W NH2 N=N0'V-N=NWNH2

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 1, June 1990, Pp 6-72 Dyeing of jute fibre with direct dyes and their fastness characteristics Faisul Islam Farouqui & Md Ibrahim Hossain Department of Applied Chemistry and Chemical Technology, Rajshahi University. Rajshahi, Bangladesh Recei ved January 1990; accepted 2 February 1990 The effect of dye conc., electrolyte (common salt) conc., dyeing time and dyeing temperature on the dyeing of jute fibres with direct dyes, viz. Congo Red, Titan YelIow, Fast Orange PRS, Durazol Red and Direct YeIlow 29, has been studied. The dye absorption increases with increase in electrolyte conc., dyeing time or dyeing temperature and decreases with increase in dye cone. In some cases, higher temperature decreases the dye absorption. The colour of dyed and modified jute fibres fades on exposure to sunlight, washing with soap solution and acid and alkali spottings. A mixture of2% potassium bichromate, 2.% blue vitriol and 3% of 30% acetic acid has been found to be effective in preventing the colour of Titan Yellow on the dyed fibres, but it does not prevent the strength loss of direct dyed jute fibres. Keywords: Direct dyes, Dyeing, Jute fibre 1 Introduction Jute being a lignified fibre differs somewhat from cotton in dyeing properties. Due to its structural peeuliarities,jute has an affinity for a wide range of dyes including basic, acid, direct and vat dyes. Some investigators - have studied the dyeing of jute with acid and basic dyes but no effort seems to has been made to study the dyeing nature and the fastness character of jute fibre dyed with the direct dyes. In the present work, the effect of dye conc., electrolyte conc., dyeing time and dyeing temperature on the dyeing of jute fibres with direct dyes, viz. Congo Red, Titan Yellow, Fast Orange PRS, Durazol Red and Direct Yellow 29, has been studied. The colour fastness of dyed jute fibres on exposure to sunlight in air, washing with soap solution, and spottings with acids and alkalies has also been studied. To obtain fast colour, the dyed fibres were treated with a mixture of metal salts, used as a modifier. 2.1 Methods of Dyeing and Selection of Optimum Dyeing Conditions Five direct dyes, viz. Congo Red (C.I ), Titan Yellow (C.I. 190), Fast Orange PRS (C.I. 236), Durazol Red (C.I ) and Direct Yellow 29 (C.I. 196), were used for dyeing jute fibre. Structures of the dyes are given below: W NH2 N=N0'V-N=NWNH2 " ~. / /1 I.,/. SO]No SOJNO 2 Materials and Methods Corchorus olitorius (Toss a) variety of jute fibre, collected from the local market (Durgapur, Rajshahi), was used. The portion between 7 and 100 em from the bottom was taken and cut into two equal pieces of 12. em, blended and washed with a solution of soda (6. g/l) and soap flake (3. g/l) at 7"C for 30 min>. The jute fibre was then bleached with sodium chlorite solution (0.%) atph and at 8-90 C for 90 min". The bleached fibre was dried at 8T and used as the experimental material. To obtain optimum conditions for dying jute with direct dyes, dye conc., electrolyte cone., dyeing time and dyeing temperature were. selected as follows: 6

2 INDIAN J. FIBRE TEXT. RES., JUNE Dye Concentration Seven dye-baths were prepared with 0., 1.0, 1., 2.0,2.,3.0 and 3.% dye (owf) and the dyeing was carried out with 20% common salt at IOO'C for 60 min After dyeing, the concentration of the exhausted dye-bath was determined". Using Grey scale? (for assessing the change in colour), the percentage of dye which gave the fibre even and maximum shade was selected Electrolyte Concentration Jute fibre was dyed using the selected dye concentration in presence ofo,, 10, 1,20,2,30 and 3% common salt (electrolyte) at IOO'C for 60 min. The electrolyte cone. at which the fibre attained maximum shade was selected by using the Grey scale Dyeing Time The fibre was dyed with the selected dye and electrolyte concentrations at IOO'Cfor 10,20, 30,0, 0, 60 and 70 min. The time at which the fibre absorbed maximum dye was selected Dyeing Temperature The fibre was dyed with the selected dye and electrolyte concentrations at 60, 70, 80,90 and loo'cfor the selected time. The temperature at which the fibre absorbed maximum dye was selected. The selected dye cone., electrolyte conc., dyeing time and dyeing temperature were taken as the optimum dyeing conditions for dyeing of jute fibre. The quantity of dye or dye assistant (common salt) required was calculated using the following formula". Stock solution required (ml) = Wxp where Wis the weight (in grams) of sample required; P, the concentration (%) of dye or dye assistant to be used (expressed on the weight of fibre); and C, the concentration (%) of stock solution. 2.2 Aftertreatment of Dyed Fibre with Metal Salts Dyed fibres were treated with a mixture of2% potassium bichromate, 2.% blue vitriol (cupric sulphate) and 3% of 30% acetic acid (owf) using the fibreliquor ratio I:0 at 8-90'C for min!". 2.3 Fastness Tests The colour fastness of dyed and modified fibres was measured using the Grey scale", the fastness grade being the control Light Fastness The dyed and modified fibres were exposed to sun on a flat board for 20 h at the rate of8 h/dayll. After c every 0 h, the change in colour of the fibres with respect to control was assessed by the Grey scale Wash Fastness The dyed and modified fibres were treated with a solution of soap flake ( gjl) at 0± 2"C for 30 min 12. After the treatment, the change in the colour of the washed fibre was assessed. Similarly, the wash fastness was measured at 70' and IOO C Fastness to Spottings Dyed and modified fibres were combed and compressed to form a sheet of 10em x em. The specimen was spotted with four drops of water at room temperature. The change in the colour of the spotted area was assessed after dryingl3. In the same way, the change in colour on acid 1 and alkali 1 spottings was assessed by using the following solutions. Sulphuric acid solution (relative density, 1.8) (0 g1l). Acetic acid solution containing glacial acetic acid (300 gjl). Tartaric acid solution containing crystalline tartaric acid (l00 gjl). Sodium carbonate solution containing anhydrous sodium carbonate (l00 g/\). Sodium hydroxide solution (0 g/l). Ammonia solution (10%). 2. Measurement of Breaking Strength Breaking strength of dyed and modified fibres was measured by using the tensile strength tester (Torsees Schopper type-os- 100). The length of each specimen (total length, 2 em; and weight, 0. g) between the jaws was kept at 10em and 1 twistj2 em was given along the length of the fibre. In each experiment, the breaking strength of lo specimens was measured and the mean of these values was taken as breaking strength Results and Discussion 3.1 Effect of Dye Concentration Dye absorption by jute fibre decreases with increase in dye cone. in the dye-bath (Fig. I).This may be due to the high concentration of dye ions which hinder the absorption of dye by the fibres whereas the low concentration of dye ions favours it!", With the increase in dye conc., the absolute quantity of the absorbed dye also increases while the relative quantity diminishes!". Thus, the fibre absorbs a relatively greater amount of dye from a dilute solution. Fig.l also shows that in some cases the absorption of dye by the fibre is very high. It seems that all water-soluble dyes are electrolytes and in aqueous solution they dissociate 66

3 FAROUQUI & HOSSAIN: DYEING OF JUTE FIBRE WITH DIRECT DYES into ions. In direct dyes, the coloured ion is negatively charged and the colourless compensating ion is positively charged. When the jute fibre is immersed in dye solution, the negatively charged ions of direct dye are repelled by the surface potential of cellulose. This potential barrier overcomes by the presence of electrolyte. In some cases, the effect is so pronounced that the exhaustion is very high 18. Another explanation is that the dyes are absorbed and retained by cellulose for the reason that the free partial valencies on the surface of the cellulose macromolecules get saturated by the strong partial valencies of the dye. This mutual saturation is possible only if the dye has a long stretched molecule similar to that of cellulose!". It was observed from experiments that even and acceptable colour produced onjute fibre when it was dyed with % dye (2.0% Congo Red, 3.0% Titan Yellow, 2.% Fast Orange PRS, 2.% Durazol Red and 3.0% Direct Yellow 29). Above or below these dye concentrations, dull and uneven shades were obtained. 90 ~ ~ eo.c ~~ L-~------~----~------~ o 0' 1-70S l's ~ conl.,.i,.,. Fig. I-Effect of dye concentration on dyeing of jute fibre with direct dyes: (0) ~ IUd, (0) TItan Yellow, (e) Fast ~ PRS, (6) Durazol Red, and (A) Direct Yellow ElI"ed of Electrolyte CODCeIItration Fig.2 shows that some dye absorption takes place when the jute fibre is dyed with % dye (2.0% Congo Red, 3.0% Titan Yellow, 2.% Fast Orange PRS, 2.% Durazol Red and 3.0% Direct Yellow 29) in the absence of common salt as electrolyte in the dye-bath. The chemistry of jute and direct dye (both the fibre and the dye give similar charges of ions) reveals that no dye particle would attach to the fibre without electrolyte but in practice it happens. This is because commercial dyes are not pure and usually contain inorganic salts, dextrin, and possibly wetting or dispersing agents. These are added to achieve the standard tinctorial strength and to increase absorption'v-!". Electrolyte may also be present in the water used in dyeing, either as water hardness or as soluble salts produced by water-softening treatments'". These electrolytes also effect the dye absorption. Dye uptake by the fibre increases with the increase in electrolyte conc. in the dye-bath and reaches to saturation when jute is dyed in presence of 10-30% common salt. The electrolyte, in this case, lowers the repulsion due to the similar charges on the charged fibre surface and coloured dye anions by imparting oppositely charged ion with the charged dye anion and thus, by overcoming the potential barrier, improves dyeability'y'". Another explanation is that the presence of an electrolyte in the dye-bath decreases the membrane potential of cellulose, reduces the repellency of cellulose and dye particles with the same charges and also improves dyeability!". O~O--~------~IS~----~2S~----~lS~ EI~clrolyt~ cone., '. Fig. 2-Effect of electrolyte (common salt) concentration on dyeing ofjute fibre with direct dyes: (0) Congo Red, «(») Titan Yellow, (.) Fast Orange PRS, (6) Durazol Red, and (A) Direct Yellow 29 It was observed from the experiments that even and bright shades produced when thejute fibre was dyed with Congo Red, Titan Yellow, Fast Orange PRS, Durazol Red and Direct Yellow 29 in presence of 10, 30,2,30 and 2% common salt respectively. Shades were not uniform and acceptable above or below these concentrations. 3.3 Effect of Dyeing Time Fig.3 shows that with increase in dyeing time the dye absorption by the fibre in the dye-bath increases and reaches to maximum during 30-0 min of dyeing. The maximum dye absorption occurs in 0, 0, 30, 0 and 30 min for Congo Red, Titan Yellow, Fast Ora- 67

4 INDIAN J. FIBRE TEXT. RES., JUNE 1990 nge PRS, Durazol Red and Direct Yellow 29 respectively. The dye absorption remains nearly constant with further increase in dyeing time. The reason for such a behaviour is that the cellulosic fibre immersed in a dye solution absorbs dye until equilibrium is reached. Under any given condition of temperature and electrolyte conc., the true equilibrium is reached when each fibre has been evenly dyed throughout its cross-section and when no change in the concentration of dye in the fibre and in the solution takes place with further increase indyeing time. With any particular dye-fibre system, this equilibrium may reach in a comparatively short or long time!". The equilibrium dyeing time of all the direct dyes is not same because the speed of dye diffusion inside the fibre depends on the size of the dye particles and on the state of the fibre, i.e. the smaller the dye particle and greater the fibre swelling, the higher is the mobility of the dye particles and the quicker they penetrate inside the fibre and, conversely, the greater the dye particles and lesser the swelling capacity of the fibre, the slower is their diffusion!". Experiment showed that the dyeing time was short, but it required a long time to obtain level dyeing. The dye was rapidly taken up by the fibre and fixed to the one part of the fibre while another part was left undyed or only slightly coloured. Most dyes possess two properties depending upon dyeing time. The first property is their migration or levelling power. This is the tendency of particular dye molecules,attached to the surface of the fibre, to detach themselves, re-enter the solution and again attach themselves to another region of the fibre. The second property is the effect of temperature or addition of other compound to the dye solution. These factors can effect the absorption of the dye from the solution by the fibre!". 3. Effect of Dyeing Temperature FigA shows that the absorption of Titan Yellow, Fast Orange PRS and Direct Yellow 29 by jute fibre increases with the increase in dyeing temperature and becomes maximum at IOO'C. It seems that dyes exist in solution as aggregates of various sizes and at high temperature, large dye aggregates are broken down to smaller units, causing easy penetration of smaller dye particles into the fibre 1o,19. Another explanation is that at high temperature the size of the fibre pores increases and dye particles easily penetrate into the fibre. When the dye-bath cools down, the fibre pores contract and the dye particles remain in the fibre!". Hence, at higher temperature, dye absorption is higher. It is also observed from the figure that dye absorption decreases linearly with the increase in temperature above 60 C for Durazol Red and above 90 C for Congo Red. This may be mentioned here that the 100,----:::o:=u===!:r==u==cr=C/"'I c-.~ -;;; :> ~ s 20 o~~-----~---~------~ Dyeing time,min Fig. 3-Effect of dyeing time on dyeing of jute fibre with direct dyes: (0) Congo Red, «) Titan Yellow, (.) Fast Orange PRS, (f',) Durazol Red, and (A) Direct Yellow r :::::c)=::::;'" 80 c ~ ~ 60 ~... >- c Temperature, C Fig. -Effect of dyeing temperature on dyeing of jute fibre with direct dyes:(0) Congo Red, «)) Titan Yellow, (.) Fast Orange PRS, (f',) Durazol Red, and (&) Direct Yellow 29 amount of dye absorbed by the fibre in the equilibrium condition is reduced with an increase in temperature. The exhaustion of dyes which do not actively interact with the fibre is reduced more considerably than that of dyes which interact more intensively with the fibre. The temperature at which the maximum amount of dye is practically exhausted should be adopted for dyeing with the dyes, which, in solution, approach the molecular condition and, therefore, possess the required diffusion speed. The dyes whose solutions are colloidal in a considerable degree diffuse slowly!". The optimum dyeing conditions of direct dyes are given in Table 1. 68

5 FAROUQUI & HOSSAIN: DYEING OF JUTE FIBRE WITH DIRECT DYES 3. Light Fastness Table 2 shows that the colour of dyed fibre fades on exposure to sunlight in air and the light fastness depends on the exposure period. All the dyes, except Congo Red, exhibit good colour fastness on exposure. The light fastness of different dyes on jute fibre depends upon one or more factors. One factor which certainly has an important bearing on the light fastness of various dyestuffs on jute is the change in colour of undyed jute on exposure to light. Another factor is that the different assistants used in dyeing with the various classes of dyestuffs have a marked effect on the colour of the fibre and may tend to minimize or accentuate the apparent fading of the dyestuff". At the short exposure period, the change in colour occurs rapidly and then no or slight change occurs on further increase in exposure period. This is possibly due to the mechanism of the light action produced by the dye on the fibre. An intensive oxidation of the fibre is due to the capacity of the dye molecule, excited by the absorption of the short wave or UV light, to be reduced because of the hydrogen contained in cellulose. As a result of further oxidation of the reduced dye by the oxygen of the air, dye hydroperoxide may be formed which is also capable of oxidizing the fibre! o. This oxidation reaction rapidly occurs at short period of light exposure and hence the colour of the dyed Table I-Optimum dyeing conditions for direct dyes Dye Dye Electrolyte Dyeing Dyeing cone. (common salt) time temp. 0/0 cone. 0/0 min C Congo Red Titan Yellow Fast Orange PRS Durazo 1 Red Direct Yellow fibre abruptly changes. When the reaction is completed, the change in colour or fading does not occur. It is also seen from Table 2 that Fast Orange PRS, Titan Yellow, Durazol Red and Direct Yellow 29 exhibit better light fastness on modified fibre. Durazol Red, Fast Orange PRS and Direct Yellow 29 have considerably better light fastness even in absence of modifier. Only the colour of Titan Yellow on jute fibre was prevented by the modifier, and this colour did not undergo any appreciable change during modification (Table 2). So, the modifier can be used in dyeingjute with Titan Yellow to obtain light fast colour. The light fastnesses of the dyed and modified fibre were 3,,, and 3- for Congo Red, Titan Yellow, Fast Orange PRS, Durazol Red and Direct Yellow 29 respectively. 3.6 Wash Fastness Among the direct dyes, Titan Yellow, Fast Orange PRS, Direct Yellow 29 and Congo Red withstand their colour, to a great extent, on jute fibre on washing with soap solution. The colour of the dyed fibres fades on washing and the wash fastness decreases with the increase in washing temperature (Table 3). This may be mentioned here that all the dyes used in our experiments are water soluble. The dye is more easily dissolved in the fibre mass than in water. If the dyed fibre is placed in a medium which dissolves the dye better than the fibre, the dye will be easily washed off the fibre!". The solubility of the dye increases with the increase in washing temperature. Hence, at higher temperatures, more dye will be easily washed off the fibre. A comparison of the dyed and modified fibres shows that improved wash fastness is achieved by the modifier in the case of Congo Red, Titan Yellow and Fast Orange PRS. But Fast Orange PRS shows better Fibre Dyed Modified Table 2-Light fastness of dyed and modified fibres on exposure to sunlight in air Exposure period h o o Congo Red Titan Yellow Fastness Fast Orange PRS Durazol Red Direct Yellow

6 INDIAN J. FIBRE TEXT. RES., JUNE 1990 Table 3-Wash fastness of dyed and modified fibres on washing with soap solution Fibre Washing Fastness temp. T Congo Titan Fast Orange Durazol Direct Red Yellow PRS Red Yellow 29 Unwashed 0 Dyed Unwashed 0 Modified Table --Fastness of dyed and modified fibres to spotting with acid Fibre Acid Fastness Congo Titan Fast Orange Durazol Direct Red Yellow PRS Red Yellow 29 Unspotted Sulphuric acid Blue black Black (Shade increased) Dyed Acetic acid Light black Tartaric acid Light black (Shade increased) Unspotted Sulphuric acid Light bluish Blackish black (Shade increased) yellow Modified Acetic acid Light black Tartaric acid Light bluish black (Shade increased) wash fastness in the absence of modifier and Congo - modified fibres to spottings with sodium carbonate, Red fades at the time of modification. So, the colour sodium hydroxide and ammonia solution is satisfactof Titan Yellow dyed fibre is better protected by the ory and nearly same in most of the cases. The above modifier. results show that the modifier has no positive impact on the colour fastness of dyed jute fibre to spottings with acid and alkali. So, it is not necessary to modify the dyed fibre with metal salts to achieve fast colour in these cases. 3.7 Fastness to Spottings with Water, Acid and Alkali The colour fastness of dyed and modified fibres to spotting with water was tested. In all cases, no colour change was found, i.e. fastness grade (according to Grey scale). Table shows that the colour fastness of both the dyed and modified fibres to spottings with sulphuric acid, acetic acid and tartaric acid is satisfactory with a few exceptions. Congo Red dyed and modified fibres show poor colour fastness by changing their colour to spottings, Titan Yellow increases its shade to spottings with sulphuric acid and tartaric acid, and Direct Yellow 29 changes its colour to spotting with sulphuric acid. The changes in colour of dyed and modified fibres to spotting are not the same because the acid hydrolyzes the fibre and the dye, and the hydrolysis changes its mode in presence of metal saits. Table shows that the colour fastness of both the dyed and 70 Considering the effects of sunlight in air, washing with soap solution. and water, acid and alkali spottings on dyed and modified fibres, it can be concluded that the modifier is, comparatively, more effective in preventing the colour of jute fibre dyed with Titan Yellow. 3.8 Effect of Sunlight on Breaking Strength On exposure to sunlight in air for 20 h, the breaking strength of dyed and modified fibres decreases (Table 6). It seems that on exposure, dyes have a sensitising action on photo-oxidation process, which increases the loss in resistance. The intensive oxidation of fibre is due to the capacity of the dye molecule, which is excited by the absorption ofuv light. This excitat-

7 FAROUQUI & HOSSAIN: DYEING OF JUTE FIBRE WITH DIRECT DYES Table -Fastness of dyed and modified fibres to spotting with alkali Fibre Alkali Fastness Congo Titan Fast Orange Durazol Direct Red Yellow PRS Red Yellow 29 Unspotted Sodium carbonate Dyed Sodium hydroxide Ammonia solution Unspotted Sodium carbonate Modified Sodium hydroxide Ammonia solution Table 6--Loss in breaking strength of dyed and modified fibres on exposure to sunlight in air Fibre Exposure Breaking strength, 'kg/yarn period h Congo Titan Fast Orange Durazol Direct Red Yellow PRS Red Yellow 29 Dyed Modified Loss in breaking strength, % Dyed Modified Breaking strength retained by the modifier (metal salts), % ~ ion energy is transmitted by the dye to the oxygen of the air, causing its activation. Activated oxygen oxidizes water vapour to hydrogen peroxide, which, in turn, causes the activation of the fibre 1o. 2o. The % loss in breaking strength after exposure to sunlight is higher in modified fibre than dyed fibre. This means that direct dyes are very much sensitized by the light in presence of modifier and cause degradation of the modified fibre in all possible manners. Hence, the modifier, in this case, is not only unable to prevent the strength loss of dyed fibre but also enhances the degradation of fibre. Conclusions.1 Dye uptake by jute fibre is higher at low concentration of dye and it decreases with the increase in dye concentration in the dye-bath for all the direct dyes. Even and bright shades are obtained on dyeing jute fibre with % dyes..2 The absorption of dye becomes minimum when the jute fibre is dyed with direct dyes in absence of common salt as electrolyte. The dye absorption increases with the increase in electrolyte cone, and reaches saturation absorption at 10-30% common salt when uniform and acceptable shades are obtained..3 Higher dye absorption is obtained by increasing the dyeing time up to equilibrium absorption. The dyeing time for saturation absorption of direct dyes is min. In most cases, dye absorption occurs within a few minutes, but it requires long time to obtain level or uniform dyeing.. Dye absorption increases with increase in dyeing temperature and reaches maximum at loot in the case of Titan Yellow, Fast Orange PRS and Direct Yellow 29 and at 90 C and 60 C in the cases of Congo Red and Durazol Red respectively.. The colour of dyed and modified fibres fades on exposure to sunlight. The fading is rapid at the short exposure period and then no or slight change occurs on further increase in exposure period. The modifier protects the colour of Titan Yellow dyed fibre from the sunlight effect..6 Washing of dyed and modified fibres with soap solution removes the attached dye molecules from the fibre and hence the fibre fades. Removal of the attached dye molecules from the fibre increases with the increase in washing temperature. To obtain fast colour from washing treatment, the modifier should be used for jute fibre dyed with Titan Yellow and Fast Orange PRS. 71

8 INDIAN J. FIBRE TEXT. RES., JUNE The effects of acid and alkali spottings on the colour fastness of both the dyed and modified fibres are nearly the same. So, the modifier is not required in these cases..8 On exposure to sunlight in air, the loss in breaking strength (%) of modified fibre is higher than that of dyed jutefibre.so, the modifier should not be used in this case. References I Patro P S. Text Dyer Printer, (8) (\971) 7. 2 Carter D. J Text Inst, 30 (1939) T Douglas A E, Text Color. 9 (\ 937) 229. Holden F G. Am Dyest Rep, 19() (1930) 169. Farouqui F I & Hossain M I, Rajshahi University Studies (in press). 6 Sarkar P B & Chatterjee H, J Text Inst, 39 (\98) T27. 7 Giles C H. A laboratory course in dyeing, 3rd edn (The Society of Dyers and Colourists, England) 197,, Farouqui F I, Rahman S M, Bakr M A, Alam M S & Faruq M 0, Rajshahi University Studies, (Part-B)-XIII (198) l. 9 International Standard ISO: 10-A (E). 10 Sadov F, Korchagin M & Matetsky A. A chemical technology offibrous materials (Mir Publishers, Moscow) 1973,31,. II International Standard ISO: (E). 12 International Standard ISO:10-COI-I982(E). 13 International Standard ISO: 10-E (E). 1 International Standard ISO:10-E0-I978(E). 1 International Standard ISO:I0-E (E). 16 International Standard ISO:08I-1977(E). 17 Farouqui F I, Ali M M, Rahman S M, 8akr M A & Faruq M 0, J Bangladesh Acad sa. 2(2) (1987) VickerstaffT, The physical chemistry of dyeing (Imperial Chemical Industries Ltd, London) 19, Cockett S R & Hilton K A, Dyeing of cellulosic fibres and relatedprocesses [Leonard Hill (Books) Ltd, LondonJI96I, 21 I, Egerton G S, J Soc Dyers Colour, 6 (199)