History of reactive dye
General Introduction
Now day’s knit fabrics are used widespread in the world. Dyed knit fabric as well as stripe knit fabric both have the appeal to the customers. As time is ticking the demand of stripe knitwear is increasing tremendously. The gateway for producing the stripe knit fabric is the dyed yarn; as a result the yarn dyeing industries of our country and in other countries are facing a boom in amount of order. The result is the importance of yarn dyeing is increasing day by day.
The quality of a good stripe effect in a knit fabric mainly depends on the effective yarn dyeing process. Considering the capability and demand our country has mainly cotton based industries. The knit products produced are mainly of cotton. So in the yarn dyeing industries cotton yarns are mainly dyed.
For cotton dyeing there are many types of dyes are available-direct, vat, reactive, azoic etc. To dye effectively, frankly saying considering all the facts like the application process, retention of the color during use, economy reactive is the most suited dye to dye cotton goods (both fabric and yarn). Reactive dyes are used extensively in dyeing cotton in every factory in our country.
As reactive dye is most frequently used, a good knowledge is required about the application process of the dye due to the efficient production of required specification product.
Shades that can be produced by reactive dye is enormous, to produce a target shade perfectly monochromatic that means the primary color are used most frequently. But matching with the monochromatic color combination not always suitable as some shades cannot be found. That’s the limitation of matching with monochromatic color. Also there are some limitations about the reactivity and production of the color in a definite time. To remove these drawbacks different dye manufactures have come with the idea of some dichromatic and trichromatic reactive dyes. These dyes are special type of dyes made for special shades to achieve. These dyes mainly bluish and some are the yellowish. For example achieving turquoise type shade a special
turquoise blue is used, to achieve lemon green a lemon yellow special color is used.
These special dyes are made specially in comparison to normal reactive dye, they are introduced with metal complex structure, their reactive group activated at higher temperature, their molecule size are relatively bigger than normal reactive dyes.
Considering the above facts the application process will definitely be different than normal reactive dye application. If process is not changed according to the structure of dyes, achieving of proper shade is really an absurd.
So in industries these special colors crate different type of problems during the application and in the stages of using that product.
Countering problems during turquoise color application in the yarn and fabric dyeing is very usual. The problems containing:-
1. Shade not matched
2. Dyeing is not uniform
3. Lack of leveling
4. Dye molecule aggregation
5. More time consumption
6. More water consumption
7. Fastness properties are not up to the mark
To minimize these problems different industries apply different type of solution, achieving a full control over the smooth application process is a gigantic task.
The main aim of our project is to go to the root of the problems that are found during application process and try to solve the problems. The main objects are given below:
1. To identify the process difference between turquoise and normal reactive dye.
2. To identify the reason why the shade become uneven when dyeing with turquoise color is done compared with normal dyes.
3. To identify the difference in pH, temperature and amount of water between turquoise color dyeing & normal reactive color dyeing.
4. To learn about the special leveling agent and the washing agent which is used on the turquoise color dyeing.
5. Measure economically viable process is which one.
6. Try to make some suggestions about the process to improve the application process to get better results while dyeing with turquoise color.
1.1. Literature review:
Reactive dyes are probably the most popular class of dyes to produce ‘fast dyeing’ on piece goods. These were first introduced a little over 40 years based on a principle which has not been used before. These dyes react with fiber forming a direct chemical linkage which is not easily broken. Their low cost, ease of application, bright shades produced by them coupled with good wash fastness make them very popular with piece good dyers. Even in threads these classes are gaining in popularity for cotton sewing.
One problem is that instead of reacting with -OH groups on cellulose, fiber-reactive group may react with HO-ions in alkali solution & become hydrolyzed. Two reactions compete, & are unfavorable because hydrolyzed dye cannot react further. This must be washed out of fabric before use, to prevent any leakage of dye, which not only increases cost of textile, but also adds to possible environmental damage from contaminated water.
1.2. Reactive dye:
1.2.1. History of reactive dye:
On the occasion of 100 years celebration of synthetic dye manufacturing, two chemists of ICI Company (UK) named Stephen and Rattee tried to manufacture new dye stuff. Thus they succeed to invent a new dye in 1956 which was named REACTIVE DYE. This was manufactured for dyeing cellulosic fiber. The 1st three Reactive dyes were Procion Yellow R, Procion brilliant Red 2B and Procion Biue 3G. For this effort they were awarded Gold Medal of the Society of Dyes and colorists for the year 1960.
1.2.2. Introduction:
Reactive dyes are so called because their molecules react chemically with the fiber polymers of some fiber to from a covalent bond between the dye molecules and fiber polymer. Reactive dye is a class of highly colored organic substance, primarily utilized for tinting textiles that attach themselves to their substance by a chemical reaction that from a covalent bond between the dye molecules & fiber. the dyestuff thus become a part of the fiber and is much less likely to be removed by washing them are dyestuff that adhere by adsorption. The vary first fiber-reactive dyes were designed for cellulose fiber, and are still use mostly in this way. There are also commercially available fiber- reactive dyes have been develop for other fiber, but these are not yet practical commercially. The dye contains a reactive group that, when applied to a fiber in a weakly alkaline dye bath, form a chemical bond with the fiber. A fiber-reactive dye will form a covalent bond with the appropriate textile functionality is of great interest, since, once attached, they are very difficult to remove.
1.2.3. Properties of reactive dye:
1. Water soluble dyes.
2. Makes covalent bond with the fibers.
3. A certain amount of dye is hydrolyzed during dyeing (10-60%)
4. Dyeing is carried out alkali condition (pH-11.5)
5. Huge electrolyte is necessary for dyeing with reactive dyes.
6. Fastness (wash, light, Rubbing, perspiration) properties are generally
good.
7. Easy applicable as well as protein fibers. (Wool & silk)
8. Very popular and wide used in the wet processing industry in
Bangladesh.
9. Comparatively cheap.
10. All kinds of shade is found.
11. Dyeing method is easy
1.2.4. Chemical structure & description of reactive dye:
Reactive dyes differ from other coloring matters in that they enter in to chemical reaction with fiber during dyeing & so become a part of fiber substances. A reactive dye is represented as R-B-X, where, RChromogen, B-Bridging group X-Reactive system. When it reacts with fiber, F, it forms R-B-X-F. Wet fastness of dyed material produced, depends on stability of true covalent bond
1.2.5 Reactive Systems:
Reactive dyes are based on Cyanuryl chloride. Cold brand dyes (M brand) are based on di-chloro triazinyl derivatives whereas “H” brands are mono-chloro triazinyle derivatives. Reactivity of Chlorine atoms decreases greatly as they are successively substituted. Thus di-chloride derivative (M) is more reactive than mono chloro reactive (H) dyes. This is shown by fact that “M” dyes react readily with cellulose at room temperature in presence of mild alkalis such as sodium carbonate, where as “H” dyes need to be heated at least to 60°C & require stronger alkalinity before reaction take place at a reasonable rate. Other popular systems are based on Vinyl suplhones & tri-chloro pyrimidyl.
1.2.6 Fiber-Reactive Dyes-Definition:
A fiber-reactive dye forms a covalent bond with appropriate textile functionality. It is important that once attached, they are very difficult to remove.
1.2.7 Early fiber-reactive dyes:
The first fiber-reactive dyes were designed for cellulose fibers, & they are still used mostly in this way. There are also commercially available fiber-reactive dyes for protein & polyamide fibers. In theory, fiber reactive dyes were developed for other fibers, but these are not yet practical commercially. Although fiber reactive dyes were a goal for quite some time, breakthrough came fairly late, in 1954. Prior to then, attempts to react dye & fibers involved harsh conditions that often resulted in degradation of textile. The first fiber-reactive dyes contained 1, 3-5-triazinyl group, & were shown by Rattee & Stephen to react with cellulose in mild alkali solution. No significant fiber degradation occurred. ICI launched a range of dyes based on this chemistry, called Procion, which were superior in every way to vat & direct dyes, having excellent wash fastness & a wide range of brilliant colors. Procion dyes could also be applied in batches, or continuously.
1.2.8 Note the four different components of dye:
Chromogen is as mentioned before (Azo, carbonyl or Phthalocyanine class). Water solubilising group
(ionic groups, often sulphonate salts), which has expected effect of improving solubility, since reactive dyes must be in solution for application to fibers. This means that reactive dyes are not unlike acid dyes in nature. Bridging group links chromogen & fiber-reactive group. Frequently, bridging group is an amino, -NH-, group. This is usually for convenience rather than for any specific purpose. Fiber-reactive group is only part of molecule able to react with fiber. Different types of fiber-reactive groups are mentioned. A cellulose polymer has hydroxyl functional groups, & it is these that reactive dyes utilize as Nucleophilics. Under alkali conditions, cellulose-OH groups are encouraged to deprotonate to give cellulose-O-groups. These can then attack electron-poor regions of fiber-reactive group, & perform either aromatic Nucleophilic substitution to aromatics or Nucleophilic addition to alkenes.
1.2.9 Nucleophilic Substitution:
Aromatic rings are electronically very stable, & attempt to retain this that means instead of nucleophilic addition that occurs with alkenes; they undergo Nucleophilic substitution, & keep favourable p-electron system. However, Nucleophilic substitutions are not very common on aromatics, given their already high electron density. To encourage Nucleophilic substitution, groups are added to aromatic ring which decrease electron density at a position & facilitate attack.
Example:
But it requires harsh conditions. To improve under mild conditions, powerful electron-withdrawing
groups such as -NO2 is added.
However, it works only if there is a good leaving group, such as -Cl or -N2. Major fiber-reactive group which reacts this way contains 6 members, heterocyclic, aromatic rings, with halogen substituents. For example, Procion dye:
Where X=Cl, NHR, OR. Nucleophilic substitution is facilitated by electron withdrawing properties of aromatic nitrogens, & chlorine, & anionic intermediate is resonance stabilized as well which means negative charge is delocalised onto electro-negative nitrogen’s:
1.2.10 Nucleophilic Addition:
Alkenes are quite reactive due to electron-rich p-bond. They normally undergo electrophilic addition reactions. Again, nucleophilic additions are less favored generally, because of repulsion between Nu- & electron- rich p-bond. However, they occur if there are sufficient electron withdrawing groups are attached to alkane, much as before, with aromatic substitution. In this case, process is known as Michael addition or Conjugate addition. For this reaction type, the most important dye class is Remazol reactive dye. This dye type reacts in presence of a base such as HO-. Mechanism for reaction of one of these dyes is shown below. As before, intermediate is resonance stabilized, but this has not been shown:
1.2.11 Dyeing Equilibrium:
Previously, it is discussed on chemical aspects only & reaction processes with cellulose & water were
treated as if they were occurring quite separately. But in fact this is not so & it is found to be important in exhaustion to obtain a good efficiency. Now, it is examined what happened in a 2-stage dyeing process where dyes are exhausted from neutral dye-bath at first stage & then at a solution is made alkaline for beginning of reaction. In first stage of neutral dyeing, no decomposition of dye takes place & process is exactly same as dyeing of a direct dye with only difference is lower degree of exhaustion of reactive dyes. At end of 1st stage, there’re two equilibriums. When alkali is added to system, chemical reaction begins. In dye bath hydrolysis with water occurs, while in fiber, dissolved dye also hydrolyzes, but adsorbed dyes mainly react with fiber although possibility of aqueous hydrolysis can’t be excluded. Hydrolyzed dyes (DOH) have similar properties to parent dye (or direct dye) & don’t get adsorbed on fiber surface. Finally, when all reactive dyes present are destroyed one way or another, new equilibrium is set up between hydrolyzed dyes in dye bath, in solution inside fiber & adsorbed on cellulose while combined dye is present as a separate component, not taking part here.
1.3. Reactive Dyeing Mechanism:
Reactive dyes form a covalent bond between fiber & dye. They are classified depending on reactive group present & optimized conditions in which they are best used. Depending on type of reaction, they are broadly divided in to 2 categories:
A. Dyes reacting through Nucleophilic substitution reactions
B. Dyes reacting through Nucleophilic addition reactions
1.3.1 Dyes reacting through Nucleophilic substitution reactions:
(1) Di-chloro-triazynilamino types of dyes:
These are more reactive than mono-chloro type of dyes & require lower temperature & milder alkali for dyeing & fixation. These are known as Cold reactive dyes brand.
(2) Mono-chloro-triazynylamino type of dye:
These require higher temperature & stronger alkali for dyeing & fixation, are called hot brand reactive dye:
(3) Mono-fluoro-triazynylamino dyes:
(4) B–Triazinyl dyes.
(5) Supra type of dyes.
(6) Di or tri-chloro-pyrimidylamino dyes
1.3.2 Dyes reacting through Nucleophilic addition reactions:
(1) Dyes containing Vinyl sulphone group
As such this is not soluble in water, so it is marketed in its soluble form i.e., ?-hydroxy ethylene sulphone sulphuric acid ester derivatives RSO2 –CH2-CH2OSO3Na
(2) Dyes containing Acrylamido group:
Carbonyl group is less powerfully electron withdrawing group & also reactivity is less as compared to vinyl sulphone type
(3) ?? chloro acrylamido dye:
Due to presence of chlorine atom, they are more reactive than acrylamido dyes.
1.3.3 Special type of reactive dye:
The reactivity of the cross linking agent does not enable one to predict the degree of fixation of the dye with the fiber. The structure of the dye molecule is always the deciding factor, since substituents, configuration and diffusion characteristic of the dye play a dominant role in this dyeing. Metal complex dyes were found to be particularly satisfactory for the purpose. They have high tinctorial strength and most of the are very fast to light. On cotton they are very bright. There is mainly touch of two or more touch of color in this dyes. Turquoise is one of this type. Main purpose to use these dyes is that some bright blue, yellow colors cannot be found by primary color matching. Example of a turquoise dye is Cibacron turquoise blue G. The structure is given below:
N
NaS C C Na
C N N C
N Cu N Cl
C N N C
NaS C C NH
N
1.3.4 Chemistry behind Reactive Dyeing:
Dyeing principle is based on fiber reactivity & involves reaction of a functional group of dyestuff with a site on fiber to form a covalent link between dye molecule & substance. 4 structural feature of typical reactive dyes molecule are:
1) Chromophoric grouping, contributing color
2) Reactive system, enabling dye to react with hydroxy group in cellulose.
3) A bridging group that links reactive system to chromophore,
4) One or more solubilising group, usually sulphuric acid substituent attached to chromophoric
group for their color, although Azo chromophore –N=N- is by itself the most important.
All reactive dyes contain sodium sulphonate group for solubility & dissolve in water to give colored sulphonate anions & sodium cations. Most reactive dyes have 1 to 4 of these sulphonate groups; General form of reactive dye is as follows:
S—–R—-B—-X
Where,
S = Water solubility group
R = Chromophore
X = Reactive System
B = Bond between reactive system & Chromophore
1.4 Reaction between Cellulose & Reactive Dyes:
Dyeing of cellulosic fibres with reactive dyes consists of two phases:
ð Firstly, exhaustion phase, where dye is absorbed by material in neutral medium,
ð Secondly fixation phases, where reaction between dye & fiber takes place.
Cellulose in its reaction with reactive dyes is considered as alcohol. Electro negativity of oxygen atoms governs tendency of hydroxyl group to ionize. Cellulose is consequently ionized under alkaline conditions & can act as nucleophilic reagent & shows subsequent reactions with acid halides (nucleophilic substitution). Mechanism of nucleophilic substitution is as below:
Most of reactive dyes require alkaline catalyst for fixation on fiber. During dyeing with vinyl sulphone dyes, vinyl sulphone group is formed from parent dye under alkaline conditions, may be represented by:
Mechanism of nucleophilic addition reaction is as below:
When alkali is added to vinyl sulfone dye, it is converted to
1.4.1 Requirement of sequestering agent during dyeing with reactive dyes:
Water in dye bath may contain metallic ions. Hence, there is a danger of uneven dyeing such as specking. Reduction of concentration of dye is caused by dyestuff’s coagulation & reduced solubility. Metallic ions can also be introduced by impurities in Glauber’s salt or common salt, so even when soft water is used in dyeing, presence of metallic ions can lead to problems. Here, sequestering agents are effective in neutral to alkaline conditions & agents combining effects of sequestering agents with those of anionic surfactants &marketed for use with reactive dyes are now being developed.
1.4.2 Role of washing off agents in reactive dyeing:
Washing off agents are necessary to remove dye from dyed material in order to correct faulty dyeing.
Soaping agents disperse hydrolysed dyestuff & keep them in water bath, preventing their re-deposition o substrate. Inorganic salts have 2 main functions in exhaustion dyeing with reactive dyestuffs:
1) Improving affinity of dyestuffs
2) Acceleration of dyestuff’s association & lowering of its solubility
And, then reacts with fiber as below:
Improving affinity & thus exhaustion of dyestuff during primary exhaustion serves to raise exhaustion rate of reactive dyestuffs. As reactive dyestuffs have a lower affinity than direct dyestuffs, more inorganic salt is required when using reactive dyestuffs in order to accelerate absorption. Thus, while around 10g/l of Glauber’s salt is usually appropriate for dyeing with direct dyes, an average of 50g/l is used with reactive dyes. Amount of inorganic salt used varies according to type of dyestuff used, recently developed highfixation dyestuffs with improved affinity allow amount of inorganic salt to be reduced. Amount of inorganic salt used can also be reduced when concentration of dyestuff is low. Following displays amount of Glauber’s salt used exhaustion rate & fixing rate for a conventional dye & a high-fixation dye.
As inorganic salts accelerate association of water-soluble dyestuffs & lower dyestuffs solubility, an excess of inorganic salt slow down absorption of some dyestuffs, & so care is necessary when inorganic salts are used. Effectiveness of inorganic salt is not decided by ratio of its quantity to quantity of fabric (o.w.f.) but rather by its dye bath concentration (g/l). Hence, its effect can be reduced by lowering its concentration.
1.5 Reactivity & affinity of dyes:
If reactivity of dye is increased considerably, reaction rate with fiber increases. So, dyeing can be carried out in a very short time. However, here, dye hydrolysis rate also increases, leading to deactivation of part of dye resulting in dye wastage. If, on other hand, dye reactivity is decreased, extent of hydrolysis can be reduced considerably that, how ever results in slower reaction rate with fiber also. Ultimate dyeing object is to react as much of dye as possible with fiber with minimum dye hydrolysis, is actually achieved in 2 stages:
ð 1st from aqueous medium under neutral conditions when dye does not react with fiber or with water, Then Glauber’s salt/common salt is added to exhaust dye onto fiber as much as possible. Then
ð 2nd step of dyeing i.e. fixation of dye on fiber is carried out by adding alkali (usually soda ash).
Since exhausted dyes are already on fiber, it is more likely that exhausted dye reacts with fiber in
preference to water. However, dye present in dye bath containing substantial amount of reactive dye can now react with water since it is under alkaline conditions. It is already stated that hydrolyzed dye cannot further react with fiber due to affinity force; it is adsorbed by fiber & is retained in it.
During subsequent washing or soaping substantively held hydrolyzed gets stripped into washing fastness of dyeing. If affinity of original dye is reduced to a very low value this problem will not arise, & a rigorous treatment of dyeing with boiling soap or detergent solution removes almost all hydrolyzed dye. However, if affinity is very low, exhaustion of dye bath prior to fixation cannot be achieved substantially. This results in larger amount of reactive dye remaining in dye bath & getting hydrolyzed when alkali is added subsequently. If dye has high affinity for cellulose like a direct dye, it becomes difficult to remove hydrolyzed dye from dyeing since it is also adsorbed by & retained in fiber by fairly strong affinity forces, though not as strong as covalent bond formed between dye & fiber. Hence in actual practice low affinity dyes are selected for converting into reactive dyes.
1.5.1 Dye bath pH:
For most of dyes optimum pH is 10.8 to 11.0 at 20-25°C soda ash is the best alkali for dyeing at 30°C for cotton, mercerized cotton & linen. Increased fixation (due to higher temperature) & increased dye bath stability & better reproducibility are advantages of soda ash as fixing agent.
1.5.2 Amount of alkali:
Amount of alkali used for fixing depends on depth of shade dyed & liquor ratio employed. Depending on the percentage of shade we can express the amount of alkali needed in the following chart:
| Shade% | <0.2 | 0.2-0.5 | 0.5-1 | 1-1.5 | 1.5-2 | 2-2.5 | 2.5-3 | >3.5 |
| Soda ash g/l | 6 | 8 | 10 | 10 | 12 | 15 | 20 | 20 |
1.5.3 Dyeing Temperature:
As increase in temperature affects rate of physical & chemicals processes involved in dyeing, it is important in reactive dyeing also. Affinity of dye for fiber decreases with increases in temperature (dyeing is an exothermal reaction), & at same time rate of dye hydrolysis increases, adversely affects color yield fixation. However, rate of diffusion of dye in fiber increases with increased temperature. At temperatures lower than 20°C, rate of fixation is very low. Hence for most of dyes a temperature, while for some others’ dyeing at 50-60°C with sodium carbonate as alkali gives maximum color value. Some special dyes like the turquoise color needs higher temperature for migration, the temperature maintained should be 80C.
1.5.4 Electrolyte Concentration:
Since reactive dyes have low affinity for cellulose, exhausting dye bath can increase fixation, by adding common salt or Glauber’s salt prior to fixation. Amount of salts required to produce adequate exhaustion decreases with decreasing liquor ratio. According to shade percentage the amount of electrolyte should be added can be determined. The chart is given below:
| Shade% | <0.2 | 0.2-0.5 | 0.5-1 | 1-1.5 | 1.5-2 | 2-2.5 | 2.5-3 | >3.5 |
| Gruber salt g/l | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 |
1.5.5 Dyeing Cycle Time:
Generally, dye may be added in two portions. Salt may also be added in two lots. Exhaustion takes place in 20-30mins. Alkali is then added in 2 lots (also in Progressive dosing® system developed by Hoechst) & dyeing is continued for 30-90min. Shade depth & dye reactivity decides dyeing time. For deeper shades, longer times are required.
1.5.6 Liquor Ratio:
With increased liquor ratio, both exhaustion & fixation takes place to increased extent. However, rate of fixation of most of dyes is not significantly affected. As liquor ratio is decreased, effectiveness of increasing salt addition also decreases. Hence lower amounts of salts are sufficient to get optimum exhaustion.
1.5.7 Dyeing of Hot Brand Reactive dyes:
In this case dye is not as reactive as cold brand dyes & hence higher temperatures are required for achieving adequate fixation. Dye bath pH depends on dyeing temperature, is in range of 65-80°C for cotton & viscose rayon. As with cold brand reactive dyes, & increase in temperature generally results in weaker shades of hot brand reactive dyes because of decreased affinity at higher temperatures & consequent reduced fixation. Similarly lower temperatures reduce reactivity & hence produce lower color value unless dyeing time is prolonged or pH is increased larger amounts of common salts or sodium sulphate should be used for exhaustion (50g/l, 75g/l for shades of up to 1%, 1-3% & above 3% respectively). Dyeing time is generally same as in case of cold brand reactive dyes.
1.5.8 Finishing:
After completion of dyeing process dyed substrate, is rinsed with cold water. Then soaping is carried out to remove hydrolyzed dye present on fiber. This dye reacted with water molecule, hence is called hydrolyzed dye & remains unreacted on fiber surface. Soaping treatment thus removes unrelated dye present on fiber thus improving fiber brilliancy. Then few hot washes are given & with one cold wash it is sent for drying.
1.6 pH:
In all textile processes in which aqueous solutions are used, balancing the pH of the solution is primary. pH control is critical for a number of reasons. The effectiveness of oxidizing and reducing agents is pH dependent. The amount of chemicals required for a given process is directly related to the pH. The solubility of substances, such as dyes and impurities, vary with pH. The corrosive and scaling potential of processing solutions is also heavily influenced by pH. All of these issues affect quality and costs.
Along with surface tension, pH plays an important role in the wetting and saturating processes. For example, caustic solutions cause inters febrile swelling in cotton cellulose and cannot be squeezed out as easily as water, which can reduce quality in subsequent processing. Between the color kitchen and processing, controlling the pH improves the lab-to-bulk reproducibility of color. Monitoring and controlling pH ensures consistency of color from batch to batch, as well. Maintaining the correct pH is also critical in processes where a specific pH permits a reaction mechanism necessary for the purification of fibers: bleaching with sodium hypochlorite or hydrogen peroxide, desizing with oxidizing agents or removing soluble products and others.
1.7. Temperature:
As we were thinking, hotter temperatures in general increase the rate of any reaction. The same thing occurs with dye, but also with the water that the dye is dissolved in. The dyes can react with either the callous fiber or the water, the latter reaction being known as hydrolysis. The effect of the added energy is much greater on the dye reaction rate than on the ability of the dye to soak into the fiber. Increasing temperature too much causes the dye to rate with water before it even gets into the fiber. in fact, it’s better to let to dye soak into the fiber for some time before beginning your due reaction by adding soda ash (on other pH incases) and any heat.
The cellulose molecules in cotton material can dye well at 80?C, if the dye is already located in the fiber, adjacent to the cellulose molecule, before it reaches that temperatures. It works fine to heat the dye reaction up excessively warm, if the dye is in place already.
1.8. Time:
Time is the very important for the dyeing process. it can be ensure the shad matching with customer requirement. Different dyestuff can be dyed by different time. Dyeing process & dyeing production depend on the time. The depth of shade and the reactivity of the dye decide the time of dyeing for deeper shades, longer times are required.
1.9. Experimental:
1.9.1. Materials:
1. Grey fabric
2.Auxiliaries and Dyes
3. Dyeing machine
4. Testing equipment
1.9.1.1. Grey fabric:
We take the grey fabric as single jersey knitted fabric, which are 95
G.S.M.
1.9.1.2. Auxiliaries and Dyes:
1.9.1.2.1. Auxiliaries:
We have used various types of auxiliaries, such as:
1. Sandoclean PCLF- Detergent
2. Feloson NOF- Detergent
3. Ck- wetting agent
4. Tex-D-900- Sequestering agent
5. Sirrix 2UD- Sequestering agent
6. Centafoam SC- Antifoaming agent
7. H2O2- Hydrogen Per-oxide
8. Caustic soda flax
9. Imacol C2G- Anticreasing agent
10. Centableach SB and SOF- Stabilizer
11. Centalizer ASB and Crocks- Per-oxide Killer
12. Acetic acid
13. Bio-Polish 80L- Enzyme
14. Drimazin E2R and 200 BF- Leveling agent
15. Salt and Soda
16. Sandoper Sp- Soaping agent
17. Sandofix EC- Fixing agent
18. Softener W. Alkamine CWS, MEJ – Softener, etc.
1.9.1.2.2 Dyes:
Drimarin Yellow CL3GL: 1.121 %
Drimarin Blue CLBR: 0.4617 %
Drimarin T.Blue CLB: 2.812%
1.9.1.3. Dyeing machine:
This experiment is use for Fong`s dyeing machine (Winch dyeing
m/c).
1.9.1.3.1 Specification of Fong`s dyeing machine:
-Suitable for material weigh approx, 500~2500 g/m.
-Standard nozzle size of DN250 covers wide rang of material being
processed.
-Optional nozzle size of DN300, DN200, and DN150 are for
exceptional
material wt.
-Spacious fabric storage chamber capacity up to 350 kg/chamber.
-Minimum liquor ratio at approx, 1:6* to run the machine.
1.9.1.3.2 Technical data of Fong`s dyeing machine:
– Minimum liquor ratio to run the machine: approx, 1:6* with full
load
– Maximum lifter reel speed: 300 m/min
– Design temperature: 98?C
– Design pressure: atmospheric
– Heating rate:
25?C-98?C, average 5?C/m
(with dry saturated steam pressure at 7 bar)
-Cooling rate:
98?C-80?C, average 2.5?C/m
(with cooling water at 3 bar, 25?C)
*The figure of liquor ratio present is based on fong`s manufacturing
laboratory results. It may be different fabric quality.
1.9.1.4. Testing equipment:
1. pH meter.
2. Temperature meter.
3. Digital watch.
1.9.2. Method:
1.9.2.1 General method for the dyeing with the reactive dyes:
Given the below method for the dyeingwith the reactive dyes
1. Discontinues method- a) Jigger dyeing m/c (woven fabric)
b) Winch dyeing m/c (Knitted fabric)
c) Jet dyeing m/c (knitted + woven)
2. Semi-continues method- a) Pad jig method
b) Pad Batch method
3. Continues method- a) Pad dry method
b) Pad steam method
This experiment we have to use discontinues method as winch dyeing m/c (Knitted fabric) of hot brand reactive dye.
1.9.3. Process description:
Dyeing procedure consists of four steps. This four steps are necessary for completing the whole dyeing process. Green color is a critical color. So it takes necessary steps for dyeing and finishing. We use Fong`s dyeing machine for this experiment. Four steps are as follows:
1. Scouring
2. Bleaching
3. Enzyme treatment
4. Dyeing
1.9.3.1 (i) Scouring:
We take the single jersey fabric of weight 400kg (Grey fabric). The chemical used for scouring process are NOF, 2UD, PCLF, FFC, Caustic. The required amount of chemicals used for this process are as follows:
Scouring Recipe:
1. NOF: 0.5 g/l.
2. 2UD: 0.5 g/l.
3. PCLF: 0.6 g/l.
4. 2UD: 0.3 g/l.
5. FFC: 0.05 g/l.
6. Caustic: 2.5 g/l.
7. Process temperature: 70?C.
8.Time: 90 minute
Process flowchart:
First process:
fig: process flow chart for scouring
Two processes are both good. However, the first process is preferable because in this process fabrics are better cleaned and absorbency power will be increased by removing
the natural impurities, dirt or grease from cloth more clearly.
1.9.3.2 (ii) Bleaching:
Normally scouring and bleaching is done together in the dyeing machine. We separate this process from scouring. Bleaching creates a permanent whiteness effect in the fabric which is helpful for dyeing cotton fabric. Sometimes acid and peroxide killer are given in the bath together which is preferable. Another point is the choice of acid for bleaching. Strong acid is more beneficial than Acetic acid because Strong acid controls the PH more strictly. Chemicals used for this process are as following
Bleaching Recipe:
1. H2O2: 4.0 g/l.
2. Centalizer ASB (Per-oxide destroyer): 0.6 g/l.
3. Stabilizer SOF: 0.25 g/l.
4. Strong acid: 0.6 g/l.
5. Bleaching temperature: 80°C
6. Time: 40 minute
fig: process flow chart for bleaching
1.9.3.3 (iii) Enzyme treatment:
Enzyme treatment must be done for any knit fabric dyeing for better handling properties. Short fibers or hairiness fibers are removed from the surface of the fabric. Normally enzyme % is (0.9-1.0). Two process are applied. The using chemical for this process are as follows:
Enzyme recipe:
1. Bio-Polish 80 L: 0.9 % (on the weight of the fabric).
2. Acetic acid: 0.6 g/l.
3. pH: 4.5 – 5.5
4. Enzyme temperature: 55°C to 70°C
First process is to be done in two steps. At temperature 55°C 0.6 % enzymes are given in to the machine at runtime 30 minutes. The fabric is tested for hairiness. Then add 0.3% enzyme at running time 20 minutes, cut the fabric and check the hairiness. If good then temperature is raised up to 70°C and after runtime of 10 minutes bath drop. Second process is to be done in one step. At temperature 55°C 0.9% enzyme are introduced in the machine at running time 1 hour, then bath drop. Between two processes the first process is better because in this process hairiness fibers are smoothly removed which is helpful for the next dyeing process
1.9.3.4 (iv) Dyeing conditions:
For this experiment, we used two processes. One is the migration process and another is the isothermal process. In isothermal process, at 60°C, salt, soda and color is given to
the dye bath. In migration process, color (30°C), salt (60°C), then runtime 30 minutes at 80°C, soda (60°C), then again the temperature raised up to 80°C has been completed in the dye bath.
Dyeing recipe:
Shade %: 4.3947 %
Drimarin Yellow CL3GL: 1.121 %
Drimarin Blue CLBR: 0.4617 %
Drimarin T.Blue CLB: 2.812%
Salt: 60 g/l
Soda: 15 g/l
Temperature: 60?C
Time: 45 minute
fig: process flow chart for dyeing
1.9.4 Process study:
1.9.4.1 Exhaustion and fixation study:
The dye-bath exhaustion and fixation was studied by known methods, collecting the samples of exhausted liquor at various intervals and studying the absorbance by diluting the exhausted liquor up to various fold by known methods.
1.9.4.2. Solubility:
Due to the presence of the OH and NH functional group in the dye molecule, dissociation resulted in a higher solubility during the dyeing process at low liquor ratio.
Also, the presence of the sulfuric chromospheres (two to three) and the novel sulphatoethyl sul-phone groups promoted the solubility of the new bi-functional (MCT/SES) dyes. Also, during the dyeing process 7 no urea was required and the dye was highly soluble in the presence of common salt at a low liquor ratio.
1.9.4.3. pH:
The pH of dye bath during exhaust dyeing method was widely taken into consideration. Here, we first used the neutral pH and gradually increased to alkali by dosing the Na2CO3/NaOH to a pH of 11.5 to differentiate the probable exhaustion in both cases. Both SES and MCT groups functioned as the reactive sites. However, we recommend dyeing process for this type of dye exhaust dyeing method set at 60°C with a control dye bath pH.
1.9.4.4. Color measurement:
The (%R) percent reflectance of the dyed material was measured at different wave lengths in the visible region (400- 700 nm) using a ACS-600 color control system.
1.9.4.5. Shade evaluation:
The hue over the knitted cotton fabric was checked by matching it with standard shade cards. The resultant variation the hues had occurred since the subsequent offers the bath
chromic shift good penetration and higher depth. The shade appeared at a somewhat higher wavelength of the dye.
1.9.4.6. Fastness test:
The Rubbing fastness was assessed on a Crock meter which is nearly 4 to 5.
19.4.7. Substantives:
The dyes showed medium-to-good substantively which can be detected by the exhaustion and fixation study. This can be due also to the presence of the two precursor groups as the reactive sites involved in the dye substrate. The substantively of the hydrolyzed byproduct can be readily detected from the amount of unfixed dye and can easily be
Removed after three or four washes at different temperatures
1.10. Testing:
Color measurement of the dyed fabrics. The dyed fabric obtained was divided into four pieces:
i) A reference sample.
ii) The second piece was measure the shade % by Spectrophotometer as different stage.
iii) The three piece was soaped for 30 minutes at the boil in a bath containing 3 g/L non-ionic detergent.
iv) The four piece was soaped and extracted with 50% aqueous dimethyl formamide for 15 minutes at the boil. The color yield of the dyed samples were evaluated using
a Perkin-Elmer Spectrophotometer and by applying the Kubelka-Munk equation as follows:
Where:
R = Decimal fraction of the reflectance of the dyed fabric.
Ro = Decimal fraction of the reflectance of the Undyed fabric.
K = Absorption coefficient.
S = Scattering coefficient.
1.11. Effect of reaction temperature:
Although, we are aware that the first chlorine atom in the dichlorotriazinyl compound reacts with dye bases at temperatures ranging from (30-100°C), yet for purposes of understanding the factors affecting the coloration of cotton using the present process we chose to follow, the reaction at higher temperature also. Results of experiments on the effect of temperature on the extent of reaction reactive dyes as measured by color
strength values are summarized in Table (1)
Table 1: Effect of reaction temperature of dyes with the color strength on dyed cotton fabrics.
| Type-weight (g) and no. of mmole of dye | Temperature
(°C) |
Color strength (K/S) | |
| After
soaping |
After
DMF |
||
| 1. Drimarin Yellow CL3GL: 4.48 (22.62) | 30 | 5.07 | 3.77 |
| 45 | 11.52 | 10.65 | |
| 60 | 19.01 | 14.17 | |
| 75 | 20.8 | 20.80 | |
| 85 | 24.0 | 22.80 | |
| 100 | 18.24 | 18.24 | |
| 2. Drimarin Blue CLBR: 1.86 (9.55) | 30 | 0.356 | 0.307 |
| 45 | 0.802 | 0.515 | |
| 60 | 1.624 | 1.156 | |
| 75 | 1.883 | 1.475 | |
| 85 | 5.89 | 3.33 | |
| 100 | 8.45 | 8.12 | |
| 3. Drimarin T. Blue CLB: 11.248 (58.31) | 30 | 19.67 | 19.23 |
| 45 | 22.30 | 2.09 | |
| 60 | 27.77 | 27.20 | |
| 75 | 32.78 | 32.55 | |
| 85 | 39.23 | 39.10 | |
| 100 | 45.78 | 45.23 | |
*Reaction time 20 min. at ph 6.5.
Color strength
Temperature
fig: Show the effect of reaction temperature of dyes with the color strength on dyed cotton fabrics.
The above data reveal that-
a) Reactive compound has some stability under the experimental conditions used and that an increase in temperature of the reaction dyes generally causes a corresponding increase in the concentration of the reactive dye, partially formed in-situ, as indicated by increase of color strength values on cotton fabrics.
b) Compound 2 gives always appreciably higher values of K/S as compared to all other compounds at different temperatures.
c) In case of dye (2) an increase in temperature of the reaction is accompanied by an increase in color strength until it reaches a maximum at 85°C. Further increase of temperature causes a slight decrease.
d) Although the increase of the color strength in the case of dye (3) is considerable (about 10 times) when the temperature is raised from 30 to 100°C, yet the values of K/S obtained are relatively high due to the insolubility of this dye in the reaction medium and to the enhanced hydrolysis of I at higher temperatures.
e) The increase of color strength values of dyes (1) and (2) between 30 and 100°C are also relatively small. The K/S values remain also low.
f) Maximum color strength values in case of dyes are attained at 100°C.
The results & comments from the table & graph showing the data:
Increase of temperature of dyes (1), (2) and (3) leads to a decrease in color strength values due probably to the reaction of dye (I) with two molecules of the dye under the experimental conditions used. This would definitely lead to decreased concentration of the reactive dye in the reaction medium. On the other hand, decrease of temperature of dyes (2) and (3) leads to increase in color strength
1.12. Effect of reaction time:
The effect of reaction time on color strength is shown in Table 2. These data are self explanatory and show that under the conditions used a time ranging from 30-80 minutes gives optimal color strength values depending on the type of soluble dye used. Increase in time above these limits seems to favor the hydrolysis of dye compound I or the in situ formed dye.
Table 2: Effect of reaction time of dyes with the color strength on dyed cotton fabrics.
| Type-weight (g) and no. of mmole of dye | Time (minutes) | Color strength (K/S) | |
| After
soaping |
After
DMF |
||
| 1. Drimarin Yellow CL3GL: 4.48 (22.62) | 30 | 0.797 | 0.773 |
| 40 | 1.415 | 1.267 | |
| 50 | 1.930 | 1.228 | |
| 60 | 2.519 | 2.254 | |
| 70 | 1.885 | 1.398 | |
| 80 | 0.823 | 0.414 | |
| 2. Drimarin Blue CLBR: 1.86 (9.55) | 30 | 2.208 | 2.025 |
| 40 | 3.435 | 3.166 | |
| 50 | 4.605 | 4.342 | |
| 60 | 4.990 | 4.450 | |
| 70 | 3.298 | 2.934 | |
| 80 | 2.343 | 2.098 | |
| 3. Drimarin T. Blue CLB: 11.248 (58.31) | 30 | 4.306 | 3.828 |
| 40 | 4.985 | 4.554 | |
| 50 | 5.268 | 4.987 | |
| 60 | 6.173 | 5.781 | |
| 70 | 5.769 | 5.370 | |
| 80 | 4.895 | 4.483 | |
*Reaction temp. 85°C for dye (1) and 100°C for dye (2) and (3) at pH 6.5.
Color strength
Time (minute)
fig: Show the effect of reaction time of dyes with the color strength on dyed cotton fabrics.
The results & comments from the table & graph showing the data:
Increase of time at 60-80 minute for reaction of dyes (1), (2) and (3) leads to a decrease in color strength values due probably to the reaction of dye with two molecules of the dye under the experimental conditions used. This would definitely lead to decreased concentration of the reactive dye in the reaction medium. On the other hand, decrease of time of dyes (1), (2) and (3) leads to increase in color strength 60 minute stage.
1.13. Effect of reaction pH:
The effect of reaction pH on color shade% is shown in Table 3. These data are self explanatory and show that under the conditions used a pH ranging from 4-12 gives optimal color shade% values depending on the type of soluble dye used. Increase in pH above these limits seems to favor the hydrolysis of dye or the in situ formed dye.
Table 3: Effect of reaction pH of dyes with the color shade% on dyed cotton fabrics.
| Type-Shade% of dye | pH | Color Shade% | |
| After
soaping |
After
DMF |
||
| 1. Drimarin Yellow CL3GL-1.121% | 4 | 0.607 | 0.535 |
| 5 | 0.763 | 0.678 | |
| 6 | 0.880 | 0.733 | |
| 7 | 0.964 | 0.846 | |
| 8 | 1.025 | 0.983 | |
| 9 | 1.092 | 1.028 | |
| 10 | 1.120 | 1.090 | |
| 11 | 1.150 | 1.126 | |
| 2. Drimarin Blue CLBR-0.4617% | 4 | 0.118 | 0.094 |
| 5 | 0.194 | 0.123 | |
| 6 | 0.258 | ||