattice distances or even changes

One of the most important features of cellulosic substrates is their propensity to absorb moisture from ambient air, expressed in terms of either moisture regain or moisture content. Water absorption causes swelling of the substrate, which alters the dimensions of the fibre, and this, in turn, will cause both changes in physical properties such as the size, shape, stiffness, and permeability of yarns and fabrics,(Morton & Hearle, 1993) as well as sorption/desorption characteristics (Široká et al., 2008), and in mechanical properties such as tensile modulus and breaking stress,(Kongdee et al., 2004) and, therefore, interaction between cellulose and water plays an important part in the chemistry, physics and

Cellulose accessibility largely depends on the available inner surface, supramolecular order, fibrillar architecture, and also fibre pore structure. In most cases, there is interaction with water which consequently destroys weak hydrogen-bonds, but cannot penetrate into the region of high order, in contrast to, for example, aqueous solutions of sodium hydroxide, and therefore cellulose is not dissolvable in water. In Fig. 8, an overview is given about the depth of fibre reorganization/dissolution and also indicates the fields of its application; sorbed water on such a polymer can cause structural changes predominantly in the amorphous or intermediate phases. However, there is also a significant role associated with pores, capillaries, and the network of voids, which do not have uniform size and shape.

Fig. 8. Different stages of cellulose fibre reorganisation at different level: a) solvent, b) yarn,

From the chemistry perspective, cellulose-water interactions are basically a competition of hydrogen-bond formation between hydroxyl groups in the polymer and hydrogen-bond formation between one hydroxyl group of a cellulose chain and a water molecule or a water cluster.(Klemm et al., 1998) Differential scanning calorimetry (DSC) may be used as valuable technique to explore the interaction of either water or moisture with various natural and synthetic polymers with hydrophilic groups, and thermal properties of polymers and water.

in the crystal lattice.(Krässig, 1993b)

**3.1 Accessibility and swelling of cellulose 3.1.1 Cellulose water/moisture interactions** 

technology of cellulose isolation and processing.

and c) fabric level.
