Bamboo Fiber- I

Bamboo is a regenerated cellulosic fiber. There are three types of bamboo fibers:

1. Pure Bamboo

2. Bamboo Charcoal

3. Bamboo Viscose

1. Pure Bamboo

Pure bamboo is produced by physical and mechanical process like linen and hemp. It has high strength and is environment friendly. However it suffers from poor spinnability properties and high cost.

2. Bamboo Charcoal- An application of Nano Technology

In making this fiber, the bamboo is dried and heated at 800 deg. C until it becomes bamboo charcoal. Then the charcoal is sent for further processing to turn it to nano particles. These ultra fine bamboo particles are then embedded into viscose or polyester fiber. The fiber is then drawn into yarn and processed as usual.

Generally nano-bamboo charcoal powder is added during the process of spinning solution.Thus polyester, nylon and viscose fibers can be manufactured embedded with bamboo charcoal fiber.

This fiber has strong adsorption capacity.  It can adsorb bad odor and chemicals. It shows an excellent anti-pilling tendency and the material washes well. It has strong anti-microbial properties. In an actual test of a pair of socks, after wearing without washing for a week, the socks not only have no odor, they were also dry. The disadvantage with this fiber is that it is only available in grey and black colors.

Source 1 2 3 4

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Indigo Dyeing using Fermentation Vat

Some Notes on Indigo Dyeing using Fermentation Vat

1. Indigo itself doesn not exist as such in nature. It is easily formed by oxidation of a a part of plant called IndigoFera by exposure to air. 

2. Simply speaking, Indigo itself is a blue solid. It is insoluble in water, acid and alkalies. If Hydrogen is added to it, or chemically speaking it is "reduced" by many reducing agents- It changes to "Indigo White" which is colorless. This indigo white can dissolve in water, in presence of alkalies, to a bright yellow liquid. When Textile substance is dipped in it and exposed to air, white indigo takes up oxygen and get converted into blue coloring matter. 

3. In fermentation method water is made alkaline with the the addition of Lime or Alkali. Then substances are added which can ferment easily in the presence of alkali, for example wheat bran (madder is added to expedite the fermentation). It takes about two to three days to ferment and then indigo is added. This bath can be used for several days or even weeks. Fresh indigo and other ingredients are added from time to time. The color of bath is light greenish yellow in color with a blue or bluish green scum. Goods immersed in this bath turns yellow. When they are taken out and exposed to air, the yellow color quickly changes to blue.

3. The color of the bath is very important. If it is bright yellow, it means too much alkalanity and more indigo should be added. If the color is too dark, it needs more lime or other alkali. 

4. After the color has changed, the goods should be rinsed well in two or three waters. After that should be boiled for several minutes in a soap bath to washoff the loose dyestuff and prevent rubbing. Rubbing can also be prevented by building up deep shades by successively dippings in the moderately weak vats, rather than obtaining the shade once for all. 

Here are some tips (Source)

1. Keep the vat covered. The level of water in the pot should be to the brim.

2. Wet out your fibers well. Any air remianing in the fiber will oxidise the indigo in the vat. 

3. Enter the fiber into the vat very carefully, to avoid any air in the wet. 

4. Always work under the vat. 

5. For greens, dye with indigo first. Then rise well and overdye with alum mordant and any yellow dye ( traditionally Turmeric). For purples, dye the Indigo first, rise well, mordant and dye with any red dye. 

Remember, you can use various chemicals to  reduce the indigo vat. The alkalnity of these chemicals vary from Soda Ash ( Sodium Carbonate), Slaked Lime ( Calcium Hydroxide), Sodium Hydrosulphide to Caustic Soda ( Sodium Hydroxide) in that order(from low to high). 

Sources

http://www.archive.org/stream/dyesdyeing00exmorich/dyesdyeing00exmorich_djvu.txt

http://www.aurorasilk.com/info/indigo_tutorial.shtml

http://www.pburch.net/drupal/?q=node/909

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Some Notes on Denim Washing

There are four main processes in the Denim washing

- Pretreatment

- Stone or Enzyme Wash- To adjust the surface effect

- Bleaching- To adjust the color

- Finishing- To adjust the handfeel of the garment

Pretreatment involves removal of impurities from the garments and desizing the garment. It also involves prevention of creases in the garment. Wetting Dispersing agent is used in desizing process. It should be able to rapidly wet the jeans so that it can prevent white lines of creases and prevents back staining. Back staining is the redeposition of indigo dyed short fibers, or loose indigo, removed during desizing, stone-washing or enzyme washing. Backstaining reduces the contrast of warp and undyed weft. It also stains pockets and labels and it is more prone ot ozone and yellowing. An anticrease agent is added to prevent crease formation during the washing process. 

Enzyme in garment Industry

Enzyme is a kind of protein. They help the chemical reaction but themselves do not take part in chemical reaction. The starting molecule in a reation is called substrate and the yield molecule is called substate. Enzymes and substrate work like lock-key model so only one enzyme is useful for one type of substrate. Enzymes are better than chemical catalyst because they act in mild conditions such as room temperature. They are also biodegradable. Many enzymes are used in garment washing. An enzyme called Amylase is used in removing starch in desizing. Celullase is used in breaking and removing cellulose fibers. Laccase is used in biobleaching and catalase is used as an anti peroxide. 

Stone and Enzyme Wash

Cellulase weaken the surface fibers which are then mechanically torn off during processing, taking with them indigo. However, they need mechanical action to work. Hence they are used with stones. Cellulase is also used in biopoloshing, which removes surface fibers and make the surface smooth. 

Bleach 

Laccase enzyme decolorises indigo without using bleach. It provides very good contrast and since it attacks only indigo dye and not the fiber so it gives excellent tensile strength. 

Yellowing

The discolouration of textiles, i.e. a change of shade or loss of whiteness, giving a yellow tint, is commonly known as YELLOWING.Yellowing is due to many reasons. Cotton, yellows with age. However aging cannot make severe yellowing happen. Certain lubricants used in weaving and knitting can cause yellowing. The Anti oxidants present in these oils can cause a type of yellowing called as phenolic yellowing. The anti oxidants are also present in packaging materials and silicon softeners. Also temperature of drying and curing during processing can scorch the fibers and cause yellowing. 

Indigo dyed fabrics are more prone to yellowing. Indigo when exposed to NOx or Ozone can produce yellow colored compounds. Indigo itself through simple oxidation can transform into yellow colored compounds. 

There are specialised anti-yellowing softeners available. This work by either forming a protective filem, or by reacting the pollutants to form colorless compounds.

The source of these notes this presentation. This also contains images and chemical reactions. You can also view images of various denim washes here. One more resource is here.

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Resources for Textile Technology Students

If you are a student of textile technology, you will find this site very useful. The owners of the sites are themselves textile students who have put together all the resources at one place.

While surfing I came across one more site, again very useful for textile students.

Please do not miss their blog.


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