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Mordanting Mordants are used to improve the bond between the dye and the fabric, as well as extending the range of hues that can be obtained from the dyestuff. To make the mordant take better, an ‘assistant’ can be added, which may mean less mordant is needed. The main problem is that typical mordants are based on heavy metals which are extremely toxic, causing environmental problems and presenting health threats to workers if not properly trained.
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PREPARED BY ©right Name : MAZADUL HASAN SHESHIR ID: 2010000400008 Batch: 13th Batch (Session 2009-2013) Department: Wet Processing Technology Email: mazadulhasan@yahoo.com Blog: www. Textilelab.blogspot.com Southeast University Department of Textile Engineering
What is Mordant? What is Mordant? A mordant is a chemical binding agent that adheres well to both the fibers and the dye. A mordant is a substance used to set dyes on fabrics by forming a coordination complex with the dye which then attaches to the fabric. A mordant is always a polyvalent metal ion. The resulting coordination complex of dye and ion is colloidal and can be either acidic alkaline. Mordants can be added before, during or after the dyeing process. Most recipes use mordanting before dyeing. The type of mordant used can change the color of both the dye-plus-mordant solution and influence the shade of the final product. Some mordants (FeSO4) darkent the color, some (SnCl2) brighten the color. They improve light and wash fastness properties.
Mordanting Mordanting Mordants are used to improve the bond between the dye and the fabric, as well as extending the range of hues that can be obtained from the dyestuff. To make the mordant take better, an ‘assistant’ can be added, which may mean less mordant is needed. The main problem is that typical mordants are based on heavy metals which are extremely toxic, causing environmental problems and presenting health threats to workers if not properly trained. The main mordants are alum, tin, iron, chrome and copper: alum is non-toxic but is an irritant if inhaled, chrome is poisonous and can provoke an allergic reaction to anyone with sensitive skin, copper is poisonous and has little effect on vegetable fibres, tin is poisonous and an irritant and, despite being used in small quantities, iron is harmful if ingested. Mordants can be obtained from plants, such as oxalic acid which is found in rhubarb leaves, alum which comes from clubmoss, and tannin from oak galls and sumac leaves. As a general rule, the weight of the mordant and the weight of the yarn to be dyed are the same. It takes around 6-8 litres of water to mordant enough yarn for one t-shirt by hand. Vegetable fibres take longer to prepare than animal fibres, making the former’s preparation process more expensive. Vegetable fibres also usually need to be treated with tannic acid before and after scouring.
Common Dye Mordants Mordants are used to set the color when using natural dyes. Different mordants will give different results. Alum (Aluminium Potassium Sulfate): This is the most widely used mordant. The compound is the hydrated aluminium potassium sulfate with the formula KAl(SO4)2.12H2O. Chrome (Potassium Dichromate, K2Cr2O7): Chrome brightens dye colors and is more commonly used with wool than with any other fiber. Extremely toxic material, therefore chrome should not be inhaled and gloves should be worn while working with chrome. Left over mordant water should be disposed of at a chemical waste disposal site and treated as hazardous waste.
Common Dye Mordants Tara Powder (CaesalpiniaSpinosa): Tara powder is a natural tannin product. It is needed for darker colors on cotton, linen and hemp. Tartaric Acid: A must for cochineal. This mordant will expand the cochineal colors. Tin (Stannous Chloride): Tin will give extra bright colors to reds, oranges and yellows on protein fibers. Using too much will make wool and silk brittle. To avoid this you can add a pinche of tin at the end of the dying time with fiber that was pre-mordanted with alum. Tin is not commonly used with cellulose fibers. Copper (Copper Sulfate): This mordant is used to bring out the greens in dyes. It will also darken the dye colors.
Mordant Dyes: Mordant Dyes: Dyes which have no affinity towards textile fibers are attached with the fiber with the help of mordants are known as mordant dyes. Most commonly used mordants are inorganic chromium, so sometimes these dyes are called chrome dyes. Chrome dye is an acid dye, which forms a chelate complex with chromium atoms. Restricted use due to eco-toxicity problems. These dyes have some mordant attracting groups which have some influence on the metal ions. A metal ion takes the place of hydrogen in the –OH or –COOH group in azo dyes. The mordants have affinity both for fiber and dye. So, dyes which have no affinity to fibers can be applied by using suitable modant, as dyes have mordant attracting groups. Fibers most readily dyed with mordant dyes are wool, modacrylic and nylon fibers, in wool dyeing only chromium salt are of importance so mordant dyes used for woold dyeing are usually called chrome dyes.
Properties of Mordant Dyes Properties of Mordant Dyes 1. Mordant dyes have no affinity for textile fibers. They are attached to the fibers with the help of mordants. These mordants have affinity both for the dye and fiber. 2. Mordant dyes are capable of combining with metallic oxides to form insoluble color lakes. 3. Mordant dyes may be natural or synthetic. Natural mordant dyes are obtained from madder, cochineal, logwood etc. Synthetic mordant dyes are marketed as pastes or powders. 4. Mordant dyes are mostly applied on natural protein fibers, nylon and modacrylic fibers. 5. The light, wash fastness of mordant dyes is very good with rating from 4 – 6. 6. Most mordant dyes are soluble in cold water. 7. The main feature of the mordant dye molecule is that there remains a metal ion (mainly chromium) as a central atom which is bonded to neighbouring –OH, -COOH or azo group.
The three methods used for mordanting are: The three methods used for mordanting are: 1. Pre-mordanting (Chrome): The substance is treated with the mordant and then dyed. 2. Meta-mordanting (Metachrome): The mordant is added in the bath itself. 3. Post-mordanting (Afterchrome): The dyed material is treated with a mordant. The type of mordant used changes the shade obtained after dyeing and also affects the fastness property of the dye.
Brief Description of Methods of Application Pre-Mordanting (Chrome Mordant Process): This is a two bath process. In this process the material is impregnated with an insoluble chromium hydrate ( Chromic Oxide Cr2O3.2H2O ) and then dyeing is done in a separate bath. Chrome hydrate is a hydrated form of chromic oxide bound with more or less two molecules of water. It is insoluble in water and compatible with many organic materials.
Brief Description of Methods of Application Meta-mordanting (Chromate Process): In meta-chrome process dyeing and mordanting are carried out simultaneously in the same bath. Here the mordant is present in the form of chromate which does not form the lake with the dye and which is gradually converted into dichromate. The pH of the bath is kept around 6 – 7. This method has the advantage of facilitating shading and requires less time than the after chrome process. Chromates and dichromates are salts of chromic acid and dichromic acid, respectively. Chromate salts contain the chromate anion, CrO42- and usually have an intense yellow color. Dichromate salts contain the dichromate anion Cr2O72- and usually have an intense orange color.
Brief Description of Methods of Application Post-mordanting(After-chrome Process): This is the oldest and the most common mordant dyeing process. Here, the material is first dyed with an acid dye and then mordanting with chromium is carried out in a separate bath or mordanting can be done in the same after exhaustion of the dye has been completed.
Meta-Chrome Dyeing Process There are a certain number of acid mordant dyes which can be dyed and mordanted simultaneously by using metachromemordants contain one part of sodium or potassium dichromate with two parts of ammonium sulphates.
Common recipe: Amount Material 2 – 5% Metachrome Mordants 5 – 10% Glauber’s Salt 250 – 500 gm/l Surface Active Agent Scoured wool is treated in a bath containing the abouve chemicals at 40⁰C for 20 min. After 20 min the dissolved dye is added and the liquor is brought to the boil over a period of 45 min and retained at this temperature for further 60 – 90 min. In case of dyeing heavy shades it is advisable to complete exhaustion by adding 0.5 – 1% acetic acid (40%) 30 minutes before the dyeing is finished. Ammonium acetate may be used in place of ammonium sulphates in the mixture when using colors known to be unlevel dyeing.
Advantages Disadvantages Advantages Disadvantages 1. Dyeing is carried in one stage 2. Less time required 3. High Production 4. Easier shade matching 1. Range of shades is limited 2. In case of unlevel dyeing it is impossible to correct it.
Mordanting Cotton Mordanting Cotton Cotton is very time consuming to mordant. First it needs scouring and then it needs a three step process, with consecutive mordant baths of alum, tannin and then alum again. Scouring Cotton: It is necessary to scour the cotton, even if it is to dye with indigo. Scouring removes the dirt and grease that fibres accumulate during manufacturing and transit. Half fill a 10 litre stainless steel pot with water. Carefully add 35gm soda ash into the pot. Place the wet fabric into the water and stir well with a spoon. Leave the spoon inside the pot to prop the lid slightly open. Bring the water to the boil. Adjust the heat to low boil/hard simmer and allow the fiber to boil half covered for two hours. Stir the fabric every 15 minutes to make sure it is being adequeately scoured. After two hours remove the saucepan from the heat source and allow the fabric to cool down until it can be safely removed from the water. Finally rinse the fabric If necessary the process may be repeated.
Mordanting Cotton with Alum-Tannin-Alum: 100 gm of fabric is used in a 10 liter saucepan. Total weights to mordant 100 gm of fabric: Alum: 50 gm (25 gm in each of Baths 1 & 3) Soda Ash: 12 gm (6 gm in each of Baths 1 & 3) Tannic Acid: 6 gm (for bath 2 only) Pre-wet 100 gm of cotton fabric in warm water for at least two hours.
Bath 1: 1. Fill half of dye pot with water. 2. Bring nearly to boil. 3. Dissolve 25 gm of alum in a small container with boiling water. 4. Slowly add alum to pot and stir well. 5. Weigh out 6 gm of soda ash and add slowly and carefully to the water in the pot. 6. Soda ash causes the water to bubble vigorously. 7. When bubbles have subsided add more hot water to the pot. 8. Add pre-wetted fabric. 9. Heat to simmering point. 10. Simmer for an hour. 11. Stir fabric every fifteen minutes. 12. Leave fibres in the pot for 24 hours. 13. Wring well and dry. 14. Leave the fabric to age for at least a week. 15. When you are ready for the next step, wash the fibre well.
Bath 2 (Tannin): 1. Fill the pot 2/3 with hot water. 2. Dissolve 6 gm of tannic acid in a small container with boiling water. 3. Add tannic acid to pot and dissolve well. 4. Add pre-wetted cotton. 5. Simmer for one hour, leave for 24 hours. 6. Wring well and dry. 7. Leave the fabric to age for at least a week. 8. Wash the fabric well. 9. Bath 3 (Second Alum Bath): 10. Repeat alum mordanting as described for Bath 1.
Mordanting Silk 1. De-gummed silk, that is “prepared for Dyeing” (PFD), should be used. 2. Weigh the silk, using no more than 100 gm of silk for a 10 litre saucepan. 3. Wash it by hand or by washing machine using silk washing liquid. 4. Leave the silk to soak in hot tap water overnight. 5. Next, weigh the alum, using 6% of the weight of dry silk (i.e. for 100 gm of silk use 6 gm of alum). 6. Put the alum in a small container and pour boiling water into the container. 7. Stir it well until the alum has dissolved. 8. Fill a 10 litre saucepan ¾ full with hot tap water. 9. Add the dissolved alum and stir well. 10. Then add the pre-soaked fabrics, which are usually warm from the tap water. 11. Leave the silk in the pot for 48 hours without adding any heat and stir gently and occasionally. 12. At the end of the 48 hours take the silk from the vat and leave it to dry. 13. Keep it for at least a week before washing it and dyeing it.
Mordanting Wool Scouring the wool: 1. Wool needs to be well scoured before it is dipped in the dye pot. 2. To scour wool, fill a bowl with warm water (between 50 and 60⁰C). 3. Add some soap or washing liquid and leave the wool to soak for two hours or overnight, 4. Rinse carefully.
Mordanting with Alum 1. 100 gm scoured wool (dry weight) 2. 8 gm alum 3. 7 gm cream of tartar 4. 10 liter stainless steel stock pot or saucepan. 5. Weigh the wool and leave it to soak in water for at least an hour or even overnight. 6. Fill a saucepan ¾ full of cold water. 7. Pour boiling water into a small heatproof container and add the cream of tartar, stirring it well until it has dissolved then add it to the saucepan. 8. Pour boiling water in a small heatproof container and add the alum, stirring it well until the alum has dissolved. 9. Add the dissolved alum to the saucepan. 10. Add the pre-soaked scoured wool to the saucepan. 11. Raise the temperature of the saucepan slowly to a simmer (87⁰ to 93⁰C) for most wool. Fine wools may need a lower temperature. 12. Simmer gently for an hour. Make sure the fibres are submerged and stir very gently and occasionally. 13. Leave the wool to cool in the saucepan. 14. Dry the wool using a large colander. 15. Put the wool on a towel and let it dry. 16. If ready to dye, rinse the wool well to remove any unfixed alum.
Alizarine Dye Alizarine Dye Among the few naturally occurring dyes madder is extensively used to produce bright red shades. It is named as Turkey Red as it (madder red) was best dyed in Turkey. Alizarin is an organic compound that is historically important as a prominent dye. It is an anthraquinone originally derived from the root of the madder plant. In 1869, it became the first natural pigment to be duplicated synthetically.
Dyeing of cotton with Alizarin The dyeing procedure of cotton with Alizarin Dye (Mordant Dye) is described below: Cotton fabric is boiled in the solution of 1 Part of TR oil 10 parts of water For 12 hours Fabric is dried at 60⁰C for 20 minutes. Treated again with Aluminium Acetate (10 ⁰Tw) at 60⁰C for 2 hours. Dry at 60⁰C for 20 minutes. Again treated with two parts of Sodium Phosphate and 10 parts of water at 40⁰C for 20 minutes. 1 – 1.5% dye (owf) is added in the solution with Calcium Acetate at 25⁰C for 30 min. The fabric is hot rinsed (70⁰C) for 30 minutes. Finally the fabric is washed with soap solution and water and then dried.
