Comparative Study Between High temperature Method and Carrier Method of Disperse Dye
রবিবার, ২ জানুয়ারী, ২০১১
Introduction:
Bangladesh is mainly a developing country and depends ofn agriculture. But now a days Bangladesh economy is going to be depending on textile sector. Out of five basic human demands clothing is one of them. The textile industry has played an important role in Bangladesh ‘s economy for a long time. Currently, the textile industry in Bangladesh accounts for 45% of all industrial employment and contributes 5% to the total national income. A huge 78% of the country’s export earnings come from textiles and apparel, according to the latest figures available. Dying is one of the major sector in textile which is growing day by day.
The general structure of a polyester is shown below:
They tend to be fairly hydrophobic (though this depends on the structure of R1 and R2), but not as much as, say, a long hydrocarbon would be, since the -COOC- groups cause some polarity. The polymer chains in a sample of polyester are highly crystalline (for a polymer) and quite tightly packed together. The result of this is that polyesters have very little affinity for large ionic dyes- the dyes simply cannot either distribute between the chains, or form satisfactory intermolecular interactions. Therefore, acid and direct dye classes are useless for this polymer2.
Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, and they find minor use dyeing cellulose acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional groups like -NO2 and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility, improve the dipolar bonding between dye and polymer and affect the colour of the dye. However, their small size means that disperse dyes are quite volatile, and tend to sublime out of the polymer at sufficiently high temperatures2.
The dye is generally applied under pressure, at temperatures of about 130oC. At this temperature, thermal agitation causes the polymer's structure to become looser and less crystalline, opening gaps for the dye molecules to enter. The interactions between dye and polymer are thought to be Van-der-Waals and dipole forces2.
The volatility of the dye can cause loss of colour density, and staining of other materials at high temperatures. This can be counteracted by using larger molecules, or making the dye more polar (or both). This has a drawback, however, in that this new larger, more polar molecule will need more extreme forcing conditions to dye the polymer2. Chemical removal of Phosphate ions from disperse dye filtrates.
DISPERSE DYE
Disperse dye is originally developed for the dyeing of cellulose acetate. They are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent then sold as a paste or spray dried and sold as a powder. They can also be used to dye nylon, triacetate, polyester and acrylic fibres. In some cases a dyeing temperature of 130 deg C is required and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.
Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, and they find minor use dyeing cellulose acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional groups like -NO2 and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility, improve the dipolar bonding between dye and polymer and affect the colour of the dye. However, their small size means that disperse dyes are quite volatile, and tend to sublime out of the polymer at sufficiently high temperatures.
Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, and they find minor use dyeing cellulose acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional groups like -NO2 and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility, improve the dipolar bonding between dye and polymer and affect the colour of the dye. However, their small size means that disperse dyes are quite volatile, and tend to sublime out of the polymer at sufficiently high temperatures.
The dye is generally applied under pressure, at temperatures of about 130oC. At this temperature, thermal agitation causes the polymer's structure to become looser and less crystalline, opening gaps for the dye molecules to enter. The interactions between dye and polymer are thought to be Van-der-Waals and dipole forces.
The volatility of the dye can cause loss of colour density, and staining of other materials at high temperatures. This can be counteracted by using larger molecules, or making the dye more polar (or both). This has a drawback, however, in that this new larger, more polar molecule will need more extreme forcing conditions to dye the polymer2.
The most important class is the azo class. This class of azo disperse dyes may be further sub-divided into four groups, the most numerous of which is the aminoazobenzene class. This class of dye can be altered as mentioned before, to produce bathochromic shifts. A range of heterocyclic aminoazobenzene dyes are also available. These give bright dyes, and are bathochromically shifted to give blues. The third class of disperse dye is based on heterocyclic coupling components, which produce bright yellow dyes. The fourth class are disazo dyes. These tend to be quite simple in structure. Other than these, there are disperse dyes of the carbonyl class, and a few from the nitro and polymethine classes. Below is an example of a disperse dye. It is the same as the chime molecule at the top of the page. Recently, Sokolowska-Gajda and Freeman reported an effective methods for the diazotization of 2-amino-6nitrobenzothiazole in a mixture of acetic acid and dichloroacetic acid, followed by coupling with N-β-cyanoethyl-N-β-acetoxy-ethylaniline to form disperse red 177. Although the yield of this two step synthesis was good (87%), it was somewhat lower than anticipated from the work of others, in which the diazotization was conducted in the phosphoric acid (12). In addition, there is now reason to be concerned about the toxicity of an HOAc/CHCl2CO2H effluent. Similarly, the use of H3PO4 causes an environmental problem known as eutrophication.
Classes of disperse dye
Dyes may be classified in a variety of ways, some of which are unique to the particular application category. Disperse dyes are no exception. As might be anticipated, chemical classification by chromophore is generally the least useful to the dyer. However, there are some chemical differences between disperse dyes which affect their performance in dyeing. These include the ease with which they are reduced and the ease with which they are hydrolyzed.
1 Reduction clearing
Because disperse dyes have such limited solubility in water, some particulate disperse dye may still be occluded on fiber surface after the dyeing phase is complete. If this condition is suspected, the last stage of the total dyeing process may need to be one where surface dye is removed. Adverse results of excess dye on the fiber surfaces include considerably reduced wet fastness, wash fastness, sublimation and drycleaning fastness, as well as dulling of the shade.
With experience, the presence of excessive amounts of surface dye can be determined by simply agitating a sample of the dyed goods in a little cold acetone for a few seconds, when surface dye will dissolve. The acetone will not extract dye from within the fiber, which remains unswollen, but will dissolve surface color.
The usual practical procedure for removing this unwanted dye is called reduction clearing and uses a bath of about two grams per liter of both caustic soda and sodium dithionite ( hydro ); as 100% solid products, plus about one gram per liter of a stable surfactant.
A treatment for 20 minutes at approximately 70C (160F), is often sufficient to clear the fiber surfaces, but the ease of removal varies from chromophore to chromophore and dye to dye. Provided the clearing temperature is not above the dyeing transition temperature, no dye will be stripped from within the polyester fibers.
The largest majority of disperse dyes contain the azo group, -N=N-. This group is easily split into two amino groups by treatment with reducing agent:
-N=N- red -NH2+H2NSuch dyes are particularly suitable for reduction clearing since the amino residues are virtually colorless unless deliberately oxidized to form totally different products.
Some bulky azo dye molecules, notably the navies as a group, are so sensitive to reduction that under conditions of too high pH they can cleave at the azo group, even during the dyeing process, to give dyeings of a characteristic lighter, duller and greener appearance. The condition is more pronounced in polyester/cotton blends.
Another chromophore still found in some of the brighter blue, pink and red disperse dyes, despite its cost, is anthraquinone. This is more difficult to reduce and is not destroyed during normal reductive clearing. However, as in the case of vat dyes, the anthraquinone residue is at least partially and reversibly reduced to a soluble sodium leuco form which can be washed away but which on subsequent exposure to air becomes insoluble again
2 Hydrolysis of Dye Ester
Another chemical group frequently found in disperse dyes is an ester group, often an acetyl group, O-CO-CH3, and like the acetyl groups in cellulose acetate it is susceptible to hydrolysis in neutral and alkaline conditions:
Dye-O-CO-CH3 H2O Dye-OH+HO-CO-CH3The products are acetic acid and a different azo disperse dye, whose color may be quite different from that of the parent dye. Usually the wavelength of maximum light absorption (minimum reflectance) is shifted to a longer wavelength. This is known as a bathochromic shift, in which colors change in the general direction: Yellow » orange » red » violet » blue » green. However two additional, widely different points are worth noting here.
The presence of hydrolysable groups in many disperse dyes and their protection is the principle reason why dyeing are generally made on the slightly acid side. The pH has no fundamental role in the dyeing mechanism as such and some disperse dyes without ester groups do not need a weakly acidic dyebath.
Dyes and dyeings in any application category have traditionally been presented- eg., in shade cards, the Color Index and until recently, in Buyers guide – in the same bathochromic series order listed above. Blacks are shown last and browns are sometimes presented after orange and sometimes between green and black. To simplify processing by computer, the Buyers guige now lists dyes alphabetically by color- i.e., black, blue, brown, green, orange, red, violet, yellow- and the color indexd is considering the possibility of doing the same. While it makes no coloristic sense, the alphabetical system simplifies the processing of the data.
A group of sisperse dyes utilizes the alkaline hydrolysis of esters in an ingenious way. These products contain ester groups in the reverse orientation relative to the dye chromophore to that shown above. During alkaline scouring, the surface dye becomes a water soluble carbxylate salt and is easily removed by washing,
Dye-CO-O-CH3+NaOH Dye-COO¯Na + CH3- OH3 Energy Level
Most disperse dye classifications are based on some form of generalized grouping according to their rates of dyeing and resistance to sublimation. For example, a major company from the United Kingdom has chosen to classify its disperse dyes into four groups, A-D, where subgroups A contains those dyes with the highest rate of dyeing on polyester and the lowest sublimation fastness, while the dye in subgroup D are just the reverse.The fact of the matter is that the relative dyeing, physical and most fastness properties of disperse dyes lie scattered around a line from generally small molecules, with low polarity, poor heat and sublimation resistance, rapid rates of dyeing and good leveling characteristics, to generally much larger molecules which are quite polar without being ionic, with good hesat and sublimation fastness, poor leveling and low rates of dyeing. Note that light fastness is not a property which is dependent on the molecular size or polarity.
A disperse dye is suitable for dyeing cellulose acetate, carrier dyeing polyester, high temperature dyeing of polyester and dyeing of polyester and cotton blends by thermofixation runs along the same line from A to D. But the precise position of an individual dye relative to others on the line depends on the particular physical property selected and therefore any subdivision is somewhat arbitrary.
In the U.S it is normal to classify disperse dyes into three sub-groups called low, medium and high energy. These cover the same range of properties as the A-D classification mentioned earlier. Again the groups are somewhat arbitrary. But disperse dyes within any one of the subgroups are much more likely to have similar dyeing and fastness characteristics ( other than light fastness) and are consequently more suitable for dyeing together than dyes outside the same subgroup. Because of the number of available dyes, there is still plenty of room for selecting dyes within any subgroup which can deliver the particular characteristics desirable in the final dyed product.
As an illustration, one major manufacturer carries a line of just over 30 disperse dyes principally for polyester: about 25% are low energy dyes of which six are very suitable for carrier dyeing, a different six are very suitable for high temperature dyeing and one is suitable for dyeing the polyester in polyester/cotton blends by thermofixation; about 25% are medium energy dyes of which three are recommended for carrier dyeing, nine are very suitable for high temperature dyeing and five are very suitable for thermohixation; nearly 50% are high energy dyes of whichonly one is recommended for carrier dyeing, four for high temperature dyeing and 11 for thermofixation.
4 Fastness properties on Polyester
The fastness properties of disperse dyes on polyester cover a wide enough range for an adequate dye selection to be made for most end uses. The same dyes generally show poorer fastness on nylon.
Light fastness ratings at the ISO standard depth (1/1 SD) can easily be in the 6-7 range on the Blue wool scale of 1-8, although they do drop slightly if the light source is a carbon arc, as opposed to xenon lamp. As the depth of shade decreases, light fastness drops, a phenomenon shared by dyeing of all application classes of dyes.
If extremely high light fastness is needed (automotive fabrics ), a nonionic UV inhibitor may be added to the dye bath and applied to the fiber along with the dye. These compounds, often benzotriazoles, work much like sunscreen, screening out and dissipating UV radiation to prevent sunburn.
Wet fastness tests are frequently conducted after the goods have been reduction cleared and heat set; at 180C ( 356F ) for 30 seconds, and are assessed in terms of the staining on multifiber or adjacent nylon piece goods. Ratings of 4+ out of 5 are readily achieved on regular denier fibers. What is interesting here is that the ratings are very dependent upon the extent of clearing of the fiber surfaces, the duration and temperature of the heat treatment and whether the fabric has been treated with a finish of any kind. Heating disperse dyed goods causes the dyes to tend to migrate towards the hotter fiber surfaces and some of the disperse dyes are quite soluble in hydrophobic surface films; e.g., in some softeners which may have been applied. Fastness to crocking or rubbing as well as dry-cleaning suffers if dye migrates to the fiber surface or surface layer.
For those dealing in imports and exports of dyed goods, it is vitally important to be aware that the methods of fastness testing and consequently th ratings for dyed goods, vary from country to country. The international organization for standard ( ISO ) has developed a series of fastness test which are often different from test methods used in the U.S Soil compared tests for 30 fastness properties as run in 22 countries. The U.S methods of test wee essentially the same as the ISO SN105 methods in only 7 of 30 cases. The moral is do not buy or sell to colorfastness or any other specifications you do not understand
3 Common and Generic Names for Disperse Dyes
Colour Index Names for PROSperse Disperse Dyes
| | PRO chem # | Name | Colour Index Name | |
| | D118 | Bright Yellow | | Disperse Yellow 218 |
| | D225 | Clear Orange | | Disperse Orange 25 |
| | D333 | Fuchsia | | Disperse Violet 33 |
| | D350 | Flame Scarlet | | Disperse Red 325 |
| | D360 | Bright Red | | Disperse Red 60 |
| | D426 | Turquoise | | Disperse Blue 26 |
| | D450 | National Blue | | Disperse Blue C-4RA (manufacturer's mix?) |
| | D459 | Bright Blue | | Disperse Blue 56 |
| | D460 | Deep Navy | | Disperse Navy 35 |
| | D650 | Cool Black | | Disperse Black C-MDA (manufacturer's mix?) |
| | D770 | Meadow | | In House Mix |
| | D773 | Sage | | In House Mix |
| | D880 | Iris | | In House Mix |
| | D885 | Lilac | | In House Mix |
| | D125 | Buttercup | | In House Mix |
Disperse dye application: General
At a rough of estimate, refs. 5 and 8 devote the equivalent of about 100 pages of the AATCC magazine to the many different aspects of dyeing man –made fibers with disperse dyes. To illustrate the technical depth of coverage 43 pages deal with the variety of textile forms in which polyester can be dyed and the special precautions necessary for their handling.
Here a general treatment will fulfill the present need.
Of course a great deal more is now known about the detailed physical properties of polymers in general fibrous polymers in particular than was known when synthetic fibers were introduced 50 years ago.
The importance of fiber morphology- the particular arrangement of polymer molecules within fibers was quickly appreciated. The general orientation of the polymer molecules the extent to which segments of the molecules were physically bound to those of adja-cent molecules to give crystalline areas, the extent to which other segments were free to move as if in an amorphous viscous liquid how much of the fiber was actually unoccupied by polymer mol-ecules (free volume) and other considerations such as the size and distribution of the crystalline and amorphous areas have all been studied extensively.
As a result a quasi – quantitative picture can be drawn to show, for example, why polyester fibers cannot be readily dyed in the absence of either high temperatures or carriers, or why heat, tension and other influences such as the addition of different co monomers affect the dyeing properties of nylon and polyester fibers
It is interesting to note that by far the most sensitive of all available methods for detecting subtle difference between fibers, or changes in fibers, is still competitive dyeing. Unfortunately for the fiber physicists, competitive dyeing will not reveal precisely what these sublime morphological differences are, only that they are present
1 Disperse dyeing on polyester
There are other fibers besides polyester, notably nylon and secondary cellulose acetate, which are readily dyeable with disperse dyes. Further information about their dyeing, singly and in blends, will appear throughout this project. Nevertheless, polyester dyeing is easily the most important outlet for disperse dyes and the next sections will be devoted to this fiber.
2 Polyester fiber physical factor
The next few sections will deal briefly with those factors which affect the accessibility and the availability of polyester fibers towards disperse dyes. Fiber accessibility differences influence the rate of dyeing, particularly in the early stages; fiber availability differences influence the extent of dyeing which can be achieved at equilibrium. Both can contribute to bare or barrenness. The former is the more usual cause of dyeing problems and is fortunately easier to overcome.
3 Drawing
Un-drawn and partially oriented yarns (POY) can be dyed quite readily since the fiber molecules have not yet been well-oriented. After drawing, the molecules become much better aligned in the fiber direction and as the draw ratio increases, the rate of dyeing or fiber accessibility decreases. The fiber availability does not change much in drawing until one reaches the high draw ratios of industrial yarns.
Accessibility differences between fibers can be overcome provided that the dyes being used and the conditions of dyeing are conducive to leveling in the diffusion and equilibration stages of dyeing which follow the initial differential strike.
4 Heat setting and Tension
There is no doubt that polyester fibers and filaments alone, in yarns or in polyester woven or knit fabrics are morphologically changed during heat setting. If this were not the case, there would be no virtue in heat setting. The resulting headset products can be expected to dye at different rates than the original fibers.
It is hard to be definite about the magnitude of the effects to be anticipated in practice for they vary, not only with the temperature and duration of the heat setting but also upon the conditions of tension in which the goods are held. If fabrics are used, the fully relaxed, natural dimensions of the fabrics affect the tension conditions. Even the individual dyes used can influence the results.
The work of Marvin showed that pieces of filament polyester fabric held to constant dimensions and heat set at temperature intervals between 120-230C (248-446F) dyed to different depths when dyed with 2% owg C.I. Disperse Red 1 for 90 minutes at the boil without a carrier. Under these conditions dyeing was not complete, equilibrium exhaustion was not achieved and the percentages exhaustion, from dye baths containing the differently headset goods, reflect the changes in the relative rates of dyeing.
Fabric set at 120C showed 53% exhaustion, which fell to minimum values of about 34% exhaustion at heat setting temperatures between 150-190C (302-374F), rising rapidly to 75% at 230C. If the fabrics had been allowed to relax the minimum would have tended to rise.
5 Glass transition temperature
Polyester fibers are intrinsically slow dyeing at the boil. Below 70-80C (158-176F) they are for all practical purposes un-dyeable. This leaves only 20-30C in which the rate of diffusion can increase before the atmospheric boil is reached.
Even though the rate of dye diffusion increases very rapidly, even exponentially, above this 70-80C degree temperature range, few dyes will diffuse fast enough at the boil to reach exhaustion during a normal dyeing time if no carrier is present.
The temperature above which polyester dyeing begins to occur more rapidly has been called the dyeing transition temperature. This temperature is reduced when a carrier is present and may even be affected by some of the dye molecules themselves. It cannot be just coincidence that this temperature closely corresponds to a more fundamental physical property of polymers known as the second order or glass transition temperature, Tg, which anc be measured quite independently.
The glass transition temperature is the temperature at which the moveable segments of the polymer chains become quite suddenly susceptible to deformation and displacement, the polymer properties change from glassy to rubbery and in the increasing thermal agitation of the polymer segments, the dye molecules can grasp the opportunity to slip between them into the body of the fiber.
6 Fiber structure modification
The inclusion of alternative co monomers into regular polyester (mentioned in section 12.3), apart from offering the possibility of making the fiber dyeable with cationic dyes, has the effect of lowering both the melting point of the fiber and also its glass transition temperature. The effect can be attributed to the new monomer disreputing the molecular orderliness of the structure, making it easier to leave the glassy state. The same effect can be achieved with the introduction of other non-diffusible, large molecules into the polymer.
Fiber manufacturers have devoted much time and effort in attempts to find new polyester fibers which retain all the desirable characteristics of the present products while adding disperse dye ability at the boil, without carrier, for dyes of high enough energy level have outstanding heat and sublimation fastness. The target remains elusive. One of the problems is the deterioration of some of the physical characteristics of the fiber with the lowering of the glass transition temperature. Another is cost.7 Fiber Fineness
Much attention has been given recently to dyeing microfibers. These are fibers with fineness of less than one decitex; i.e., fibers for which 10000 meter would weigh less than a gram. One decitex equals 0.9 denier. It is important to appreciate that the division between micro and regular fibers is quite arbitrary. Wool dyers have been making allowances for differences in fiber fineness for more than 50 years. It is also important to note that these are not microdenier fibers, a misnomer which relates to fibers of fineness approximately 10th *6 denier.
What has changed is that man-made fibers can now be made substantially finer than the finest natural fibers and that the magnitude of the difference in fineness possible between micro and regular man-made fibers, and which might confront a dyer, is very much greater than it has ever been. This means that dyers will not simply need to adjust dye formulations slightly to compensate for fibers of different dtex, but they will need to make adjustments which could be several hundred percent in the amounts of dye used to achieve the same apparent depth of shade.
A useful preliminary relationship between the percentages of dye on weight of goods © needed to achieve a particular depth of shade on polyester fibers of two different fineness (dtex) is given bellow:
Here, the subscripts m and r can be used to indicate micro and regular fibers but could also be used to designate any two fibers of different fineness ( denier, dtex). The value of n is normally taken to be 0.5, which means the right hand term of the above equation .
Putting arbitrary values for dtexr (4.5) and dtexm(0.5) into above equation gives:
The liquor ratio will be determined to a large extent by the equipment to be used. It could be as high as 20-30:1 for becks, 5-10:1 for jet dyeing machines and 3-5:1 for package dyeing machines. Continuous padding applications use even less liquor, 0.6-2:1.
The point of departure chosen here is a conservative, generalized procedure for dyeing piece goods in a jet-dyeing machine at 10:1 liquor : goods ratio. A typical standard HT dyeing method might include x% disperse dye(s) owg, a suitable pH buffering system to control pH to 4.5 to 5.5 (e.g., 1 gram per liter ammonium sulfate adjusted, with the bath at full volume, to pH 4.5-5.5 with formic acid); about 0.5 grams per liter of a suitable anionic dispersing agent. Alternatively, acetic acid is frequently used to adjust the pH without the addition of ammonium sulfate, although this is not a true buffer system.
The dyes are dispersed separately in water and added to a bath at about 50-60C (120-140F) containing the ammonium sulfate, the dispersing agent and the goods
The pH is adjusted to approximately 5 with acid and the liquor level to 10:1, while the temperature is raised to 70C (158F ) and the dye liquor is circulated through the goods. This temperature is still below the glass transition temperature and no dyeing will have taken place.
With good circulation, the bath temperature is raised to 130C (266F) at 1.5C (3F) per minute and held there for 60 minutes. The dyebath is then dropped at as high a temperature as possible.
The goods are rinsed and given a reduction clear in a bath containing the equivalent of two grams per liter of both 100% solid caustic soda ( sodium hydroxide ) and hydro ( sodium hydrosulfite, properly known as sodium dithionite ) at 70C for 20 minutes. The last steps in the procedure are rinsing and neutralization.
The process outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. outline is similar to the one given by Schuler except that he used an atmospheric dyeing with carrier as an example. The last decade has seen carrier use in most highly developed countries fall dramatically for obvious environmental reasons. However, in some small commission dyehouses, in garment dyehouses and in some principally cotton goods and single knit goods dyehouses, the cost of purchasing pressure dyeing equipment is still considered to be prohibitive and a rear geard action is being fought against the elimination of carriers, they include defoaming agents for the purpose. Although silicone derivatives are wonderfully efficient defoamers, they are capable of forming water resistant spots on the fiber surfaces if there is any cracking of the emulsions. Their use is to be avoided where practicable.
Chemical Principle of Polyester
Ment of PET with boiling Per causes a change in the morphology of the fibre which appears to involve an increase in the degree of orientation of the fiber. Liquid PER has a lower specific heat and latent heat of vaporization than liquid water so that heating costs are lower for per dyeing. Although the thermal conductivity of liquid PER is lower than that of water to be of little significance since heating of PER dyebaths is mostly carried out by convection rather than conduction. Whereas water, which is polar, having both high permittivity and dipole moment, possesses a unique structure athat influences the conventional dyeing of PET with disperse dyes, PER is non polar and aprotic and does not have any of the particular properties of water with the result that, it is considered, differences may arise between the dyeing processes in the two solvents. Nevertheless as discussed below, a close similarity is found between the mechanism of adsorption of disperse dyes on PET from water and PER. In the context of the role of the solvent in disperse dyeing. Heit obtained curvilinear isotherms for the equilibrium adsorptioin of CI disperse red 1 on to cellulose diacetate at 25C from various organic solvents in which the dye was sparingly soluble and also found that dye uptake varied with the solvent used, which these workers demonstrated was not attributable to differences in fibre swelling caused by the different solvents. The findings of Heit together with the observation of Bird and Harris that this particular dye gave a linear isotherm on cellulose diacetate when applied from an aqueous dyebath, suggests that the solvent from which dyeing occurs may be involved in dye fibre interaction. Thompson from a study of the adsorption of azobenzene on cellulose duacetate when applied from an aqueous dyebath, suggests that the solvent from which dyeing occurs may be involved in dye fibre interaction.
The solubility of disperse dyes in PER, which increases markedly with increasing temperature, differs greatly for different dyes; Milicevic found little correlation between solubility in PER at 121C and partition coefficient on PET and, in a manner indentical to that of aqueous phase transfer, the partition coefficient decreases and the saturation value increases with increasing temperature.
As observed for aqueous dyeing, Datye observed that for the application of several disperse dyes from PER on to PET film, the heats of dissolution of the dyes in both the substrate and PER were positive whilst the heat of dyeing was negative. However, owing to the much greater solubility of disperse dyes in PER than in water, the partition coefficients obtained using PER are considerably lower than those obtained for aquous application, typical values for dyeing from PER being less than 10 as opposed to values of between 30 and 800 obtained typically for aqueous dyeing. Harris and Guion demonstrated that the low partition coefficient observed for CI disperse Violet 1 when applied to PET from PER, was attributable to the close similarity of the total solubility parameter of the dye to that of both the fibre and PER, the suggestion being that owing to the similarity of δt of both the solvent and fibre, the solubility of the dye in each of these phases I similar in magnitude and the dye therefore has little preference for the fiber. The low partition coefficient of the dyes on PET when applied from PER characteristically result in low dye exhaustion and hence low colour yields; since the characteristic low values for K accrue from the high solubility of the dyes in PER, then a reduction in the solubility of the dye in the solvent will therefore increases K and hence increase dyebath exhaustion. Consequently, although dyebath exhaustion increases with decreasing liquor to goods ratio, little suaccess has been achieved using temperatures in the region of 120C owing to the very high solubility of the dyes at these temperatures.
Dye demonstrated that in a manner similar to that observed for diffusion in aqueous systems, the diffusion coefficient of Polyester fiber is as follows:
Uniformed Disperse dye and swelling agent
A process describe for the tone-in-tone printing and pad-dyeing of textile material from fiber mixtures of synthetic and natural material with at least one disperse dye with the use of solvents having swelling properties, which process comprises printing or impregnating the textile material with a printing paste or padding liquor in which one or more disperse dyes have been produced by reaction of coulpling components with diazo components; subsequently subjecting the printing or the dyeing, after intermediate drying, to a heat treatment and finally to the finishing process.
Textile material made form fiber mixtures of natural and synthetic organic material can be dyed by this process whereby suitable natural material is, in particular, cellulose material made from natural and regenerated cellulose, such as hemp, linen, jute, viscose silk, spun rayon or especially cotton.
Suitable synthetic organic materials are, e.g., fiber materials made from synthetic polyamide such as condensation products from hexamethylenediamine and adipic acid ( Polyamide 6.6 ) or subacic acid (Polyamide 6.10); also mixed condensation products, e,g., from hexamuthylenediamine, adipic acid and ε-caprolactam (Polyamide 6.6/6); besides polymerization products from ε-polyester material, e.g., linear high-molecular esters of aromatic polycarboxylic acids with polyfunctional alcohols. Finally, also suitable as synthetic fibre material are cellulose 2.5-acetate fiber and cellulose triacetate fibers.
The textile material preferably dyed or printed by this process is made from fiber mixtures of two constituents (especially polyester and cotton); it is also possible to use fiber mixtures containing three or more fiber materials.
This process is characterized in that the dyes used are nto finished, finely-dispersed disperse dyes, but disperse dyes that are produced actually in the printing paste or padding liquor itself.
A printing paste or padding liquor suitable for the process is obtained by a method wherein a coulpling component is mixed, e.g., in the presence of alkalies, with a pasting agent such as alcohol or Turkey red oil; this mixture is dissolved in water at a temperature of about 10-40C particularly at 15 to 25C, a thickening agent is added, advantageously an anionic or nonionic dispersing agent is then introduced; and finally the diazo component, e.g., in the form of a stabilized color salt or diazotized color base, is added as well as a solvent having swelling properties.
In the printing paste or padding liquor produced in this manner, the formation of the disperse dye occurs as a result of the reaction of the coupling component with the diazo component. The solvent having swelling properties can be added to the printing paste or padding liquor at any point of time; e.g., it can be added at the commencement of the production process as an aqueous solution.
The coupling components to be used can be of varying nature. Suitable compounds are those usable for the production of azo dyes, for example acetoacetic acid amides and acetoacetic acid arylides, hydroxyquinolines, pyrazoles, phenols, napthols, particularly however amino-and /or hydroxynaphthalenes or N-alkyl, N-aryl or N-acyl derivatives thereof, and especially hydroxynaphthoic acid arylamides. Also suitable are amines of the benzene or naphthalene series, coupling in the p-position.
The diazo components to be used are known. Suitable as such are the compounds generally used for producing azo dyestuffs, such as diazotized substituted anilines, naphthylamines, diphenylamines, heteroaromatic amines or diamines of the formula H2N-A-NH2, whereby A can represent the phenylene, naphthylene or diphenyl group, or a group of the formula
where B can be oxygen, sulfur, -NH-, -SO2-, -N=N-, -NHCO- or –NH-CO-NH-. Suitable substituents are, in particular, methyl, chloro, nitro, methoxy, ethoxy, phenoxy, hydroxyl, carboxy, carbalkoxy and carboxylic acid amide groups. Suitable thickening agents are those generally used in thextile printing, such as types of gum, tragacanth, starch ether and carob bean flour derivatives.
The preferable anionic or nonionic dispersing agents which can be added to the printing paste serve in particular to effect a good fine dispersion of the disperse dyes, and hence to render possible the atteainment of better fastness to rubbing. The dispersing agent customarily used in dyeing with disperse dyes can be used. Suitable solvents having swelling properties are glycols or glycol derivatives, especially polyglycols, such as polyethylene glycol.
Example: (a) Production of Printing Paste – 5 grams of the coupling component ot the formula bellow are stirred to a paste with 5 grams of sulfonated castor oil ( Turkey red Oil) and 5 grams of NaOH 36C Be, and the paste dissolved in 187 grams of boiling water.
By the addition of 500 grams of a 4% by weight aqueous solution of carboxy-methylated locust been flour, the solution obtained is thickened to a viscosity of 6,000 to 10,000 cp. There is then added 30 grams of a fatty alcohol oxythylation product (addition product of 18 mols of ethylene oxide with a mixture of alcohols having 11 to 18 carbon atoms). There is finally added, with stirring, a solution of 18 grams of stabilized diazo salt of the amine of the formula shown below in 150 grams of water and coupling is effected. An addition is subsequently made of 100 grams of polyethylene glycol (MW~400).
Chemical Constitution and fastness of Disperse dyes
largely due to the work of Baddiley and Shepardson of British Dyestuffs Corporation and of Ellis’ of British Celanese, when a second group of dyes of simple chemical structure was introduced. These new dyes were prepared by the “colloidal solubilization of insoluble aminoazo and aminoanthraquinone compounds, and were readily absorbed front their aqueous dispersions to give dyeings of satisfactory fastness. These dyes, now commonly known as disperse dyes, are widely used for the dyeing of cellulose, acetate, as well as other synthetic fibers such as polyamides, polyesters, polyacrylonitriles and cellulose triacetates, which have been introduced very recently.
Disperse dyes belong maihnly to three well-defined chemical classes: (a) Nitroarylamine, (b) Azo and (c) Anthraquinone. Most of them contain amino or substituted amino groups and are devoid of solubilizing groups, sycg as SO3Na. in spite of their satisfactory application, properties and tinctorial power, these dyes have certain defects. Some of them tend to sublime at high temperature; some, especially blues and violets belonging to aminoanthraquinones, are affected by the oxides of nitrogen and ozone present in the atmosphere and a few others fade readily when exposed to light. During the early development the relation between the structure and fastness of dyes was not well understood and. Therefore a large number of dyes was synthesized, and only a few with satisfactory fastness were marketed as commercial dyes, in spite of their deficiencies in one or two properties. Recently, however, attention has been given to this relationship and a systematic investigation of the same is being carried out in some of the industrial and technological laboratories. As a necessity, disperse dyes are of low molecular weight in order to fabour diffusion and high solubility in the fibre and have only practical solubility in water. For the same reason it is essential that a disperse dye should not be very soluble in water unless it has a compensating very high solubility in the fibre, as in the case of a Solacet dye which, being a sodium salt of sulphuric acid ester of dye, is soluble in water as well as in the fiber. Not only the molecular weight, but size and shape also have effect on substantives. All these factors put severe limitations on the structural modifications to be made for achieving desired fastness. Quite often a structural change made to achieve good fastness to one agency has an adverse effect on other properties and, therefore, to develop dyes of practical utility is a problem of balancing compromise among several requirements.
The relation between chemical constitution and fastness is a complex one, because of the fact that the fastness not only depends on chemical constitution but also several other factors. Although is is possible to have an approximate idea of the grade of fastness of a particular group of dyes as a whole, such gradation is not so general as to warrant the conclusion that all members in the series have the same grade of fastness Even disperse dyes, which are in a state of molecular dispersion in the fiber substance and are comparatively simple in chemical structure than the dyes belonging to other groups, show considerable variation in their fastness when applied to different fibres. Nevertheless, in this group of dyes this relationship is much more clear than in the other groups of synthetic dyes, and attempts will be made to discuss this in a qualitative way.
The important categories of fastness of disperse dyes are the fastness to light, gas-fumes, sublimation and washing.
1 Light fastness
The effect of light on dyed fabric is a very complicated subject which is not yet clearly understood. The light fastness is influenced not only by the chemical constitution but by several other factors, such as the type and the physical structure of the fiber, the physical state of the absorbed dye, the method of dyeing employed, the nature of bonds holding the dyestuff and the fiber and after treatments likely to be given to the dyed fabric for improving its performance characteristics.
On absorption of light the dye molecule undergoes electronic transition and is converted into an excited state involving either a singlet and/or a triplet state. There is evidence that such an excited molecule of extremely short existence is much more reactive than one in the ground state and reacts or moisture in the atmosphere. To have an idea of such secondary effects, it is necessary to have an idea of the reactivity of the electronically excited molecule. Since it is not possible with the present state of our knowledge to assess this reactivity, it has been extremely difficult to systematize its effect. Moreover, a dye which is resistant on one fiber is faded rapidly on the other. In sojme cases the dye is oxidized by the atmospheric oxygen and in others it is reduced by the substrate. Dyed fabric when exposed to light undergoes changes in two ways involving phototropism and fading. Phototropism is a reversible change in shade shown by some disperse dyes on short exposure to light, the original shade is restored, however on storage of the dyed fabric in the dark. The exact nature of such a change is not known, but it is assumed to involve a transcisre-arangement. Phototropism is much more common in the yellow and orange dyes of the aminoazobenzene series; and it has been found that this defect is reduced by the introduction of strong electron withdrawing groups such as, nitro, cyano, acetyl, in the 4’ position of the aminoazobenzene molecule or by attaching an electron withdrawing group to the amino nitrogen. In this case the reduced basicity of the amino groups seems to have a favorable effect.
The most important problem in the action of light is the fading involving an irreversible change. In the case of disperse dyes, especially, on polyester fiber, it has been found by Shroeder that the best dyes are those which are stable aromatic structures with a minimum of attackable groups. Table 2 giving the light fastness will illustrate this point
Also in the case of anthraquinone disperse dyes on cellulose acetate this structural effect is not so clear-cut. However, when the same dyes are applied on polyester fiber the fading is found to be related to the basicity of the amines. For example, table 3 shows order of fastness obtained for the aminoantharaquinone dyes on polyester fiber.
In general, the fastness to light is dependent on the electron mobility or the π-electron delocalization. The higher is this mobility the lower is the fastness. In the molecule of p-nitrodimethylaminoazobenzene the predominant contributing structure (1) increases the electron mobility and, therefore, its fastness is lower than that of the aminoazobenzene or azobenzene. In a given series, it is possible to extend the range of shade by the introduction of substituents at the resonating positions, however, such modification often results into lower fastness to light
Amino or alkylamino groups are powerful auxochromes and the introduction of such basic groups quite often has an adverse effect on fastness to light as well as on the fastness to gas. Structural changes made to render amines less basic improve light fastness, especially on polyester fiber. Electron withdrawing groups attached to the amino nitrogen or inserted in the ortho position often improve light fastness. Also hydrogen bonding of the amino group with an ortho or peri substutuent containing an electron donor atom has a fabourable effect on light fastness. Among the electron withdrawing froups, the fluoroalkyl groups seem to be very effective, not only on the fastness to light but also on the fastness to gas fading. Dickey and co-workers have synthesized several fluoroalkylaminoantharaquinone dyes and have found that the 2 fluoroalkyl groups improve fastness to light and gas considerably; whereas the alkyl groups, having fluorine atoms on the C3 or C4 atoms, have no additional effect on the above properties. Similarly, the 2,2,2-trifluoroethyl, 2,2-difluoroethyl, and I-(trifluoromethyl) ethyl groups confer excellent light and gas fastness upon the dyes and were found to be decidedly superior to the unfluorinated ethyl group in this respect. Interestingly, the 2,2-difluoropropyl and 3,3-difluoropropyl groups were equal to the ethyl group in effect on light fastness and the 4,4-difluoropropyl groups were equal to the ethyl group in effect on light fastness and the 4,4-difluoropentyl group was inferior to the ethyle group. Similar studies carried out in the azo series have revealed that, generally, the fluoroalkylaminoazonenzenes exhibit greater stability to light than their unfluorinated homologues. Another series to dyes containing CF3 groups in the 2-position of aminoanthraquinone was studied and was foun to have excellent fastness to light and good fastness to gas. In general, the dyes containing a CF3 group were found to be superior to the corresponding dyes having a CN, CONH2, SO2CH3SCH3, or CH3 group. Very recently Ko Naiki has synthesized several disperse dyes of the aminoanthraquinone series and has studied their dyeing and fastness properties. He has found that an electron attractive N-substituent, such as the β-chloroethoxycarbonyl group, increases the light fastness and an electron donating group, such as the β-hydroxyethyl group, decrease the light fastness.
These observations suggest that a substituent which lower the basicity of the amino group modifies the electronic transition of the dye molecule in such a way that the resulting excited state becomes less reactive to lead to secondary ractions with the substrate or the environmental elements and, as a result, the dye structure becomes more resistant to light.
The fastness of disperse dyes belonging to the diphenylamine group can be accounted similarity. These dyes, in spite of their low inctorial value, are used as substitutes for azo yellows which have deficiencies in light fastness and are phototropic. In general, these dyes have excellent fastness to light, excepting the compounds with a para nitro group. The dyes, with an ortho nitro group, however, are resistant to light. In the p-nitro structure there is extended conjugation leading to the higher electron mobility, whereas in the ortho derivative the conjugation is limited. Another favouable factor in the ortho nitro dyes is the possibility of hydrogen bonding which seems to modify the electronic transition and confer on the dye the necessary resistance to light.
To view the details please click and download the article :
0 মন্তব্য(গুলি):
একটি মন্তব্য পোস্ট করুন