Salt and Alkali Free Reactive Dyeing on Cotton Fabric

Last Updated on 29/01/2021

Salt and Alkali Free Reactive Dyeing on Cotton Fabric

Engineer Md Selim Hossain
Jr. IE Officer, Urmi Group
Contact: 01722972420

ABSTRACT
This project is on ‘‘Salt and Alkali Free Reactive Dyeing on Cotton Fabric”. This is a dyeing process where cotton fabric is dyed without salt and soda ash.

The experiment was conducted in the Laboratory of DIU, Department of TE & lab dip of NTL. The aim of this project is to dye the fabric without salt and alkali which will be economic, non-toxic and easily process able for the textile processing.

The use of salt and soda makes the effluent toxic for the environment. In conventional method of dyeing on cotton with reactive dyes, alkali pH should be maintained in dye bath. This method requires more electrolytes for exhaustion and alkali for fixation.

In this project, fiber modification techniques based on polyacrylamide have discussed. Color fastness test is done after dyeing the cotton fabric. It is to be hoped that by the end of this thesis paper the reader will have a better idea about “Salt and Alkali free reactive dyeing on cotton fabric”.

INTRODUCTION
In current practice, cellulosic fibers are predominantly dyed with reactive dyes in the presence of a considerable amount of salt and fixed under alkaline conditions. However, dye fixation efficiency on cellulosic fibers is generally low (varying from 50 – 90%). This, results in a highly colored dye effluent, which is unfavorable on environmental grounds. Furthermore, the high concentrations (40 – 100g/I) of electrolyte and alkali (5 – 20 g/I) required in cellulose fiber dyeing may pose additional effluent problems.

In this work, a new fiber – modification technique based on cationic acrylic copolymer is used. Pretreatment of cellulosic fiber with Polymer is believed to offer an opportunity for increasing both the substantively and reactivity of fibers towards reactive dyes under neutral conditions. The nature of a reactive polymer resin is such that it may react with nucleophilic sites in cellulosic fibers or in the polymer itself, thus fixing the polymer to the substrate. During subsequent dyeing, further reactions between the polymer and the dyestuff, the fiber and the dyestuff, and the fiber and the polymer and can be expected to take place, forming crosslink within the fibers.

Cotton fabric:
Cotton is a natural fiber that comes from the seedpod of the cotton plant and is used to make many fabric types at every price point. The fiber is hollow in the center and, under the microscope, resembles a twisted ribbon.

Physical properties of cotton:
Physical properties of cotton fibers are given below:

• Color: The color of cotton fiber could be white, creamy white, bluish white, yellowish white or grey.
• Tensile Strength: Cotton is moderately strong fiber. Tenacity of 3-5 gm/den. The wet strength of cotton is 20%
• Elongation at break: It has an elongation at break of 5-10%.
• Elastic Recovery: At 2% extension it has an ER of 74% and at 5% extension it has an ER of 45%.
• Specific Gravity: Specific gravity is 1.54.
• Moisture Regain (MR %): Standard moisture regain is 8.5.
• Effect of Heat: Cotton has an excellent resistance to degradation by heat. It begins to turn yellow after several hours at 120⁰C and decomposes marked by at 150⁰C. As a result of oxidation, cotton is severally damaged after few minutes at 240⁰C.
• Effect of Sun Light: There is a gradual loss of strength when cotton is exposed to sun light and the fiber turn yellow. By sun light much of the damage is caused by UV-light and by the shorten weaves of visible light.
• Moisture Content (MC %): Standard moisture content is 7.834.

Chemical Properties of Cotton:
Chemical properties of the cotton fiber are given below:

• Effect of Acids: Cotton is attacked by hot dilute acids or cold concentrated acids which it disintegrates. It is not affected by acids.
• Effects of Alkalis: Cotton has an excellent resistance to alkalis. It swells in caustic alkalis (NaOH) but it does not damaged. It can be washed repeatedly in soap solution without any problem.
• Effect of Organic Solvent: Cotton has high resistance to normal cleaning solvents. Cotton is dissolved by the copper complexes, such as cuprammonium hydroxide, cupriethylene diamine and concentrated 70% H2SO4.
• Effects of Insects: Cotton is not attacked by moth-grubs or beetles.
• Effect of Micro Organism: Cotton is attacked by fungi and bacteria.

Reactive Dyes:
The reactive dyes are best for cotton for its better range of application and better fastness properties. Reactive dyes are mostly used in the world about 30%, because this dye is so cheap and suitable for cotton dyeing. It makes a covalent bond with the fiber polymer and act as an integral part of fiber.

In a reactive dye a chromophore contains a substituent that is activated and allowed to directly react to the surface of the substrate.

Popularity of Reactive Dye:
Reactive are mostly used for dyeing cellulosic fibers. At past cellulosic fibers were dyed with direct and vat dyes, but after the introduction of reactive dyes their utility has become limited.

Reactive dyes are superior to direct dye in the following aspects:

• Ability to procedure bright shades of wide range.
• High leveling quality.
• Good washing fastness.
• Good light fastness.

And it is superior to vat dyes in the following aspects:

• Simple dyeing method therefore one stage dyeing.
• Low temperature dyeing (below 100°C)
• Lower cost, i.e. cheaper.

Again, its dyeing process is fast and gives brighter shades than metalized azo dyes. For the above reasons reactive dyes are more popular.

Properties of reactive dye:

• Reactive dyes are anionic dyes which are used for dyeing cellulosic protein polyamide fibers.
• Reactive dyes are found in powder, liquid and print paste from.
• During dyeing, the reactive group of this dye forms covalent bond with fiber polymer and becomes an integral part of fiber.
• Reactive dyes are soluble in water & cheap.
• They have very good light, perspiration, wash & rubbing fastness with rating about 6.
• The dyes have very stable electron arrangement and the degrading effect ultraviolet ray.

Structure of Reactive Dyes:

General structure of reactive dyes:

The general structure of reactive dye is: D-B-G-X.

Chemical structure of reactive dyes:

Here,
D= dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse, premetallised dye etc.
B = bridging part.
Bridging part may be –NH- group or –NR- group.
G = reactive group bearing part.
X= reactive group.

Classification of reactive dyes:
Reactive dyes may be classified in various ways as below:

1) On the basis of reactive group:
a) Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-

1. Triazine group
2. Pyridimine group
3. Quinoxaline dyes

Example:

Triazine derivatives: procion, cibacron.
Pyridimine derivatives: reactone
Quinoxaline derivatives: levafix.

b) Activated vinyl compound:

• Vinyl sulphone
• Vinyl acrylamide
• Vinyl sulphonamide.

Example:
Vinyl sulphone: remazol
Vinyl acrylamide: primazine
Vinyl sulphonamide: levafix.

2) On the basis of reactivity:

• Lower reactive dye: Medium reactive dye: here pH is maintained 11-12 by using Na2CO3 in dye bath.
• Higher reactive dye: here pH is maintained 10-11 by using NaHCO3 in dye bath.

3) On the basis of dyeing temperature:

a) Cold brand:
These types of dyes contain reactive group of high reactivity. So, dyeing can be done in lower temperature i.e. 320-600C.

For example: PROCION M, LIVAFIX E.

b) Medium brand:
This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.

For example, Remazol, Livafix are medium brand dyes.

c) Hot brand:
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930 C temperature is required for dyeing.

For example, PRICION H, CIBACRON are hot brand dyes.

Dyeing cycle and Important factors/phases in Reactive Dyeing:

• pH of the substrate prior to dyeing
• pH of the dye bath
• Pretreatment of the substrate
• Solubility of the dyestuff
• Dyeing temperature
• Quality of water and salt
• Electrolyte concentration
• Dyeing time
• Washing off sequence
• Type of alkali.

Functional group of reactive dyes:

Trade Names of Reactive Dye:

Some trade names of this dye are mentioned:

Polyacrylamide:
Polyacrylamide (IUPAC poly (2-propenamide) or poly (1-carbamoylethylene)) is a polymer (-CH2CHCONH2-) formed from acrylamide subunits. It can be synthesized as a simple linear-chain structure or cross-linked, typically using NHYPERLINK. Polyacrylamide is not toxic. In the cross-linked form, the possibility of the monomer being present is reduced even further. It is highly water-absorbent, forming a soft gel when hydrated, used in such applications as polyacrylamide gel electrophoresis and in manufacturing soft contact lenses. In the straight-chain form, it is also used as a thickener and suspending agent. More recently, it has been used as sub dermal filler for aesthetic facial surgery.

Uses of polyacrylamide:
One of the largest uses for polyacrylamide is to flocculate solids in a liquid. This process applies to water treatment, and processes like paper making. Polyacrylamide can be supplied in a powder or liquid form, with the liquid form being subcategorized as solution and emulsion polymer. Even though these products are often called ‘polyacrylamide’, many are actually copolymers of acryl amide and one or more other chemical species, such as an acrylic acid or a salt thereof. The main consequence of this is to give the ‘modified’ polymer a particular ionic character.

Another common use of polyacrylamide and its derivatives is in subsurface applications such as Enhanced Oil Recovery. High viscosity aqueous solutions can be generated with low concentrations of polyacrylamide polymers, and these can be injected to improve the economics of conventional water flooding.

It has also been advertised as a soil conditioner called Krilium by Monsanto Company in the 1950s and today “MP”, which is stated to be a “unique formulation of PAM (water-soluble polyacrylamide)”. It is often used for horticultural and agricultural use under trade names such as Broadleaf P4, Swell-Gel and so on. The anionic form of cross-linked polyacrylamide is frequently used as a soil conditioner on farm land and construction sites for erosion control, in order to protect the water quality of nearby rivers and streams.

The polymer is also used to make Grow-Beast toys, which expand when placed in water, such as the Test Tube Aliens. Similarly, the absorbent properties of one of its copolymers can be utilized as an additive in body-powder.

The ionic form of polyacrylamide has found an important role in the potable water treatment industry. Trivalent metal salts like ferric chloride and aluminum chloride are bridged by the long polymer chains of polyacrylamide. This results in significant enhancement of the flocculation rate. This allows water treatment plants to greatly improve the removal of total organic content (TOC) from raw water.

Environmental effects of Polyacrylamide:
Concerns have been raised that polyacrylamide used in agriculture may contaminate food with acrylamide. While polyacrylamide itself is relatively non-toxic, it is known that commercially available polyacrylamide contains minute residual amounts of acrylamide remaining from its production, usually less than 0.05% w/w.

Additionally, there are concerns that polyacrylamide may de-polymerise to form acrylamide. In a study conducted in 2003 at the Central Science Laboratory in Sand Hutton, England, polyacrylamide was treated similarly as food during cooking. It was shown that these conditions do not cause polyacrylamide to de-polymerise significantly. California requires (current as of 2010) products containing acrylamide as an ingredient to be labeled with a statement that it is “a chemical known to the State of California to cause cancer.”

In a study conducted in 1997 at Kansas State University, the effect of environmental conditions on polyacrylamide were tested, and it was shown that degradation of polyacrylamide under certain conditions does in fact cause the release of acrylamide. The experimental designs of this study as well as its results and their interpretation have been questioned, and a 1999 study by the Nalco Chemical Company did not replicate the results.

Raw Materials:

• Grey fabric
• Chemicals
• Dyes

Fabric Specification:
100% cotton knitted fabric (single jersey)

• Yarn count: 32Ne
• Wales per inch (WPI): 42
• Course per inch (CPI): 54
• Twist per inch (TPI): 14
• Gram per square meter (GSM): 171

Used chemicals:

• For Scouring and bleaching: (Ant creasing agent, Detergent, Sequestering agent, Caustic Soda, Soda ash, Hydrogen peroxide)
• For Neutralization and peroxide kill: (Acetic Acid, Hydrogen Peroxide Killer)
• The scoured and bleached fabric is treated with Polyacrylamide.
• For Dyeing: (Wetting agent, Sequestering agent, Reactive Dye).

Names of Dyes:

• Reactive Dyes (Remazol Blue RR)

Apparatus:

• Beaker
• Spirit lamp
• Stand
• Pipette
• pH scale
• Stop Watch
• Glass rod
• Thermometer
• Padding Machine
• Curing Machine
• Fire Box

Conventional Dyeing Method:

3.1) Method:

The dye bath is set with calculated amount of dye solution and water using MLR 1:20. Enter the wetted well bleached fabric into the bath, raise the temperature to 40o c and work for 10 min then add the calculated quantity of salt in three portions at regular intervals (10 min). Raise the temperature to 50 o c and continue dyeing for 30 min, add the calculated quantity of soda ash and continue the dyeing for further 30 min. Finally take the material out, wash the material with cold water and then give soaping treatment to remove the unfixed dyestuffs and chemicals. The dyeing temperature and recipe of various reactive dyes are shown in table 3.

Fabric modification technique:

Treatment with polyacrylamide:
Pad the material with calculated quantity of polyacrylamide and water with 70% expression. After padding the material is dried at ambient temperature and then cured at 120oc for 7 min.

Dyeing of pretreated fabric:
Set the bath with calculated amount of dye solution and water. Enter the pretreated fabric into the bath. Raise the temperature to a specified level at 1.5o c / min, and dyeing continue at the set temperature for the further 60 min. Finally take out the material, soaped thoroughly and washed with cold water and dried.

3.3) Results:

Determination of fastness to washing:
The wash fastness was tested following ISO (standards) test no: 2

Discussion:
The probable mechanism for the fixation of reactive dye on the polymer treated cotton sustain may be expressed as follows:

The pretreatment of cotton fabric with polyacrylamide demonstrates the introduction of functional amino groups which increase the substantivity and also the reactivity of cotton. The cationic charged amino groups may be involved in the adsorption of anionic chromophore of reactive dyes.

The improved dye ability is postulated due to the presence of amide groups (-CONH2) available from the polyacrylamide which also tents to improve the reactivity of cellulosic substrate. The attachment of the dye molecules onto the partially-modified cellulosic substrate is by covalent bonding since no dyes strips out from the dyed sample. This is also indicative through the fastness properties wash fastness.

The fastness values (given in table 1 and 2) of all such dyed samples are quite satisfactory and comparable with those of conventional dyed samples. The dry crease recovery angle values of the polymer treated samples are 80o while that of conventional dyed sample is 68o. Therefore, as expected, the polymer treated dyed samples indicate an improvement in the wrinkle recovery.

A high level of dye exhaustion on the treated fabric can be achieve in the absence of salt and alkali at a temperature as low as (Normally at 60-80oc) that used in the conventional dyeing process. Further increases in temperature may improve dye bath exhaustion, but only to a limited extent. However higher temperatures (90-100^oC) are generally recommended for dyeing modified fabrics to obtain better penetration and fixation.

Modern Method

Recipe:
For scouring and bleaching:

• Wetting agent: 0.7 gm/l
• Anti-Creasing agent: 0.5 gm/l
• Sequestering agent: 0.7 gm/l
• Soda ash: 2.0 gm/l
• Hydrogen Peroxide: 3.0 gm/l
• Stabilizer: 0.7 gm/l
• M: L: 1:10
• Temp: 98° C
• Time: 60 min

For Neutralization and Peroxide kill:

• Acetic acid: 0.50 gm/l
• Peroxide Killer: 0.20 gm/l

Fabric modification:

• Cotton fabric is padded with the polyacrylamide.
• Sample 1: 40% polyacrylamide
• Sample 2: 50% polyacrylamide
• Sample 3: 60% polyacrylamide

For Dyeing:

• Sequestering agent: 1 gm/l
• Wetting agent: 1 gm/l
• Leveling agent: 1 gm/l
• Reactive Dye (Blue): 2%
• M: L: 1:10
• Temp: 60°C
• Time: 60 min

Method of fixing:

• Fixing agent – 1 gm/l
• Temperature – 45˚C
• Time – 10 minutes
• M: L: 1:10

Preparation of Fabric:
The fabric sample was desized using the acid desizing method. The fabric was scoured by the alkali method using a standard procedure. Then, it was subjected to a bleaching process using hydrogen peroxide as the bleaching agent.

Pretreatment:
The padding method was used for pretreatment of cotton with PVAmHCl. The pH of the pretreatment solution was maintained by the buffer potassium dihydrogen phosphate (7 gpl) and sodium hydroxide (1.45 gpl). Padding was carried out using two dips (4 min each) and two nips. Fabric samples were predried at room temperature and then baked at 102oC for 12 min in a rapid baker. Padding was done at different concentrations of PVAmHCl.

Dyeing:
The fabric was dyed with reactive dye using the procedure recommended by the dye manufacturer. One fabric sample was considered as a control sample. Exhaust dyeing was carried out at a liquor ratio of 1:30. Dyeing of the fabric pretreated with different concentrations of PVAmHCl was carried out at 80oC for 60 min. Fixation was conducted for 20 min using 6 to 8 gpl of Na2CO3 and 0.01 to 0.5 gpl of caustic lye.

Testing:
The details of various tests conducted on the fabric are as follows. Colour strength (K/S Value) Colour strength K/S was measured on a Minolta Spectrophotometer. These values are calculated using the following “KUBELKA-MUNK” equation: where K is the absorption co-efficient, R is the reflectance of the dyed sample and S is the scattering co-efficient at the wavelength of maximum absorption.

Table: 07

Result of fastness test:

Table: 08

The results of wash and rubbing fastness are presented in Table 8.

The fastness properties of dyed cotton fabrics pretreated with PVAmHCl were determined. The results were compared with those of conventional dyeing. The wash fastness was excellent for all samples from the salt-free dyeing, confirming the effectiveness of dye fixation due to pretreatment with PVAmHCl. Rubbing fastness was also observed to be good when compared with that obtained by conventional dyeing.

Determination of fastness to washing:
The wash fastness was tested following ISO-105 X 63320. Here the tested temperature was 60°C which treated at 60 min. The fastness result is good.

Determination of fastness to rubbing:
The rubbing fastness was tested following ISO-105 X 12. The fastness result is good.

When the cotton fabric is treated with polyacrylamide, the primary hydroxyl groups of cellulose is partially modified into amide groups, which intern leads the cellulose to act like as wool fiber and hence reactive dyes can be dyed on cotton at neutral pH in the absence of electrolyte and alkali. The cationic charged amino groups may be involved in the adsorption of anionic chromophore of reactive dyes and the dye molecules are attached onto the partially modified cellulosic substrates by covalent bond formation.

CONCLUSION
Pretreatment of cotton with polyacrylamide enhances the possibility of dyeing cotton at neutral pH with various commercial reactive dyes. Such pretreatment, as applied through pad – dry – cure process, brings about some chemical changes in the treated fabric.

Fastness properties are adequate and quite comparable with conventionally dyed samples. The dyeing of cotton with reactive dyes using polyacrylamide in the dye bath improves the dye ability of cellulosic fabrics with reactive dyes and reducing effluent discharge.

When dyeing the modified substrates, reactive dyes can be much more efficiently exhausted and fixed onto cellulosic fabrics under neutral conditions in the absence of salt. The modifications show an overall suitability for different reactive dyes. The modified dyeing does not suffer either from a significant drop in light fastness, wash fastness.

REFERENCES

• http://www.fibre2fashion.com/industry-article/textile-industry-articles/salt–alkali-free-reactive/salt–alkali-free-reactive4.asp
• http://www.autexrj.com/cms/zalaczone_pliki/3_01_11.pdf
• Technology of textile processing by Dr. V. A. Shenai, part ii.
• http://en.wikipedia.org/wiki/Polyacrylamide
• Lecture Sheet, Sumon Mozumder, Daffodil International University.

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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