Pigment Dyeing

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Dyeing of Cotton Fabric with Pigment Colour

By: Sankar Ray Maulik

Dyeing of Cotton Fabric with Pigment ColourBy: Sankar Ray Maulik1. Introduction Cotton fibre can chiefly be dyed with direct, reactive, vat, sulphur and azoic classes of dyestuffs. In textile applications this environment friendly fibre has some distinct advantages like moderate dry and wet tensile strength, appreciable moisture regain, moderate extensibility and soft feel, which makes it suitable for apparel and diversified applications. Chemical modification of cotton to improve its affinity for acid and reactive classes of dyestuffs and as well as natural colourants has received considerable attention in recent years [1-4]. Most of these modifications were based on the introduction of cationic groups in the form of quaternary, tertiary or secondary amino residues in the molecular structure of cotton cellulose. Unlike this, research works related to the application of pigment on cotton cellulose through an exhaust technique was scanty [5-7]. Pigments are insoluble in water and have no affinity for textile. Use of pigments for printing of textile by ancient Chinese in the eighteenth century by using blocks had been reported in the literature determining the aesthetic appeal and acceptability of the products made from them. The main attention of the study embodied in the present paper centers round the modification of cotton cellulose by different aminating agents to impart pigment affinity and to compare the results with the conventional pigment dyeing process. Optimisation of dose level of those aminating agents in terms of depth of shade, mechanical parameters and assessment of different colourfastness properties of those pigment dyed fabrics were also carried out and the results are reported in the present work.[8]

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Colouration of cotton cellulose with pigment emulsion has always played a key role in

2. EXPERIMENTAL

2.1 Materials Loom state cotton fabric having 20 tex warp count and 20 tex weft count and 360 ends/dm and 320 picks/dm with 120 gm/m2 in weight were used in this study. Acramin Red FGR (pigment), commercial polyamine compound (Solidogen CPD), binder, acrylamide and citric acid were used

as and when required. All other chemicals used in this study were of laboratory reagent grade supplied by M/s Loba Chemie Pvt. Ltd., Mumbai, India.

2.2 Methods

2.2.1 Desizing, scouring and bleaching of cotton fabric In order to remove size and other chemicals from the cotton fabric, the latter was desized, scoured and bleached prior to dyeing in the manner as described below: Desizing of cotton fabric was performed using a 0.25(N) hydrochloric acid solution at the temperature of 500C for duration of 2 hours, at a fabric-to-liquor ratio of 1:20 (w/v), in a laboratory winch machine. The desized cloth was washed thoroughly using hot water, which was followed by a cold wash prior to scouring treatment. Scouring treatment of the desized cotton fabric was performed by pad-steam technique[9-11]

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Application of sodium hydroxide was made by padding the fabric with 10% sodium hydroxide solution containing 2% of an anionic wetting agent (sulphonated caster oil) in a two bowl padding mangle and the squeezing pressure for the padding operation was adjusted to enable a wet pick up 100%. The caustic padded fabric was subsequently steamed in a laboratory steamer at 1000C for 10 minutes. After steaming, the cotton fabric was washed thoroughly with cold water, neutralised with dilute acetic acid, washed again with water and finally dried in air. Bleaching of the scoured fabric was performed using a solution containing hydrogen peroxide (0.1%), sodium meta-silicate (0.08%) and sodium hydroxide (0.05%) at a temperature of 800C for a period of 1 hour in the laboratory winch machine. The bleached fabric was washed thoroughly with cold water, neutralised with dilute acetic acid, washed again with water and dried in air.

2.2.2 Conventional pigment dyeing process Application of pigment emulsion was done at different specified conditions following a pad-drycure technique. For the above purpose, the impregnation of the cotton fabrics in a solution containing pigment emulsion, binder, acetic acid and different specified catalysts was performed separately at nearly 100% wet pick up in a miniature laboratory model two bowl padding mangle. The impregnated and padded fabrics were then dried and finally cured at a temperature of 1400C for 5 minutes using a dry heat in a laboratory drying and curing chamber. Soaping of all the dyed

fabric samples was performed employing 2 g/l non-ionic detergent at 600C for 10 minutes. Finally, the fabric samples were cold washed and dried.

2.2.3 Application of pigment in presence of citric acid Scoured and bleached cotton fabric was padded in a solution containing pigment emulsion, binder, acetic acid, citric acid and sodium di-hydrogen phosphate at nearly 100% wet pick-up in a laboratory model two bowl padding mangle. The padded fabric was then dried and finally cured at a temperature of 1400C for 5 minutes. Soaping of the dyed fabric sample was done at a temperature of 600C for 10 minutes employing 2 g/l non-ionic detergent.

2.2.4 Cotton fabric modified with acrylamide and dyeing with pigment emulsion Pre-soaking of scoured and bleached cotton fabric with potassium peroxodisulphate (K2S2O8) solution of 5 g/l concentration at room temperature for 15 minutes and subsequent application of aqueous acrylamide monomer on the pre-soaked cotton under different specified concentration were performed separately by padding technique in a laboratory two bowl padding mangle. Squeezing pressure for the padding operation was adjusted in each case to enable a wet pick up of 100%. The padded fabrics were then subjected to drying in a drying oven at 950C for 5 minutes. The dried fabrics were then allowed to get cured in a laboratory curing chamber at a temperature of 1400C over a period of 5 minutes. The aminated cotton fabrics were then subsequently dyed with pigment emulsion following an exhaust technique keeping a fabric-to-liquor ratio of 1:20 at 700C for 10 minutes. Fixation of pigment was carried out by treating those fabrics in acetic acid solution for 5 minutes at room temperature followed by treatment with binder for another 15 minutes at a temperature of 500C. Soaping of all the dyed fabric samples was done employing 2 g/l non-ionic detergent at 600C for 10 minutes. Finally, the fabric samples were cold washed and dried.

2.2.5 Cotton fabric modified with polyamine compound and dyeing with pigment emulsion Cotton fabrics were first treated with non-ionic wetting agent at room temperature for 10 minutes. These pre-wetted fabrics were then treated with different specified dose level of polyamine compounds in presence of acetic acid following an exhaust technique for 5 minutes at room temperature. This process was further continued for another 10 minutes at 700C temperature.

Those pre-treated (aminated) fabrics were then separately dyed with pigment emulsion following an exhaust technique at 700C for 10 minutes. Both the pre-treatment and dyeing process were performed at a fabric-to-liquor ratio of 1:20 keeping the dye bath pH ~5. The fixation of the pigment was carried out by treating those dyed fabrics with acetic acid at room temperature for 5 minutes, followed by the application of binder at 500C for 15 minutes. The dyed fabrics were then washed with 2g/l non-ionic detergent at 600C for 10 minutes, followed by cold washed and finally dried.

2.2.6 Measurement of K/S value Dye receptivity of fabric samples dyed with pigment emulsion under different specified conditions as estimated in terms of K/S (Kubelka-Munk function) [12] was determined. The value is based on measuring the reflectance of each dyed fabric samples at the respective wavelength of maximum absorption (max) in a Macbeth 2020- plus reflectance spectrophotometer and converting the reflectance value to (Kubelka-Munk function) K/S as detailed below using the appropriate formula and relevant software attached to the computer aided equipment following the standard procedure: [K/S = (1-R) 2 / (2R)], where K is the coefficient of absorption, S is the coefficient of scattering and R is the reflectance of the substrate at wavelength .

2.2.7 Determination of stiffness Fabric stiffness as expressed by the bending length, was measured in accordance with IS: 6490 1971 (cantilever test) in a SASMIRA Stiffness Tester with a specimen size of 25 x 200 mm [13].

2.2.8 Measurement of wrinkle recovery angle The wrinkle recovery angle of the fabric samples was measured using a SASMIRA Crease Recovery Tester in accordance with IS: 4681 1972 [14]. Average crease recovery in each of warp and weft direction was computed.

2.2.9 Determination of tear strength Tear strength measurement of all the fabric samples were done in accordance with the method prescribed in IS: 6489 1971 in an Elmendorf Tear Strength Tester with a sample size of (100 2 mm) x (63mm 0.15 mm) [15].

2.2.10 Measurement of tensile properties Breaking strength and elongation at break of fabric samples were measured according to a method prescribed in IS: 1969 1968 in a ZWICK/ROELL ZOI0 CRT Tensile Strength Testing Machine [16].

2.2.11 Assessment of colourfastness to washing Colourfastness to washing of cotton fabric samples dyed with pigment emulsion under specified conditions was assessed in a launder-o-meter in accordance with a method prescribed in IS: 3361 1984 (ISO II) [17].

2.2.12 Assessment of colourfastness to light Colourfastness to light of cotton fabric samples dyed with pigment colour was assessed on a Mercury Bulb Tungsten Filament (MBTF) lightfastness tester following a method prescribed in IS: 2454-1984 [18].

2.2.13 Assessment