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close this bookDyeing of Sisal and other Plant Fibres: A Handbook for Craft Instructors (NRI)
close this folderPart 2: Use of Different classes of dyes
View the documentReactive dyes
View the documentDirect dyes
View the documentAcid dyes
View the documentBasic dyes
View the documentDisperse dyes

Reactive dyes

Introduction

The direct, acid, basic and disperse dyes are attached to the fibre by purely physical bonds. The reactive dyes were developed in order to give better fastness properties by chemically fixing the dye to the fibre. They are often derived by linking simple acid dyes to a chemical which combines with the cellulose in the fibre. Reactive dyes of special interest to the craft worker are those that can be applied in the cold using simple equipment (one method has been described fully by Canning et al., 1 977).

Manufacturers' trade names

Reactive dyes are of several types, ranging from those that can be applied in the cold, such as the 'Procion MX' range from Imperial Chemical Industries plc (ICI), to those that are usually applied at higher temperatures, such as the 'Procion H' range. Only the 'Procion MX' and 'Dylon Cold' dyes have been investigated at TDRI.

Some other ranges which contain similar dyes are*:

'Acticrom F' (Mult)

'Mikacion M' (KYK)

'Amaryl' (Amar)

Ostazin' (Chem)

'Basilen M' (BASF)

'Vilmafix A' (VIL)

'Chemictive' (CE)

'Xiron' (FW)

'Helaktyn F' (POL)


Dyes in some ranges are slightly less reactive than the 'Procion MX' dyes but could probably be applied to sisal by methods similar to that described in this section; some examples are*:

'Cibacron' (CGY)
'Drimarene K' (S)
'Levafix E' and 'EA' (BAY)
'Temazol' (HOE)

Choice of dyes

Tests carried out at TDRI (Canning and Jarman, 1974; Edwards and Canning, 1981) for light fastness, water fastness and penetration have shown that of the twenty-five 'Procion MX' dyes available in April 1982, the following nine are the best choices for dyeing sisal and similar fibres:

Procion Yellow MX-8G (Cl Reactive Yellow 86) Procion Yellow MX-4R (Cl Reactive Orange 14)

Procion Orange MX-G

(Cl Reactive Orange 1)

Procion Red MX-G

(Cl Reactive Red 5)

Procion Red MX-5B

(Cl Reactive Red 2)

Procion Red MX-8B

(Cl Reactive Red 11)

Procion Rubine MX-B

(Cl Reactive Red 6)

Procion Blue MX-3G

(Cl Reactive Blue 1)

Procion Brown MX-3RD

(not listed in the Colour Index)

A further dye found satisfactory, Procion Yellow MX-4G, has been withdrawn. Equivalents (Cl Reactive Yellow 22) are available from other manufacturers (i.e. BASF, CE, KYK, Mult and VIL, see Appendices 2 and 3).

The following dyes penetrate less well into the fibre but can be used when durability is not of prime importance:

Procion Yellow MX-3R

(Cl Reactive Orange 86)

Procion Yellow MX-GR

(Cl Reactive Yellow 7)

Procion Orange MX-2R

(Cl Reactive Orange 4)

Procion Scarlet MX-G

(Cl Reactive Red 8)

Procion Scarlet MX-3G

(not listed in the Colour Index)

Procion Blue MX-R

(Cl Reactive Blue 4)

Procion Blue MX-2G

(Cl Reactive Blue 109)

Procion Blue MX-4GD

(Cl Reactive Blue 168)

Procion Blue MX-7RX

(Cl Reactive Blue 161)

Procion Navy MX-4RD

(not listed in the Colour Index)

From the nine 'Procion MX' dyes recommended for sisal-like fibres a wide range of shades can be obtained which should meet the needs of any craft worker. In fact over one hundred shades including yellows, oranges, reds, violets, blues, greens, browns and a black have been produced at TDRI using only three of these dyes- Procion Yellow MX-8G, Procion Red MX-5B and Procion Blue MX-3G (see Table 1).

With 'Dylon Cold' dyes, shades A.10 Primrose, A.16 Camellia, and A.28 Riviera Blue are satisfactory for mixing to produce a wide range of shades. Of the remaining 'Dylon Cold' dyes, most will produce satisfactory colours but the following do not penetrate into the fibre and should be avoided:

Dylon Cold A.13 French navy
Dylon Cold A.15 Tartan green
Dylon Cold A.17 Cafe au fait
Dylon Cold A.50 Charcoal

Application of dyes

The use of dyes which are chemically reactive toward fibres is a new concept in dyeing. However, when exhaust dyeing using dyes such as ICI 'Procion MX' or Dylon 'Cold', the method of application differs from traditional methods only in that dyeing takes place in the cold.

In exhaust dyeing (see Glossary) the fibre is immersed in a dye solution to which salt is added. When the dye has been adsorbed by the fibre, alkali (usually soda ash) is added to the dyebath and the fibre is left in this solution for a further period of time. The alkali causes most of the adsorbed dye to react with the fibre and fix in such a way that it is impossible to remove the colour with water, giving extremely high water fastness. However, the loose dye must be either removed by hot water washing, or fixed to the fibre by after-treatment. If this is not done, the water fastness will be poor. For some end-uses a combination of washing and after-treatment may be required.

The amounts of salt and soda to be used in exhaust dyeing vary with the depth of shade. Those generally recommended by ICI for cotton dyeing with 'Procion MX' dyes are given in Table 2.


Table 2: Recommended concentrations of common salt and soda ash to be used with ICI 'Procion MX' dyes

Although these quantities will produce satisfactory results with sisal, experienced dyers may vary the composition of the dyebath since salt and soda requirements are also influenced by:

(i) the relative costs of the salt, soda and dyestuff; and

(ii) the exhaustion characteristics of the dye.

By varying the dyebath composition, it is possible to determine the optimum conditions for producing specific colours at the lowest cost .

Penetration of dye into the fibre is improved considerably by the use of a warm process and this is recommended for articles such as carpets, which will be subjected to abrasive wear. However, temperatures above 50°C should not be used since too much of the dye will lose its reactivity through reaction with water.

An alternative method of applying these dyes, pad-batch dyeing, has been described by Canning et al. (1977) and will be mentioned only briefly. However, workers who use this method will find the information given in this handbook on after-treatments and blending useful. In the pad-batch method the fibre is first wetted with a concentrated alkaline dye solution ('padding') and then left in a wet state for a period of time ('batching') to allow the dye to penetrate and fix to the fibre strands. The method makes very effective use of the dye although, as with exhaust dyeing, washing is needed to remove unfixed dye.

The exhaust method is easier to control, therefore it should be used when producing matched shades. However, the pad-batch method (although it can be a little messy) will usually be less costly and less time consuming. Since it allows dyes to penetrate uniformly into the structure of yarns and fabric, the pad-batch method is ideally suited to the dyeing of these materials.

Most craft workers will not be familiar with reactive dyes. However, provided that the following points are borne in mind, they should experience little difficulty.

1. The reactive dyes react not only with fibres, but also with water and body tissues. Therefore the dyes need careful handling. Avoid breathing dye powder by wearing a mask, wear gloves when handling and quickly wash off any dye which gets on the skin (see Safety precautions and first aid treatment).

2. The reactivity, which is essential for the production of water fast shades, is destroyed when moisture is present. The loss of reactivity is considerably more rapid when the dye is also warm or alkaline (after adding soda). Make sure therefore that:

(i) Dye powders are stored in airtight containers in a cool place.

(ii) Dye solutions are kept cool-especially if alkali (soda) has been added.

(iii) Dye solutions are used immediately after being prepared-they must not be stored for later use.

3. Despite taking all precautions, some deterioration will occur and not all of the dye will fix to the fibre. Unless the deteriorated dye is removed by hot water washing or fixed to the fibre by after-treatment, the potentially excellent water fastness properties of these colours will not be achieved. The choice of method must be made before dyeing is started and the following points should be taken into consideration:

(i) Use of hot water washing to remove loose dye: Hot washing has the advantage that any potential health hazard from loose dye is avoided without the use of additional chemicals which could themselves be potentially harmful. Fibre finished in this way is more likely to find acceptance for articles such as children's toys. However, with some dyes-especially reds and in deep colours-several hot washes may be needed to remove all the loose dye.

(ii) Use of cationic after-treatment to chemically fix the loose dye: Some commercial after-treating agents are very effective in fixing loose dye and it has been found possible to eliminate the hot wash normally needed to obtain good colour fastness. By using these treatments, dye could be saved since the colours obtained will be deeper than those obtained after washing the fibre. Although these treatments are widely used, workers should check with their marketing organisation that the dyed fibre will be suitable for its intended end-use.

Recipe for producing an Emerald Green Shade on 2.5 Kg of Sisal

This recipe is based on the use of the exhaust dyeing method-reactive dyes cannot be applied by the standing bath method .

Materials and equipment required

Sisal


2.5 kg

Procion Yellow MX-8G

37.5 g

(1.5 per cent on fibre)

Procion Blue MX-3G

37.5 g

(1.5 per cent on fibre)

Common salt (sodium chloride)

2.25 kg

(45 g/l)

Soda ash

400 g

(8 9/l)

Spring balance



Laboratory balance



Beakers (or similar containers)

4


Buckets



Dye vat


(minimum capacity 60 litres)

Measuring cylinder or dipstick



Stirring rods


1 small for bucket; 1 long for dye vat

Water


50 litres (Liquor ratio 20:1)

Drying lines




Preparing for dyeing


Preparing for dyeing (continued)


Preparing for dyeing (continued)


Dyeing


Dyeing (continued)


Dyeing (continued)


Dyeing (continued)


Removal of unfixed dye by washing


Figure Removal of unfixed dye by washing (continued)

After-treatment

Safety note: After-treating agents are acidic and in concentrated form can be corrosive causing skin burns. The concentrates should therefore be handled with care. Users should wear protective clothing and have ready access to a copious supply of water. Once diluted, the agents are less dangerous but similar precautions should be taken (see Safety precautions and first aid treatment).

Introduction

Unfixed dye is usually removed from the fibre by boiling in detergent and washing in hot and cold water as described in the recipe. However, since this treatment requires a metal (preferably stainless steel) vessel and a source of heat it can be expensive for the craft worker. However, a new method has been developed at TDRI which is both simpler and cheaper. The unfixed dye is treated with a cationic agent which forms an ionic bond with the water solubilising group on the dye molecule. The larger molecule which is formed becomes trapped in the internal structure of the fibre making the dye more water fast. After-treatment causes some loss of light fastness and some change in colour. The agents mentioned here do not produce marked changes in colour.

Fixing Agent IS (Textile Dyestuffs and Chemicals Ltd) can be used to give a low cost treatment with no appreciable loss of light fastness. Alternative agents* are:

Hydrocol KNC (Rudolf and Co. KG)
Sandofix WE-56 (S)
Fixitol P (Durham Chemicals Distributors Ltd)
Matexil FC-PN (ICI)

Of these, the Hydrocol and Fixitol cause the least loss of light fastness but the effectiveness of Fixitol tends to vary with different dyes. Both Matexil and Sandofix cause appreciable loss of light fastness of some shades.

The amount of an agent required depends on the amount of loose dye in the fibres- deeper colours need larger amounts of agent than pale shades, and pad-batch dyed fibre will need more agent than exhaust dyed fibre. Also, fibre that has been hot washed will need less agent than unwashed fibre. Craft workers will need to experiment to find the optimum level of treatment for their fibre. The following methods for use with Fixing Agent IS will provide a basis for experiments.

There are two alternative methods for applying the agents-an exhaust method, and a pad-batch method. The pad-batch method gives better results but the fibre must first be dried.

In the following methods it is assumed that the fibre has been dyed by the pad-batch method using 20 9 of dyestuff in each litre of dye liquor (2 per cent on weight of fibre) then washed by rinsing in cold water only. The method is also based on the use of Fixing Agent IS in dry powder form.

The manufacturers of Fixing Agent IS recommend that the agent be used at 50 - 60°C in soft water slightly acidified with acetic acid. However, satisfactory results have been obtained at TDRI using the agent in the cold without acid. It is recommended though that alkaline waters, such as those softened with soda, are rendered just acidic with acetic acid before use. Anionic substances must be avoided so fibre must be rinsed free from wetting agents such as soaps or washing-up liquid.

Pad-batch method

1. Take 1 litre of water for each kilogram of fibre of the same colour to be treated. Pour this into a bucket or other suitable vessel.

2. Read section on Safety and first aid treatment. Weigh out an amount of Fixing Agent IS powder equivalent to 45 9 for each litre of water taken (in experiments at TDRI the amount of Fixing Agent IS was halved and the water fastnesses of the resultant colours were still of a high order).

3. Mix the after-treating agent to a smooth paste with a little water from the bucket.

4. Rinse the pasted powder into the bucket of water and stir well until all the powder has dissolved.

5. Divide the dyed, rinsed and dried fibre into small bundles.

6. Take one bundle of the fibre and dip it briefly into the after-treatment liquor (about 5 seconds, but no longer). Knead and swill the fibre round whilst it is immersed to ensure that every strand is wetted.

7. Immediately squeeze the excess liquor on the fibre back into the bucket. The fibre should take up its own weight of liquor but not be so wet that it drips. Each litre of liquor will treat 1 kg of fibre.

8. Place the wet fibre into a plastic bag to prevent it from drying.

9. Repeat steps 6, 7 and 8 using the same plastic bag. Surplus liquor can be saved for later use but do not use it for a new colour unless it is clean.

10. When all the fibre of one colour has been wetted with after-treatment liquor, close the bag and leave it overnight in order that the after-treating agent can penetrate into the fibre to fix loose dye.

11. Remove the fibre from the bag and rinse surplus after-treating agent and any loose colour from the surface of the fibre with cold clean water.

12. Hang the fibre in a shady place to dry.

Exhaust method

Note: This method may be used on either wet or dry fibre. However, since better results are obtained when using wet fibre, it is best used directly after the first rinse following the dyeing stage.

1. Take 5 litres of water for each kilogram (dry weight) of fibre to be treated. Pour this into the bucket or other suitable vessel (with dry fibre use 6 litres for each kilogram of fibre). The fibre must be all of the same colour.

2. Read section on Safety precautions and first aid treatment. Weigh out an amount of Fixing Agent IS powder equivalent to 45 9 for each kilogram of fibre to be treated (4.5 per cent on weight of fibre).

3. Mix the after-treating agent to a smooth paste with a little of the water from the bucket.

4. Rinse the pasted powder into the bucket of water and stir well until the powder has dissolved.

5. Place the dyed and rinsed fibre into the liquor ensuring the whole amount is immersed rapidly.

6. Stir well for at least 5 minutes-repeated dipping of the fibre, ensuring it is immersed each time, gives effective stirring.

7. Leave the fibre in the liquor for a further 5 hours stirring frequently within the first hour then at intervals of about 30 minutes.

8. Remove the fibre and rinse it in clean water to remove any loose dye and aftertreating agent.

9. Hang the fibre in the shade to dry.

10. Discard the liquor where it will not contaminate food or water.

Storage

The agents are reported to remain stable for 6 - 12 months when stored in cool places (20 - 30°C). However, the agents mentioned in this handbook remained effective after being kept in the laboratory at TDRI for 2 years but this is no guarantee that they will remain effective for so long in the tropics.