Materials Science in Light Industry Production (Материаловедение в производстве изделий легкой промышленности). Учебное пособие

4. Прочитайте и переведите текст.

Dyes

A dye can generally be described as a coloured substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fibre.

Both dyes and pigments appear to be coloured because they absorb some wavelengths of light preferentially. In contrast with a dye, a pigment generally is insoluble, and has no affinity for the substrate. Some dyes can be precipitated with an inert salt to produce a lake pigment, and based on the salt used they could be aluminum lake, calcium lake or barium lake pigments.

Archaeological evidence shows that, particularly in India and the Middle East, dyeing has been carried out for over 5000 years. The dyes were obtained from animal, vegetable or mineral origin, with no or very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.

5.Ответьте на вопросы.

1.What is the dyes application field?

2.Why do both dyes and pigments appear to be coloured?

3.What is the difference between the due and the pigment?

4.How long has dyeing been carried out in India and the Middle East?

5.What sources were the dyes obtained from?

6.Определите, являются ли следующие утверждения

верными в соответствии с текстом упражнения 4.

1. The dyes are generally applied in an aqueous solution.

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2.The dyes may require mordant to improve the fastness of the dye on the fibre.

3.Both dyes and pigments appear to be coloured because they absorb some wavelengths of light preferentially.

4.Some dyes can be precipitated with an inert salt to produce a lake pigment.

5.Archaeological evidence shows that, particularly in India and the Middle East dyeing has been carried out for over 5000 years.

6.Dyes obtained from the plant kingdom have been widely used on a commercial scale.

7.Дайте краткую аннотацию текста к упражнению 4.

Lesson 22. Natural Dyes

1. Прочитайте и переведите следующие глаголы:

to combine well, to come from, to provide, to pollute, to dye

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into common use, textile colours came from natural dyes including cochineal, brazilwood and logwood. Natural dyes can, however, easily become the dyes of the future. They are a renewable resource and not dependent on petroleum as are many synthetic dyes.

Providing alum is used as a mordant, natural dyes use no toxic or polluting chemicals, and the organic matter left over from dye plants can be put on the compost. Combined with the natural colours of wool and cotton, natural dyes such as indigo and cochineal are arguably the only possible colours for dyeing organic textiles.

6.Ответьте на вопросы.

1.What are the best known natural dyes?

2.What natural source does cochineal come from?

3.When did synthetic dyes come into common use?

4.What are the benefits of natural dyes?

5.What are the only possible colours for dyeing organic textiles?

7.Дайте краткую аннотацию текста к упражнению 5.

Lesson 23. Sulfur Dyes

1. Прочитайте и переведите следующие глаголы:

to absorb, to insolubilize, to eradicate, to break, to exhaust, to facilitate, to bleed, to stain, to come out, to apply, to produce, to phase out, to treat, to dye, to rub

2. Прочитайте следующие интернациональные слова вслух и, основываясь на значениях соответствующих русских

слов, определите их значение:

basis, products, chlorine, technology, electro-chemical, agent, to form, oxygen, oxidation

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3.Прочитайте и переведите следующие прилагательные: robust, deep (colour), toxic, water insoluble, alkali

4.Прочитайте и переведите текст.

Sulfur Dyes

Sulfur dyes are the biggest volume dyes manufactured for cotton. They are cheap, generally have good wash-fastness and are easy to apply. The dyes are absorbed by cotton from a bath containing sodium sulfide and are insolubilized within the fibre by oxidation. During this process the dyes form complex large molecules which are the basis of their good wash-fastness. These dyes produce robust dyeing that has all round fastness except to chlorine. Due to the high polluting nature of the let out dye-baths, slowly sulfur dyes are being phased out. Sulfur dyes are primarily used for dark colours such as blacks, browns, and dark blues. The deep indigo blues of denim blue jeans are a product of sulfur dyes.

Recent advances in dyeing technologies have allowed the substitution of toxic sulfide reducing agents. Glucose is now used and both low sulfide and zero sulfide products are available.

Even new developments are done in the field of reducing the dye by means of electro chemical reducing. But this work is just on research stage and is expected to come to industry very soon which will eradicate the problems of polluting sulfide.

Sulfur dyes are water insoluble. They have to be treated with a reducing agent and an alkali at temperature of around 80 degree Celsius where the dye breaks in small particles which then become water soluble and hence they can be absorbed on the fabric.

It is allowed to exhaust, i.e. allowed to go on to the fabric by means of heating and adding common salt which facilitates the dye to go to the fabric surface. After the adsorption of the dye on fibre surface it is removed from the dye solution and then taken for oxidation. Now in oxidation step the dye which has broken in smaller particles joins and again forms the parent dye which is insoluble in water by means of oxygen.

The oxidation can be done in air as well if it needed to be done faster than oxidizing agents like Hydrogen peroxide can be

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used. Now as the dye has become water in-soluble in fibre so it won’t bleed in the water when washed and will hence not stain other clothes. But it had poor fastness to rubbing. The dye from the fibre comes out gradually if the dyed fabric is rubbed against any thing, even on its surface. Also the fastness to chlorite bleach is poor because chlorite breaks the colour imparting group in the dye and hence the coloured part becomes colourless.

Sulfur dyes are very cheap dyes. Out of all the sulfur dyes 50% production is done of the sulfur black colour as it is very important from point of industry because all black colour dyed fabrics need very high concentration of black colour to dye the fabric and gives it the jet black colour appearance. Sulfur dyes do not have a pure red colour in its shade bank. A pink or scarlet colour is available.

5.Ответьте на вопросы.

1.What are sulfur dyes manufactured for?

2.What are the basic characteristics of sulfur dyes?

3.What does the process of dyeing include?

4.What is the basis of the good wash fastness?

5.Why are sulfur dyes being phased out?

6.What is done in the field of reducing the dye?

7.What are the recent advances in dyeing technologies?

6.Дайте краткую аннотацию текста к упражнению 4.

7.Перескажите текст упражнения 4 подробно.

Lesson 24. Organic Dyes

1. Прочитайте следующие интернациональные слова вслух и, основываясь на значениях соответствующих русских

слов, определите их значение:

acid, nylon, acrylic, neutral, anionic, cationic, category, acetic acid, sodium chloride, sodium sulfate, pH indicator, potassium dichromate, extreme, alkaline liquor, indigo, chromophore, substrate,

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covalent, cellulose acetate, polyester, disperse, diazoic

2. Прочитайте и переведите следующие глаголы:

to discover, to prepare, to replace, to classify, to apply, to add, to carry out, to improve, to reform, to utilize, to develop, to ground, to sell, to dry, to require, to allow, to attach

3.Прочитайте и переведите следующие прилагательные: water-soluble, substantive, hazardous, incapable, subsequent, unique, initial, costless

4.Прочитайте и переведите текст.

Organic Dyes

The first human-made (synthetic) organic dye, mauveine, was discovered by William Henry Perkin in 1856. Many thousands of synthetic dyes have since been prepared.

Synthetic dyes quickly replaced the traditional natural dyes. They cost less, they offered a vast range of new colours, and they imparted better properties upon the dyed materials.

Dyes are now classified according to how they are used in the dyeing process.

Acid dyes are water-soluble anionic dyes that are applied to fibres such as silk, wool, nylon and modified acrylic fibres using neutral to acid dye bath. Attachment to the fibre is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fibre. Acid dyes are not substantive to cellulosic fibres. Most synthetic food colours fall in this category.

Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibres, but find some use for wool and silk. Usually acetic acid is added to the dyebath to help the uptake of the dye onto the fibre. Basic dyes are also used in the colouration of paper.

Substantive dyeing is normally carried out in a neutral alkaline dyebath, at or near boiling point, with the additioleavesin of either sodium chloride (NaCl) or sodium sulfate (Na2SO4). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

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Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. 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. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant, potassium dichromate, is applied as an after-treatment. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.

Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. The colour of denim is due to indigo, the original vat dye.

Reactive dyes utilize a chromophore attached to a substituent that is capable of directly reacting with the fibre substrate. The covalent bonds that attach reactive dye to natural fibres make them among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are by far the best choice for dyeing cotton and other cellulose fibres at home or in the art studio.

Disperse dyes were originally developed for the dyeing of cellulose acetate, and are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent and then sold as a paste, or spray-dried and sold as a powder. Their main use is to dye polyester but they can also be used to dye nylon, cellulose triacetate, and acrylic fibres. In some cases, a dyeing temperature of 130 °C is required, and a pressurized dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.

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Azo dyeing is a technique in which an insoluble azoic dye is produced directly onto or within the fibre. This is achieved by treating a fibre with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final colour is controlled by the choice of the diazoic and coupling components.

Sulfur dyes are two parts "developed" dyes used to dye cotton with dark colours. The initial bath imparts a yellow or pale chartreuse colour. This is aftertreated with a sulfur compound in place to produce the dark black we are familiar with in socks for instance. Sulfur Black is the largest selling dye by volume.

5.Ответьте на вопросы.

1.What is the first human-made organic dye?

2.Why did synthetic dyes replace the traditional natural dyes?

3.What are the characteristics of synthetic dyes?

4.What groups are the synthetic dyes classified into?

6.Определите, являются ли следующие утверждения

верными в соответствии с текстом упражнения 4.

1.Most synthetic food colours fall in the category of acid dyes.

2.Vat dyes are also used in the paper colouration.

3.It is important to note that many reactive dyes, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.

4.Such reactive dyes as Procion MX, Cibacron F, and Drimarene K, are very easy to use.

5.The main use of vat dyes is to dye polyester but they can also be used to dye wool, linen and silk.

6.Cibacron F is the largest selling dye by volume.

7.Сопоставьте понятие с его объяснением.

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8. Дайте краткую аннотацию текста к упражнению 4.

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