Dyeing of jute, flex, modacrylic, polyamide fibres and their blends

Dyeing of hemp fibre

 This is of no significance as the products manufactured from hemp fibre are almost exclusively used for technical textile purposes (fire-engine hoses and belts, etc.).

Dyeing of hat trimmings of straw, panama and Sisal for hemp

1. For dyeing straw: acid and 1: 1 metal-complex dyes

2. For dyeing panama: disperse and cationic dyes

3. For dyeing sisal: direct, acid, and 1: 1 and 1: 2 metal complex dyes.

Iridescent effects by piece-dyeing

 A prerequisite is that the warp and the weft have different affinities – usually acetate/triacetate or triacetate mixtures. Single-bath dyeing can be carried out with direct and disperse dyes, usually giving contrasting shades.

Jute fibre Dyeing

The jute fibre dyeing is similar like cotton fibre dyeing.  The high proportion of non-cellulosic material gives jute an affinity for cationic dyes (mordant unnecessary) and acid dyes. Unlike cotton, jute is sensitive to alkalis. The light fastness of jute dyeings is poorer than on cotton.

Dyeing of leather(goods) Because of the wool like chemical nature of leather, appropriately modified dyeing methods are used depending on the type of tanning process. The usual treatment with aqueous dye solutions given to new articles (by brushing on or dipping) has only a limited application for second-hand goods (garment dyeing). For expediency, dyeing is carried out using tried and tested commercially available

Dyeing of linen (flax) fibre

 In principle, dyeing is carried out using all the dye classes that are suitable for cotton (Õ Dyeing of cotton). Dye penetration is generally more difficult, especially in the case of vat dyes. The best penetration and levelness is achieved with reactive dyes.

Loose material (loose stock, loose fibre) Dyeing, 
Advantages: Any unlevelness in dyeing is evened out during the subsequent spinning process, large quantities can be produced to one shade by blending several batches and a low liquor ratio is possible in dyeing.

Disadvantages: satisfactory processing in spinning isusually only achieved through the application of spinning oils and dressings. The spinning of coloured yarns demands total separation of different shades in spinning and laborious cleaning is necessary when changing colours. Unavoidable co-processing of short fibres and dyeable impurities. Continuous dyeing can be carried out by a pad steam process (e.g. the Smith Piston Pad Dyeing Machine).

Dyeing of modacrylic (acid dyeable) and wool fibre blends

This modacrylic and woo fibre blend can only be dyed in solid shades with dyeing difficulty because of the considerably higher affinity of the acid dyes for the wool fibre component. The best possible solid shade dyeings are achieved with the Chem Acryl process and other process variants (manufacturer: Chemstrand Corp., Decatur, Alabama/USA).

An addition of the following dyeing auxiliaries is necessary: cationic and non-ionic dyeing assistants which retard the exhaustion of selected acid dyes and bring about a satisfactory balance between the dye on both fibre components in the sulphuric acid bath.

Modacrylic fibre dye

Dyeing of ombré or shadow effects, shadow dyeing on one and the same hank, e.g. by hand using square or U-section rods. Firstly, the palest colour is dyed from a full vat dye then, after dropping a little of the dyebath, a dye addition is made and a somewhat darker shade is dyed – this procedure is repeated with the increase in depth of shade becoming less and less as ever smaller additions of dye are made. In this way, light to dark shadow effects of the same colour, i.e. so-called tonal gradations, are obtained. Ombré variations are produced by using different dyes. Excellent ombré dyeing are obtained on thoroughly pretreated dry goods by employing a material-specific dye selection (hot and cold dyeing types and no pre-mixed dyes if possible) as well as the absence of wetting agent (undesired upward migration of dye) with, if necessary, controlled additions of salt and temperature regulation. The most efficient results are obtained on the hank dyeing machine where good dye penetration is achieved by raising and lowering the entire yarn carrier assembly. With increasing depth of shade, the hanks are lowered to a lesser and lesser extent into the dye liquor which is correspondingly increased in strength with additions of dye. By dropping the liquor level approx. 5 cm for each individual shade a reduced depth of immersion is achieved.

After reaching half the original bath volume, the yarn carrier assembly is lowered to a reduced depth. For piece goods, dyeing on the star frame is very practical (star dyeing machine) by continually raising and lowering the frame with the aid of a beam assembly (a cable running over a boom-arm); this method has proved particularly suitable for sensitive qualities (e.g. pure silk).

Polyamide fibre dye

Various dye classes of dye are suitable for dyeing polyamide fibres, and dye selection is based on the form of the material, the fastness requirements and the dyeing properties.

I. Disperse dyes: these dyes have good affinity and levelling properties. Affinity differences in the fibre are easily levelled out. The wet fastness properties of medium to deep dyeings are unsatisfactory.

II. Acid dyes: the most widely used class of dyes for dyeing polyamide fibres. They offer a wide colour gamut and good fastness properties, especially following an aftertreatment with products to improve the wet fastness. For combination dyeings it is essential to use dyes with similar rates of exhaustion. The selected dyes must not exhibit any blocking action. In order to cover up affinity differences in the material, anionic leveling agents, which possess an affinity for the fibre, are used in the dyebath.

III. Metal-complex dyes: these dyes have good light and wet fastness properties. Their use is limited (except for black) since differences in the polyamide material cannot be levelled out in most cases. Fastness properties can be improved with a tannin/tartar emetic (potassium antimony(III) tartrate) aftertreatment. IV. Metal-containing disperse dyes: the fastnesses properties are the same as those of the metal-complex dyes. Material-dependent affinity differences are largely covered in dark shades. Improved fastness properties are possible with a tannin/(tartar emetic) (potassium antimony(III) tartrate) aftertreatment.

V. Reactive disperse dyes: dyeable as disperse dyes; chemical bonding with the fibre takes place following an alkaline aftertreatment thereby giving good wet fastness properties.

VI. Direct dyes: the selection is limited: used chiefly for reasons of shade and price.

VII. Naphthol dyes: of no importance.

VIII. Chrome dyes: of interest only for black shades (applied by the so-called Metachrome process in which dye and mordant are applied simultaneously from a single bath).

IX. Reactive dyes: the light fastness of these dyes varies appreciably on polyamide. Wet fastness properties are good. Any affinity differences that may arise are not covered in all cases. Combination dyeings are only possible to a limited extent. The build-up is also limited.

X. Logwood black: This dye is of interest for reasons of shade and fastness but, the method of dyeing is very involved.

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