Study on hot brand reactive dyes and its application system on cotton goods in exhaust method.
Introduction:
The problem of dyeing cotton with direct dyes in washing fastness is overcome by introducing reactive dyes. In this reactive dyeing, dyes are held on substrate by chemical reaction and hence a better resistance to fading or bleeding is achieved. Reactive dyes are the most important class of dyes for dyeing and printing for cotton and other cellulose blends. They represent about 45% of colorants used for coloring cellulose fibres because of its application method, wide range of shades, improve fastness properties and cost efficiency.
Hot brand reactive dye is one of the types of reactive dyes. These types of reactive dyes have lower reactivity towards cotton. High dyeing temperature is required and normally dyeing is carried out at the temperature between 800-850c, these types of dyes also requires strong alkaline medium and NAOH is used to bring the PH at 10.5-11.
Moreover, these dyes offer optimum fixation when used with urea in high thermo fixation temperature or used in a long steaming time. Besides, these dyes hold a low to medium substantivity and medium to high reactivity, which efficiently avoids Tailing. Tailing is avoided by selecting dyes of low or medium substantivity, using small padding troughs. These troughs are fed to constant level and operate at the highest running speed commensurable with the needs of the rest of the process.
In our final project, we dyed cotton goods by hot brand reactive dyes in exhaust method. And also found difference in color because of variable temperature and fastness properties also.
Broad Objectives:
To know about hot brand reactive dyeing and its application system on cotton goods in exhaust method.
Objectives:
v Comparison of the color appearance of cotton fabrics dyed using hot brand reactive dyes at different temperature.
v Describe exhaust dyeing method on cotton goods.
v Comparison of different fastness properties e.g. washing fastness, rubbing fastness between standard temperature and different temperature of dyeing.
Reactive dyes:
Reactive Dyes are capable of forming chemical covalent bonds with the Hydroxyl groups of cellulose fibre and therefore, better anchored to the substrate and not depend on the relatively weak physical forces to give better levels of fastness. All of the features that are desirable for a reasonably ‘fast to wash’ Direct Cotton dyes are not essential for Reactive class of dyes (because of the more strong covalent bond), though cannot be totally discarded as undesirable.
Some of them could be counter productive. For example, Reactive Dyes with features listed under I and 2 of the direct cotton dyes would exhibit problems of low migration and or difficulty to wash off the hydrolyzed dye. Certain quantity of Hydrolyzed dye is inevitable after the fixation stage and non removal of such unfixed dye would entail bleeding/staining of white during washing. Migration is facilitated by increase in temperature; but higher temperatures induce hydrolysis of Reactive dye during the fixation phase and therefore it would be necessary to bring down the temperature to the most favorable temperature for the reaction between dye stuff and substrate before alkaline addition can be made.
There fore, in the case of Reactive dyes the following aspects are most important 1. Degree of Exhaustion of the dye bath on to the fibre (both primary and secondary) that is directly related to the substantivity should be maximized /optimized (assisted more by salt addition than by the physical forces). 2. The migration of the dye within the substrate during the primary exhaustion phase should be maximized. 3. Efficiency of reaction of the exhausted dye to the fibre should be maximized during fixation phase. 4.
The kinetics of reactivity has the final influence on the success of dyeing, irrespective of high levels of success achieved in the exhaustion stages, though exhaustion is an important (primary and or secondary) pre-requisite… 5.
The above four aspects need to be performed within a reasonable span of time. 6. The corollary here is that the extent of hydrolysis of the dye during exhaustion and fixation stages needs to be minimized.
Types of reactive dyes:
| Types | Exhaust dyeing temperature(0c) | Alkali recommended |
| High reactivity(cold brand) | 25-40 | Weak Alkali(NaHCO3) |
| Medium reactivity(Warm brand) | 40-60 | Mild Alkali(Na2CO3) |
| Low Reactivity(hot brand) | 60-95 | Strong Alkali(NaOH) |
Hot brand reactive dyes:
Hot brand reactive dye is one of the types of reactive dyes. These types of reactive dyes have lower reactivity towards cotton. High dyeing temperature is required and normally dyeing is carried out at the temperature between 800-850c, these types of dyes also requires strong alkaline medium and NAOH is used to bring the PH at 10.5-11.
Example includes:
Monochlorotriazine(MCT)
Dichloroquinaxoline(DQT) and
Trichloro pyrimidine reactive dyes
Figure of Monochlorotriazine (MCT):
Cl
Sunfix Hot Brand Reactive Dyes:
(Monochloro Triazine Based)
These are monochlorotriazine reactive dyes having a low reactivity and low substantivity. Since these dyes have low reactivity, they require more severe conditions for fixation with cellulosic materials. They are readily soluble by pouring water of 80-85ºC on powder & stirring well. They are applicable on cellulosic materials by both dyeing as well as printing methods.
In comparison with cold brand dyes, the `H’ brand dyes require either a long steaming time or a high thermo fixation temperature (with urea) for optimum fixation. H dyes of low to medium substantivity and medium to high reactivity are most suitable, dyes of very low substantibity may lead to migration problems in dyeing prior to fixation.
When low concentration of highly substantive dyes is used, tailing becomes evident. Tailing is avoided by selecting dyes of low or medium substantivity, using small padding troughs fed to constant level and operating at the highest running speed commensurate with the needs of the rest of the process.
In this project we used Sunfix hot brand reactive dyes based on Monochloro Triazine.
Literature Review:
Dyeing of cotton using direct dyes has rather poor washing fastness because only weak polar forces bind the molecules to the cellulose polymer chains. Direct dye molecules therefore can easily diffuse out of the cotton during washing. The idea of immobilizing a dye molecule by covalent bond formation with reactive groups originated in the early 1900s.
Reactive dyes are the water soluble anionic dyes. They react with the fibre to form covalent bonds. They posses a reactive group in their dye molecules which reacts with the hydroxyl groups presents in the cellulose to form a stable chemical linkage. Thus the dyestuff becomes a part of the fibre substrate. In 1955, Ratte and Stephen developed a procedure for dyeing cotton with reactive dyes containing dichlotriazine groups.
The dye is enclosed in microcapsules, tiny (few micrometers in diameter) drops of liquid … 24 June 1991; ^ “Generra: Hot Star. Camel yarn dyed by reactive hot KVIC method (RH-KVIC). 14 … is not known for it outdates the beginning of record history.
Material and Method:
Raw Material that are used in this project:
1. Fabric
2. Dye stuff
3. Chemical and auxiliaries
Fabric Types:
100% cotton fabric
Single jersey with lycra(1*1)
Dyes that are used in this project:
| Sunfix M Turquoise PGR | Reactive Blue 72 |
| Sunfix Blue H3RP / P3R | Reactive Blue 49 / 99 |
| Sunfix Red P3BN | Reactive Red 29 |
Method:
In this project Exhaust dyeing method is used for dyed of cotton goods by sunfix hot brand reactive dyes.
Primary Exhaustion Phase
Exhaustion of dye from the dye bath to the cellulose during Primary Exhaustion phase is governed by the following three physical processes and the phenomenon of substantivity
Adsorption
Diffusion,
Absorption/ Exhaustion/Migration
Secondary Exhaustion
The observations and inferences in the above deliberations related to primary exhaustion in a Reactive exhaust dyeing process are incomplete without the final fixation. When Alkali is added, the cellulose ionizes to form Cell-O- and H+ (Cell O– Na+) and starts forming covalent bonds with the reactive functional groups of the dye Chromophore.
When more and more of dye anions are covalently bond, the distribution coefficient shifts to fiber phase effecting further exhaustion due to deficiency of dye anions in the cellulose phase and dye bath concentration starts depleting further. The degree of alkalinity in terms of pH plays a major role in shifting the fixation of dye to its hydrolysis reacting with water. Any exhaustion during this stage if it is hydrolyzed dye it would be far more undesirable In a reactive dye system therefore, primary exhaustion alone does not govern the efficiency of dyeing. The degree of secondary exhaustion also would influence the efficiency.
During the secondary exhaustion when alkalie is added, there is a second reaction that also sets in motion in parallel ( i.e. the hydrolysis of the Reactive dye with water) in competition to the fixation of the dye that is the primary aim. The dye anion is equally facilitated to react with OH of water to form the hydrolyzed dye in which state the dye is as good as a direct dye with all its ‘undesirable’ characteristics.
It is the reactive group in the dye, pH and temperature that influence the hydrolysis of dye in preference to reacting with cellulose. It becomes critical that the hydrolysis is curbed to maximize efficiency.
The relationship between temperature and reactivity is that higher temperatures require lower alkalinity; to optimize on hydrolysis. They can be broadly grouped under ‘High’ ‘Medium’ and ‘Low’ categories requiring 40º C. 60 º C and 80º.C respectively – levels of pH 12.5 for High (cold dyeing), 11.5 for Medium (Warm) and 10 – 11.0 for Low (Hot Dyeing) for the reaction to proceed more favorably towards the substrate.
The term more reactive is used in the sense that it requires lesser levels of alkalinity and lower temperatures (and not the reaction itself. Given the right temperatures, alkalinity and time the reaction proceeds to completion in all cases.)
Migration phase
Since fiber surface area is a factor in diffusion process, the exhaustion would proceed to locations where relatively more surface area is presented like in the amorphous areas and less densely packed crystalline areas in that order in the cellulose and therefore the dye concentration within the cellulose substrate would not be uniform/even.
Such a situation would result in uneven build up of the dye both in hue and intensity. In a trichromatic mixture the situation could be worse.
The process of Migration of the exhausted dye depends on the molecular size of the dye its spatial profile (Steric) and the solubilizing groups present. The other external factors would relate to temperature, machinery used and the package profiles and densities (in case of package dyeings)
Raising the temperature would provide the required thermal energy; but cannot be increased arbitrarily due to limitations discussed under ‘Temperature’. Both exhaustion and migrations can be maximized /improved by better mechanical agitations that would facilitate intimate surface area contact of the cellulose with dye liquor and by improved flow designs that facilitate better liquor exchange at the fiber liquor inter-phase.
Migration phase should precede the fixation phase as once the reactive dye forms a covalent bond with Cell O- it is anchored strongly and cannot be shifted.
Properties of major types of hot brand reactive dyes
| Hot Brand Reactive Group | Reactivity | Exhaust Dyeing Temperature(0c) |
| MCT(Sunfix) | Low | 70-85 |
| TCP | Low | 70-95 |
| DCQ | Low | 50-70 |
Dyeing Process:
We have used:
Sunfix dyes (Reactive Blue 72)of Monochlorotriazine dyes.
For every class of dyes we have used 4 different shades as 0.042, 0.42.
After the dyeing process we measured different fastness characteristics of the dyed fabric about which we have discussed later.
For Exhaust dyeing system on Cotton:
It has been done at 800c temperature and in our project it is standard.
Recipe:
Dye : 0.042/0.42%
Salt : 12/20 g/l
Soda : 5/10 g/l
Wetting Agent : 1 g/l
Sequestering Agent : 1 g/l
Temperature : 800c
Time : 45 min
M: L : 1:8
Recipe calculation:
Recipe% * Sample Weight
=
Stock%
Sample Weight is 5 gm.
0.042 * 5
Recipe calculation=
o.1
= 2.1
12 * 80 * 100
Salt=
1000 * 20
= 4.8
5 * 80 * 100
Soda=
1000 * 10
= 4
So,
Additional water : 80-(2.1+4.8+4)
: 69.1
Procedure:
For dyeing with MCT based sunfix (Reactive Blue 72), Hot brand reactive dyes, first the machine is loaded with water and material. The temperature is adjusted as appropriate. Dyeing starts at 50°c during the next 45 minutes add the salt required in three portions of increasing sizes at intervals of 10 minutes. Start to raise the temperature while adding the second portion. A rate of raise is not greater than 2°c/minute should allow the required temperature 80°c in approximately 20-30 minutes. Allow 15 minutes after the last addition before adding soda ash slowly over 15 minutes and continue dyeing at 80°c for 30-60 minutes.
Dyeing Curve:
800c Shade check
20c min
Drain
10 min 15 min 20 min 40-60 min
Dyes
+auxilaries
+sample Salt Salt
+salt
Soda
Dosing
Dyeing curve at 800c temperature
Dyeing process at 940c temperature,
Recipe:
Dye : 0.042/0.42%
Salt : 12/20 g/l
Soda : 5/10 g/l
Wetting Agent : 1 g/l
Sequestering Agent : 1 g/l
Temperature : 940c
Time : 45 min
M: L : 1:8
Dyeing Curve:
940c Shade check
500c 20c/m
Drain
10 min 22 min 20 min 45 min
Dyes+
Auxiliaries+
Sample Salt
+salt Salt Soda
Dyeing curve at 940c temperature
The sample that is dyed at (80 & 94) 0c temperature and recipe% 0.042 is shown as follows:
Standard
800c temp.
Recipe%= 0.042
940c temp.
Recipe%= 0.042
The sample that is dyed at (80 & 94) 0c temperature and recipe% 0.42 is shown as follows:
Standard
800c temp.
Recipe%= 0.42
940c temp.
Recipe%= 0.42
Relative Comparison of the sample at temperature difference:
Fastness:
The color fastness of a colored textile is defined as it resistance to change when subjected to particular set condition. Fastness is the ability of a colored material to withstand the action of different agencies that come to play on it during its manufacture or use. Fastness is the ability of a colored substrate to retain its appearance when it is exposed to environment.
The dyed samples were tested according to ISO standard methods.
For wash fastness according to ISO 105 C01:
Fabric specimen : 10*4
Soap : 5gm
Temperature : 400c
Time : 30 min
For rubbing fastness according to ISO 105 c01:
Fabric specimen : 14*5cm
For staining bleached fabric: 5*5
Gray scale rating:
| Rating | Result |
| 5 | Excellent |
| 4 | Good |
| 3 | Fair |
| 2 | Poor |
| 1 | Very poor |
Relative Fastness comparison of the sample:
Fastness to washing:
| Temperature
Recipe% |
800c(Standard) | 940c | ||
| 0.042 | 0.42 | 0.042 | 0.42 | |
| Rating | 5/5 | 5/5 | 5/5 | 4/5 |
Comment:
v From experimental data we can see that the wash fastness of the dyed sample at 800c temperature is better than 940c temperature when recipe% is 0.42.
v But in the case of recipe% 0.042 there is no significant difference between the sample at 800c temperature and 940c temperature.
Fastness to rubbing:
| Temperature
Recipe% |
800c(Standard) | 940c | |||
| 0.042 | 0.42 | 0.042 | 0.42 | ||
| Rating | Dry rub | 5/4 | 5/4 | 5/3 | 4/4 |
| Wet rub | 5/4 | 5/3 | 5/4 | 4/3 | |
Comment:
ü From the above result it is observed that the rubbing fastness of the dyed sample at 800c temperature is better than the dyed sample at 940c temperature.
ü Both dry and wet rubbing fastness is better at 800c temperature than 940c temperature.
Overall comments about shade for dyed sample at temperature difference:
ü Shade% of Cotton fabric dyeing in exhaust method by hot brand reactive dye is better at 800c temperature than that of 940c temperature.
ü Fastness properties to wash and rubbing is better at standard temperature (800c) than 900c temperature.
ü Appling this method maximum time we can get our required shade.
Suggestion:
ü For further research related to this project, combination shade dyeing as well as using different types of application method and as well as different temperature.
Conclusion:
The cotton fabric dyed with hot brand reactive dye in exhaust dyeing process to give a excellent results. Hot brand reactive dyes can be exhausted almost entirely on to the cellulose fibres. Dyeing on the cotton gave better color strength at 800c temperature than 940c temperature. The color fastness of these dying at different temperature is approximately same. The results on the different temperature is indicate that in case of hot brand reactive dyes perfect temperature is too much important for matching the shade properly.
Reference:
1. Dyeing and Chemical Technology for Textile Fibres – E.R Trotman.
2. Textile Preparation and Dyeing – Asim Kumar Roy Chowdhury.
3. A Hand Book of Dyeing Technology – Mohammad Mahbubul Alam.
4. Internet.
Dyes:
Dyes are the chemical substances which are applied and fixed on substrates for coloration.
Dyeing:
The objective of dyeing is the uniform coloration of the mass of fibre constituting the materials, usually to match a pre specified color.
Reactive dyes:
Reactive Dyes are capable of forming chemical covalent bonds with the Hydroxyl groups of cellulose fibre and therefore, better anchored to the substrate and not depend on the relatively weak physical forces to give better levels of fastness. All of the features that are desirable for a reasonably ‘fast to wash’
Hot brand reactive dyes:
These types of reactive dyes have lower reactivity towards cotton. High dyeing temperature is required and normally dyeing is carried out at the temperature between 800-850c, these types of dyes also requires strong alkaline medium and NAOH is used to bring the PH at 10.5-11.
Fastness:
Fastness is the ability of a colored material to withstand the action of different agencies that come to play on it during its manufacture or use. Fastness is the ability of a colored substrate to retain its appearance when it is exposed to environment.