Dyeing kinetics of radiation-grafted polyester fabric using different dyes

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 32, June 2007, pp Dyeing kinetics of radiation-grafted polyester fabric using different dyes E H El-Gendy a & N M Ali National Center for Radiation Research and Technology, Atomic Energy Authority, P O Box 29, Nasr City, Cairo 11731, Egypt M M Marie Faculty of Applied Arts, Helwan University, Cairo, Egypt and I A El-Shanshoury National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, P.O. Box 29, Nasr City, Cairo 11731, Egypt Revised received 17 June 2006; accepted 20 July 2006 Dyeing kinetics of radiation-grafted and ungrafted polyester fabrics using basic, direct and disperse dyes have been studied in the temperature range K and then compared. The effects of graft yield, ph of the dye solution, dyeing time, dye concentration and dyeing temperature on the colour difference of ploy (ethylene terephthalate) fabric have been studied for basic Rhodamine Red, direct Congo Red and Disperse Red dyes. The colour difference increases rapidly with the increase in graft yield and tends to level off at higher degrees of grafting. The best dyeing conditions are achieved at ph 9, 5.5 and 5.5 for direct, basic and disperse dyes respectively. The kinetic parameters (rate, rate constant, order, activation energy and pre-exponential rate constant) have also been evaluated for the different dyes. Analysis of the kinetic parameters and dyeing mechanisms reveals that the dyeing of polyester fabric is diffusion-controlled, and the dyeing rates follow the order: basic dye (1% grafted) >> direct (1% grafted) > disperse (1% grafted) > disperse (with a carrier) > disperse (without a carrier). Grafting improves significantly the dyeing affinity of polyester fabric towards basic, direct and disperse dyes. Keywords: Basic dye, Direct dye, Disperse dye, Polyester, Radiation grafting IPC Code: Int. Cl. 8 D06M14/00 1 Introduction The extremely crystalline nature of poly (ethylene terephthalate) [PET] fibres creates problems in obtaining dark shades by conventional dyeing methods, even with the temperature of the dye at the boil. In order to overcome this problem, polyester fibres are dyed using carriers or by using high temperature dyeing techniques. The dyeing process is carried out at temperatures above the boil (in the range K) and under pressure ranging from 0 kpa to 170 kpa. The expensive techniques of dyeing polyester fibres at high temperatures and pressures and the poisoning effect of the carrier necessitated the need to find out other cheap and adequate dyeing methods. Radiation grafting with vinyl monomers is usually carried out to modify the properties of polyester fibres. Increases and decreases in physical properties have been reported for the grafting of a To whom all the correspondence should be addressed. eglal_elgendy@hotmail.com/egendy@gawab.com natural and synthetic materials with different vinyl monomers Modifications in the swelling properties and the dye ability of PET fabric towards reactive and basic dyes using gamma radiation grafting have already been studied. 11, 12 Electron beam radiation grafting of PET, cotton and PET-cotton blends with special monomers were studied by several authors Basic and direct dyes have no affinity towards polyester fabrics. This drawback has been overcome by the addition of acidic groups to the polymer macromolecules via radiation grafting of the fabrics in methacrylic acid 12,21 (MAA) and acrylic acid 22 (AA) aqueous solutions. Dyeing kinetics of MAA-grafted PET with Astrazonrot Violet and Rhodamine Red 21 and AA-grafted PET with Sandocryl Blue 22 basic dyes were studied. In these investigations, the effect of ph of the dye bath and the degree of grafting on the colour strength (CD) of the dyed fabrics has been studied. The dependence of CD on the dyeing time, dye concentration and dyeing temperature has been

2 El-GENDY et al.: DYEING KINETICS OF RADIATION-GRAFTED POLYESTER FABRIC USING DIFFERENT DYES 233 studied and the dyeing rates, rate constants, preexponential rate constants and the activation energies evaluated. The dyeing rate increases with the increase in monomer concentration and dyeing temperature. Activation energies ranging from 6 kj mol -1 to 13 kj mol -1 were found, depending on the grafted monomer and type of used dye. This paper reports a comparative study on the dyeing kinetics of AA-grafted and ungrafted PET fabrics dyed with basic Rhodamine Red (RR), direct Congo Red (CR) and Disperse Red (DR) dyes in the temperature range K. The effects of the graft yield, ph of the dye solution, dyeing time, dye concentration, and dyeing temperature (T) on the colour difference of the dyed fabrics are investigated. The kinetic parameters [dyeing rate (R), reaction order (n), rate constant (k), pre-exponential rate constant (A), and the activation energy (Q) of the dyeing process] have been determined and a comparative study among the three different red dyes presented. 2 Materials and Methods 2.1 Materials Mill scoured, thermally stabilized (heat treated at 493 K for 1.5 min) low density polyester fabric, produced from Hankook Synthetic Inc. (Korea), was used. It is constructed from 100% polyester filament (flat yarn 75 den/36f bright trilobal raw white SDY type). Scouring was carried out in a solution containing g/l data scour WS-100 and sodium carbonate (0.5 g/l) at boiling for 1 h. The fabric was thoroughly washed with hot water, dried at ambient temperature and then used for grafting. Acrylic acid (AA) monomer (Aldrish, Germany), pure chloroform (El-Nasr Chemical and Pharmaceutical, Egypt), HPLC methanol (Aldrish, Germany), and nonionic Sandozin NIT liquid detergent (Sandoz, Switzerland) were used as such. RR (C.I ), a basic dye; CR (C.I ), a direct dye; and DR (C.I ), a disperse dye produced by Sandoz, Basle, Switzerland were used. 2.2 Methods Radiation Grafting Grafting was carried out by the direct irradiation method in a 60 Co γ source at a dose rate of 1.45 Gy/s with different doses and AA concentrations to achieve a wide range of graft yield. Dry and weighed polyester samples (ca 1.0 g) were swollen in chloroform 12 overnight before being put in widemouth tubes with ground-glass stoppers. Now methanol, the monomer and a 2 wt % of the grafting solution of chloroform, 12,13 were added to each tube so that the fabric-to-liquor ratio (FLR) is 1:40. The solution containing the fabric was deaerated by bubbling nitrogen for 5min. The grafted fabrics were removed from the reaction tube after irradiation to the desired dose. The occluded homopolymer was extracted from the grafted fabric with boiling water. The samples were then dried at 313 K in a vacuum oven to a constant weight. The degree of grafting (GY) was determined as the percentage increase in weight Dyeing Procedure and CD Measurements Stock dye solution (1%) was prepared by pasting the dye in acetic acid before the addition of required distilled water. Aqueous dye solutions containing 2% of weight of fabric (owf) dye were prepared from the dyestuffs at a fabric-to-liquor ratio 1:50. The ph of the dye bath for RR and CD dyes was adjusted using a Beckman ph meter and adding few drops of diluted sodium hydroxide solution under stirring. The dyeing was carried out in the presence of 2 g/l dye solution, 1% sodium sulphate, and 0.1 g/l Sandozin NIT liquid wetting agent. The DR aqueous dye solutions contained 2 g/l dispersol T surface active agent, benzyl alcohol carrier, and Sandozin NIT wetting agent. The temperature of the dye bath was then raised to 363 K and kept constant for 45 min. After dyeing with DR dye, a reduction and clearing bath containing 2 g/l sodium hydrosulphite and 3 g/l sodium hydroxide was used at 353 K for 20 min. The dyed samples were rinsed in hot water containing nonionic detergent followed by tap water and allowed to dry. A computerized micro colorimeter unit made by Dr. Lange (Germany) was used for the colour measurements. 21 The L *, a * and b * values of ungrafted and grafted fabrics before dye sorption were measured and taken as references. The CD intensity of the grafted samples after dyeing was determined as follows: ΔE * = [(ΔL * ) 2 + (Δa * ) 2 + (Δb * ) 2 ].. (1) 3 Results and Discussion 3.1 Effect of ph on Colour Strength The effect of ph of RR, CR and DR dye solutions on CD of grafted and ungrafted fabrics is shown in Fig. 1. The results indicate that all dyes show high

3 234 INDIAN J. FIBRE TEXT. RES., JUNE 2007 Fig. 1 Effect of ph on CD of 5.1% grafted and ungrafted PET fabric dyed with RR, CR, and DR dyes [2% owf dye; 1:50 FLR; and 45 min at 361 K] colour strength in acidic solutions except the CR dye. At a constant GY of about 5%, the affinity of the dyes towards the fabric increases with the increase in ph reaching maximum values at ph 5.5, 5.5 and 9 for RR, DR, and CR dyes respectively. A further increase in the ph decreases rapidly the CD of all dyes. The maximum CDs for the 5.1 % grafted fabrics are 78, 55, and 44 for the basic RR, direct CR and disperse DR dyes respectively, while those for ungrafted PET fabrics dyed in disperse dye solution with and without carrier are 50 and 29.5 respectively. These results show that the relative affinity of the dyes towards 5.1% grafted and dyed fabrics with RR, CR dyed, DR carrier-dyed with respect to ungrafted and DR dyed fabrics in solutions without a carrier followed the ratio 2.64 : 1.86 : 1.49 : The CD of the grafted and DR-dyed fabric exceeds that of carrier dyed one at GY higher than 6%. The higher the GY for all dyed fabrics the higher is the CD. Consequently, the carrier-free dyeing of grafted PET with basic, direct and disperse dyes at the proper GY improves considerably their dyeing ability over that dyed by the well-known conventional method using disperse dyes in solutions containing carriers. Thus, all the dyeing kinetics experiments were carried out at a ph of 5.5, except the direct CR which was carried out at a ph of Effect of Grafting on Colour Strength The effect of degree of grafting (GY) on the CD of PET fabrics dyed with RR, CR and DR dyes is shown in Fig. 2. The increase in CD over that of ungrafted fabric is plotted as a function of GY. Dyeing conditions used were as given in Fig. 1. The results Fig. 2 Effect of degree of grafting on the CD of PET fabric dyed in RR, CR, and DR dye solutions adjusted to ph 5.5 for RR and DR, and to ph 9 for CR dye show fast linear increase in CD with the increase in GY up to about 3% for the RR and CR dyes. The initial rate of increase in CD per unit increase in GY for the RR and CR dyes is 16.9 and 7.84 CD/GY respectively. A further increase in GY produces a decrease in rate of change in CD, with a tendency to level off at graft yields higher than 20%. The disperse DR dye, however, shows a linear dependence of CD on GY till 26% GY with a slope of 1.19 CD/GY. The results also indicate that the affinity of ungrafted fabrics towards DR dye is about four times higher than that of RR or CR dyes. AA-grafting improves considerably the CD of the fabrics dyed with RR, CR and DR dyes. The dependence of CD on GY for different dyes supports the results presented in Fig. 1 and emphasizes the high affinity of AA-grafted fabrics towards the RR and CR dyes in comparison with the DR dye. Moreover, the affinity of grafted fabrics towards the RR dye, measured by the slope of the CD-GY relationship, is more than twice to that of CR dye. Consequently, best dyeing results can be achieved at GY as low as 3% for the RR and CR dyes without affecting other properties of ungrafted fabrics. Therefore, dyeing kinetics experiments were carried out at graft yields around 3% to avoid discrepancy in the results due to deviation in CD values from linearity at higher yields (Fig. 2). 3.3 Kinetic Parameters In the kinetic study, the CD of the grafted and dyed polyester fabrics was measured by the E * value per unit of graft yield to avoid the contribution of degree of grafting in the CD measurements (Fig. 2). In

4 El-GENDY et al.: DYEING KINETICS OF RADIATION-GRAFTED POLYESTER FABRIC USING DIFFERENT DYES 235 previous inverstigations 6,21,22, it has been shown that the dyeing intervals are in the order of seconds. In each experiment, grafted and ungrafted samples were dyed together in the same dye bath, and the increase in CD per graft yield was calculated. The concentrations of the dyes were in rather than wt% so that the dye molecules in the aqueous solutions are constant and independent of the molecular weight of the dye Basic and Direct Dyes The dependence of CD/GY of grafted PET fabrics on the dyeing time t for C values ranging from to mol L -1 is shown in Figs 3 and 4 for RR and CR dyes respectively. The dye solutions were adjusted to the ph 5.5 and 9 for the RR and CR dyes and the fabrics were dyed in the temperature range K. The general features of the curves are nearly the same, except that the colour strength increases with increasing C and T. The colour strength increases linearly as the dyeing time increases up to about 5 s; this is followed by a slower increase with a tendency to level off close to 200 s. The initial rate of dyeing (R ) is calculated from the slope of the linear part of the CD-t relationship. The results show that as C and T increase, R is increased (Table 1). It is known that the initial R value is related to C according to the following equation 21,22 : R = k C n (2) The logarithm of both sides of Eq. (2) gives log R = log k + n log C (3) The plot of log R versus log C produces a straight line, the slope of which is n and the intercept yields Table 1 Dependence of dyeing rate (R) on dye conc. (C) and dyeing temp. (T) for RR and CR dyes Temp. (T) K Dyeing rate (R), (CD/GY) s -1 RR dye CR dye Fig. 3 Dependence of CD of AA-grafted PET fabric on the dyeing time (t) for basic RR dye concentrations (C) ranging from to and adjusted to ph 5.5 at 278, 303 and 333 K Fig. 4 Dependence of CD of AA-grafted PET fabric on the dyeing time (t) for direct CR dye concentrations ranging from to and adjusted to ph 9 at 283, 303 and 363 K

5 236 INDIAN J. FIBRE TEXT. RES., JUNE 2007 log k at C of 1 mol L -1. Figure 5 shows logarithmic plots of R versus C at different T for RR and CR dyes. The relationship is linear, and the equations relating the different parameters, as displayed on the computer chart, are as follows: RR dye log R 278 K = log C (4) log R 303 K = log C (5) log R 333 K = log C (6) CR dye log R 283 K = log C (7) log R 303 K = log C (8) log R 363 K = log C (9) The equations show that the values of n are almost constant and independent of T, with an average value of 0.49 and for the RR and CR dyes respectively. The values of the intercepts yield log k for the different dyeing temperatures. Consequently, the R-C dependence can be written as follows: (R) RR dye = k C (10) (R) CR dye = k C (11) The values of k for different T values were calculated from the intercepts for both dyes and are given in Table 2. It is observed that k increases with the increase in T. Moreover, the values of k for the RR dye are four times higher than those for CR dye for the same T. The dependence of k on T is presented in Fig. 6 by an A rrhenius-type plot of the natural logarithm of k versus inverse of T. The relationship is linear and the slope gives the value of Q/R, where R is the universal gas constant. The Q values of 16.7 and 14.5 kj mol -1 were calculated for the RR and CR dyes respectively. The intercept of the relationship is the natural logarithm of the pre-exponential rate constant (A). The values of ln A for the RR and CR dyes are and respectively. The corresponding values of A are and CD GY -1 s -1. The results obtained for the RR and CR dyes show that the order of dyeing process is dependent on the type of dye and independent of T. The values of Q for both dyes are close; however, the A value for the RR dye is 17.5 times higher than that for the CR dye. It should be noted that A is independent of C and T of the dye bath and its value is calculated at a constant C of 1 mol L -1. The difference in the value of A for both dyes could be attributed to the different molecular structures and molecular weights of the dyes. The RR, Table 2 Values of rate constant (k) of the RR and CR dyes at different dyeing temp.(t) Temp. (T) Rate constant (k), (CD/GY) s -1 K RR dye CR dye Fig. 5 Logarithmic plots of R versus C at different T for AAgrafted fabrics dyed with basic RR and direct CR dyes Fig. 6 Arrhenius-type plot of natural logarithm of k versus the inverse of absolute temperature for AA-grafted and dyed with basic RR and direct CR dyes

6 El-GENDY et al.: DYEING KINETICS OF RADIATION-GRAFTED POLYESTER FABRIC USING DIFFERENT DYES 237 being a basic dye, is unique in that its coloured component is cationic. In the dye liquor, the dye dissociates into the dye cation and the chloride anion and the dye cation reacts readily with the carboxylic groups of the AA-grafted PET fabric. Basic dyes have good substantivity for the AAgrafted fibres and exhaust well within narrow limits of temperature. Consequently, a retarder is added to the dye solution to avoid unleveled dyeing. The unexpected, relatively high Q of the RR dye is attributed to the addition of sodium sulfate retarder to the dye solution. The cationic retarder competes with the cationic dye molecules for the dye sites on the PET fibre polymer causing a repulsive positively charged layer. This prevents the dye molecules from rushing into the fibre and slows down the basic dye to replace the cationic retarder, ensuring a more level dyeing. Once the dye molecules overcome the potential barrier they leave the dye solution and react with the AA-grafted fibre as shown above. Increasing the temperature of the dye liquor provides the dye with sufficient energy to enter the fibre polymer system. The CR dye, being a direct dye, has a structure completely different from that of basic dyes. It has a linear configuration with diazo groups. It contains two NH 2 groups and two sodium sulfonate groups. The sodium sulfonate auxochromes are responsible for the good aqueous solubility of the direct dye. Sodium sulfate is added to the aqueous dye liquor to obtain adequate exhaustion of the dye molecule by the fibre polymer system via neutralization of the negative surface charge of the AA-grafted fibre with the sodium ion, enabling the dye anion to enter the fibre more readily. Moreover, the presence of the sulfate ions in the dye liquor also assists the dye to enter the fibre more readily. The application of heat to the dye liquor increases the energy of the components of the dye liquor, swells the fibre and accelerates the rate at which dyeing occurs. The addition of sodium sulfate in the CR dye solution to assist the deep shade of the dyed fabric results in the decrease in activation energy of the dyeing process and consequently the increase in A if compared with those of ungrafted fabric. However, the low value of A of the CR dye in comparison with that of the RR dye can be attributed to its higher molecular weight (696 versus for the RR dye) and its slower reaction and separation rates from the dye liquor. The reactive sites in the CR dye are the NH 2 groups. They react with the hydrogen ions of the dissociated AA molecules forming + NH 3. The + NH 3 then reacts with the F-COO - forming F-COO - + NH 3 - Dye. This reaction is slower than that of the RR dye since it depends on the structure and molecular weight of the dye molecules Disperse Dye Grafting of polyester with AA improves the dyeability of the fabric towards DR dye (Figs 1 and 2). Consequently, AA-grafted PET fabrics were dyed with DR disperse dye at different t, C and T, and the kinetic parameters were compared with those dyed in solutions with and without a carrier Dyeing Rates of Carrier-free Dyeing The dependence of CD of ungrafted PET fabrics on the dyeing time for C values ranging from to and different T for the DR dye is obtained. Similar trend is observed as in Figs 3 and 4 for RR and CR dyes except that the values of CD/GY are different. The dye liquor was adjusted at ph 5.5 and the dyeing was carried out in solutions without a carrier at temperatures ranging from 283 K to 363 K. The CD increases as t, C, and T increase. The initial R values were calculated at the corresponding C and T values and are given in Table 3 for both grafted and ungrafted samples. Logarithmic plots of R versus C at different values of T are linear, and n is independent of T and yields an order of The values of log k, as displayed on the computer chart at 283, 303 and 358 K are , 1.378, and respectively. Consequently, the equation relating R to C for the DR dye could be presented as follows: (R) DR dye = k C (12) The values of k for the DR dye at different T values are calculated and increase with the increase in T Dyeing Rates of Grafted Fabrics The DR solutions were adjusted to ph 5.5 and the fabrics grafted to 2-3% were dyed at 283, 303, and 363 K. The increase in CD due to grafting is divided by the GY and added to the value of ungrafted fabric dyed with DR dye in carrier-free solutions. The general features of the dependence of CD/GY of AAgrafted PET fabric on the t and T for C values of , , and mol L -1 are similar to those of RR and CR dyes. The initial R values were calculated at the corresponding T values and are given in Table 3. The logarithmic plots of R versus C at

7 238 INDIAN J. FIBRE TEXT. RES., JUNE 2007 different values of T show that n is independent of T and yields an order of The values of log k at 283, 303 and 363 K are , , and respectively. Consequently, the equation relating R G to C for the DR dye could be presented as follows: (R G ) DR dye = k G C 0.33 (13) Dyeing Rates of Carrier Dyeing The effect of addition of a carrier to DR solutions with different C adjusted to ph 5.5 and dyed at different T and t on the colour strength of ungrafted fabrics has been studied and the curves are found to be similar to those obtained for grafted and dyed samples with differences in CD values depending on C and T. Logarithmic plots of R versus C at different T shows that n is independent of T with an average of The intercepts of linear relationship give values of , , and for log k at 283, 303, and 258 K respectively. The corresponding values of k are 22.4, 29.82, and 51.5 CDs -1 respectively. It is obvious that R for DR dyed samples is related to C, as shown by the following equation: (R carrier ) = k carrier C 0.33 (14) Q and A for DR Dye It has been shown that k for ungrafted and grafted samples dyed in DR dye solutions with and without a carrier increases with the increase in T. This dependence is plotted according to Arrhenius equation (Fig. 7). The relationship is linear and gives values of , 0.99, and for Q/R of ungrafted samples dyed in solutions with and without a carrier as well as those grafted and dyed in solutions without a carrier respectively. The corresponding Q values are 8.59, 8.276, and 9.64kJ mol -1 respectively. The intercepts of Fig. 7 give the natural logarithm of A. The corresponding A values for samples dyed in solutions with and without a carrier as well as those grafted and dyed samples are 929 CD s -1, 714 CD s -1, and 1488 CDGY -1 s -1 respectively. The Arrhenius-type equation for the differently treated fabrics is as follows: (k) without carrier = 714 e (J/mol)/ RT, CD s -1 (15) (k) with carrier = 929 e (J/mol)/ RT, CD s -1 (16) (k G ) without carr. = 1488 e (J/mol)/ RT, CDGY -1 s -1 (17) The kinetic study of the differently treated PET fabrics shows that the values of Q and A of ungrafted and dyed fabric increase with grafting as well as dyeing in solutions containing a carrier. The increase in Q, due to AA-grafting by 1% and the addition of a carrier in the dye solution, is 16.5% and 3.8% of that Table 3 Dependence of dyeing rate (R) on dye conc. (C) and dyeing temp. (T) for ungrafted and grafted fabrics for DR dye solution without a carrier Temp. (T) K Dyeing rate (R) a Ungrafted Grafted 2.00 Ungrafted Grafted Grafted Ungrafted a For ungrafted sample, measurement unit is CD s -1 and for grafted sample, measurement unit is CD/GY s -1. Fig. 7 Arrhenius-type plot of the natural logarithm of k versus the inverse of the absolute temperature for AA-grafted and ungrafted PET fabrics dyed with DR dye in solutions with and without a carrier of ungrafted and dyed in solutions without a carrier, while the corresponding increase in A is 108% and 30% respectively. It is obvious that the increase in Q and A due to grafting is much higher than that resulting from the presence of a carrier in the dye liquor. This indicates that both grafting and carrier dyeing of ungrafted fibres enhance the affinity of the disperse dye towards PET fabric. However, the efficiency of dyeing is higher due to 1% grafting of the fabric if compared with that due to carrier dyeing. Moreover, it is expected that the degree of improvement in the DR affinity towards grafted fabrics will increase following a linear function with the increase in GY at a rate of 1.19 CD/GY. There is no universally accepted explanation for the way in which carriers assist in dyeing polyester fibres using disperse dyes. 23 However, the most common explanation is that carriers swell the polyester fibre polymer and thus allow the disperse dye molecules to enter the PET fibre more readily. Moreover, swelling

8 El-GENDY et al.: DYEING KINETICS OF RADIATION-GRAFTED POLYESTER FABRIC USING DIFFERENT DYES 239 of polymers via grafting opens their structure with the result of enhancing the grafting and the subsequent dyeing processes. 4,5,7,12,13 The degree of swelling increases with an increase in graft yield. According to the increase in Q and A due to grafting and carrier dyeing, and the improvement in dyeing properties of the fabric due to grafting over carrier dyeing, it could be concluded that the degree of swelling due to AA-grafting is much higher than that of carrier dyeing. 24 Consequently, carrier-free dyeing using AA-grafted fabrics could be readily used commercially in dyeing polyester fibres with disperse dyes. 3.4 Comparative Study The results obtained for the basic RR, direct CR, and disperse DR dyes show that the reaction order of the dyeing process is almost constant and independent of the dyeing temperature or the type of dye. This indicates that the dyeing process for grafted and ungrafted fabrics is of the same nature although the other kinetic parameters are different. The differences in R, k, Q, and A can be attributed to dye structure, dye molecular weight, dye concentration, dyeing temperature, fabric pre-treatment, and additives in the dye solution. To unify the study, the comparison between the differently treated and dyed samples is limited to the pre-exponential rate constant A, and the apparent activation energy Q. It is known that A is calculated from the intercept of ln k-1/t relationship while k is obtained from the intercept of log R-log C dependence. Consequently, the A values are independent of T or C. Moreover, the Q values follow the same dependence. The apparent Q values 16.6 and 14.5 kj mol -1 for dyeing AA-grafted PET with the basic RR and direct CR dyes respectively are high enough to explain the reaction between the grafted polyester fabric and the RR and CR dyes. The Q value can be partly due to the bigger structure and molecular weight (478.5 and 696 for RR and CR dyes) of the dyes and partly attributed to the retarding effect of the sodium sulfate added to the dye solution. However, the Q values (8.28, 8.59, and 9.64 kj mol -1 ) for the differently treated and DR dyed fabrics are considerably lower than those of grafted and dyed with RR (16.7 kj mol -1 ) and CR (14.5 kj mol -1 ) dyes. In general, the low value of Q for the differently treated and DR dyed fibres is mainly due to low molecular weight of the dye (348.5) as well as to its lack of polar groups, evidenced by the insolubility of the disperse dyes. However, the Q of ungrafted fabric dyed with DR is slightly lower than that of dyed in the presence of a carrier or grafted and dyed in absence of a carrier. Carriers are added to assist the disperse dyes to enter the fibre polymer enabling dark shades to be produced. Carriers may increase slightly the size of the dye molecule in a way that it will increase the value of Q. Moreover, the introduction of COO - groups in the grafted fabric may interact with the slightly negative charge, resulting from the presence of the chloride ion in the dye structure, increasing the Q of the dyeing process. The values of A for the grafted and dyed PET are , , and CD GY -1 s -1 for RR, CR and DR dyes respectively, while those for samples dyed in the absence and presence of a carrier are and CD s -1 respectively. These results show that only 1% grafting of the fabrics enhances significantly the dyeing rates. Accordingly, the order of the dyeing process is as follows: Basic RR dye (1% GY) >> Direct CR (1% GY) > Disperse (1% GY) > Disperse (with carrier) > Disperse (without carrier) Grafting increases the swelling of the polyester fibre polymer and introduces COO - groups. This allows the dye molecules to enter the polyester fibre more readily and react at a faster rate especially with the cationic and anionic dyes as shown before. Moreover, the addition of a carrier plays the same role in fibre swelling. The constancy of the reaction order, the extremely high reaction rates, and the calculated values of Q suggest that the diffusion of dye molecules through the fabric to reach grafted areas (dye sites) in the bulk of the fabric matrix is the rate controlling. Because the diffusion of the dye and its subsequent reaction with grafted and ungrafted fabrics are dependent processes, the slowest process (diffusion through the dyed polymer fibres to reach dye sites) is rate controlling. The apparent activation energies for the different dyeing processes are those required by the dye molecules to overcome the energy barriers at polymer surface. It is, therefore, dependent on the dye structure, dye molecular weight, dye charge, polymer surface charge and polymer swelling condition. These factors are responsible for the control of diffusion of the dye through the dyed and grafted PET fabrics. Once the surface layer of the fabric reacts with the dye, the newly formed structure starts opposing the dye diffusion and slows down the dyeing process. This explains the leveling off of the CD values after the initial fast increase at about s of the dyeing time. An increase in C increases the

9 240 INDIAN J. FIBRE TEXT. RES., JUNE 2007 dye concentration gradient and hence increases the driving force for the diffusion process, which results in higher CD values at constant dyeing times and temperatures. The diffusion process is temperaturedependent in a way similar to that given by an Arrhenius equation. The exponential dependence of k on the absolute temperature emphasizes that the rate controlling process is diffusion controlled. The results also indicate that dyeing AA-grafted PET fabrics with the different types of dyes, in particular with basic dyes, could be carried out at temperatures lower than those usually applied in industry and at extremely short dyeing times. This considerably reduces the energy consumption for heating the dye bath and decreases the time necessary for dyeing the polyester fabric, hence cutting down the dyeing cost to a minimum and emphasizes the importance of studying the dyeing kinetics for the economy of the process. 4 Conclusions 4.1 The best dyeing is achieved at ph 5.5 for RR and DR and at ph 9 for CR aqueous dye solutions. 4.2 AA-grafting considerably increases the CD of the fabrics. The initial dyeing rate R increases with the increase in C and T of the dye bath. 4.3 The dyeing process follow the 0.34 order kinetics for all dyes, except for CR dye (0.49 order ) and is independent of T. 4.4 The rate constant k increases exponentially with the increase in T. Q values 16.7, 14.5, and 9.64 kj mol -1 and A values , and are calculated for dyeing RR, CR and DR dyes on AA-grafted PET fabrics respectively. 4.5 AA grafting and the addition of a carrier in the DR dye solution improves the affinity of the disperse dye towards the polyester fabric. The efficiency of DR dyeing of AA-grafted fabric is higher than that of ungrafted fabric dyed in the presence of a carrier. The increase in dye uptake is attributed to the swelling effect due to grafting and carrier dyeing. 4.6 The rates of dyeing for different types of dyes follow the order: Basic RR (at 1% GY) >> Direct CR (at 1% GY) > Disperse (at 1% GY) > Disperse (with carrier) > Disperse (without carrier) 4.7 The mechanism of the dyeing process for all dyes is diffusion controlled and the dyeing rates are dependent on the type of dye (polar or non-polar), structure and molecular weight of the dye, dye concentration, dyeing temperature, additives in the dye liquor and pre-treatment of the fabric. 4.8 Dyeing AA-grafted PET fabrics with the different types of dyes, in particular with basic dyes, could be carried out at temperatures lower than those usually applied in industry and at extremely short dyeing times. This considerably reduces the energy consumption for the heating of the dye bath and decreases the time necessary for dyeing the polyester fabric. References 1 Chapiro A, Radiation Chemistry of Polymeric Systems (Wiley-Interscience Publishers New York), Hebeish A & Guthrie J T, The Chemistry and Technology of Cellulose Copolymers (Springer, Berlin), Hebeish A & Mehta P C, Text Res J, 39 (1969) El-Salamawi K, El-Hosamy M B, El-Naggar A M & El- Gendy E H K, Am Dyest Rep, 82 (1993) El-Gendy E H K, Indian J Fibre Text Res, 27 (2002) El-Gendy E H K, Indian J Fibre Text Res, 27 (2002) El-Gendy E H K, Kamal H & Hegazy E, Proceedings, 5 th Arab International Conference Polymer Science and Technology (The Egyptian Society of Polymer Science & Technology), 1999, Taher N H, Dessouki A M & El-Arnaouty M B, Rad Phys Chem, 35 (1998) El-Naggar A M, Marie M M, El-Gendy E H & El-Meligy A A, Am Dyest Rep, 86 (1997) Hegazy E A, Taher N H, Ebeid A R, Rabei A & Kamal H, J Appl Polym Sci, 39 (1990) Stannett V & Hoffman A S, Am Dye Rep, 57 (1968) El-Gendy E H, Indian J Fibre Text Res, 25 (2000) El-Gendy E H, Indian J Fibre Text Res, 29 (2004) Stannett V, Walsh W K, Bittencourt E, Liepins R & Surles J R, J Appl Polym Sci, 31 (1977) Liepins R, Surles J R, Morosoff N, Stannett V & Barker R H, Radiat Phys Chem, 9 (1977) Zahran A H, Stannett V, Liepins R & Morsoff N, Rad Phys Chem, 16 (1980) Choi T H, Lee J K, Kong Y K & Chang H S, INIS KAERI396RR12980 (International Nuclear Information System of the International Atomic energy Agency, Vienna, Austria), Kong Y K, Chang H S, Lee J K & Choi J H, J Korean Nucl Soc, 12 (1980) Kaji R, Neyagawe O, Onkuna H & Okada J, ISSB (International Nuclear Information System of the International Atomic energy Agency, Vienna, Austria), Nor H M, INIS PPAT47 (International Nuclear Information System of the International Atomic Energy Agency, Vienna, Austria), El-Gendy E H, J Appl Polym Sci, 94 (2004) El-Gendy E H, Marei M M & Ali N M, J Eng Appl Sci, 52 (2005) Gohl E P G & Vilensky L D, Text Sci (CBS Publishers & Distributers, Delhi, India), El-Gendy E H & Ali N M, Polym Int, 55 (2006) 236.