Tuesday, 16 February 2010
Ergonomics in Apparel Industry
Workers involved in sewing activities such as manufacturing garments, are at a risk of developing musculoskeletal disorders. Therefore it is imperative that the design of sewing station, stitching, finework,scissor work and material handling should be ergonomically appropriate. This site talks about ergonomical solutions for the same. A lot of sketches and diagrams are given for easier understanding. Some very quick rules of thumb can be derived from the sketches:
1. Chair Height is correct when the work surface is at elbow height and the sole of the foot should rest on the floor.
2. Schedule frequent and short breaks to stretch and change position.
3. Height and Tilt adjustable tables help employees access their work without using awkward postures.
4. Edges of work surfaces should be padded or rounded, so that the workers can rest their arms against them.
5. Use of Adjustable task lighting and magnifying glasses at workstation can take care of fine work inspection.
6. Shorter width table should be used for scissorwork so that the workers dont have to bend and reach so far.
7. Lifting of weight should be done at waist level.
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Monday, 15 February 2010
Distinguishing Linen from Cotton
The Following are the basic differences on the basis of which we can distinguish Linen from cotton:
1. Linen is about 20% more heavy than cotton.
2. It has a leathery feeling that is absent in cotton .
3. Cotton feels warmer(about 15-30% warmer) and holds heat better than linen.
4. On holding linen against light, the threads and the fibers composing the threads appear uneven and streaked as it is not possible to make linen yarn as uniform as cotton yarn.
5. On burning a linen thread, the fibers lie in the same position as before with no change except the scorched appearance. Burning a cotton thread causes the fibers to spread like a tuft.
6. Linen absorbs oil much better than cotton. To distinguish Linen with cotton in a piece of fabric, first remove all the impurities by washing and boiling. Then when if the fabric is dipped in oil, the linen fibers look transparent if held against the light. The Cotton remains nearly opaque.
7. Linen stands the action of sulphuric acid better than the cotton. To check a blend, first remove all the impurities then dip in con. sulphuric acid for a minute or two. Wash in water and dry on a blotting paper. All that remains on the blotting paper is linen. The cotton almost immediately dissolves in acid.
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Is Indigo Natural or Synthetic !! How was it manufactured earlier
Is Indigo Natural or Synthetic? How Was Indigo Produced?
The answer to the first part of the question is simple: both. Indigo began its textile journey as a natural dye obtained from plants. Later, with the development of modern chemistry, the same blue colouring substance began to be manufactured synthetically.
Today, most of the indigo used in the textile industry, especially in denim, is synthetic. But historically and culturally, indigo is deeply associated with natural dyeing traditions of India, China and many other parts of the world.
Indigo belongs to the category of water-insoluble dyes. More specifically, it is a vat dye. This means that indigo, in its blue form, does not dissolve in water and cannot be applied to fabric directly like many other dyes. It has to be chemically converted into a soluble form before dyeing, and then converted back into the blue insoluble form on the fibre.
Table of Contents
- Indigo in History
- Chemical Structure of Indigo
- How Natural Indigo Was Produced
- Indigo as a Vat Dye
- Why Stirring Was Important
- From Natural Indigo to Synthetic Indigo
- Natural Indigo vs Synthetic Indigo
- Indigo and Denim
- A Small Correction to Understand the Old Process Better
- Conclusion
- Related Reading
- General Disclaimer
Indigo in History
Indigo is one of the oldest dyes known to human civilization. It is believed to have been used for dyeing in India and China from very early times, possibly as far back as 2000 BC. The name “indigo” itself is connected with India. The Greeks and Romans referred to it as a blue dye coming from India, often described as “Indian blue.”
Originally, indigo was obtained from plants, especially from species such as Indigofera tinctoria. The leaves of the plant contained the precursor of the dye, but not the ready-made blue dye in a simple usable form. The blue colour had to be developed through fermentation, reduction and oxidation.
This is what makes indigo so fascinating. It is not merely a colouring matter extracted like juice from a plant. It is a dye that requires chemical transformation before it becomes useful.
Chemical Structure of Indigo
The main colouring compound in indigo is called indigotin. Its molecular formula is:
\[ C_{16}H_{10}N_2O_2 \]
The structure of indigo consists of two indole-like units joined together through a central double bond. It also contains two carbonyl groups \((C=O)\) and two nitrogen atoms. A simplified way to understand the molecule is:
\[ \text{Two indole-type units} + \text{central double bond} + \text{two carbonyl groups} \]
The indigo molecule is highly conjugated. This means that electrons are spread over a large part of the molecule. This extended conjugation is responsible for the absorption of visible light and the characteristic deep blue colour of indigo.
This structure also explains why indigo is stable and water-insoluble. For dyeing, the molecule has to be temporarily converted into another form.
How Natural Indigo Was Produced
Natural indigo was traditionally obtained from the leaves and stems of indigo plants. The harvested plant material was placed in a vat filled with water. In older traditional processes, urine or other alkaline fermenting materials could also be used. Fermentation was then allowed to take place.
Inside the plant, the main precursor of indigo is indican, a colourless glucoside. During fermentation, indican breaks down into indoxyl and glucose.
Hydrolysis of indican:
\[ \text{Indican} + H_2O \rightarrow \text{Indoxyl} + \text{Glucose} \]
This step is important because the plant does not directly give a strong blue dye. It first gives indoxyl, which is the immediate precursor of indigo. When the fermented liquid is stirred or beaten with poles, oxygen from the air enters the liquid. This oxygen oxidises indoxyl into indigo.
Oxidation of indoxyl:
\[ 2\,\text{Indoxyl} + O_2 \rightarrow \text{Indigo} + 2H_2O \]
As indigo is insoluble in water, the blue particles begin to separate out and settle at the bottom of the vat. The liquid above is drained off, and the remaining blue sludge or mash is collected. This mash is then dried in the open air and sold in the form of pressed cakes, lumps or powder.
This traditional method explains why indigo production was both an agricultural activity and a chemical process. The farmer grew the plant, but the dyer or processor had to understand fermentation, aeration, settling and drying.
Indigo as a Vat Dye
Indigo is insoluble in its blue form. Therefore, to dye fabric with indigo, it must first be reduced into a soluble form called leuco-indigo. This reduced form is pale yellowish or greenish and can dissolve in an alkaline dye bath.
Reduction of indigo:
\[ \text{Indigo} + 2e^- + 2H^+ \rightarrow \text{Leuco-indigo} \]
In this reduced form, indigo can enter or deposit onto the fibre. When the yarn or fabric is removed from the dye bath and exposed to air, oxygen converts leuco-indigo back into blue indigo.
Oxidation after dyeing:
\[ \text{Leuco-indigo} + \frac{1}{2}O_2 \rightarrow \text{Indigo} + H_2O \]
This is the magical moment in indigo dyeing. The material may come out of the vat looking yellowish-green, but slowly turns blue as it reacts with oxygen in the air.
Practical textile point: This conversion from insoluble blue indigo to soluble leuco-indigo, and then back to insoluble blue indigo, is the heart of vat dyeing.
Why Stirring Was Important
In traditional indigo production, the fermented mass was stirred or beaten with poles. This was not merely a mechanical operation. It had a chemical purpose.
During fermentation, the precursor compounds were converted into reduced or reactive forms. When the liquid was stirred, air entered the vat. The oxygen in the air converted indoxyl into indigo. Since indigo is insoluble, it appeared as blue particles and settled at the bottom.
\[ \text{Fermentation develops the precursor} \]
\[ \text{Stirring introduces oxygen} \]
\[ \text{Oxygen converts the precursor into blue indigo} \]
\[ \text{Insoluble indigo settles at the bottom} \]
This is why the process required both patience and skill. Too little fermentation, too much fermentation, insufficient aeration or poor settling could all affect the quality of the final dye.
From Natural Indigo to Synthetic Indigo
Thus, indigo began as a natural dye. For centuries, India was one of the important sources of natural indigo. Indigo was exported as a valuable dye material, and the term “Indian blue” became associated with it.
However, in the nineteenth century, European chemists began studying the structure and synthesis of indigo. Adolf von Baeyer made major contributions to the chemistry of indigo and succeeded in synthesising it in the laboratory. Later, in 1897, BASF began industrial-scale production of synthetic indigo.
This changed the dye industry completely. Synthetic indigo gave manufacturers a more consistent, predictable and scalable source of blue dye. Natural indigo depended on crop quality, climate, fermentation conditions and extraction skill. Synthetic indigo could be produced in large quantities with more uniform strength and shade.
Over time, synthetic indigo almost completely replaced natural indigo in large-scale textile production.
Natural Indigo vs Synthetic Indigo
| Point | Natural Indigo | Synthetic Indigo |
|---|---|---|
| Source | Plant-based, mainly from indigo-bearing plants such as Indigofera tinctoria. | Manufactured chemically. |
| Main colouring compound | Indigotin. | Indigotin. |
| Molecular formula | \(C_{16}H_{10}N_2O_2\) | \(C_{16}H_{10}N_2O_2\) |
| Consistency | May vary from batch to batch. | More uniform and predictable. |
| Scale | Suitable for craft, heritage and natural dyeing. | Suitable for industrial denim production. |
| Process control | Depends on fermentation and extraction. | Depends on chemical manufacturing controls. |
| Present use | Niche use in natural dyeing, handcraft and sustainable fashion. | Dominant in denim and industrial textile dyeing. |
The important point is that the main blue molecule is the same: indigotin. The difference lies mainly in the source, impurities, production method, consistency and environmental profile.
Indigo and Denim
Today, indigo is most strongly associated with denim. Cotton warp yarns are dyed with indigo, while the weft often remains undyed or lightly coloured. In denim dyeing, yarns are repeatedly dipped into the reduced indigo bath and then exposed to air for oxidation.
This repeated dipping and oxidation builds up the blue shade gradually. One interesting property of indigo dyeing is that the dye often remains more concentrated near the surface of the yarn rather than penetrating fully into the core. This is one reason denim fades beautifully with wear.
As the outer surface of the yarn is abraded, some of the indigo is removed, revealing lighter areas. This gives denim its characteristic worn, faded and aged appearance. So, in denim, fading is not always a defect. It is often part of the desired aesthetic.
A Small Correction to Understand the Old Process Better
In older descriptions, it is sometimes said that hydrogen was created by microorganisms and acted as a reducing agent. This is a simplified way of explaining the process. More accurately, fermentation creates reducing conditions in the vat. These reducing conditions help convert dye precursors into forms that can later be oxidised into indigo.
Similarly, when the liquid is stirred, the aim is to introduce oxygen. Oxygen converts the soluble or reduced precursor into insoluble blue indigo. The blue particles then settle at the bottom.
\[ \text{Reduction during fermentation} \]
\[ \text{Oxidation during beating or aeration} \]
This reduction-oxidation cycle is also central to indigo dyeing on fabric.
Conclusion
Indigo is both natural and synthetic. Historically, it was obtained from plants and processed through fermentation, aeration, settling and drying. Later, chemists discovered how to produce the same blue colouring substance synthetically. With industrial production by BASF in the late nineteenth century, synthetic indigo gradually replaced natural indigo in most commercial textile applications.
The beauty of indigo lies in its chemistry. It is a water-insoluble vat dye. It must first be reduced to a soluble leuco form, then applied to the fibre, and finally oxidised back to the blue insoluble form.
This is why indigo is not just a dye. It is a story of plants, fermentation, chemistry, trade, denim and textile technology.
General Disclaimer
This article is intended for educational and general textile knowledge purposes only. The chemical reactions shown are simplified to explain the main principles of natural indigo formation and vat dyeing. Actual indigo extraction, dye reduction, denim dyeing, effluent treatment and chemical handling require proper technical knowledge, safety precautions, process control and laboratory or mill-level validation.
Saturday, 13 February 2010
Health Hazards in Textile Industry- Skin
Textiles have function of a 'second skin', substituting for the biological properties that other animals have evolved to cope with specific environments on this planet. Thanks to textiles, humans have even been able to enter the most extreme and inhospitable environments, such as interplanetary space.
At the same time, however, dermatologists and consumers have become increasingly aware of the risks garments may cause to human health.
Contact dermatitis is the name given to localised rash or irrittion of the skin caused by the contact with a foreign substance.
When an allergen is involved there is an immune system reaction. The rash can show up a day or two after contact with the allergen. It will usually disappear in a few weeks, even if it is not treated.This is called Allergic Contact Dermatitis ( ACD)
When an irritant is the cause, the rash usually appears right away, possibly damaging the skin. The longer the skin is exposed to the offending substance, the more it will be damaged. The hands are often affected by this type of rash when harsh chemicals and substances are handled. This is Called ICD ( Irritant Contact Dermatitis).
Irritant dermatitis is one concern, but allergic contact dermatitis especially to certain colors used in textiles and to textile finishers even more so. The treatment of textiles or their raw materials with insecticides has alarmed authorities and prompted the industry to set safety standards known as 'eco seals'.
Textile is rated at number 5 of the top ten skin-unfriendly occupations.
At each stage their are irritants or allergens that are a potential cause of dermatitis.
Fibers commonly cause ICD and rerely ACD. The synthetic and wool fibers tend to be the irritants.The process of making yarns and preparation exposes to the irritants such as spinning oil, heat and polyvinyl alcohol.
During weaving the same irritants as in case of spinning apply.
Preparation process also exposes the workers to irritants.
It is dyeing, however, which is the principal cause of Occupational Skin Disease in the industry.The two groups of dyes i.e. reactive and disperse are the most frequest sensitisers.Chemicals and metals used are modants to give color their permanence can be irritants or allergens.
A complete list of Irritants and Allergens in the textile industry is given here.
To conclude, As This site says - "The interaction between textiles and the skin is a close and reciprocal one. Therefore, a mutual exchange must be established between those who create textiles and those who treat skin. Thus a textile engineer must understand basic skin anatomy and microbiology. Similary a demermatologist must need to know about the structure of fibers, fabrics, dyes and finishes."
Sources:
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