Download complete project materials on Investigation Into the Effect of Caustic Soda On Cotton Fabric In Mechanization from chapter one to five
CHAPTER ONE
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INTRODUCTION
1.0 Background of the Study
It is a clear fact that we are in an era of fast modernization, this means changes in fashion and the way of life of the people.
For this reason manufacturers have to meet the demand of consumers, hence, their aim is always towards achieving modern ways in the economic method of manufacturing their goods.
Certain properties are desired in some products before they can appeal to potential customers. This is particularly true with textile trade, especially in the industrial business.
Because of this, manufacturers of textile must engage their attention with finding ways and means of attaining certain standards and improving on the standards as competitors are likely to be doing.
Failure to maintain the standards of products, then means a great loss to their business.
The textile manufacturers in order to be able to meet with consumers demands, improve on their materials, as sophisticated machinery are used to produce better quality goods a wide variety of chemicals are used to improve the properties of raw materials, for example fibres, yarns and fabrics.
The production of quality textile materials with the desired properties are governed by many factors, which include the quality of the raw material, the use of modern equipment and lastly, the employment of right processing sequence and method.
The finishing process of textile materials normally improve some existing properties of the materials, or impart new ones. In order to achieve this improvement on the properties, it is essential that the fabric undergo certain pre-treatment sequence before the final finishing can be imparted.
The mercerization process, named after it inventor, John Mercer (1844) is an important textile process involving the treatment of cotton fabric, yarn, cotton with concentrated caustic soda (sodium hydroxide) solution of about 20-30 percent strength (20-30%).
Mercer (1844) padded a piece of cotton cloth with a strong caustic soda solution (60-70% NaoH) at 16.50c (600f), with water while in the alkaline state, then neutralized the alkali with dilute sulphuric acid (Hcl) and
finally washed to remove the neutralized acid. On observation, he found the changes the properties of the cloth which he padded with alkali.
- Shrinkage in the area of the cloth and length of the yarn
- Increased tensile strength
- Increased extension at break
- Increased moisture sorption
- Preferential absorption of caustic soda during the process
- Increased reaction at low temperature
- Increased substantiality for dyes.
- fibre deconvolution (untwisting) and
- More circular Fibre cross-section.
The cloth mercerized in the above manner did not acquire lustre. It was the Bristish chemist Lowe that founded in (1899) that solution acquired lustre if the cloth was held under tension during the treatment, to prevent the shrinkage caused by the alkali.
In addition to the observation made earlier by Mercer (1844).
Lowe discovered that the following effect occurred with the tension applied:
- Greater fibre deconvolution
- Improved dimensional stability.
The mercerization process, whether it is done under tension or not, it causes an increase in the chemical reactivity of the cotton material this renders the fibres more receptive to the absorption of dyes and chemical finishes.
In some cases, cotton fabrics are mercerized mainly to obtain improved dye affinity and chemical reactivity in recent years. Introductory textile (2009) mercerization without tension has been used to produce stretch yarns and fabrics,
characterized by their greatly increased elasticity, such materials are of importance in manufacture of bandages and other similar applications in medicine.
There are several techniques involved in the mercerization process. Mercerization today is practiced on both piece goods (fabrics)and yarn. Although many of the same principles and techniques apply to both: some basic differences exist between the two processes.
In the discussion which follows piece goods mercerization is first examined followed by yarn mercerizing.
Piece goods (fabrics) mercerization by far the largest volume of cotton is mercerized in the fabric form which tends itself to maximum processing flexibility, but the lustre obtained is not as high as with yarn mercerization, fabric mercerizing is carried out on one of two types of machine classified as chainless or chain.
The former applies tension directly to the warp and weft whilst the later only applies indirect tension across the weft with chainless machine the fabric needs to be designed to allow for width loss, or most be entered to a greater width prior to mercerizing, which is difficult and sometime impracticable.
Fabrics may be mercerized in the grey loomstate without any treatment what so ever after scouring and bleaching. The choice adopted will depends upon the type of goods, the particular plant setup, and on the requirements of the final mercerized fabric.
Theoretically, mercerizing of grey good should be the easiest alternative. However large quantities of impurities are brought into the caustic soda solution, and these may interfere with mercerizing or with caustic soda recovery systems.
In addition, powerful wetting agents are required in the mercerizing liquor for satisfactory results the wetting agent enables the caustic soda to penetrate and react with the cotton cellulose.
If maximum luster and smoothness are of prime importance, then thorough desizing, scouring and bleaching before mercerizing is essential.
If maximum tensile strength must be maintained it would be considered safer to mercerize before bleaching. Over bleaching prior to mercerizing should be avoided, as it leads to the dissolution of some of the cellulose by the caustic soda, causing a loss in tensile strength.
All goods, whether they are wet or dry, grey or bleached should be delivered to the mercerizing caustic soda solution in open-width form and in smooth condition as possible.
Wrinkles, particularly in heavy goods, tend to leave marks which show up in subsequent dyeing. A small amount of tension necessary in the goods before entry into the mercerizing bath so as to present fabric evenness.
If the goods being mercerized are in the wet state, prior mangling is essential to leave an amount of moisture throughout the material and so ensure that, on impregnation, the concentration of the caustic soda is uniform In the whole fabric.
For best results, the goods should be dry on entering the caustic soda solution.
The squeezed pressure on the goods after caustic soda impregnation is of great importance. The squeezed rolls should be adjusted so that the content in the goods is at least 100% on the weight of the goods the use of high squeeze pressures which reduce the caustic soda content in the goods to as low as 60% is not recommended.
Although low caustic content does mean less caustic soda consumption and easier washing, it also means, stabilization, inferior lustre, or all the three.
Dyeing: the processes of dyeing is to impart colour on textiles, produces waste liquors which are contaminated with dyes and dyeing assistants which are terrried effluent
Dyes are complex colored organic compounds of widely varying chemical types.
Only about 50% on wt of a commercial dye is a dye stuff, the remainder being usually a non-hazardous filler (e.g sugar) and surfactant sometimes contains metals such as potential toxicants, depending upon their concentration and chemical form in the environment. Heavy metal contents of drinking water are strictly limited.
The characteristics of the waste dye liquor are dependent on the fibre dyed, but the waste is generally highly coloured and high in biological oxygen demand (BOD) and dissolved solids. Dyeing additives such as acetic acid and carriers have high BOD.
The condition of permanence distinguishes dyeing from tinting (when the material is given a colour which is very easily removed with a detergent and water).
Yarns are tinted occasionally so that different counts and quantities can be identified during weaving or any operation which precedes dyeing. In the permanence or fastness of the colour bestowed was qualified by the adjective comparative.
There is probably no dye which can be guaranteed not to alter shade under all conditions.
There are great variations in the fastness of different dye stuffs, but there have been many significant milestones in the search for better fastness, before effective mercerization process and proper absorption of dyes can be achieved, the following pre-treatment has to be ensured
- Singeing
- Desizing
- Scouring bleaching and mercerization
1.1 Statement of the Problem
The study researched into the difference in absorption of dyes by mercerized fabric and the mercerized one before bleaching.
1.2 Aims/Objectives of the Study
- To investigate the effect of caustic soda on cotton fabric in mercerization.
- To study how mercerization affects dye uptake on mercerized cotton fabric using vat dye.
1.3 Significance of the Study
To be able to prove the importance of mercerization on cotton fabric before being dyed and what effect dye has on mercerized cotton fabric.
This also should be beneficial to the manufacturer because it will give him knowledge about the extent to which mercerization influence fabric dye uptake.
To analysis the effect of mercerization on ability of a fabric to absorb dye and it will also be of benefit to the consumers because they will have fabrics with good quality and aesthetic properties.
1.4 Scope of the Study
This study investigates the effect of strong caustic soda on dye uptake of 100% cotton fabric. However, the research was limited to the examination of how 100% cotton fabric can absorb dye when being mercerized.
1.5 Research Methodology
The research methodology is intend to be carry out in the following sequence
- Desizing
- Scouring
- Bleaching
1.6 Definition of Terms
Mercerization:- this is an important industrial process involving the treatment of cotton fabric or yarn with concentrated caustic soda (sodium hydroxide) mercerized cotton is sometimes referred to as pearl cotton.
Dyes:- these are complex organic compounds of widely varying chemical types.
Scouring:– this is the process of removing natural impurities such as waxes, fats and peptic matter from fabric.
Bleaching:- this is the removal of natural colouring matter from textile materials.
Vat:- is a large vessel
Vatting:- this is the process in which the insoluble vat dye is been converted to water soluble
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