Now You Know Scope of CVC Knit Fabric Dyeing without Pretreatment

Scope of CVC Knit Fabric Dyeing without Pretreatment

Authors: Arifur Rahman Raju, Md. Minhazul Islam
Md. Shahin Khandakar Nayem, Md. Aowsaf Islam
Mesbah Uddin Ahmed, Md. Nazmul Islam
Md. Shahidul Karim, Md. Azhar Uddin
Sudipta Bhattacharjee, Md. Mazidul Haque Ridoy
Md. Mahfuzul Haque Refat, Md. Rezaul Karim
B.Sc. in Textile Engineering
Textile Engineering College, Noakhali, Bangladesh
Email: shuvotex1@gmail.com

ABSTRACT
Nowadays CVC knit fabric is dyed with pretreatment. As a result huge amount of chemicals, water, time, money etc are required. But if it is done without pretreatment, the result could have been better and the cost will be minimized. By comparing pretreated and without pretreated fabric, the color fastness properties are same. But the strength, K\S value is comparatively higher than the pretreated fabric. On the other hand without pretreated fabric can save chemicals, time, water, money etc. So considering these results it can be introduced in garments or textile industries as a new era of less pollution dyeing system will be opened obviously.

CHAPTER ONE 

INTRODUCTION

1.1 INTRODUCTION

Dyeing is the process of adding color to textile products like fibers, yarns and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dyes are obtained from flowers, nuts, barriers and other forms of vegetables and plants as well as from animal and mineral sources. These are known as natural dyes. The other class of dye is known as synthetic dyes. These are based on a particular type of chemical compositions. Some of these dyes are –Acid dyes, Basic dyes, sulphur dyes, Vat dyes, Reactive dyes, and Pigment dyes. Color is applied to fabric by different methods of dyeing for different types of fiber and at different stages of the textile production process. Pretreatment is done for removing the natural impurities of textile raw material. This impurities include by products on cotton such as waxes, proteins etc. For knit fabric (polyester-cotton blend) scouring and bleaching are done as pretreatment. Scouring is the process in which the fabric is treated with alkali (NaOH) at room temperature or a suitable higher temperature and by this process oil , fat, wax & other natural & added impurities are removed .Absorbency of the fabric also increases a greater extent in this process. Natural coloring matters and remaining trace impurities are removed from the grey fabric by bleaching. So, the fabric gets a permanent white color which is very important for the following dyeing or printing process .Sodium hydroxide (NaOH) is main agents for scouring. After scouring process the excess NaOH which is given up by mixing with water of pond, river, canal. As a result pH of water increase which causes lack of oxygen in water which result in death of living organism of water .It also decreases the fertility of cultivated land .In bleaching process mainly sodium hydrochloride or hydrogen peroxide is used. These chemicals are harmful for health .The water with these chemicals is restricted to give up without any treatment .So effluent treatment is done before giving up this water. This treatment adds labor cost, electricity cost which ultimately affects total production cost. Beside this extra cost is added for pretreatment.

1.2 AIM

Dyeing of CVC fabric without pretreatment for reducing harmful effect due to use of excess chemicals, minimizing process cost and others.

1.3 OBJECTIVES

• To save chemicals
• To improve physical properties of CVC fabric
• To reduce dyeing processing steps
• To denote minimum shade percentage
• To reduce processing cost
• To reduce usage of water
• To produce eco friendly dyeing process

CHAPTER TWO

 LITERATURE REVIEW

2.1 INTRODUCTION
One researcher carries on his research about dyeing of P/C blend fabric and takes it as challenge to the modern textile industries due to its variation in color value, shade depth, tensile strength & surface residual weight loss. The researcher measures his research result on the basis of test of color fastness, determination of weight loss, abrasion resistance, SEM Topography, FTIR analysis, Thermal analysis, X-Ray diffraction studies, dyeing behavior of fabric, weight loss and abrasion resistance measurement, Tearing strength measurement etc. The water fastness or wash fastness and light fastness can be improved by the proper analysis of the thermodynamic equilibrium of dye fiber bond and its stoichiometry. A group of investigators make their research on dyeing of polyester/cotton fabric using disperse/reactive dye stuffs in one bath method of dyeing processes. In order to improve the adhesion of chitin to the surface of P/C fibers, Pretreatment in NaOH solution was performed. The data obtained shows that it is possible to dye P/C fabrics finished by chitin with only one disperse/reactive dyestuff. The dyed sample showed good rubbing and washing color fastness properties within the range of color change. The color strength of dyed samples increased with the increased deposition of chitin on the fabric. A research also goes on dyeing of P/C blend fabric which is suitable for one bath or two bath methods. Two bath methods are suitable. Two bath dyeing method are really long and complicated. One bath two step procedure is shorter as compared to two bath method but drawbacks are lower dye ability and poor reproducibility. A clan of research examines the process of dyeing polyester/cotton fabric with a highly effective fiber reactive and a disperse dyestuffs. Enamely (E)-4 hydroxy-5-((4-((2-sulphonyl)amino)-1,3,5-triazine-2-yl)amino)-3-((2-sulphonyl)diazenyl)nepthalene-2,7-disulphonic acid and (E)-5-((4-nitrophenyl)diazenyl)pyridine-2(1H)-1. Dyed textiles there were characterized by good dry rubbing and washing fastness but medium wet-rubbing fastness properties.

2.2 CVC KNIT FABRIC

CVC fabric is a result of polyester and cotton blending in the certain proportion. Interwoven CVC fabrics are characterized by enlarged percentage of cotton yarn that provides better hygienic properties in comparison with TC fabrics and better strength characteristics in comparison with 100% cotton fabrics. Also they guarantee low shrinkage, high color-fastness and perfect durability. Most types of CVC fabrics have the same constructions as T/C fabrics and differ from them by enlarged percentage of cotton only. CVC fabrics are perfect for producing medical and chef clothes, shirts. All CVC fabrics are suitable for work wear, uniforms and corporate clothes for all kind of industries. CVC fabrics have a good hygienic properties, they are very comfortable to wear and durable due to combination of polyester and cotton fibers. Knit fabrics are fabrics made from interlocking loops of thread, which is in contrast to the lengthwise and crosswise weaving of threads found in woven fabrics. The result is a fabric that has varying degrees of stretch-ability, from slight to extreme elasticity. Knit fabrics are popular due to their ability to drape well on any body type, their comfort and their versatility. Along with degrees of stretch, knit fabrics can be made of different fibers and come in a variety of weights. Knit fabrics are different from woven fabrics in that the strands of yarn are looped together as opposed to being straight. Knitted fabrics have been made for hundreds of years. The traditional method involves taking wool yarn and looping it around two needles. In modern times this same fabric can be produced much quicker by machines that can also knit many different types of material, such as cotton, silk and polyester.

Fig: CVC fabric

2.3 DISPERSE DYE
Disperse dyes are non-ionic. They dye all the synthetic and cellulose acetate fibers by using a direct dyeing technique. Only dyeing temperature varies from one fiber to another. Thus they are one of the major classes of dyestuff. The development of disperse dyes for dyeing secondary cellulose acetate fibers in the early 1920’s was a major technological breakthrough. Their major use today is for the coloration of polyesters, the most important group of synthetic fibers. Disperse dyes are relatively insoluble in water at room temperature & have only limited solubility at high temperatures. They possess substantively for hydrophobic fibers such as nylon and polyester, in which they are quite soluble. These dyes are present in the dye bath as a fine aqueous suspension in the presence of a dispersing agent. The water dissolves a small amount of the dye in monomolecular form. The hydrophobic fibers then absorb the dye from the solution because these dyes are non ionic organic compounds of relatively low molecular weight. Many sublime on heating and dyeing by absorption of dye vapor is also possible. Disperse dyes have slight water solubility because of the presence of polar substituent’s in their molecular structures.

Fig: Dispersed dye

2.4 REACTIVE DYE
Reactive dyes are the youngest and most important dye class for cellulosic material. Worldwide consumption of reactive dyes for cellulosic materials in mid 1980’s was about 10 to 12 %, whereas in Japan alone it represents about 40% of total dye consumption. The reactive dyes offer a wide range of dyes with varying shades, fastness and costs with high brilliancy, easy applicability and reproducibility. However, good preparation of the material is a prerequisite. The color yield and brilliancy of shades are enhanced significantly by mercerization. The dyes are unstable to hypochlorite. Hence, bleaching with hypochlorites may create problem during subsequent dyeing with reactive dyes. Reactive dyes comprise a chromospheres and a reactive group. They differ fundamentally from other dye classes in the fact they chemically react with the textile fiber forming covalent bonds. The conventional dyes on the other hand, owe their weight fastness because of physical association, non specific chemical bonding (e.g. Hydrogen bond) or insolubilisation inside the fiber. There is no clear border line between physical and chemical interactions between molecules. Vander wale’s forces and hydrophobic bonding usually considered physical processes, whereas hydrogen bonding and columbic attraction of ions can be considered as physical or chemical phenomena. On the other hand, the formation of co-valent bond is definitely a chemical process.

Fig: Reactive dye.

2.5 BASIC MECHANISM OF CVC FABRIC DYEING

2.5.1 MECHANISM OF DYEING BY DISPERSED DYE

The dyeing of hydrophobic fibers like polyester fibers with disperse dyes may be considered as a process of dye transfer from liquid solvent (water) to a solid organic solvent (fiber). Disperse dyes are added to water with a surface active agent to form an aqueous dispersion. The insolubility of disperse dyes enables them to leave the dye liquor as they are more substantive to the organic fiber than to the inorganic dye liquor. The application of heat to the dye liquor increases the energy of dye molecules and accelerates the dyeing of textile fibers. Heating of dye liquor swells the fiber to some extent and assists the dye to penetrate the fiber polymer system. Thus the dye molecule takes its place in the amorphous regions of the fiber. Once taking place within the fiber polymer system, the dye molecules are held by hydrogen bonds and Vander Waals’ force.

2.5.2 MECHANISM OF DYEING BY REACTIVE DYE

The cellulose anion is a nucleophile which can take part in the substitution and addition reactions. Nitrogen containing heterocyclic rings of dye molecule bearing halogen- substituent’s (-Cl,-F etc.) undergo neucleophilic substitution. Heteroatom’s (Nitrogen etc.) in aryl ring activate the system for neucleophilic attack because of their electro negativity or Carbon-Carbon double bond is polarized by the powerfully electron attacking sulphone group. This polarization confers a positive character on the terminal carbon atom, favoring neucleophilic addition of cellulose ion.

Fig: Neucleophilic substitution reaction.

CHAPTER THREE
MATERIALS AND METHODS

3.1 RAW MATERIAL AND EQUIPMENTS USED

3.1.1 RAW MATERIALS
Fabric Specification:

• Types of Fabric : Knit(plain)
• GSM : 153
• CPCm, WPCm, Weave design

3.1.2 CHEMICAL EQUIPMENTS

Table 3.1 Chemical specification

Chemical	Commercial Name	Company/Supplier/Country
Wetting agent	T.R oil	Bangladesh
Sequestering Agent	EDTA	Bangladesh
Sodium Hydroxide	Caustic Soda	Bangladesh
Hydrogen Peroxide	Bleaching agent	Bangladesh
Stabilizer	Potassium stearate	Bangladesh
Reactive Dye		Bangladesh
Salt	Sodium Chloride	Bangladesh
Soda	Sodium Carbonate	Bangladesh
Disperse Dye		Bangladesh
Dispersing Agent		Bangladesh
Carrier		Bangladesh

 

3.1.3 MACHINE EQUIPMENTS

Table 3.2 Machine Specification

Machine Name	Model	Manufacturing name	Origin
PRECISA Balance	BJ1000C	Precisa Grabimetrics AG	Switzerland
Oven dryer	HX-30	Parsons	England
Sample dyeing machine	Good brand	Jeffreys Rochdale	England
Compactor Dryer Machine		Copower technology	Taiwan
Wash Fastness Tester( Rota Wash)	SDLM228B	SDL. Textile Machine Manufacturing Co.	England
Color matching cabinet	CAC-60	Verivide	England
Spectrophotometer	650	Data Color	USA
Rubbing Fastness Tester	SALO BS	MESDAN	ITALY

 

3.2 OPERATION SEQUENCE

3.2.1 PRETREATMENT
For this project, the required amount of knit fabric is collected from store. Total fabric are scoured and bleached at the same bath in sample winch dyeing machine. The combine recipe for scouring and bleaching are following:

Recipe:

• NaOH : 5 gm/L
• Hydrogen Peroxide : 5 gm/L
• Stabilizer : 2 gm/L
• Wetting Agent : 1 gm/L
• Sequestering Agent : 1.5 gm/L
• Temperature : 100
• Time : 30 min
• M: L : 1:10

The bath is set at room temperature. In the bath 2000ml (for 200gm fabric) water is taken. Then wetting agent, sequestering agent, caustic soda, Hydrogen peroxide, stablizer are added. Then the sample fabric is loaded and the process is run for 30 minute. After raising the temperature to 100°c, Then the sample fabric is unloaded and washed with 1g/L acetic acid solution for 1-2 minute.Then sample fabric is washed by normal cold water. Finally the sample is dried.

Fig: Graphical representation of pretreatment

3.2.2 DYEING

Recipe (Polyester Fabric):

• Disperse dye :4%
• Dispersing agent :2gm/L
• Carrier :3gm/L
• Sequestering agent :1gm/L
• Wetting agent :1gm/L
• Time :40 minute
• Temp :100°c
• pH :4-5
• M:L :1:10

Recipe (Reduction Cleaning):

• Hydrose :4gm/L
• NaOH :4gm/L
• Sequestering agent :1gm/L
• Wetting agent :1gm/L
• Time :30 minute
• Temp :90°c
• M:L :1:10

Recipe (Cotton Fabric):

• Reactive Dye :4%
• Salt :4gm/L
• Soda :16gm/L
• Sequestering agent :1gm/L
• Wetting agent :1gm/L
• Time :40 minute
• Temp :60°c
• pH :10-11
• M:L :1:10

The dyeing process is done on sample dyeing machine (Rota dyer). At first in a beaker stock solution is prepared for every chemical and disperses dye in according to the recipe. Then total liquor is prepared as per recipe. After that liquor is taken in the tube of Rota dyer machine. Then pretreatment and without-pretreatment fabrics are loaded and the tube set on Rota dyer machine. Then the process is run for 40 minute after raising the temperature 100°C. Finally the fabrics are unloaded and washed with cold water, then hot water and cold water. After that in beaker, stock solution is prepared by every chemical for reduction cleaning. Then total liquor is prepared as per recipe. After that liquor is taken in the tube of Rota dyer machine. Then the fabrics are dyed by disperse dye are loaded and the tube are set on Rota dyer machine. Then the process is run for 30 minute after raising the temperature 90°C. Finally the fabrics are unloaded and washed with cold water. At last in beaker stock solution is prepared for every chemical and reactive dye in according to the recipe. Then total liquor is prepared as per recipe. After that liquor is taken in the tube of Rota dyer machine. The fabrics are loaded and the tube is set on Rota dyer machine. Then the process is run for 40 minute after raising the temperature 60°C. Finally the fabrics are unloaded and washed with cold water, then hot water and cold water. After that the pretreatment and without-pretreatment fabrics are dried.

Fig: Graphical representation of dyeing

3.3 TEST METHOD

3.3.1 STRENGTH TEST (BALL BURSTION)

This test is done by coated fabric. Not for ordinary knitted fabrics. In the test a 25 mm diameter steel ball is passed through the stretched fabric can the force is required do so the recorded. This test cannot be carried using an attachment on a standard tensile tester. The result from this test is not directly comparable with the result of diaphragm bursting test. This test measures force only not the force per unit area.

Fig: Ball Bursting

3.3.2 FASTNESS MEASUREMENT

3.3.2.1 RUBBING FASTNESS OF DYEING

A specimen of size 14 cm × 5 cm is cut. The test specimen is locked onto the base of crock meter. A white cotton fabric of size 5 cm × 5 cm is set to the finger of the crock meter using the spinal clip. The covered finger is lowered on the test sample. Hand crank is turned 10 times at the rate of 1 turn/sec. The white rubbing test cloth is removed and evaluated with the grey scale.

Fig: Rubbing fastness tester

3.3.2.2 WASH FASTNESS OF DYEING SAMPLE

In accordance to ISO105C03 a specimen of size 10×4 cm is cut. A multi-fiber of same size is also cut. The test specimen and multi-fiber are aligned and sewn together to form a composite specimen.

After treating the samples are rinsed in cold distilled water twice and then for 10 minutes in cold running tap water. Then the samples are squeezed and the stitching is removed from three sides leaving one short side 4 cm sewed. Then it is dried at maximum 60⁰C temperature. Now the change in color of uncovered portion is assessed with staining and color change grey scale.

Fig: Rota wash machine

3.3.2.3 COLOR FASTNESS TO PERSPIRATION

In accordance to ISO 105 EO2 a specimen of size 10×4 cm is cut. A multi-fiber of same size is also cut. The test specimen and multi-fiber are aligned and sewn together to form a composite specimen.

The composite test sample was wetted out in solution at room temperature. The material ratio was 1:50 and left for 30 minutes excess solution was poured of and placed between two glass plates under a pressure of 4.5 kg and placed in an oven for 4 hour at 37±2º C temperature. The specimen was removed and dried in warm air not exceeding 600C. Then evaluation was done by grey scale.

Fig: Perspire-meter of perspiration fastness test

3.3.3 CALCULATING VALUE OF CMC
CMC: Color matching of computer.CMC value indicates shade matching. ∆L*(Darker Lighter): ∆L* indicates darkness or lightness of the shade. If ∆L* value is positive (+) then the shade is lighter. If ∆L* value is negative then the shade is darker.

∆a*: ∆a* value indicates radish of the shade. If the ∆a* value is positive (+) then the shade is more red. If the ∆a* value is negative then the shade is less red. ∆b*: ∆b* value indicates yellowness of the shade. If ∆b* value is positive (+) then the shade is more yellow. If the ∆b* value is negative then the shade is less yellow.

Fig: Spectrophotometer

3.3.4 EQUATION FOR CALCULATING K/S VALUE

The basic information required for the color match prediction is the relationship between reflectance of the dyed material and concentration of the dyestuffs. For textile dyed materials the light scattered by a single particle is re-scattered by many other particles before emerging from turbid media. This is called multiple or dependent scattering, which is very complex to explain. The medium is characterized by optical parameters k and s which are commonly known as K-M absorption and scattering co-efficient respectively. Memory is synchronized with the position of the beam on the specimen in the microscope, and the resulting image is therefore a distribution map of the intensity of the signal being emitted from the scanned area of the specimen. In older microscopes image may be captured by photography from a high-resolution cathode ray tube, but in modern machines image is saved to computer data storage.

CHAPTER FOUR
RESULTS & DISCUSSION

4.1 EVALUATION OF STRENGTH TEST

Table 4.1 Strength test

Sample		Sample condition		Strength (N)
Shade	Color
Original				481.80
1%	Blue	Without pretreated		420.70
1%	Blue	pretreated		410.90
1%	Yellow	Without pretreated		450.30
1%	Yellow	pretreated		374.60
1%	Combined	Without pretreated		485.90
1%	Combined	pretreated		364.10
2%	Yellow	Without pretreated		425.70
2%	Yellow	pretreated		370.40
2%	Blue	Without pretreated		395.70
2%	Blue	pretreated		314.20
2%	Combined	Without pretreated		484.40
2%	Combined	pretreated		354.80
3%	Blue	Without pretreated		431.40
3%	Blue	pretreated		395.90
3%	Yellow	Without pretreated		459.80
3%	Yellow	pretreated		277.96
4%	Blue	Without pretreated		450.70
4%	Blue	pretreated		328.70
4%	Yellow	Without pretreated		449.80
4%	Yellow		pretreated	284.89

 

From the above graphical representation it shows that the strength of without pretreated fabric is greater than the treated one. The reason behind this may be in the without pretreated fabric less oxy-cellulose generated than the pretreated one. As a result strength loses occurred more for the pretreated sample than without pretreated one.

4.2 EVALUATION OF COLOR FASTNESS TO RUBBING

Table 4.2 Evaluation of color fastness to Rubbing

Fabric condition	Dry	Wet
Without pretreated	5	4/5
Pretreated	5	4/5

From the above table, it is seen that color fastness to rubbing are almost same for pretreated & without pretreated sample.

4.3 EVALUATION OF COLOR FASTNESS TO WASH

Table 4.3 Evaluation of color fastness to wash

Fabric condition	Color change	Color staining
		wool	acetate	cotton	nylon	polyester	acrylic
without pretreated	4.5	4.5	3	3.4	3.4	4.5	4.5
pretreated	4.5	4.5	3	3.4	3.4	4.5	4.5

 

From the above table it is clear that color fastness to wash are almost same for pretreated & without pretreated sample.

4.4 EVALUATION OF COLOR FASTNESS TO PERSPIRATION

Table 4.4 Evaluation of color fastness to perspiration

Fabric condition	Color change	Color staining
		wool	acetate	cotton	nylon	polyester	acrylic
without pretreated	4.5	4.5	4.5	3.4	4	4.5	4.5
pretreated	4.5	4.5	4.5	3.4	4	4.5	4.5

 

From the above table it is clear that color fastness to perspiration are almost same for pretreated & without pretreated sample.

4.5 VALUE OF LCH

Table 4.5 Value of LCH

Sample		Sample condition		L	C	H
Shade	Color
1%	Blue	Pretreated		52.270	26.947	266.683
1%	Blue	Without pretreated		49.062	27.520	266.415
1%	Yellow	Pretreated		86.754	22.707	88.264
1%	Yellow	Without pretreated		85.060	26.932	86.809
1%	Combined	Pretreated		50.279	18.799	268.216
1%	Combined	Without pretreated		48.820	20.447	264.583
2%	Yellow	Pretreated		88.256	34.698	94.686
2%	Yellow	Without pretreated		84.983	40.196	92.694
2%	Blue	Pretreated		44.197	30.154	268.143
2%	Blue	Without pretreated		40.901	30.059	269.047
2%	Combined	Pretreated		50.286	18.293	244.988
2%	Combined	Without pretreated		49.353	17.152	240.008
3%	Blue	Pretreated		41.737	29.636	268.742
3%	Blue	Without pretreated		40.876	28.799	268.307
3%	Yellow	Pretreated		85.121	30.786	92.160
3%	Yellow	Without pretreated		83.419	32.029	84.553
4%	Blue	Pretreated		38.136	29.216	270.157
4%	Blue	Without pretreated		35.900	29.680	272.559
4%	Yellow	Pretreated		83.909	33.631	88.680
4%	Yellow		Without pretreated	84.011	37.419	89.222

 

From the above table it is seen that value of L is lower for the without pretreated sample than the pretreated sample, it indicates the without pretreated sample may contain more color than the pretreated sample .Here for 4% Blue sample, value of L for pretreated sample is 38.136 & for without pretreated sample is 35.900.It is because the without pretreated one may contain more color than the pretreated sample.

4.6 VALUE OF Δa, Δb & CMC

Table 4.6 Value of Δa, Δb & CMC

Sample		Sample condition		Δa	Δb	CMC
Shade	Color
1%	Blue	Pretreated		-0.16	-0.57	1.48
1%	Blue	Without pretreated
1%	Yellow	Pretreated		0.81	4.20	2.56
1%	Yellow	Without pretreated
1%	Combined	Pretreated		-1.34	-1.57	1.77
1%	Combined	Without pretreated
2%	Yellow	Pretreated		0.92	5.62	2.98
2%	Yellow	Without pretreated
2%	Blue	Pretreated		0.48	0.07	1.68
2%	Blue	Without pretreated
2%	Combined	Pretreated		-0.83	1.73	1.65
2%	Combined	Without pretreated
3%	Blue	Pretreated		-0.20	0.84	0.63
3%	Blue	Without pretreated
3%	Yellow	Pretreated		4.20	1.12	3.50
3%	Yellow	Without pretreated
4%	Blue	Pretreated		1.26	-0.43	1.61
4%	Blue	Without pretreated
4%	Yellow	Pretreated		-0.26
4%	Yellow		Without pretreated		3.80	1.80

 

If the CMC value is less than one, the result is very good. And the above one the result is also very good. From the above representation the results are closer to one. So the untreated fabric color is better than the treated fabric.

4.7 VALUE OF K/S

 

From the above graphical representation, it is clear that the without pretreated sample value of K/S is higher than the pretreated sample. Its reason may be the color deepness of the without pretreated sample is more than the treated sample. The without pretreated one may contain more color.

CHAPTER FIVE

 CONCLUSION

5.1 CONCLUSION
It has been found that it is more cost effective way to dye fabric without pretreatment. The strength loss of fabric occurred less for without pretreated fabric than the pretreated one. For 2% Blue Pretreated fabric the strength becomes 314.20N, where for without pretreated sample the strength becomes 395.70N. It is clearly shows that less strength loss of dyed sample when it is not pretreated, which may be because of less formation of oxycellulose. It is one of the most important findings of this thesis. Another important factor of this thesis is the higher K/S value of the without pretreated fabric than pretreated sample. For 1% yellow sample K/S value of without pretreated sample is 0.53 & for pretreated sample it is 0.38. It clearly indicates that the without pretreated dyed sample may contain more color than the pretreated dyed sample (for same shade %). As a result waste of dye can be minimized by approaching this technique .Though the color fastness(to wash /rubbing/perspiration) are same for both kind of sample, it can be practiced largely in the industries for reducing cost of dyeing as well as time and energy.

5.2 LIMITATIONS
For this thesis only CVC knit fabric is used, thus result for other types of fabric still uninvestigated. The time is too short to use different types of fabric. Again in some cases result is unexpected due to power interruption, lack of soft water, inability of equipments.

5.3 FUTURE WORK
In this thesis only CVC fabric is used. It can be more informative if other types of fabric such as nylon, polyester, wool, and acrylic would be used. It can be applied on woven fabric also. The fastness properties of untreated fabric may be improved by using proper amount of dye. The result would be better if there is no power interruption, no lack of soft water, unavailability of equipment etc.

REFERENCES

1. Corben BP, Potter MD, Textiles, Fiber to Fabric, Gray Division/MC, 1985.
2. A. D. Broadbent, Basic Principle of Textile Coloration. 2001, England: Society of Dyers and Colourists.
3. M. F. Hossain, Practice of Textile Coloration. Vol. 1. 2007, Dhaka: Book Fair Publications.
4. J. E. Both, Principle of Textile Teasting 1968, England: Butterworths.
5. P. S. Chinta and S. Dhar, Problems in Dyeing and Their Remedies, Research Gate, 2007.
6. E. FEILMANN, Some Unsolved Dyeing Problems, Journal

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