Microwave dyeing is a speedy way to dye fabric when space or time is limited for a more involved method. This is a fast, easy dyeing technique for small items. Only use microwave safe items while dyeing (never use fabric with metal trim including zippers or buttons). Microwave dyeing takes into account only the dielectric and the thermal properties. The dielectric property refers to the intrinsic electrical properties that affect the dyeing by dipolar rotation of the dye and influences the microwave field upon the dipoles. This is a terrific method of dyeing small amounts of fabric in the microwave using ‘Procion dyes’.
The aqueous solution of dye has two components which are polar, in the high frequency microwave field oscillating at 2450MHz. It influences the vibrational energy in the water molecules and the dye molecules. The heating mechanism is through ionic conduction, which is a type of resistance heating. Depending on the acceleration of the ions through the dye solution, it results in collision of dye molecules with the molecules of the fiber. The mordant helps and affects the penetration of the dye and also the depth to which the penetration takes place in the fabric. This makes microwave superior to conventional dyeing techniques.
In the electromagnetic spectrum, between radio waves and infrared radiation, the wavelengths between 1 m and 1 mm (analogous to a frequency from 300 MHz up to 300 GHz) are occupied by microwave frequencies (Figure 2). As a form of electric heating, microwave heating is assumed to be generation of heat in conductive materials with low electricity by the action of a high-frequency electric field.
Because of its similar physical properties, microwave heating must be observed as a form of dielectric heating. In response to high-frequency field polarity changes, dipole molecules experience oscillations with the alternating field influence.
In comparison with chemical bond energy, microwave photon energy is low; thus, the molecular structure of a compound is not directly affected by microwaves and its electronic configuration is unaltered. Microwave heating is an alternative to conventional heating, producing fast, effective, and uniform heating due to penetration of material particles by microwave energy. Microwave energy is directly and internally absorbed by materials in volumetric heating and converted into heat, leading to rapid, controlled, selective, and uniform heating. In addition to this, diffusion of dye molecules is enhanced by microwave heating, increasing the rate of dye fixation in polymeric textiles.
Dielectric and thermal properties are the properties considered in microwave dyeing. The dielectric property is the intrinsic electric property that causes dyeing through dipolar rotation of the dye and the influence of the microwave field on dipoles. There are two polar components in an aqueous dyeing solution, and the high-frequency microwave field oscillates at 2450 MHz, stimulating the vibrational energy in the molecules of water and dye. This mechanism of heating results in ionic conduction, a type of resistance heating. The resultant collision of dye molecules and fiber molecules is subject to acceleration of ions through the dye solution. The penetration of the dye into the fabric and the depth of the penetration are enhanced by the mordant, making this technique both environmentally benign and superior to conventional dyeing techniques. The microwaves accelerate a huge number of chemical processes. Reactions that run for a long time at high temperatures under conventional conditions are mostly achieved more quickly with less energy input in microwave assisted dyeing, as microwave heating is volumetric heating (which is fast), while conventional heating is surface heating (which is slow) (Figure 3).
Equipments for Microwave Dyeing:
- Procion Dye,
- Jam Jars /small Bowls / containers for mixing,
- Soda Ash,
- Bicarbonate of Soda,
- Plastic sheeting (or surface protector),
- Sample fabrics such as cotton, linen, viscose,
- Brushes / foam applicators or spray bottle,
- Microwaveable container,
- Cling film,
- Gloves, and
Microwave Dyeing Procedure:
- Weigh the dry yarn or fiber to be dyed.
- Thoroughly soak the fiber/yarn to be dyed (minimum 1 hour in hot water or preferably overnight in cold)
- Shake dye container thoroughly and Measure the correct amount of dye powder for the weight (when using Landscape or Gaywool dyes, use 10 grams to 100 grams of fiber – 2 x 5 mil. Measuring spoons full – mix the dye powder in about ¾ of a cup of hot water and stir thoroughly. NB. If you are using 2 different colors to random dye, then you will need to mix 5 grams per 100 grams of fiber of each color.
- To random dye, place dripping fiber in a wide shallow microwave safe container such as pyrex. Spread out fiber to cover the base in one thickness only if possible.
- Pour most of dye over one end of fiber, and other color over the other end. Use the back of a spoon to push the fiber down into the pool of dye and spread it around, leaving a white section between the colors.
- Cover loosely (steam must escape but you don’t want splatters) and cook on high for up to 6 minutes (dependent on power of m/w) – should have steam condensed over lid and be very hot. Remove from m/w, remove lid, turn fiber over with tongs, add the remainder of the dye (dyes) on the underside or any white spots, then add about a cup of water with tbsp white vinegar in it.
- Recover the dish and again cook on high for 6 minutes.
- Leave fiber in container to thoroughly cool. (Half your dye-fixing happens during the cooling down process) All dye should be absorbed into the fiber leaving just cloudy water. (Except, if you have used turquoise or bright pink, when you will have some residue in the water).
- Rinse thoroughly in cold or tepid water until water runs clear.
- Dry in shade – if yarn, then hanging, if fiber then flat on a table and open with fingers before it is dry.
- To even dyeing, premix dye and add to several cups of cold water in the container to be used (enough to well cover the textile fiber). Stir thoroughly and then add wet fiber. Move fiber around in the dye mixture for a minute or so before cooking. Again give it 5 or 6 minutes, turn and add vinegar, then re cook as above.
Landscape and Gaywool dye all animal fibers (wool, silk, mohair, alpaca, etc.,) as well as nylon, but not other synthetics or cotton. For these you need another type of dye. The Iberia range of dyes can be used for most synthetics and natural fibers.
Limitations / Problems of Microwave Assisted Dyeing:
- Yarn is supposed to be even color but is patchy with a light band under the ties. Yarn is tied too tightly (should be fig. 8 ties loose enough to spread out into a flat ribbon).
- Yarn is an uneven depth of color, either dye was not completely stirred in, yarn was not thoroughly wetted out or there was not enough liquid for good circulation of dye.
- Yarn is colored but a lot of color remains in the water. Cooking time was not long enough, or hard water was used – try adding more vinegar. Usual cause is yarn taken out of liquid before it has cooled – wastes dye!
- Yarn is right color but a lot of dye rinses out. Too much dye powder used for weight of fiber. NOTE; When using turquoise (Opal or Iris or Kingfisher), or Galah (bright pink) use 1/3rd less dye than usual and give at least 3 rinses.
- Sustainable Textiles: Production, Processing, Manufacturing & Chemistry by Subramanian Senthilkannan Muthu
- Sustainability in Textile Dyeing: Recent Developments By Aravin Prince Periyasamy and Jiri Militky
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.