Dissolution of Polyfunctional Reactive Dyed Cotton in Cadoxen Solvent

-------------.._. n"._ Indian Journal of Textile Research Vol. 6, June 1981, pp. 85-89 Dissolution of Polyfunctional Reactive Dyed Cotton in Cadoxen Solvent W B ACHW AL & P N ABHY ANKAR Department of Chemical Technology, University of Bombay, Bombay 400019 Received 6 November 1980; accepted 4 March 1981 The kinetics of dissolution of polyfunctional reactive dyeings has been studied and found to be different from that of bifunctional reactive dyeings. For cotton dyed with polyfunctional reactive dyes, the initial faster rate of dissolution was followed by an extremely slow rate and the samples did not dissolve completely even after 24 hr. The initial rate of dissolution of cotton dyed with bifunctional reactive dyes was very slow and was followed by a higher rate and complete dissolution in 24 hr.ln the case of polyfunctional dyeings, the activation energy at the faster rate of dissolution was 7-8 kcaljmole, suggesting that the disruption of hydrogen bond is the governing factor for dissolving the non<rosslinked fraction. At the extremely slow rate of dissolution, activation energy was 19-20 kcal/mole, which is similar to that for bifunctional dyeings, indicating that dissolution involves disruption of crosslinks. The difference in the behaviours of poly- and bifunctional reactive dyeings has been explained on the basis of higher alkali stability of the dye-fibre bond and the larger size of crosslinks in the former case. The method of application of dyes has also been found to have an effect on the extent of dissolution, as it influences the state of swelling of the fibre at the time of formation of crosslinks. Considerable difficulties have been experienced in the dissolution of cotton materials dyed with reactive dyes in conventional solvents, such as cuprammonium hydroxide and cupriethylenediamine1-5. Conditions for the dissolution of cotton dyed with various types of reactive dyes in a modified cadoxen solvent were standardized and no anomalous behaviour was observed in contrast to the results of earlier workers with cuoxam6,7. Cadoxen solvent, on account of its colourless nature and relatively high stability for cellulosic solutions, has been found to be useful for many analytical applications, such as estimation of dye content and extent and distribution of crosslinks in the finished cotton samples8,9. The rates of dissolution in cadoxen were determined at different temperatures for undyed cotton and cotton dyed with typical mono- and bifunctional reactive dyes. A distinct difference in the behaviours was observed for undyed cotton and cotton dyed with monofunctional reactive dyes on one hand and bifunctional reactive dyes on the other. For the first type of samples, the initial rapid rate of dissolution was followed by a slower rate. The initial rate of dissolution of cotton dyed with a bifunctional reactive dye was very low and was followed by a second step with slightly higher rates t 0, 11. The rate constants of dissolution in both the stages were increased to some extent on increasing the temperature. For monofunctional dyeings, a low value for activation energy was obtained (4 kcaljmole). In the case of bifunctional dyeings, the activation energy was found to be high ( 16 kcalfmole), indicating that the dissolution probably involves a chemical reaction disrupting the existing crosslinks by the alkali in the solvent12. Hence, it was considered worthwhile to study the rates of dissolution in cadoxen of cotton materials dyed with polyfunctional dyes like Procion Supra and to compare the same with those for monoand bifunctional dyeings. Dyeing conditions and the dye contents of samples were varied and for typical samples, the rates of dissolution were determined at different temperatures and activation energies calculated. Experimental Procedure Preparation of cadoxen solvent-cadoxen solvent containing cadmium (5 ±0.1%), ethylenediamine (28 ± 1%) and sodium hydroxide (0.5 M) was prepared 13. Preparation of dyed samples-well scoured and bleached fabric was used for dyeing. The fabric samples were dyed with Procion Supra dyes using the pad-batch (PH) and pad-dry-cure (PDq methods and with dichlorotriazine and monochlorotriazine dyes using the exhaust method as follows. Procion Supra dyes (PH method): The fabric sample was padded (80% expression) in dye solution (x g dye, 5-10 g NaOH and 60 g urea/litre) and batched in polythene sheet for 24 hr at 30 C. It was then rinsed with cold water, hot water, soaped at boil with 2 g/litr neutral detergent for 15min, and again rinsed with hot water and then with cold water. Procion Supra dyes (PDC method): The fabric sample was padded (80% expression) in dye solution 85

INDIAN J TEXT RES., VOL. 6, JUNE 1981 (x g dye, 20 g Na2C03 and 200 g urea/litre), dried at 80 C for S min, cured at 110 C for 5 min and washed as above. Dichlorotriazine dyes: The fabric sample was dyed in a laboratory jigger at 30 C. The material was worked in neutral dye solution for 10 min and Glauber's salt (40 g/litre) was added; dyeing was continued for 20 min more. Finally, soda ash (8 g/litre) was added and dyeing was completed in 30 min more. Samples were soaped and washed as mentioned earlier. Monochlorotriazine dyes: The fabric sample was dyed at SO C in neutral dye bath for 10 min and Glauber's salt (80 g/litre) was added; dyeing was continued for 20 min. Finally, soda ash (20 g/litre) was added and the temperature was raised to the required level. Dyeing was carried out for 60 min at this temperature. The material was soaped and washed as mentioned above. Estimation of dye onfibre-finely cut dyed samples (10 mg) were dissolved in 70% sulphuric acid. The optical densities of the solutions were measured on a Biochem colorimeter using a filter of maximum absorption. The dye content (gjkg) was calculated by referring to a calibration curve for purified dye in sulphur;ic acid. Determination of amount of dissolved cellulose by viscometric method-cadoxen solvent (100 ml), previously brought to the required temperature, was added to the flask containing 40 mg of dyed sample. The flask was shaken in a thermostatically controlled shaker bath (accuracy, ± 0.1 0q. After the required period, the flask was removed and the solution filtered quickly through a sintered glass funnel (Gz). The filtrate (about 2S ml) just sufficient for viscosity measurements 'could be collected in a few seconds. The filtrate was brought to 30 C and the flow time measured in an Ostwald viscometer. From the values of flow time for solvent and solution, the specific viscosity '15Pwas calculated. The amount of dissolved cellulose was determined with reference to a calibration curve of'15p against concentration. Calibr:ationcurvefor dissolved cotton-solutions of known concentrations of undyed cotton in cadoxen were prepared by shaking the sample of cadoxen for 2 hr. The flow time of these solutions was measured at 30 C aqd a graph of specific viscosity ('15;>against concentration was plotted. Results Dissolution of dyeings of Procion Supra (polyfunctional) dyes in cadoxen has been studied and compared with the dissolution behaviour of a dichlorotriazine (bifunctional) and monochlorotriazine (monofunctional) dyeing and undyed cotton. The amount of dyed cotton dissolved after different 86 DISSOLUTION PERIOD, min Fig. I-Amount of material dissolved in relation to the period of dissolution [(- x - x -) undyed cotton; (-0-0-) Chemictive Brill. Rose 3BH (monofunctional) dyeing; (-e-e-) Chemictive Brill. Rose 3 B (bifunctional) dyeing; (-.-.-) Procion Supra Red H-4 BP (polyfunctional) PDC dyeing; and (-0-0-) Procion Supra Red H-4 BP (polyfunctional) PB dyeing] periods was determined by measuring the viscocity of the filtrate. Fig. 1 shows the amount dissolved in relation to the period of dissolution for undyed, monofunctionally and bifunctionally dyed cotton, and typical polyfunctional dyeings with similar dye content but dyed by different methods. The values for dissolution of different reactive dyeings at various time intervals are given in Table 1. The undyed and monofunctionally dyed cotton dissolve very fast in the initials min (> 80%), whereas a bifunctional dyeing dissolves to a very little extent ( < 5%). In the case of polyfunctional dyeing, at higher dye content levels, the extent of dissolution in the initial 5 min is almost the same as that of the bifunctional dyeings. However, at lower dye content levels, the amount of material dissolved is higher for polyfuctional dyeings. After 1 hr of treatment, undyed cotton and monofunctionally dyed cottons dissolve almost completely, whereas bifunctional dyeings dissolve only to the extent of 5%. In the case of polyfunctional dyeings also, the extent of dissolution is very low ).

ACHW AL & ABHY ANKAR: DISSOLUTION OF POLYFUNCTIONAL REACTIVE DYED COTTON IN CADOXEN SOLVENT content Table 71.0 1440 13.7 87.5 62.7 30.0 51.0 60 40.0 36.0 58.75 77.5 100 17.0 10.0 14.0 46.0 23.0 93.7 65.0 98.0 47.5 80.0 52.0 37.7 75.0 81.0 82.0 95.0 56.0 71.5 I-Dissolution min min Dissolution, 2.5 5.0 4.3 7.2 1.7Dye 0.0 % of Different g/kg H-4 H-2 Rose BP(PB) RP(PB) Rp(PDq BP(PDq 3 BHB Reactive Dyeings Dyeing - )(I o o!500 1000 DISSOLUTION PERIOD, mln 1500, I (5-7%). However, in the same period dyeings with lower dye content dissolve to a greater extent. After 24 hr, the bifunctional dyeing dissolves completely, but most of the polyfunctional dyeings still remain insoluble, with the exception of dyeings with very low dye content, e.g. Procion Supra Red H - 4 BP (2.5 gjkg) and Procion Supra Yellow H - 2 RP (1.7 and 3.4 gjkg). The insolubility of polyfunctional dyeings even after 24 hr suggests the presence of more alkaliresistant crosslinks as compared to bifunctional dyeings. It can also be seen that, in general, dyeings prepared by PB method dissolve to a greater extent as compared to dyeings prepared by PDC method at a given dye content. The kinetic data for dissolution were analyzed as a pseudo first order reaction and showed the presence of two stages of dissolution in all cases. The plot of log (a - x) against dissolution period for the dyeings is shown in Fig. 2. The rate constants of dissolution of different reactive dyeings are given in Table 2. The undyed cotton and monofunctionally dyed cotton show a very high initial rate constant of dissolution (322 x 10-3 min -1), whereas the bifunctional dyeing shows initially very low rate constant of dissolution (1.0 x 10-3 min -1). For polyfunctional dyeings, the initial rate constants vary between 10 and 100 x 10-3 min -1, i.e. the rate constants are higher than those for bifunctional dyeings, but much lower than those for monofunctional dyeings. Fig. 2-Rate of dissolution of cotton material [(- x - x -) undyed cotton; (-0-0-) Chemictive Brill. Rose 3 BH (monofunctional) dyeing; (-e-e-) Chemictive Brill. Rose 3 B (bifunctional) dyeing; (-.-.-) Procion Supra Red H-4 BP (pol)'functional) PDC dyeing; and (-0-0-) Procion Supra Red H-4 BP (polyfunctional) PB dyeing] In the second step of dissolution, monofunctional dyeing and undyed cotton show a lower rate constant (42 x 10-3 min -1). Bifunctional dyeing shows a slightly higher rate constant (3 x 10-3 min -1), but the polyfunctional dyeings show extremely low rate constants in the second step, i.e. 0.03-1.0 x 10-3 min -1. The above comparison of rate constants also suggests that after the initial partial dissolution, further dissolution of polyfunctional dyeing is extremely difficult. Discussion. The above interesting and complex behaviour of bifunctional and polyfunctional dyeings during dissolution can be understood by considering the various possible modes of reaction of dyes with the fibre and the state of fibre swelling during as well as after dyeing (Fig. 3). Even in deep shades, it is not likely that all the cellulose chains in accessible region are involved in reaction with the dyes and some undyed fraction (1) will be present. A major portion of the dye is also likely to react only at one reactive centre, while the other reactive group 87

INDIAN J TEXT RES., VOL. 6, JUNE 1981 gets hydrolyzed. This will form a monofunctionally dyed fraction (II) and (In). They will have a dissolution behaviour similar to that offraction (I). As established in the earlier investigations on dissolution and swelling of reactive dyed materials14 15, a part of the Table 2-Rate Dyeing otton upra Brill. Red Yellow content 18.0 11.2 18.4 5.0 9.2 3.4 gjkg Rose H-4 H-2 BP(PB) Bp(PDq RP(PB) 3iBH 3!B H-2 RIj<PDq Constants of Dissolution of Different Reactive Dyeings 4.3 7'.2 2.5 5.0 1.7Dye 0.0 103.5 24.0 53.2 10.3 30.0 10.5 12.9 416.0 102.2 91.2 70.0 Rate constant (10-3 min -1) First step 322.5 Second step 42.0 1.0 3.0 0.235 0.029 0.65 0.45 0.8 0.562 3.15 1.55 2.5 5.0 bifunctional or polyfunctional dye is likely to react at two centres forming a crosslink (Fig. 3, VI and VII). Such crosslinks will hinder the penetration of solvent and subsequent swelling of cotton, which is a primary requirement for dissolution, However, the length of crosslinks formed with polyfunctional dyes is likely to be larger because of the presence of two reactive systems compared to one in the case of dyeing with bifunctional dyes. There is also a possibility of both the reactive centres in a dye reacting at two positions on the same cellulosic chain (Fig. 3, IV and V). However, such a blocking of groups in the same chain is not likely to have any effect on the rate of dissolution. When the dissojution period is prolonged, the cadoxen solvent with its alkalinity (due to ethylenediamine and free alkali, ph 12) will gradually lead to the disruption of crosslinks and further dissolution of the sample. The extent of-disruption of crosslinkswillnaturally depend upon the resistance of cross links to alkaline hydrolysis. On the basis of the above discussion, the results of percentage dissolution and rate constants of dissolution (Tables I and 2) are explained below. The high insolubility of the bifunctional dyeing in 5 and 60 min is likely to be due to the compact nature of the crosslinked structure after dyeing, which prevents penetration of the cad oxen solvent with its bulky nature from having its action on the undyed or uncrosslinked fraction present. In the case of polyfunctional dyeings, the amount of material dissolved in the initial 5 min is larger and DICHLOROTRlAZINE PROCION SUPRA x...:x GENERAL STRUCTURE DYE CI CIY o ( x - REA CTIVE GROUP I RElICTIVE DYED MATERIAL UNDYED FRACTION C I I I40NOFUNCTIONAL I) YEO FRACT ION L-OH I-lUll CROSSLINKING ON SANE CELLULOSIC CHAIN IYI L CROSSLINKING OF TWO DIFFERENT CELLULOSIC CHAINS + C:AOOXEN SOLVENT Fig. 3-Possible r-- lull reactions during dyeing and dissolution rt'"'nl ALKAU OF SOLVENT! l-...oh 88

ACHW AL & ABHY ANKAR: DISSOLUTION OF POL YFUNCTIONAL REACTIVE DYED COTTON IN CADOXEN SOLVENT increases up to 60 min due to the better penetration possibilities for these dyeings, as the crosslinks lire likely to be larger. As the dye content increases, the number of crosslinks formed is bound to increase, explaining the observed fall in the amount dissolved and the lower rates of dissolution. The possibility of formation of larger number of crosslinks with polyfunctional dyes as compared to bifunctional dyes along with the high alkali stability of such crosslinks can explain the low values of rates of dissolution between 60 min and 24 hr and incomplete solubility even after 24 hr. During dyeing by PB process, the wet cotton material is likely to be in swollen state, while the structure is bound to collapse in PDC process. In the swollen fibre state, the extent of crosslinking is likely to be less and the crosslinks will be formed in accessible portions which are near the crystalline regions. The above factors can explain the higher values of extent of dissolution observed for PB dyeings as compared to PDC dyeings at similar levels of dye content. From the data on dissolution of polyfunctional dyeings at different temperatures, activation energies for the two steps were calculated using Arrhenius equation. For the first step, activation energy is 7-8 kcal/mole, showing that during dissolution of the undyed portion, hydrogen bonds are the only bonds to be broken to cause dissolution. In contrast to this, in the second step, covalent bonds between the dye and the fibre are to be disrupted. The bond energies of reactive dyes with cellulose are reported to be around 20-22 kcaljmole, which is close to the observed value of 19-20 kcal/mole. Thus, the study of rate of dissolution of reactive dyeings is very useful in detecting the presence of crosslinks and in understanding the influence of length of crosslinks and physical state of the substrate during the formation of crosslinks. References I VickerstatT T, Me/liand TextBer, 39 (1958) -765_ 2 Fowler J A & Preston C, J Soc Dyers Colour, 74 (1958) 372. 3 Wegmann J, Melliand Text Ber, 39 (1958) 1006_ 4 NeveU T P, J Soc Dyers Colour, 77 (1961) 158. 5 Ageter A, Text-Prax, 18 (1963) 557. 6 Achwal W B & Vaidya A A, J Soc Dyers Colour, 85 (1969) 404. 7 Frost A & Duvcen V, J Soc Dyers Colour, 84 (1968) 304_ 8 Achwal W B & Vaidya A A, Text Res J, 39 (1969) 817. 9 Achwal W B & Soudagar S V, Assessment of extent and distribution of cross/inks infinished cotton, paper presented at the symposium on finishing, Textile Association, Bombay, 1973. 10 Achwal W B, Behaviour of solutions of reactive dyed cellulosic materials in cadoxen, paper presented at the symposium on physicochemical aspects of interaction of dyes in solution and in fibre systems, Centre of Advanced Study in Applied Chemistry, Department of Chemical Technology, Bombay University, Bombay, 1969. II Achwal W B, Krishevsky G E & Vaidya A A, lzvest Vuzov Text Prom, 3 (1970) 102. 12 Achwal W B, Kinetics of dissolution in cadoxen of reactive dyed cotton materials, paper presented at the symposium on dyepolymer interactions, Centre of Advanced Study in Applied Chemistry, Department of Chemical Technology, Bombay University, Bombay, 1971. 13 Achwal W B & Gupta A B, Antew Makromol Chem, 2(1968) 190. 14 Achwal W B & Joshi G W, J Text Ass, 36 (1975) 114_ 15 Bagwe V B & DaruwaUa E H, J Soc Dyers Colour, 93 (1977) 338. I r 89