Monday, November 16, 2009
Mineral colors
Mineral color contains metallic insoluble precipitates, which are deeply colored. These insoluble precipitates have found great application as pigment for paint. For other purposes of dyeing, the precipitates themselves are not used but they actually created in and on the fibers from the soluble substances
Examples:
Mineral colors are very limited, only about half a dozen are valuable to dyes or printers:
• Chrome yellow
• Chrome orange
• Chrome green
• Iron buff
• Prussian blue
• Manganese blue
Requirements for dyeing with mineral color
• They should be dyed under special conditions avoiding metallic contact
• They shouldn’t be wet handled
• They must be padded evenly.
• They shouldn’t have any crease before drying.
• During production of mineral khaki metal surface is used, acidity must be well controlled and pH must be adjusted to 4.
Advantages
• Very simple to apply
• Lower cost
• Easily available
Disadvantages
• Less affinity to fibers, so mechanical pressures in between the roller is required
• For commercialization some technical experience is required
• Tendering may happen due to uncontrolled pH
Mineral Khaki
A combination of iron buff and chrome green in proper proportions produces mineral khaki, which is extensively used for military uniforms. It has excellent fastness to light and wash.
Dyeing procedure
• The cotton is padded with solution containing FeSO4
• Now treated with boiling solution of Na2CO3.
• Now wash
FeSO4 + 2NaOH Fe(OH)2 + Na2SO4
Cr2(SO4)3 + 6NaOH Cr(OH)3 + 3Na2SO4
• Now the fabric is aired for the conversation of Chromium hydroxide to Chromium oxide and Ferrous hydroxide into Ferric oxide by atmospheric oxygen.
Cr(OH)3 [O] Cr2O3
Fe(OH)2 [O] Fe2O3
These oxides then combine to give khaki shade.
Recipe:
For 1% shade of khaki or Procion Yellow M4GS: 0.25%
Indanthrene yellow FSI : 0.5% Procion Blue M85GS: 0.50%
Indanthrene Black Brown NI: 0.5% Procion Brown: 0.25%
NaOH: 16 gm/L NaCl: about 35g/L
Hydrose: 5 gm/L Na2CO3: 3 gm/L
M:L = 1:5
Temp: 80 – 100°C
Time: 60- 90 min
Posted by Chariots of knowledge
Oxidation color
Some dyestuffs like aromatic amine, diamine, aminophenol etc found as intermediate compounds, which rapidly produce the final color through oxidation in the fiber substances; this class of dye is known as oxidation colors.
Oxidation colors high molecular wt., water insoluble ingrain colors. Water insoluble species is produced by oxidation reaction performed on aromatic amines and diamines.
Important Oxidation colors:
1. Aniline black
2. Diphenyl black
3. Solaniline black
4. paramine brown
5. Fuscamine brown
Why oxidation color is called ingrain dye?
Ingrain dyes are, by definition, any water insoluble colors formed in situ (on the fabric) from water soluble intermediate i.e. the dyes which are developed on fiber but they are not readymade.
The oxidation colors are formed from water soluble oxidation amines, which formed the final color on fabric through oxidation. Thus they are not readily available, but as intermediate compounds. Hence they are called ingrain dyes.
Aniline Black
Aniline black, the oxidation product is the important member of oxidation color for textile use. It is called oxidation aniline color. It is invented in 1863 with sodium chlorate and copper sulfate etc.
Aniline black dyeing and prints produce some of the most intense blacks: These colors are almost completely color stable to acids, bases and exposure to light. By far, the greatest use of aniline black is dyeing and calico printing for cotton. Silk and wool are dyed only when extensive precautions are taken against tendering.
Reagent used for dyeing
1. Soluble sat of aromatic amine: aniline or n aminophenylamine, anyline hydrochlorides
2. oxidising agents: NaClO3, KClO3, NaHCO3, KMnO4 etc.
3. Catalyst/Oxidation carrier: CuSO4, CuS, FeCl3, potassium ferricyanide
4. Hygroscopic agent: NH4Cl
5. Migration inhibitor: Na-alginate, gum etc
6. Acid liberating agent: HCl
Classification of Aniline Black:
Based on method of dyeing and chemical used:
1. Prussiate Black/Steam Aniline Black:
Oxidation catalyst: Na4[Fe(CN)6] sodium Ferro cyanide (yellow prucciated of soda, hence the name)
Oxidation by NaClO3
Color produced by steaming (> 98ºC, 5min)
2. Diphenyl Black/Copper Sulfide Aniline Black
CuS as catalyst
NaClO3 as oxidizing agent
3. Chromate Aniline
4. Aged Aniline black
Dyeing Method
Recipe:
Aniline Black 8-10%
HCl: 15%
K2Cr2O7: 10%
CuSO4: 4%
Temperature: 100C
Time 90min
M:L = depends on machine
Procedure:
• First make solution with aniline and hydrogen chloride (sometimes paste preparation). Add water to make proper solution; if necessary boil to make clear solution.
• Potassium dichromate solution is made and added to dyebath
• The material is impregnated with this solution at room temperature for 30min
• CuSO4 solution is made and is added to dyebath
• Temperature rises slowly to boiling and dyeing for 30-45min
• The substance is hot air aged with removal of the hydrogen chloride fumes. There are also emissions of volatilized amine. Temperature should not be violently fluctuated
• Oxidation occurs during drying process and the dye becomes fixed.
• Good penetration is possible since the salt of dyestuffs has no fiber affinity.
After treatment
1-2% soaping at 100°C for 10 -15min
Wash and dry
For aniline black: 5gm/L solution of dichromate or bisulfite is necessary which will not develop green tint and also molecular wt is increased by 10%.
Thus dyeing of aniline black on cellulosic fiber fabric includes four steps:
1. impregnation with the aniline liquor
2. Drying of the impregnated fabric
3. developing either by ageing or steaming
4. after treatment
Defects
1. Tendering: Presence of mineral acid causes formation of oxycellulose and hydrocellulose
2. Greeninsh color: lack of proper oxidation
Remedies - a chroming treatment with sulfuric acid
3. Bronziness: presence of excess acid causes reddish tone turn the black shade bronzy.
Remedies – treatment with a dilute solution (0.05%) of tannic acid and then dried without washing
Advantages
• Jet black dyeing on cellulose are main use
• can produce more deep color
• for some shade, vat black are 5-10% expensive by weight
• less tendering than sulfur and vat black
• Rapid color develops during steaming
• No corrosion of boiler
• almost completely color stable to acids, bases and exposure
• reduction of time
Disadvantages
• Loss of cellulosic strength due to sulfuric acid form
• effluent treatment is difficult
• more chemical may cause dyeing problem
• dye range is limited
Mordant Dyeing
The term ‘mordant’ is derived from the Latin ‘mordeo,’ which means to bite or to take hole of. Mordant dye have no affinity to textile fiber, they are attached by a mordant, which can be an organic or inorganic substances. The most commonly used mordant is inorganic chromium, so sometimes this dye is called chrome dyes. Other inorganic mordants are Al, Cu, Fe and organic mordant. Tannic acid is rarely used.
Mordant improves the fastness of the dye on the fibre such as water, light and perspiration fastness. The choice of mordant is very important as different mordants can change the final colour significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. Fiber most readily dyed with mordant dyes are the natural protein fibers, particularly wool and sometime synthetic fibers modacrylic and nylon.
It is often noted that when a mordant dye forms a lake with a metal, there is a strong colour change. This is because metals have low energy atoms. The incorporation of these low energy atoms into the delocalised electron system of the dye causes a bathochromic shift in the absorption. It is this delocalised electron system which is fundamentally responsible for colour in dyes. Since different metal atoms have differing energy levels, the colour of the lakes may also differ.
The most commonly used mordant dye is undoubtedly hematein (natural black 1), whose status as a natural product supercedes its mode of dyeing, apparently. Others are eriochrome cyanine R (mordant blue 3) and celestine blue B (mordant blue 14), both used as substitutes for alum hematoxylin but with a ferric salt as the mordant. Alizarin red S (mordant red 3) is valuable for the demonstration of calcium, particularly in embryo skeletons
Reason for so named
Some natural and synthetic dyes can be applied or fixed on wool and other textile fibers with the help of an auxiliary chemical called a mordant. These dyes are therefore called mordant dyes.
The mordant have affinity both for a fiber can be applied by using a mordant.
In wool dyeing, only chromium salts are of importance and hence mordant dyes for wool are usually called chrome dyes.
Classification
On the basis of origin
1. Natural: Alizarine
2. Synthetic: Acid chrome
1. Natural Mordant dye
Alizarine: Alizarine is an example of natural mordant dye. It is obtained from the root of the madder. Alizarine is known as polygenetic mordant dye because it develops a variety of colors on different mordants.
Mordant Color
Al Red
Sn pink
Fe Brown
Cr puce brown
Cu yellowish brown
Haematin: this is extensively used before and only one still in use found from logwood. It yield navy blue or black colors of good fastness with chromium compounds. This is used in nylon and wool.
Recipe: haematin dye: 8-10%
Acetic acid: 1cc/l [pH 4-6]
temperature: 50-90°C
Time: 2hr
As it is time consuming process, the natural mordant dyes are used in lesser extent.
2. Acid mordant dyes:
Acid color + chromium = acid chrome
Few dihydroxy azo dyes could co-ordinate so easily with chromium and they could be dyed as acid dyes and mordanted by aftertreatment with K or Na dichromate. Such dyestuffs are known as the acid mordant dyes & are used extensively for wool & also for polyamide fibers.
They have good wet fastness and most of them possess satisfactory light fastness.
Methods of dyeing:
There are three general methods of application of mordant dyes as described below:
1. Chrome mordant process: two bath process
First bath: mordanting with insoluble chromium hydrate
2nd bath: dyeing
2. Afterchrome process: two bath/single bath process
First bath: dyeing
2nd bath: mordanting with chromium
3. Methachrome (or chromate) process
Dye + mordant (dichromate) in same bath
Mechanism of dyeing
Fig shows an example of mordant dye and shows the formation of dye mordant complex. The chromium cation has a valency of 6 (i.e. 6 bonds) which represented by six lines toward the chromium cation.
The mordant dye is shown to the Cr cation by three of the six bonds. The other three bonds have molecules of water attached to them. It is thought that the three molecules of water are there as an intermediate step only and will gradually be water replaced by another mordant dye anion. Thus two mordant dye molecules form a complex with the Cr cation to form a lake or a dye chromium complex. The formation of these relatively large complexes results in very good wash fastness of dye.
Dyeing procedure of Alizarine dyes
· Boil cotton fabric in solution of 1 part TR oil and
10 part water for 12 hrs
· Dry at 40-60°C
· Treat again with 10°Tw acetate at 60°C for 2hrs
· Dry at 40-60°C
· Again treat with 2 part Sodium phosphate
10 part water at 30-45°C
· Dye 1-1.5% shade with calcium acetate at room temperature for 20 mins
· Wash for 30 min at 70°C
· Soap wash, dry
Dyeing of wool with synthetic mordant:
Dyeing recipe
Dye 1-5%
Acetic acid (80%): 2-5% [pH 4-5]
Glauber salt: 10-25%
H2SO4: 1%
L:R= 1:20
Time 45-60 min
Mordanting recipe:
K dichromate: 2%
Temperature: 80-100°C
Time 45 min
M:L = 1:20
Dyeing procedure
· Prepare the dye bath with acetic acid and glauber salt.
· Temperature of the bath is raised to 50-60°C and the goods are entered
· The liquor is brought to boil for 30 min
· H2SO4 is now added to complete exhaustion and boiling is continued for another 30 mins
· When dye bath is exhausted and boiling has been continued for long enough for the color to be level, the temperature is allowed to drop and Potassium dichromate is added
· Chroming is continued at boil for 30 min
It is extremely important to make certain that goods are dyed uniformly before the dichromate is added because there will be no further migration afterward. The dye liquor must also be virtually exhausted before mordanting, because of dye remains in solution it will be precipitated on the surface of the fibers in form of its insoluble lake and cause poor rubbing fastness.
Disadvantages:
· Color matching is difficult as the process of mordanting means that the color builds up gradually
· Length periods of applications are both detrimental to protein and polyamide fibers and rather costly.
· Dichromate salts become pollutants once they are discharged into sewerage.
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Rayon Fiber (Viscose)
Rayon Staple Fiber
Rayon Textile Filament Fiber
Rayon Industrial Filament Fiber
First
Current U.S Rayon Fiber Producers: None currently
Federal Trade Commission Definition for Rayon Fiber: A manufactured fiber composed of regenerated cellulose, in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. (Complete FTC Fiber Rules here.)
Basic Principles of Rayon Fiber Production — In the production of rayon, purified cellulose is chemically converted into a soluble compound. A solution of this compound is passed through the spinneret to form soft filaments that are then converted or “regenerated” into almost pure cellulose. Because of the reconversion of the soluble compound to cellulose, rayon is referred to as a regenerated cellulose fiber.
There are several types of rayon fibers in commercial use today, named according to the process by which the cellulose is converted to the soluble form and then regenerated. Rayon fibers are wet spun, which means that the filaments emerging from the spinneret pass directly into chemical baths for solidifying or regeneration.
Viscose rayon is made by converting purified cellulose to xanthate, dissolving the xanthate in dilute caustic soda and then regenerating the cellulose from the product as it emerges from the spinneret. Most rayon is made by the viscose process.
Viscose Process
Most commercial rayon manufacturing today utilizes the viscose process. This process dates to the early 1900s, with most of the growth in production occurring between 1925 and 1955. In the early period, production was mainly textile filament, although the first staple was produced in 1916. High performance rayons, such as tire cord, did not appear until the late 1930s, with the advent of hot-stretching and addition of larger amounts of zinc to the spin bath. Invention of modifiers in 1947 brought on super tire cords and marked the beginning of the high-performance rayon fibers.
All of the early viscose production involved batch processing. In more recent times, processes have been modified to allow some semi-continuous production. For easier understanding, the viscose process is a batch operation. Click on each process step for a brief explanation.
Cellulose
Purified cellulose for rayon production usually comes from specially processed wood pulp. It is sometimes referred to as “dissolving cellulose” or “dissolving pulp” to distinguish it from lower grade pulps used for papermaking and other purposes. Dissolving cellulose is characterized by a high a -cellulose content, i.e., it is composed of long-chain molecules, relatively free from lignin and hemicelluloses, or other short-chain carbohydrates.
Steeping
The cellulose sheets are saturated with a solution of caustic soda (or sodium hydroxide) and allowed to steep for enough time for the caustic solution to penetrate the cellulose and convert some of it into “soda cellulose”, the sodium salt of cellulose. This is necessary to facilitate controlled oxidation of the cellulose chains and the ensuing reaction to form cellulose xanthate.
Pressing
The soda cellulose is squeezed mechanically to remove excess caustic soda solution.
Shredding
The soda cellulose is mechanically shredded to increase surface area and make the cellulose easier to process. This shredded cellulose is often referred to as “white crumb”.
Aging
The white crumb is allowed to stand in contact with the oxygen of the ambient air. Because of the high alkalinity of white crumb, the cellulose is partially oxidized and degraded to lower molecular weights. This degradation must be carefully controlled to produce chain lengths short enough to give manageable viscosities in the spinning solution, but still long enough to impart good physical properties to the fiber product.
Xanthation
The properly aged white crumb is placed into a churn, or other mixing vessel, and treated with gaseous carbon disulfide. The soda cellulose reacts with the CS2 to form xanthate ester groups. The carbon disulfide also reacts with the alkaline medium to form inorganic impurities which give the cellulose mixture a characteristic yellow color – and this material is referred to as “yellow crumb”. Because accessibility to the CS2 is greatly restricted in the crystalline regions of the soda cellulose, the yellow crumb is essentially a block copolymer of cellulose and cellulose xanthate.
Dissolving
The yellow crumb is dissolved in aqueous caustic solution. The large xanthate substituents on the cellulose force the chains apart, reducing the interchain hydrogen bonds and allowing water molecules to solvate and separate the chains, leading to solution of the otherwise insoluble cellulose. Because of the blocks of un-xanthated cellulose in the crystalline regions, the yellow crumb is not completely soluble at this stage. Because the cellulose xanthate solution (or more accurately, suspension) has a very high viscosity, it has been termed “viscose”.
Ripening
The viscose is allowed to stand for a period of time to “ripen”. Two important process occur during ripening: Redistribution and loss of xanthate groups. The reversible xanthation reaction allows some of the xanthate groups to revert to cellulosic hydroxyls and free CS2. This free CS2 can then escape or react with other hydroxyl on other portions of the cellulose chain. In this way, the ordered, or crystalline, regions are gradually broken down and more complete solution is achieved. The CS2 that is lost reduces the solubility of the cellulose and facilitates regeneration of the cellulose after it is formed into a filament.
Filtering
The viscose is filtered to remove undissolved materials that might disrupt the spinning process or cause defects in the rayon filament.
Degassing
Bubbles of air entrapped in the viscose must be removed prior to extrusion or they would cause voids, or weak spots, in the fine rayon filaments.
Spinning - (Wet Spinning)
The viscose is forced through a spinneret, a device resembling a shower head with many small holes. Each hole produces a fine filament of viscose. As the viscose exits the spinneret, it comes in contact with a solution of sulfuric acid, sodium sulfate and, usually, Zn++ ions. Several processes occur at this point which cause the cellulose to be regenerated and precipitate from solution. Water diffuses out from the extruded viscose to increase the concentration in the filament beyond the limit of solubility. The xanthate groups form complexes with the Zn++ which draw the cellulose chains together. The acidic spin bath converts the xanthate functions into unstable xantheic acid groups, which spontaneously lose CS2 and regenerate the free hydroxyls of cellulose. (This is similar to the well-known reaction of carbonate salts with acid to form unstable carbonic acid, which loses CO2). The result is the formation of fine filaments of cellulose, or rayon.
Drawing
The rayon filaments are stretched while the cellulose chains are still relatively mobile. This causes the chains to stretch out and orient along the fiber axis. As the chains become more parallel, interchain hydrogen bonds form, giving the filaments the properties necessary for use as textile fibers.
Washing
The freshly regenerated rayon contains many salts and other water soluble impurities which need to be removed. Several different washing techniques may be used.
Cutting
If the rayon is to be used as staple (i.e., discreet lengths of fiber), the group of filaments (termed “tow”) is passed through a rotary cutter to provide a fiber which can be processed in much the same way as cotton.
Other forms of regenerated cellulose fibers that are classified by the Commission as rayon without separate, distinctive names include high wet modulus rayon, cuprammonium rayon and saponified rayon.
High wet modulus rayon is highly modified viscose rayon that has greater dimensional stability in washing.
Cuprammonium rayon is made by converting the cellulose into a soluble compound by combining it with copper and ammonia. The solution of this material in caustic soda is passed through the spinneret and the cellulose is regenerated in the hardening baths that remove the copper and ammonia and neutralize the caustic soda. Cuprammonium rayon is usually made in fine filaments that are used in lightweight summer dresses and blouses, sometimes in Combination with cotton to make textured fabrics with clubbed, uneven surfaces.
When extruded filaments of cellulose acetate are reconverted to cellulose, they are described as saponified rayon, which dyes like rayon instead of acetate.
Rayon Fiber Characteristics
- Highly absorbent
- Soft and comfortable
- Easy to dye
- Drapes well
The drawing process applied in spinning may be adjusted to produce rayon fibers of extra strength and reduced elongation. Such fibers are designated as high tenacity rayons, which have about twice the strength and two-thirds of the stretch of regular rayon. An intermediate grade, known as medium tenacity rayon, is also made. Its strength and stretch characteristics fall midway between those of high tenacity and regular rayon.
Some Major Rayon Fiber Uses
- Apparel: Accessories, blouses, dresses, jackets, lingerie, linings, millinery, slacks, sportshirts, sportswear, suits, ties, work clothes
- Home Furnishings: Bedspreads, blankets, curtains, draperies, sheets, slipcovers, tablecloths, upholstery
- Industrial Uses: Industrial products, medical surgical products, nonwoven products, tire cord
- Other Uses: Feminine hygiene products
General Rayon Fiber Care Tips — Most rayon fabrics should be dry-cleaned, but some types of fabric and garment construction are such that they can be hand or machine washed. For washable items, use the following as a guide:
- Fabrics containing rayon can be bleached; some finishes, however, are sensitive to chlorine bleach.
- Use mild lukewarm or cool suds. Gently squeeze suds through fabric and rinse in lukewarm water. Do not wring or twist the article.
- Smooth or shake out article and place on a non-rust hanger to dry. Rayon sweaters should be dried flat.
- Press the article while damp on the wrong side with the iron at a moderate setting. If finishing on the right side is required, a press cloth should be used.
- Between wearings, rayon articles may be pressed with a cool iron. (For specific instructions, refer to garment's sewn-in care label.)
Textile Manufacturing
Weaving is a textile production method which involves interlacing a set of longer threads (called the warp) with a set of crossing threads (called the weft). This is done on a frame or machine known as a loom, of which there are a number of types. Some weaving is still done by hand, but the vast majority is mechanised.
Knitting and crocheting involve interlacing loops of yarn, which are formed either on a knitting needle or on a crochet hook, together in a line. The two processes are different in that knitting has several active loops at one time, on the knitting needle waiting to interlock with another loop, while crocheting never has more than one active loop on the needle.
Braiding or plaiting involves twisting threads together into cloth. Knotting involves tying threads together and is used in making macrame.
Lace is made by interlocking threads together independently, using a backing and any of the methods described above, to create a fine fabric with open holes in the work. Lace can be made by either hand or machine.
Carpets, rugs, velvet, velour, and velveteen, are made by interlacing a secondary yarn through woven cloth, creating a tufted layer known as a nap or pile.
Felting involves pressing a mat of fibres together, and working them together until they become tangled. A liquid, such as soapy water, is usually added to lubricate the fibres, and to open up the microscopic scales on strands of wool.
Acetate Fiber
Acetate can refer to cellulose acetate, especially fibers or other derived products.
Cellulose acetate or acetate rayon fiber (1924) is one of the earliest synthetic fibers and is based on cotton or tree pulp cellulose ("biopolymers"). These "cellulosic fibers" have passed their peak as cheap petro-based fibers (nylon and polyester) and have displaced regenerated pulp fibers.
It was invented by two Swiss brothers, Doctors Camille and Henri Dreyfus, who originally began chemical research in a shed behind their father's house in
Acetate fiber characteristics
- cellulosic and thermoplastic
- selective absorption and removal of low levels of certain organic chemicals
- easily bonded with plasticizers, heat, and pressure
- acetate is soluble in many common solvents (especially acetone and other organic solvents) and can be modified to be soluble in alternative solvents, including water
- hydrophilic: acetate wets easily, with good liquid transport and excellent absorption; in textile applications, it provides comfort and absorbency, but also loses strength when wet
- acetate fibers are hypoallergenic
- high surface area
- made from a renewable resource: reforested trees.
- can be composted or incinerated
- can be dyed, however special dyes and pigments are required since acetate does not accept dyes ordinarily used for cotton and rayon (this also allows cross-dyeing)
- resistant to mold and mildew
- easily weakened by strong alkaline solutions and strong oxidizing agents.
- can usually be wet cleaned or dry cleaned and generally does not shrink
Major industrial acetate fiber uses
- apparel: blouses, dresses, linings, wedding and party attire, home furnishings, draperies, upholstery and slip covers
- high absorbency products: diapers, feminine hygiene products, cigarette filters, surgical products, and other filters
Production
The Federal Trade Commission definition for acetate fiber is "A manufactured fiber in which the fiber-forming substance is cellulose acetate. Where not less than 92 percent of the hydroxyl groups are acetylated, the term triacetate may be used as a generic description of the fiber."
Acetate is derived from cellulose by deconstructing wood pulp into a purified fluffy white cellulose. The cellulose is then reacted with acetic acid and acetic anhydride in the presence of sulfuric acid. It is then put through a controlled, partial hydrolysis to remove the sulfate and a sufficient number of acetate groups to give the product the desired properties. The anhydroglucose unit is the fundamental repeating structure of cellulose and has three hydroxyl groups which can react to form acetate esters. The most common form of cellulose acetate fiber has an acetate group on approximately two of every three hydroxyls. This cellulose diacetate is known as secondary acetate, or simply as "acetate".
After it is formed, cellulose acetate is dissolved in acetone into a viscose resin for extrusion through spinnerets (which resemble a shower head). As the filaments emerge, the solvent is evaporated in warm air via dry spinning, producing fine cellulose acetate fibers.
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