Improvement of wash fastness of reactive dyed cotton fabrics Compiled by: M. Rezaul Karim Tutul

Improvement of wash fastness of reactive dyed cotton fabrics Dyeing cellulose fibre reactive dye is a covalent bond with fibres in form of chemical combination. Therefore, in theory, between dye & fibre covalent bond, can give good dyeing fastness properties. But in fact, colouring material in testing, use, washing, & even the Central Standing Committee took place during storage fading, discoloration or staining occurred. Especially when dyeing dark soaping wet rubbing fastness & staining fastness when dyeing light fastness & resistance to sun & chlorine bleaching fastness Deng Jun unsatisfactory.

Main cause of their poor colour fastness has two aspects:

1) Dyestuffs own problem; Reactive dyeing of cellulose fibres, although covalent bond is a form of chemical combination with fibres, but when dyes are wet, heat, light, acid, alkali & oxidant effect, its parent structure-some parts change, decomposed as azo, amino oxidation, complexation of metal ions or dyes from covalent bond hydrolysis--fibre breakage, resulting in colour, dyeing fastness properties of some less. In another example, reactive dyes & cellulose macromolecules built up between covalent bond, hydrolysis under certain conditions, break off into hydrolytic dyes & to dye products such as wet fastness & light fastness poor performance.

2) Dyeing problems/application problem: Reactive dyes in use, staining method are correct or not, directly affect staining properties of fastness. For example: of inappropriate material, dye hydrolysis, water mark, too much calcium & magnesium ions, resulting in dye aggregation precipitation; improper fixing conditions, low rate of solid colour; dye after washing, soaping bad, not fixing dye removal not net; finished with acid, alkali, dyes & other hydrolytic chain scission increases result in increase in floating colour. So-called "floating colours" means attached to fibre & fibre bonding without dye. They include: being part of or all of hydrolysis of dye; adsorbed on fibre reactive dye but not to participate; ethylene alum sulphate ester elimination reaction has occurred, sulphuric acid ester has been off, but dye & fibre bonding. As floating dye on fibres with different degrees of affinity, which has made brought to dye washable difficulties. Thus, in actual use cannot be completely removed by washing & soaping floating dye fibre. Three measures:

a) Correct choice of dyes & b) Dye colour fastness & c) Dyeing properties of chemical structure is closely related to, in order to improve colour

fastness,

First of all to choose a good dye, should note follow: stronger chemical reactivity between dye & fibre, so that between-prone combination of covalent bond Fixation rate is higher. Acid, alkaline solution stability is better. Dye-fibro-nectin bond in higher, better chemical stability in acid, alkaline, wet, hot conditions, less prone to break key. Stronger antioxidant capacity, it is not easy to be oxidized & change colour, fade. Dye colouring is better, better compatibility. 2, water reactive with calcium & magnesium ions or other heavy metal ions combine to form insoluble or insoluble metal

Improvement of wash fastness of reactive dyed cotton fabrics Compiled by: M. Rezaul Karim Tutul

dye. These dyes in presence of high concentration of electrolyte, form aggregates of different sizes, are adsorbed on surface of fibre; re-coloured spots are produced, lighter form floating colour. colour hinder penetration & diffusion of dye within fibre, reducing dye rate, making colours lighter, fabric shade become distorted, brightness decreased, decreased colour fastness, therefore, of material before, be in water Chelating and dispersing to join a strong ability to chelate dispersing agent (2g/l) (can also use sodium hexa-meta-phosphate), to purify water stain.

Select correct dyeing with high humidity as much as possible Staining: If used in wet & humidity dyes (KN type) staining humidity from 60~65 up to 75~80, then dropped to 60~65, adding alkali fixation. Fixing process by adding alkali: Solid-colour process plus alkali, dyes & fibres bond reaction, it would also happen with water hydrolysis reaction of floating dye, while hydrolysis reaction speed & strength of fixing conditions are directly related. Fixing conditions, the stronger the more intense alkaline, the faster the dye hydrolysis. Generally use 60~65, fixing a single soda alkali agent, pH value stabilized at about 11, soda gradually add. Soaping washing: washing after dyeing purpose is to remove residual alkali fibre to prevent high temperature soaping, has been fixed with dye bonding for high-temperature alkaline hydrolysis incurred broken bonds, fell off from fibre. Washing should pay attention to following matters:

First, before soaping washing with water first.

Second, choose washing ability, throwing power, emulsifying capacity & carrying capacity of a good soap lotion pollution.

Third, the best lotion soap plus 1~2g/l of chelating dispersant

Fourth, we must in neutral condition (pH = 6~7) for soaping.

Fifth, we must heat soaping.