Cationization of Cotton by Using Chitosan for Reactive Dyeing to Avoid Electrolyte (Part-1)
Md. Shibli Sadique
Dhaka University of Engineering & Technology,
DUET, Gazipur-1700, Bangladesh
Dhaka University of Engineering & Technology,
DUET, Gazipur-1700, Bangladesh
This study presents finding on the possibility of dyeing of cotton fabric with reactive dyes using chitosan instead of salt. Reactive dyeing is now the most important method for the coloration of cellulosic fibres. Reactive dyes have good fastness properties owing to the covalent bonding that occurs with the terminal (primary and secondary) hydroxyl group of cellulose at alkaline condition during dyeing. All the reactive dyeing systems require huge amount of electrolyte to exhaust the dye. These electrolytes are neither exhaust nor destroyed and hence remain in the dye bath after dyeing. All the above, only 60-65% dye utilization is attainable even with the use of salt in the normal dyeing systems. On the other hand, reactive dyeing pollutes the environment by discharging highly colored reactive dye bath and higher electrolyte concentration. To retain the desired exhaustion of dyes with elimination of salt a convenient method is introduced for cotton treated with chitosan showed a better reactivity and dyeability. In this experiment, dyeing with chitosan instead of salt shown a better possibility owing to the dye absorption test. The dyeing of chitosan treated sample-1, 2, 3 & 4 with NOVACRON RED FN-2BL (1%) dyes shows the absorption rating of 1.6, 1.7, 2.1 & 2.95 respectively at a given wavelength whereas salt treated sample (standard) show the absorption rate 1.9. Dyeing shade varies for different molecular weight of chitosan but low molecular weight chitosan give even shade.
Reactive dyeing is now the most important method for the coloration of cellulosic fibres. Reactive dyes have good fastness  properties owing to the covalent bonding that occurs during dyeing. Cotton is made of cellulose molecules which react with the dye. During reactive dyeing the hydrogen atom in the cellulose molecule combines with the chlorine (cl2) atom in the dyeing process and results in a bond. Reactive dyes used to dye cellulosic fibres. The dyes contain a reactive group, either a haloheterocycle or an activated double bond, that, when applied to a fibre in an alkaline dye bath, forms a chemical covalent bond with a hydroxyl group on the cellulosic fibre. There are some benefits, because the reactive dye consists with Chromospheres of dye part, Bridging Groups, Reactive group bearing parts and Reactive groups. Reactive groups are the responsible for the fixation on alkali condition. All the reactive dyeing systems require huge amount of electrolyte and alkali to exhaust and fix the dye respectively. These electrolytes are neither exhaust nor destroyed and hence remain in the dye bath after dyeing. All the above, only 60-65% dye utilization is attainable even with the use of salt in the normal dyeing systems. Reactive dyeing pollutes the environment by discharging highly colored reactive dye bath and higher electrolyte concentration. Higher electrolyte concentration in the effluent cause worst effects such as- impairing the delicate biochemistry of aquatic organism, destructive attack 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. To retain the exhaustion of dyes without use of salt, a convenient method is introduced for cotton treated with chitosan showed a better reactivity and dyeability. Chitosan is a non-toxic and chemically reactive, and biocompatible natural functional polymer, and has long been used as a biopolymer and natural material in many fields. Recently, chitosan effects widely studied are antistatic, bacteriostatic, biocompatibility properties conferred on various textiles. According to some previous experiences, wrinkle-resistance finishing with chitosan for fabric can improve its wrinkle degree but its handle and mechanical property got worse to a certain extent. Chitosan adsorption also increased the moisture absorption of the fibers. Chitosan with lower molecular weight increased the hydrophilicity of the treated fibers, but chitosan with higher molecular weight, decreased it.
1.2 Objectives of the Project and Thesis
The main objectives of the study to increase the dyeability reactivity dye by using eco-friendly biodegradable chitosan.
- To get desired exhaustion of dye in dyeing of cotton fabric with reactive dyes without using salt.
- To avoid the salt which impart in the environmental pollution.
- To improve color intensity of cotton fabric by using chitosan which provide more dye sites than that of untreated fabric.
- To improve the dye uptake and also to reduce the effluent load.
2.1. Reactive Dye
A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dye. Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre. This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group of cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibres. Reactive dyes in the simplest terms, all reactive dyes are made up of three basic units, a chromophore, a bridge and a reactive group/ groups (either a haloheterocycle or an activated double bond). One problem is that instead of reacting with the -OH groups on the cellulose, the fibre-reactive group may react with the HO- ions in the alkali solution and become hydrolysed. The hydrolysed dye cannot react further. This must be washed out of the fabric before use.
2.2 Properties of Reactive Dye:
- Reactive dyes are anionic dyes, which are used for dyeing cellulose, protein and polyamide fibres.
- Reactive dyes are found in power, liquid and print paste form.
- During dyeing the reactive group of this dye forms covalent bond with fibre polymer and becomes an integral part of the fibre.
- Reactive dyes are soluble in water.
- They have very good light fastness with rating about 6. The dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.
- Textile materials dyed with reactive dyes have very good wash fastness with rating Reactive dye gives brighter shades and have moderate rubbing fastness.
- Dyeing method of reactive dyes is easy. It requires less time and low temperature for dyeing.
- Reactive dyes are comparatively cheap.
- Reactive dyes have good perspiration fastness with rating 4-5.
- Reactive dyes have good perspiration fastness.
|Figure: 2.1. Typical Components of a Reactive Dye|
Dye part or chromogen (color producing part), which contains chromophores. Chromophore - a color-bearing compound, typically meaning the part of a larger organic molecule that makes it appear colored. Some chemicals groups which are responsible for the impart color to the substrate. Dyes typically have a chromophore chemically bonded to other structures that impart desired characteristics such as affinity for the fibre and solubility in water. A particular chromophore structure may be found in a variety of dye classes and in pigments. In practice, monoazo, disazo, metallized monoazo, metallized disazo, formazan, anthraquinone, triphenodioxazine, and phthalocyanine chromophores have been used for the preparation of reactive dyes.
b) The water solubilising group (ionic groups, often sulphonate salts):
The groups which have the expected effect of improving the solubility since reactive dyes must be in solution for application to fibres. This means that reactive dyes are not unlike acid dyes in nature. Solubilizing groups provide characteristics such as water solubility, substantivity, migration and wash off. The dominant solubilizing group in reactive dyes is the sulphonic substituent.
c) The bridging group:
It links the chromogen and the fibre-reactive groups. Frequently the bridging group is an amino, -NH- group or –NR- group. This is usually for convenience rather than for any specific purpose and they also influence the reactivity, degree of fixation, stability of the reactive dyeing and other dyeing characteristics, such as substantivity and migration, significantly. The typical bridging group is an imino (-NH-) group.
iv) The fibre-reactive group
This is the only part of the molecule able to react with the fibre. Reactive group do not contribute color which is determined by chromogen group. The reactivity of vinyl sulphone group is less than halogen group. If no of reactive group incresase, binding also increase depending on the dye structure. If the molecular weight of reactive group increases, reactivity also increases.
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