Cationization Of Cotton Fabrics Salt Free Dyeing & Pigment Dyeing by exhaust
Cellulosic Fabric & Its Dyeing Cotton may be described chemically as (1, 4-β-D anhydroglucopyranose) Natural cellulose fibres carry a small negative change (Μplateau = -11mv) due to presence of some carboxylic acid groups from oxidation at the primary hydroxylic sites At a pH higher than 8, some of the hydroxyl groups in the hydroxymethyl side chains may also be ionized increasing the negative charge significantly . The negative charges on the surface of cellulose repel anionic dyes and hence the efficiency of dye fixation on cellulosic fiber is generally low.
Cotton textiles are dyed mostly with reactive dyes because they produce a wide gamut of bright colours with excellent colourfastness to washing due to the covalent bonding between the fibre polymers and the dye molecules under alkaline pH conditions . The inorganic salt, such as sodium chloride or sodium sulphate, for dye transfer to and penetration into the fibre, and inorganic alkali, such as sodium bicarbonate, sodium carbonate or sodium hydroxide, for dye-fibre reaction, are required in substantial quantities to accomplish the dyeing process.
These salts and alkalis when drained to effluent generate heavy amounts of total dissolved solids leading to environmental pollution. Substantial remedies are being considered within the textile processing sector to reduce the effluent pollution and to fulfill the environmental regulations. Higher electrolyte concentration in the effluents causes worst effects such as Impairing the delicate biochemistry of aquatic organism. Destructive attacks on concrete pipes if sodium sulphate is used as electrolyte due to the formation of alumino-sulphato complexes which swell and crack concretes with considerable alumina content. Evolution of hydrogen sulphide gas under anaerobic conditions when sodium sulphate is used as the electrolyte. Dissolution of such sulphides and subsequent bacterial oxidation to the harmful sulphuric acid.
Why Cationization: To counter this problem number of studies on cotton dyeing has been carried out to improve the dye uptake and fastness properties. Most research focus is on introducing cationic sites into the cotton fabric for interaction . Molecular modification of fibre to have greater affinity and attraction towards anionic dyes. Cationisation of cotton fibre before dyeing process has been proved to be capable for abolishing the requirement of inorganic salt, and also alkali. Nevertheless, cationisation is an extra process and has yet to be taken on to industrial level. Organic chemicals have been shown to be meaningful substituent to inorganic salts in exhaust dyeings
Effects of cationizing pretreatment in the surface of cotton.
Effects of cationizing pretreatment in the surface of cotton.
The commonly used cationic agents are either tertiary amines or quaternary ammonium compounds . Other cationic agents 3-chloro-2-hydroxypropyltrimethylammonium chloride,
Trimethylol
melamine
Dimethylamine N-metylolacrylamide
(TMM),
Polyepichlorohydrin
are commonly used in
modification of cotton fibres. Dytec SFD: Polyamine quat compound for salt & alkali free dyeing of cotton Alquat CF: Polyetheramine for pigment dyeing by exhaust Alquat-5851: Poly amine Alquat APD: Polyamine
Dytec SFD Application: Step-1 Cationisation: Procedure for pre-treatment of cotton with Dytec SFD bath: Load the machine with water Add Altranol-84 and run for 5 mins. Add Dytec SFD-New and run for 5 mins. Add Sodium Hydroxide solution slowly over a 5 mins period and run the machine for 5 mins Load the fabric (MLR of 1:10) Start pre-treatment at R. T. and raise the temperature to 70ºC/1ºC per min Hold at Temperature 70° C for 30 mins. Drain the bath Note: Do not rinse or neutralize the fabric Step-2: Dyeing: To ensure uniform dyeing the above treated substrate needs to be cooled to room temperature. We recommend to take half the quantity of water (MLR-1:10) & run the fabric for 5-10 mins, add balance half quantity of water & run for 5 mins, then add dyestuff to the above cooling bath & start dyeing without salt & alkali. Kindly note that the dwell time during dyeing should be as per standard dyeing. (Note: No salt & alkali required) For eg for VS brand RT-45ºC & at 45ºC hold for 30-45 mins, raise from 45-60ºC & at 60ºC hold for 60-90 mins, drain, hot wash, soaping as usual.
Advantages of Dytec SFD Cationisation with Dytec SFD totally eliminates the salt and reduces the alkali considerably that leads to Lower COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), TDS (Total Dissolved Solvents) and no AOX (Absorbable Organic Halogens) in the effluent. Reduced number of wash offs and elimination of neutralizing. Lower water requirements Reduced effluent volume. Reduced effluent toxicity, no salt in effluent. Little or no cleaning of equipment for faster turnaround Increased dye utilization. 40-50% reduction of dyeing time for increased productivity Reduced cost of dyeing and cost of effluent treatment. Nearly 100% dye exhaustion, so fewer rinses needed. Reduction of colorant in the effluent. Possibility to create one bath dyeing of polyester/cotton blends. Fewer fixing agents and additives Brighter colors
Dytec SFD
Shade-1 : Standard Dyeing Shade-2 : Dytec SFD + NaOH (5+5) % o.w.f Shade-3 : Dytec SFD + NaOH (7+7.5) % o.w.f Shade-4 : Dytec SFD + NaOH (10+7.5) % o.w.f
BACKGROUND Of Pigment Dyeing Pigment dyeing is not really " dyeing“ in it's truest form. Pigments are insoluble in water. They are milled into a paste for garment dyeing purposes.the process is complete when a binder is added to "lock" the pigment into place. PURPOSES Pigments are generally used for light to medium dyeing for fully fashioned garments and for indoor cloth such as wall covering, furniture, table cloth and bed sheets… Pigments are also used to achieve dark shades for outdoor fabrics like tents, stores, awnings…
The process is attractive when dyeing cotton/synthetics fabrics in a single phase. Pigments are non ionic in nature when dispersed in water, so it will not have affinity towards anionic cellulose fibre in dye bath. Because of this, until mid-1980s, use of pigments to color textiles had been generally limited to pad applications because of the inability of pigments to exhaust of fibers. Invention of cationising agents brought the revolutionary changes in the field of pigment exhaust dyeing The presence of cationic charges on or in the fibre causes anionic materials such as pigments to be strongly attracted to the fiber & to be held much more tightly than without the cationic charges.
Garment dyeing gives unique fashionable apparel. Often manufacturers, trying to separate their products from the crowded market place, have elected to buy only white fabric & have it dyed after it has been assembled into garments.
Garment dyeing's enables them to avoid locking themselves into commitments on large orders of dyed rolls of fabric, reduces the risk of building & invention in color fashion. Manufacturers can even stop producing a color that doesn't sell as well as expected & respond faster to changing fashion trends.
The advantages of garment pigment dyeing are: Very short dye cycle time. Low energy/low machine time than other dye classes. Good light fastness except fluorescent colours. Novelty effects can be achieved by altering the chemicals dosage & change in processes. Conventional equipment's can be used. Greater fibre selection & flexiblity Uncomplicated & simple to implement.
Troubleshooting in Garment dyeing using pigment PROBLEM No. 1 “BLOTCHY” UNLEVEL GARMENTS Possible Cause: Garment may contain softeners, resin finishes or optical brightener. Pre-scouring with 1-2 g/l of Modscour-LF / Altranol-CD, found to be helpful. Too short a liquor ratio. 15-20 :1 is recommended Bath temperature at beginning of dyeing or pre-treat cycle too high. Not higher than 40-50°C recommended. Acetic acid added too early in pigment stage. Live steam in direct contact with garments. Baffle steam inlets. Temperature raised too fast. 1-2°C per minute gives best results. Pretreated goods allowed to dry out before pigment stage. Chemicals or pigments added while machine not running. Water of pH 7.5 or above. Chemicals or pigments not pre- diluted. Garments not thoroughly wet out before addition of pre-treat. Extraction rotation speed, after pre-treat, too high. Insufficient agitation.
PROBLEM No. 2 POOR COLOUR YIELD Possible Cause: Garments may contain softeners, resin finishes or optical brightener. Prescouring with 1.2 g/l of MODSCOUR-LF / ALTRANOL-CD, found to be helpful. Too high liquor ratio. 15 – 20:1 recommended. Insufficient agitation Excessive rinsing between cycles. Excessive time in any cycle Pretreated garments allowed to dry out before pigment stage Excessive amount of pretreat used, or pretreat omitted, or goods not pretreated for recommended time and temperature.
PROBLEM No. 3 FOREIGN COLOUR SPOTS Possible Cause: Machine not cleaned after previous dyeing. Excess pretreat not rinsed off sufficiently before pigment stage. Acetic acid not sufficiently diluted or added too quickly, at pigment stage. Pigment not sufficiently diluted or stirred before adding to dyebath. Incompatibility with antifoam used Aftertreat bath too acidic PROBLEM No. 4 POOR FASTNESS Possible Cause: Poor light fastness of fluorescents is to be expected. However, light fastness of conventional pigments is excellent. Poor wash and crock fastness is generally due to inadequate aftertreating; i.e. not enough aftertreat used, not aftertreated for recommended time or temperature. pH of aftertreat bath above 7.5 or goods not very absorbent and are surface dyed.
Alquat-CF/5851 Application: Pigment Dyeing By Exhaust : Step 1: • Bath preparation: Alquat-CF, 2-3% owf + 1% owf Glacial acetic acid, pH – 4.5 ~ 5. • Treat the fabric at room temperature, raise temperature gradually to 60-70°C and maintain for 20-25 mins. • Drain the bath Step 2: Pigmentation: • Take the pigment 4~10% owf and dissolve it. • Add pre-dissolved pigment in the dye-bath and start dyeing at room temperature • Gradually raise the temperature to 70°C & maintain at 70ºC for 20 mins. • Drain the bath • Cold water rinse • Refill or add pigment binder 3 times on weight of pigment and treat for 15 mins at 40°C, drain and dry. • Soaping.
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