{"id":1521,"date":"2019-05-17T05:06:48","date_gmt":"2019-05-17T00:36:48","guid":{"rendered":"https:\/\/dns-iran.com\/?page_id=1521"},"modified":"2019-05-17T09:06:51","modified_gmt":"2019-05-17T04:36:51","slug":"textile-dyeing-definition-types-properties","status":"publish","type":"page","link":"https:\/\/dns-iran.com\/index.php\/textile-dyeing-definition-types-properties\/","title":{"rendered":"Textile Dyeing \u2013 Definition, Types & Properties"},"content":{"rendered":"\n
\"\"<\/figure><\/div>\n\n\n\n

Introduction To Textile Dyeing<\/h3>\n\n\n\n

A compound appears colored if it selectively absorbs light in the \nvisible region and reflects the light of the wavelength in the rest of \nthe visible region. The amount of light energy absorbed in the visible \nspectrum is the only responsible factor for the shade of the colour.  \nThe main function of absorbed energy is to raise the molecule from the \nground state energy to the excited state.<\/p>\n\n\n\n

If the electrons of a molecule are tightly bound as in saturated \ncompound no light of visible will be absorbed and hence the compound \nappears colorless.<\/p>\n\n\n\n

If the electrons of a molecule are loosely bound as in saturated compound absorbance occurs in the visible region and hence the compound appears colored.<\/p>\n\n\n\n

Types and Definition Dyes<\/strong><\/h3>\n\n\n\n

Colouring materials are mainly of three types. Dyes, pigments, and lakes (ingrain dyes). A dye has three parts in its structure chromophore. chromogen and\u00a0Auxochromopores\u00a0and is soluble in a specific medium under certain conditions.<\/p>\n\n\n\n

Chromopores :<\/strong> Chromopores are group of atoms, the  \nII electrons of which may get transfer from ground state to excited \nstate by absorption of radiation, thus producing the hue.<\/p>\n\n\n\n

Auxochromopores :<\/strong> Auxochromopores are group of atoms\n which tend to increase resonance by interacting the unshared pair of \nelectrons on nitrogen or oxygen atoms of the auxochromes, with    II  \nelectrons of aromatic ring.auxochrome is a substituted acidic or basic \ngroup in dye structure to intensify depth of shade<\/a><\/strong>,\n e.g. -OH,  COOH, SO.H, -NH,,-NH(CH.). etc.. Further addition of \nsubstituents to dye structure deepens the shade and extent of deepening \nvaries with increase in molecular weight of dye.<\/p>\n\n\n\n

Chromogen retains chromophore and plays a crucial role to determine \nthe final hue and its affinity for fibre, fastness, stability, etc.<\/p>\n\n\n\n

Substantivity \/ Affinity:\u00a0<\/strong>The Substantivity of a dye for a fibre can be defined as an attraction between the fibre and the dye under given dyeing conditions, where by the dye is selectively extracted from the an application medium by the fibre. the term affinity is used as\u00a0 it\u00a0 is more clearly defined and can be given numerical value (usually in joules per mole). It is defined as the difference between the chemical potential of the dye in its standard state in the fibre and the corresponding potential in the dye. In simple terms substantivity or affinity indicates the ability of a dye to go from the solution phase to the fibre.<\/p>\n\n\n\n

Exhaustion <\/strong><\/h3>\n\n\n\n

This is a measure of the proportion of the dye absorbed by the fibre relation to that remaining in the dye bath .Thus, it indicates the amount of dye that has moved from the solution into the fibre under given dyeing conditions. It is also a measure of the substantivity of the dye for the fibre.<\/p>\n\n\n\n

Exhaustion is defined as the mass of dye taken up by the material \ndivided by the total initial mass of dye in the bath, but for a bath of \nconstant volume.<\/p>\n\n\n\n

For example, if the exhaustion of a dye bath is 75%, it means that\u00a0 75% of the dye in the dye bath has moved from the dye solution or dye liquor into the fibre. The term exhaustion is mainly applicable to batch \u2013wise dyeing which is also called exhaust dyeing .Textile yarn and fabric are often dyed by the exhaust dyeing technique.<\/p>\n\n\n\n

Aggregation<\/h3>\n\n\n\n

Aggregation numbers \u2013<\/strong> The average number of dye \nmolecules in a micelle \u2013 had been determined from diffusion \ncoefficients, electrical conductivity measurements, osmotic pressures, \nmembrane filtration, and light scattering. Aggregation increases with \nincreasing dye concentration and decreases with increasing temperature.<\/p>\n\n\n\n

Exact aggregation numbers and the number of incorporated counter \nions, which determine the actual overall electric charge of the micelle,\n are imprecisely known. It is usually assumed that a rapid exchange \noccurs between free dye molecules in the solution and dye micelles of \nvarious sizes.<\/p>\n\n\n\n

Material to Liquor Ratio<\/strong><\/h3>\n\n\n\n

This expression refers to the weight volume relationship between the fibre to be dyed and the total volume of dye bath .It is normally abbreviated as MLR and sometimes written as M:L ratio. An M:L ratio of 1: 10 means that a dye bath volume of 10 litres is required to dye 1kg of dry fibre.<\/p>\n\n\n\n

The material to liquor ratio is also referred to as  an inverse ratio\n and called the liquor to goods ratio or simply the liquor ratio and \nthis ratio is given by the following expression.<\/p>\n\n\n\n

Total volume of dye liquor in ml <\/strong><\/p>\n\n\n\n

Liquor to goods ratio =    \u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2013<\/strong><\/p>\n\n\n\n

Dry weight of material dyed in grams. <\/strong><\/p>\n\n\n\n

Thus 5 gms of material dyed at a liquor to goods ratio of 5:1 would use 5\u00d75\u00a0 =25ml of dye liquor .Alternatively ,3gms of material dyed in dye bath of 60ml has a liquor \/ goods ratio of 60\/3 or 20 \/ 1 or 20 :1.<\/p>\n\n\n\n

Shade Percentage <\/strong><\/h3>\n\n\n\n

Shade percentage refers to the quantity of dye taken for a dyeing \nexpressed as  a percentage of the dry weight of the fibre to be dyed \n.For example, If 1g of a dye is taken fordyeing100gof textile material, \nthe shade percentage is referred to as 1 % Shade. If a kilogram of fibre\n ie required to be dyed to a3.5 5shade, the amount of dye to be taken \nwould be (1000x 3.5 ) \/100 = 35 grams.<\/p>\n\n\n\n

Formula for calculation <\/strong><\/h3>\n\n\n\n

Ml of dye solution required or added  =Percentage of depth of shade x weight of fibre to be dyed in gms<\/p>\n\n\n\n

Concentration of stock dye solution in g\/100ml<\/p>\n\n\n\n

For example .if 3% shade is required to be dyed on 4gof cotton yarn using a solution of one gram of dye in200ml of water (ie 0.5g in 100ml water ) , the ml of the stock dye solution required would be, Ml of dye solution required or added = 3\u00d74 \/ 0.5 =24ml.<\/p>\n\n\n\n

THE GENERAL THEORY OF DYEING<\/strong><\/h3>\n\n\n\n
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Dyeing is the process of colouring textile materials by immersing them in an aqueous solution of dye, called dye liquor .Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dyeing, heat is usually applied to the dye liquor.<\/p>\n\n\n\n

The general theory of dyeing explains the interaction between dye, \nfibre, water and dye auxiliary. More specifically, it explains:<\/p>\n\n\n\n

  1. Force of repulsion which are developed between the dye molecules and water .<\/li>
  2. Force of attraction which are developed between the dye molecules and fibres.<\/li><\/ol>\n\n\n\n

    These forces are responsible for the dye molecules leaving the aqueous dye liquor\u00a0 entering and attaching themselves to the polymers of the fibres.<\/p>\n\n\n\n

    The Dye Molecule <\/strong><\/h3>\n\n\n\n

    Dye molecules are organic molecules, which can be classified as:<\/p>\n\n\n\n

    1. Anionic <\/a><\/strong>\u2013 in which the colour is caused by the anionic part of the dye molecule;<\/li>
    2. Cationic<\/a><\/strong> \u2013 in which the colour is caused by the cationic part of the dye molecule;<\/li>
    3. Disperse- in which the colour is caused by the whole molecule. The \nfirst two dye molecule types are applied from an aqueous solution. The \nthird is applied from an aqueous dispersion.<\/li><\/ol>\n\n\n\n

      A dye stuff is a substance which is capable of colouring a textile \nmaterial in such a manner that it associate closely with the fiber ,  \nthat it is not removable  by simple physical  means (eg : rubbing or \nmild  deterging ). It must be soluble in water, are capable of going \ninto solution by chemical means, whereby a highly dispersed condition \nmay be regarded as a form of solution.<\/p>\n\n\n\n

      An essential feature of the dyeing process is that the dye molecule \nmust be capable of entering the fibre structure, the path for the dye \nmolecules is provided by the intermolecular spaces in the fibre and once\n the dye has entered the fibre structure it becomes firmly attached to \nthe surface of the molecules either by purely physical forces (Secondary\n Valences) or by chemical combination.<\/ins><\/p>\n\n\n\n

      The former \u00a0mode of attachment is believed to be prevalent in the dyeing of cellulosic fibres, the latter mode in the dyeing of protein fibres. Acetate rayon and synthetic fibres resist penetration by the dye molecules, but certain dyes are capable of forming a solid solution with the fibrous molecule; for dyeing with other dyes, the synthetic fibres<\/a><\/strong> may be swollen with suitable agents.Swelling of the fibers appears to play a large part in dyeing of all fibres, and is principally affected by water (or solvents in the case of synthetics) and by raising the temperature of the dye bath.<\/p>\n\n\n\n

      The dyeing process can thus be considered as taking place in three phases<\/strong><\/p>\n\n\n\n