Indian Journal of Fibre & Tex tile Research Vo l. 30, M arch 2005, pp. 88-93

Dyeing properties of a mixed bi-functional reactive dye on a novel regenerated cellulosic fibre

Joonseok Koh"

Department of Textile Eng ineering, Konkuk Uni versity, Seoul 143-70 1, South Korea

Received 7 October 2003; Revised received and accepted 27 May 2004

A mi xed bi-functional reac ti ve dye has been applied to the regular viscose rayon and the new regenerated cellulosic fibre (el! Vix®), prepared from cellulose acetate by the hydrolys is o f acetyl groups, and their dyeing and fastness properties compared. It is observed that the el! Vix® ex hibits better dyeability than the regular vi scose rayon as exp lained by the differences in the supramolecul ar structure of these two fibres.

Keywords: Bi-functional reac ti ve dye, Dyeing properties, Fastness properties, Regenerated cellulos ic fi bre, Supramolecular structure

IPC Code: Int. CI.7 D06P1I38; D06P3/66

1 Introduction Rayon fibre is defined by the U.S . Federal Trade

Commission as "a manufactured fibre composed of regenerated cellulose alone or in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups". Substituents consist of manufacturing impurities, pigments, fire retardants or other additives ' .

Mostly, rayon is made by the viscose process using chemical cellulose (dissolved wood pulp) , sodium hydroxide, carbon disulfide and sometimes modifiers, which are usually based on ethoxylated natural fatty ac id amines . Some of the raw materials used in the production of rayon are recoverable. By-product sodi um sulphate is recovered and sold by rayon producers. Carbon di sulfide is recovered in varying degrees by larger plants ; on an average 30-35% CS2 is recovered, the balance being lost through volatili zati on or decomposition . Also, some zinc is collected as precipitates (zinc sulphide) in the spinning process and reworked by some producers2. Although the efforts by the major producers are expected to reduce carbon disulfide and zinc emissions, increasing environmental concern has centred on the conventi onal preparation of regenerated cellulosic fibres in which still more amount of remaining zinc and carbon disulfide needs

"Phone: +82-17-2270208; Fax : +82-2-4578895; E-mail : ccdjko@ hanmail. net

to be recovered from the waste at the plant site to meet the established water pollution regulations.

In 1980' s, Acordis Cellulosic Fibres (Netherlands) introduced lyocell fibre, the newest member of the cellulosic fibres, using a more efficient and economical process than the uni versally used viscose process. Lyocell fibre is manufactured directly from high-purity cellulosic wood pulp, whereas rayon is manufactured from a cellulose derivative that is chemically regenerated back to cellulose during the spinning process. The cellulose is dissolved in a solvent (N-oxide of morpholine) and then wet spun. The solvent is recycled, eliminating the chemistry of viscose process, which uses caustic soda, carbon disulfide and sulfuric acid to dissolve the pulp. Although environmentally safe, the solvent-spun cellulosics are unlikely to replace viscose rayon to a significant extent in the near future because of the high cost of converting or building faci lities.

Recently, SK Chemicals introduced a novel regenerated cellulosic fibre (en Vix® ) which was prepared from cellulose acetate with a degree of substitution of ;:::2.0 by saponifying ;:::75% of the total acetyl groups of the cellulose acetate fibre into hydroxyl groups . It has a composi te crystalline structure of cellulose II and IV (refs 2-5) . This regenerated fibre is claimed to o ffer envi ronmental advantages over other conventional regenerated fibres becaus-:: it does not emit toxic material s such as carbon disul fide and heavy metal ions.

KOH: DYEING PROPERTIES OF A MIXED BI-FUNCTIONAL REACTIVE DYE ON CELLULOSIC FIBRE 89

elL Vix® is a cellulosic fibre and therefore can be dyed with any class of dyestuff suitab le for other cellulosics. In the present work, a mixed bi-functional reactive dye has been applied to the regular viscose rayon and the new regenerated cellulosic fibre (en Vix®) prepared from cellulose acetate fibre and their dyeing and fastness properties compared. The results are explained by the differences in the supramolecular structure of these two fibres.

2 Materials and Methods 2.1 Materials

Viscose rayon fabrics (plain weave, warp 82 threads/inch, weft 62 threadslinch and filament fineness 2.5 denier/filament) and new regenerated cellulosic fabrics (plain weave, warp 96 threadslinch, weft 56 threadslinch and filament fineness 2.5 denier/filament) prepared from cellulose acetate fibres by alkali hydrolysis3

,4 were procured from SK Chemicals (South Korea)

The commercial sample of mixed bi-functional reactive dye Sumifix Supra Blue BRF (CI. Reactive Blue 221, a copper formazan reactive dyes with a mixed bifunctional 2-chloro-4-vinylsulphonyl­anilinotriazine type) was used as such without any purification prior to use. The bi-functional reactive dye (Fig. 1) was supplied by Nippon Kayaku . A commercial sample of soaping agent (SNOGEN CS-940N, non-ionic) was supplied by Daeyoung Chemicals. All other reagents used were of L R grade.

2.2 Methods A SO ml dyebath , suitable for a 2.0 g sample of

rayon (material-to-Iiquor ratio 1 :20), containing a reactive dye and Glauber's sal t was prepared . Dyeing was performed under each appropriate condition (Fig. 2) in an Ahiba Nuiance Laboratory · Dyeing Machine (Ahiba, Datacolor International, Switzerland). The dyed fabric was rinsed and then treated with soaping agent (0.5 gil) for 30 min at 98°C

The regenerated cellulose was dyed at various dyebath conditions using salt concentration, alkali concentration, material-to-liquor ratio, and dye concentration to investigate their effects on the dyeing properties . Exhaustion behaviour of reactive dyes on the fabric was also investigated by monitoring the exhaustion values of dyed fabrics as the dyeing proceeds.

The extent of dye exhaustion (%) achieved for an appropriate dye concentration on each of the two

Fig. I-Structure of mixed bi-functional reactive dyes (el. Reactive Blue221)

10min 5min

400C,10min

Glauber's Salt Dye Fabric

50min

Soaping

98"/1 soaping agent

Fig. 2-Reactive dyeing profile

types of fibre was determined by usi ng the foll owing equation:

A -A Exhaustion (%) = b {/

Ab ... (1)

where Au is the absorbance of dyebath after dyeing ; and Abo the absorbance of dyebath before dyeing.

The regenerated cellulosic fibres were dyed (1/1 standard depth), treated with soaping agent and then heat set (l70°C, 60 s) in order to test the colour fastness. The colour fastness was determi ned according to International Standards: ISO 105 C06/C2S (colour fastness to washing), ISO 105 E04 (colour fastness to perspiration), ISO 105 X12 (colour fastness to rubbing), and ISO 105 B02 (colour fastness to light). Staining and change in colour were assessed using grey scales.

90 INDIAN J. FIBRE TEXT. RES., MARCH 2005

3 Results and Discussion Figs 3-7 show the dyeing properties of two rayons.

The variation in dye yield has been studied with the variation in salt concentration, alkali concentration and material-to-liquor ratio to compare their effects on the shade of en Vix® and viscose rayon.

The molecules of reactive dyes are smaller than those of direct dyes and their smaller size is accompanied by a correspondingly lower substantivity. The molecules of direct dyes are deliberately made large so as to build up the physical attraction between fibre and dye, thus making them more substantive. Much smaller molecules may be suitable for use as reactive dyes because one covalent bond is about thirty times as strong as one van der Waals bond.

3.1 Effect of Salt Concentration on Dyeing Properties

Reactive dyes are usually applied with the addition of electrolyte and the extent to which reactive dyes are affected by the addition of electrolytes to the dyebath is known as salt sensitivity. The addition of electrolyte increases the strike rate of the dye. The commonly used electrolytes are Glauber's salt (sodium sulphate) and common salt (sodium chloride). When cellulose is immersed in a solution of reactive dye, it absorbs dye from the solution until equilibrium is attained and at this stage, most of the dye is taken up by the fibre. Cellulose carries a negative charge in pure water. As the dye is also anion, there is an electrostatic anion-anion repul sion between dye and cellulose. Therefore, the probability of the dye adsorbing onto the fibre (level of substantivity) is reduced . The substantivity of the dye for cellulose is the proportion of dye absorbed by the fibre compared with that remaining in the dyebath . By adding inert electrolyte such as common salt or Glaubler's salt to the dyebath, this electrostatic barrier (Donnan Potential) can be largely suppressed, facilitating dye/fibre contact and allowing better interaction of van der Waals forces ; thi s improves the substantivity. The diffusion coefficient of dye is therefore a function of both dye and electrolyte concentration6

. Fig. 3 shows that the exhaustion of dyeings and K/S values of dyed fabrics increases with the increase in salt concentration. The dye exhaustion of reactive dye is linear function of salt concentration particularly at lower dye concentrations within the cellulose in the presence of a fixed amount of added dyes although the slope decreases with the increase in

" g '" ::l

~ 80 )(

UJ

E " o N

~ en :2

__ enVix

70 . . 0- . Viscose

60~-r-.-----'---------'----------~~

o 5 10 20 40 60 20~--------------------------------~

15V ..0 , - ......... . -.- . .<)

, cr ' .'

. .cr'

10 .cr'

5+--,-.-----,---------,,---------.-~

o 5 10 20 40 60

Salt cone. ( gIl)

Fi g. 3-Effect of salt (Na2S04) concentration on exhaustion of dyei ngs and KIS value of dyed fabrics (dye cone. 1.0% owf and material·to-liquor rat io 1:20)

salt concentration. It is considered that the initial rapid rise in exhaustion and K/S values is due to the response of dye to the lowering of electrical potential barrier to diffusion as the concentration of electrolyte increases. The mixed bi-functional reactive dyes show high exhaustion of dyeings, irrespective of the amount of salts applied. The mixed bi-functional reactive dyes were designed primarily for exhaust dyeing with the triazinyl group . being used to enhance the substantivity (30-60%) of this type of dye.

It is also evident from Fig. 3 that the exhaustion of dyeings on en Vix® is higher than that on viscose rayon for the mixed bi-functional reactive dye used and the result is consistent with the previous work on investigating direct dyeing properties s. The excellent dyeing yields on en Vix® could be presumably ascribed to the lower crystallinity values (en Vix® 27% and viscose rayon 39%) and degree of orientation (en Vix® 1.93 and viscose rayon 3.63); as a useful generalization, the fibres may be regarded as

KOH: DYEING PROPERTIES OF A MIXED BI-FUNCTIONAL REACTIVE DYE ON CELLULOSIC FIBRE 91

structures in which there is a spread of molecular order, ranging from highly ordered crystalline domains to disordered amorphous regions 7. The strength originates in the crystalline material while the amorphous material provides the flexibility. Therefore, the fibre properties, including dyeing properties, vary depending upon the relative degrees of order and disorder in the structure (often described as the crystalline/amorphous ratio) and also molecular alignment (degree of orientation), i.e. lower orientation and crystallinity mean a higher rate of dye diffusion with these fibres.

3.2 Effect of Alkali Concentration on Dyeing Properties Fig. 4 shows that the KlS values and the exhaustion

of dyeings on en Vix® are higher than that on viscose rayon and this result is also consistent with the previous work5

•8

-10

. The exhaustion values of the dye used were reached to the saturation levels at low alkaline concentration values (1 giL) presumably because of the excellent dyeing properties of regenerated cellulosic fibres ; generally the salt and alkali requirements are lower for reactive dyes on regenerated cellulosic fibres than for the corresponding dyeings on cotton. The mixed bi­functional reactive dye shows excellent exhaustion even without alkali addition. The vinylsulphone group in the mixed bi-functional reactive dye enhances the subtantivity for cellulose as the precursor groups lose their ionic charge by 1,2-elimination while the triazinyl group itself has relatively high substantivity for cellulose.

3.3 Effect of Material-to-Iiquor Ratio on Dyeing Properties Fig. 5 shows the effect of material-to-liquor ratio

on the dyeability of regenerated cellulosic fibres. As expected, the reactive dyes decrease in substantivity to a greater or lesser extent when the material-to­liquor ratio is increased. It follows logically that as the liquor ratio increases the probability of contact between the dye molecules and the fibre surface decreases, i.e. fewer dye molecules (per unit of time) are adsorbed onto the fibre surface. Equilibrium between adsorption and desorption is thus displaced, desorption becomes stronger and substantivity is lower. This decrease in substantivity is relatively less marked with en Vix® than with viscose rayon. It is interesting to note that the reproducibility on en Vix® compared with that on viscose rayon is better, being particularly resilient to changes in material-to-liquor ratio. The results are in agreement with the findings of

previous works carried out by Koh et aI. 5,8-10 on direct

dyes and monofunctional reactive dyes; extremely high dye yields on en Vix® were observed. It can be observed that the en Vix® is relatively insenSItIve to process variables. The presence of two reactive

100

::::!! 90 c .2 Ui " 1 80 )(

w --' enVix

70 -.{}- .. Viscose

60+--.--~-----.------,_-----------.~

o 2 4 6 10 20r-----------------------------------,

O+--.--~----_.------,_----------_r~

o 2 4 6 10

Alkali conc. (gil)

Fig. 4--Effect of alkali (Na2C03) concentration on exhaustion of dyeings and K/S values of dyed fabrics (dye cone. 1.0% owf and material-to-liquor ratio 1 :20)

16

• • • ------14

E 12 0-_

c 0

.--0-- __ ____ -0.. N

!£.. --0..' __ rJl 10 i2 --~

8 -- enVix -·0·- Viscose

6

1 : 5 1 : 10 1 : 20 1: 30 1 : 40

Material-to-liquor ratio

Fig. 5--Effect of material-to-liquor rati o on KIS values of dyed fabr ics (dye cone. 1.0% owf and salt cone. 20 giL )

92 IND IAN 1. FJBRE TEXT. RES., MARCH 2005

groups that differ in react ivity g ives dyes that are less sensitive to salts and alkali and are less affected by the changes in material-to-liquor ratioll.

3.4 Dyeing Behaviour

Fig. 6 shows the exhaustion behaviour of reactive dye on regenerated cellulose fibres during dyeing. As expected, the dyeing rate of two rayons is not the same because of their supramolecular structuress. Different dyeing rates , brought about by the difference in physical structure, are clearly of pract ical importance. Predictably, ell Vix® shows faster exhaustion behaviour than viscose rayon, presumably due to the lower crystallinity and degree of orientation . The crystallites lie preferentially parallel to the fibre axis and are separated by reg ions of lower order and intermicellar spaces. The average size of the crystallites and the quantitative ratio of crystallites to regions of lower order are strongly fibre specific. Only water-swollen intermicellar spaces and regions of lower order of the fibre are accessible to large reactive dyes molecules. It is completely impossible for a dye to diffuse into the hi ghly oriented crystallites. Dyeing, therefore, only proceeds at the outer walls of the crystallites and in the non-oriented cellulose.

Further evidence that the dyeability of en Vix® is better than that of viscose rayon has been provided by the results of build-up properties obtained for the mixed bi-functional reactive dye. Fig. 7 shows that the en Vix® dyes to a much deeper shade than viscose rayon.

Table shows that the wash fastness and perspiration fastness of 111 standard depth dyeings of

Table I-Wash fa stness and perspiration fastness of the react ive dyes on regenerated cellulose fibres

Fastness to Staining on Acetate Callan Nylon PET Acrylics Wool

Washing ®

enVix Vi scose

Perspiration eIlVi.x@

Alkali Acid

Viscose Alkali Acid

4-5 4

5 5

5 5

3-4 4

4 4-5

4 4-5

3-4 3-4

4 4

4 4-5

5

5

5 5

5 5

5

5

5 5

5 5

5

5

5 5

5 5

the reactive dye on en Vix® are similar to that of comparable depth dyeings on viscose rayon. Also, in case of rub fastness and light fastness, the mixed bi-

100

~ 80 ~ c: o ~ ~ 60

P /

/ .r: ><

UJ

40

/ / --*- enVix

- 0- - Viscose

15 ,---------------------------~~ .. _.

~ 10 E

-0- --0- - 0- - 0 --0 0/

t: o N e

5 /

/

_.-0-_0-- -0

d /

/ I

/ /

3010 4010 5010 6010 60/15 60/25 60/35 60/45 60/55 60/65 Cooling

Temp / Holding time (OC / min)

Fig. 6---Dyeing behaviour of reactive dyes on regenerated cellulosic fibres (dye conc. 1.0% owf, salt conc. 20 giL and material-la-liquor ratio 1 :20)

50~----------------------------------'

-40 ~~~o~ - ~ - . - ---- ---- - - -. OJ

E 30 c:

0 N J.1 ~ If)

, ~ 20

p' -.- enVix 10 /

- -{)--. Viscose

O~~~-----'---------'----------~~

o 0.5 1.0 2 .0 4.0 6.0

Dye conc. (%o.w.f.)

Fig. 7-Build-up properties of reac tive dyes on regenerated cellulosic fibres (salt conc. 20 giL and material-to- liquor ratio 1:20)

KOH: DYEING PROPERTIES OF A MIXED BI-FUNCTIONAL REACTIVE DYE ON CELLULOSIC FIBRE 93

functional reactive dye shows excellent fastness results (ratings of 5), irrespective of the regenerated cellulose.

4 Conclusions The dyeing properties of a new regenerated

cellulosic fibre (en Vix®) are found be excellent in comparison to regular viscose rayon. Careful comparison of the dye yield on two rayons with the mixed bi-fl1ilctional reactive dye confirms that there is a correlation between supramolecular structures and dyeing properties; en Vix® exhibits higher exhaustion values and better build-up properties than viscose rayon, presumably due to the lower crystallinity and degree of orientation. In addition, it shows stable final colour yields, irrespective of the material-to-liquor ratio. Hence, the reproducibility of dyeing of en Vix® is expected to be excellent. Fastness properties of reactive dyes on en Vix® and viscose rayon are found to be almost identical. The results obtained suggest that this novel regenerated cellulosic fibre could be used as an important alternative to conventional viscose rayon although more detailed studies on the new regenerated cellulosic fibre is necessary before any definite conclusions can be drawn.

Acknowledgement The authors are thankful to the Ministry

of Commerce, Industry and Energy, South Korea

(Support for Industri al Technology Development program, No. 011-08-007) for providing the financial support.

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4 Kim I S, An J S & Kim B H, U SPat 6, 361, 862 (to SK Chemicals), 26 March 2002.

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11 Abeta S, Yoshida T & Imada K, Am Dyest Rep, 73 (1984) 26.