|Title of Invention||
"A PROCESS OF DYEING SILK WITH REACTIVE DYES"
|Abstract||This invention relates to a process for dyeing of silk with reactive dyes. According to the process of this invention a silk fibre or fabric is introduced in a dye bath containing a reactive dye at an acidic pH for the exhaustion purposes. The exhausted silk fibre or fabric is then subjected to the step of fixation in the dye bath having alkali so as to have a neutral or alkaline pH.|
|Full Text||OF INVENTION
This invention relate to a process of dyeing silk with reactive dyes. PRIOR ART
Conventionally, the dyeing of silk with reactive dyes is being carried out in presence substantial quantities of salt.
In study on silk using monochloroteraze dyea (c.l. Reactive Blue)it has been indicated that maximum fixation occurs in the presence of 20g/l of Glauber's salt in a neutral pH. On similar lines, Wue 4c Company concluded that at a pH of 6-7 and in presence of 40—80 g/1 salt, the fixation of reactive dyes containing ethyl sylphonyl groups was maximum. In case of Dichlorotriazine dyes, procedure for dyeing involves 4g/l Na2so4 was found to be suitable.
While developing low temperature dyeing procedures for reactive vinyl—sulphone dyes, Crukajanin et.al. have recommended a total of 70 g/1 salt, which has been added in two installments. The same procedure when extended to tussar silk necessitated use of 100 gyi Na2SO4. The pH during the dyeing Mas not allowed to exceed 9.0.
The use of large quantities of salt has also been seen in the dyeing of Haloacetyl reactive dyef which suggests 6 g/1 sodium sulphonate in mild alkaline conditions (Zhang et. al. ) . Considerable quantities o-f salt up to 418 g/i have also been used by Meyer et al in the application of Hanasol , Duma!on and Verofix type of reactive dyes.
A study of Roher. R indicated that the addition of hydrated sodium sulphonate to the dye bath increased the affinity of reactive dyes to silk. He commented that the amount of salt required varied with the depth of shade. For light to medium shades., 20-40 g/1 and 8 g/1 for darker shades of hydrated sodium mtlphonate Mas required. This was under a pH of 6.0-6.5. The degree of fixation achieved with this was 8.5-9.5X for Hanasol dyes and about 75-60X far Cibacron dyes.
A recent research carried out on the application of heterobifunctional reactive dyes on silk by Agarwal et al (1998) revealed that the amount of electrolyte required was both a function of the depth of shade and the pH of the dye bath. As the dye bath pH increased, the amount of electrolyte was suggested to be 60 g/1, whereas for alkaline it rose to 110 g/1 and in the case of an acidic pH, the optimum exhaustion and
fixation, were obtained at very low levels of electrolyte. The researchers concluded that the optimum dyeing cycle for heterotaifunctional reactive dyes on silk would be with 60 g/1 salt in a neutral bath.
One of the distinct disadvantages of the known art Mas the excessive addition of salt in the dye bath so as to achieve satisfactory exhaustion properties. Thus, the normal known process consisted in having a dye bath at neutral pH, and introducing the silk fabric into the bath having a temperature of 30-40°C. Therafter, the temperature is raised to approximately 90c and maintained for 1 to 1 1/2 hours. During such a stage, sodium sulphate or sodium chloride is added so as to provide the exhaustion properties.
It has been found that the addition of a salt is necessary as the reactive dyes should form covaltent bonds with the fibre under appropriate conditions. The main sites on silk that induce the formation of covalent bonds are the presence of amino groups4 Such amino groups are present in substantial quantities at neutral pH and above. Thus, the addition of salt was hitherto necessary, which upon addition dissociates into sodium and sulphide ions. The positively charged sodium ions
are attracted towards the negatively charged silk, and consequentially assists in the transfer of dye by surpressing the negative charge of the fibre.
The presence of such salt provides a problem of disposal of effluent and requires are effluent treatment. OBJECTS oF THE INVENTION
An object of this invention is to propose an improved process of dyeing silk Hith reactive dyes.
Another object of this invention is to propose a process of dyeing silk with reactive dyes, and wherein salt is no longer added to the dye bath.
Vet another object of this invention ia to propose a process of dyeing silk with reactive dyes, which obviates the disadvantages associated with the known art.
Still another object of this invention is to propose a process of dyeing silk with reactive dyes, which has good exhaustion and fixation properties.
A further object of this invention is to propose a process of dyeing silk with reactive dyes, which is simple.
Further objects and advantages of this invention will be more apparent front the ensuing description.
DESCRIPTION OF THE INVENTION
According to this invention there is provided a process for dyeing of silk with reactive dyes comprising of step of exhaustion carried by known method by introducing silk fibre or fabric in a dye bath containing a reactive dye characterised by an acidic pH3, subjecting the silk or fabric of step (a) to the step of fixation as herein described in the said bath by the addition of alkali like Sodium Carbonate at pH8 to have a neutral medium for fixation.
As known in the art, silk is a protein fibre having an isoelectric point at pH3 or 4 and when there is no net charge. However, as the pH increases, the negative charge of the fibre increases. Simultaneously, the main sites on silk which favour covalent bonds are the amino or NHa groups. Reactive dyes form covalent bonds with such amino groups, which are at abundance at a neutral pH or above. Though, the amino groups are present in abundance at a neutral pH or above, the fibre is negatively charged due to an increase in pH and whereby the negatively charged dye is not attracted to the negatively charged silk fibre or fabric. For this purpose, it was hitherto necessary to add sodium chloride or sodium sulphate to the dye bath so that the
positively charged sodium ions are attracted to the negatively charged silk, which then assists in the take up of the negatively charged dye onto silk. However, and as described hereinabove, there is the distinct disadvantage of the presence of salt in the effluent.
Such a disadvantage is obviated by the process of the present invention, which consists in a first step of exhaustion. Specifically, the step of exhaustion is carried out at an acidic pH. An advantage of such an acidic pH is that the silk would be positively charged and thereby allow an attraction of the negatively charged dye. Thus, in such an instance, the exhaustion is satisfactory and there is a substantial uptake of dye onto the fabric. Such a step is of distinct advantage in that satisfactory exhaustion properties are achieved even in the absence of addition of any salt to the dyebath.
Though the exhaustion of the dye onto the fabric is satisfactory by the first step of the process, a disadvantage associated therewith is that of fixation of the dye is not suitable. When the dyebath has an acidic pH, the fabric is positively charged and allows an attraction of the negatively charged dye on the
fabric. However, covalent bonds are not -farmed due to an absence o-f ami no groups, and whereby the -fixation i» negligible.
Accordingly, in accordance with the present invention, the process consists in a second step of fixation by formation of the NH2 or amino groups. Thus, the pH of the bath is gradually increased by the addition of an alkali, such as sodium carbonate so that the NH3 group will convert into NH2, group and cause a fiyatian of the dye of the fabric. The pH of the dyebath is & to 9, and preferably the dyebath has a pH of 7 to 9. If the dyebath has a pH of 18 or greater it then imparts poor fastners and low fixation properties.
Reference is not made herein to the
temperature of the dyebath, as known temperatures may be employed.
Intjrdei to find out the optimum pH at various stages of dyeing, under which maximum exhaustion and fixation would take place, dyeings were carried out at different pH levels. Three sets of dyeings were done, where at the exhaustion stage the pH was varied from 3 to 5 and then at each of these pH values, fixation was carried out at pH 7, 8 and 9. All these dyeings were carried out without the addition of salt (Table 1 ). For comparison control dyeing was carried out in neutral medium with 60 g/1 salt. The readings of the percentage exhaustion, percentage fixation and percentage realisation have been tabulated in table 1
As is evident from the table, the maximum percentage exhaustion was achieved at pH 3, ranging from 83.9% - 86.9%. For pH 4.0, it ranged between 77.5% - 87.8% and was much lower at pH 5.0, ranging from 56%-70.5%. These observations are in line with the discussions above, that at lowe/ pH values, exhaustion can be expected to be higher, probably because of increased amino acid protonation and thus reduced dye-fibre repulsion.lnfac pH3, silk is below its isoelectric point, it thus has a net positive chaigp ttilf (iiftcts the dye anions.
As for the fixation values, it can be noted from table l that as pH in the fixation stage is increased from 7 to 8, the percentage fixation increases. This is probably because of the availability of more number of unprotonated amino groups to form covalent bonds with the dye, and also due to the reaction with hydroxyl groups of silk which become functional in alkaline conditions. However, on further increasing the pH to 9, a decrease in fixation is observed, probably due to the increased dye hydrolysis with increase in alkalinity, thus making less dye available for fixation on the fibre.
A glance at the percentage realisation indicates that the maximum colour yield in the absence of salt is achieved at an exhaustion pH of 3 with the
corresponding fixation pi I of 8 and is comparable to dyeing in a neutral medium with 60 g/1 salt.
Thus a dyeing cycle with pH 3 at exhaustion stage and pH 8 at fixation stage seems to be optimum and gives satisfactory colour yield of bifunctional reactive dye on silk, even in the absence of electrolyte.
To determine the effect of addition of a small quantity of electrolyte on the dyeing performance, each of the above sets of dyeing was also carried out in the presence of 10 g/1 sodium sulphate, which is added at the time of setting of the dye bath (Table 2.). For comparison control sample was dyed at neutral pH with lOg/1 salt.
Table 2 shows that the addition of lOg/1 of sodium sulphate has not brought about any marked change in the exhaustion and fixation values. This is probably because in the absence of salt, already there were sufficient forces of attraction between the dye and the fibre, the addition of small amounts of salt did not further aid exhaustion. This is also substantiated from earlier studies, where it was found that during dyeing of silk with reactive dyes, the addition of salt did not bring about any marked effect in an acidic medium.
It is further confirmed from Table 2 that the best condition of applying bifunctional reactive dyes on silk, in the absence salt, is one with exhaustion at pH 3 and fixation at pH 8.
Table . 1: Effect of two stage salt-free dyeing cycle on the colour yield of Reactofix Blue ME 4RL on silk.
Table 2.J: Effect of 10 g/l salt on the colour yield of Reactofix Blue ME 4RL on silk dyed using the two stage dyeing cycle.
Thus, it may be concluded that, the addition of salt in the two stage dyeing cycle is not required and satisfactory results can be obtained even in its absence.
In an effort to optimise the dyeing time, dyeings were carried out with the modified dyeing cycle, giving a fixation time of 45 minutes, instead of the earlier 30 minutes. This was done at an exhaustion pH of 3 and 4 with fixation at pH 7, 8 and 9 (Table 3 ), Set of dyeings with exhaustion pH of 5 were excluded as they did not yield satisfactory results. The results reflected similar trends as earlier. The colour yield was highest with the exhaustion pH of 3 and fixation at pH 8. However, the increase in fixation time did not bring about any significant change in the exhaustion and fixation values.
Hence it may be conduced that a 125 minutes dyeing cycle, with fixation time of 30 minutes was sufficient to get optimum results.
3.1.4 Effect of modified dyeing cycle on the tensile properties of silk dyed with bifunctional reactive dyes.
As has been discussed above dyeing of silk with bifunctional reactive dyes, at an exhaustion pH of 3 and the fixation at pH 8, in the absence of salt gave satisfactory colour-yield, comparable to dyeing at neutral pH with 60 g/1 salt. The next best results were obtained with the exhaustion and fixation pH of 4 and 8 respectively. To determine the effect of dyeing under these acidic condition on the tensile properties of silk, load-elongation values of fabric dyed under the modified dyeing cycle were measured, along the warp and weft directions. For comparison, tensile properties of silk dyed at neutral pH and 60g/l salt were also determined (Table 3.5).
Table 3:Effect of increased fixation time (45 min) on the colour yield of Reactofix Blue ME 4RL on silk dyed using two stage, salt-free dyeing cycle.
1. A process for dyeing of silk with reactive dyes comprising of:
a) step of exhaustion carried by known method by introducing silk
fibre or fabric in a dye bath containing a reactive dye
characterised by an acidic pH3,
b) subjecting the silk or fabric of step (a) to the step of fixation as
herein described in the said bath by the addition of alkali like
Sodium Carbonate at pH8 to have a neutral medium for
2. A process as claimed in claim 1 wherein the dyebath in the first
step of exhaustion has pH 3 to 5.
3. A process as claimed in claim 1 wherein the dyebath in the
second step of fixation has pH 6 to 9.
4. A process as claimed in claim 3 wherein the dyebath in the
second step of exhaustion has a pH 7 to 9.
5. A process for dyeing of silk with reactive dyes substantially as
herein described and illustrated.
|Indian Patent Application Number||0860/DEL/1999|
|PG Journal Number||08/2009|
|Date of Filing||10-Jun-1999|
|Name of Patentee||DEEPALI RASTOGI|
|Applicant Address||G-47, PUSHKAR ENCLAVE, PASCHIM VIHAR, OUTER RING ROAD, NEW DELHI-110 063, INDIA.|
|PCT International Classification Number||D06P 3/66|
|PCT International Application Number||N/A|
|PCT International Filing date|