Dyeing of Cotton Knit Goods without Bleaching Operation

Last Updated on 24/03/2021

Scope of Dyeing Cotton Knit Goods without Bleaching Operation for Energy Saving and Cost Reduction

Md. Palash Hossain
Department of Textile Engineering
Dhaka University of Engineering & Technology (DUET)
Email: palashsakal@yahoo.com

ABSTRACT
Several samples of single jersey cotton knit goods of 180 GSM were dyeing through conventional and selective process (pretreated without bleaching). Both types of samples were judged after dyeing with specific shade of single and tri-chromatic. Spectrophotometer (Data Color 650) CMC result passed for specific shade region for three primary colors red (0.5%), blue (0.5%) and yellow (0.1%). In case of tri-chromatic shade it was found that 0.5% shade also possible without bleaching operation. In addition, characterization of the bleached and unbleached dyed samples was done through investigation of different fastness properties. The unavoidable cost analysis revealed the appreciable outcomes of the work.

Key words: Bleaching, cotton knit fabric, light shade, shade matching, color fastness, energy saving, cost effective

1. INTRODUCTION
Energy is one of the most important ingredients in any industrial activity [1]. However, its availability is not infinite. Global energy crisis, as well as high cost of fuels resulted in more activities to conserve energy to maximum extent. The textile industry retains a record of the lowest efficiency in energy utilization and is one of the major energy consuming industries. About 34% of energy is consumed in spinning, 23% in weaving, 38% in chemical wet processing and another 5% for miscellaneous purposes. Power dominates consumption pattern in spinning and weaving, while thermal energy is major for chemical wet processing.

Textile industries are consuming large quantity of water, which is expensive to buy, treat, and dispose. Major portion of water is used for wet processing of textile (60 to 70 %). Keeping this in mind there is acute need of energy and water conservation programmed to implement as earlier as possible.

Knit dyeing process is one of the most crucial and dominating sectors in Bangladesh, as Bangladesh earns around 40% of its foreign currency by this sector [2]. So, steps should be taken to make this sector stronger by reducing processing time, production cost and by saving environment. Process time is a very important factor for a dyer, because a dyer delivers his product within lead time that is given by the buyers. To deliver product, dyer must reduce his dying time. In this competitive world reduction of processing cost in also a major factor because higher production cost leads lower demand of the product. Hence it is very challenging task for the dyer. Moreover, it is of utmost necessity to keep our environment free from pollution of different chemicals used in dyeing factories. So, to save environment a dyer should use the least chemicals that are most essential for performing dyeing. In order to perform the cotton, knit dyeing process efficient, reduction of process time and reduction of chemicals in the preparatory stage play a significant role. However, without using peroxide in the preparatory process, it could be possible to obtain desired shade after dyeing. But actually, up to the scope of searching through internet or books, no relevant research works were found in a justified way.

To run with the processing heads, focusing on scouring, bleaching and so on can be initiated here.

Natural fibers (cotton) are yellowish or off-white in color due to color bodies present in the fiber and contain oils, fats, waxes, minerals, leafy matter and motes as impurities that interfere with dyeing and finishing. The process of destruction of yellowish or off-white color bodies is called Bleaching and the process of removing of impurities and make good absorbency is called Scouring.

1.1 Objectives with rationales

1. The cost of a process includes the amount of process time, no. of processing stage and amount of chemicals. Henceforth reduction of process time, chemicals reduce the cost.
2. Another focus lies with reduction of processing time this also depends on how many processing stages are occupied. Since in this experiment bleaching is not conducted, it saves a lot of time which is economical.
3. Since wastewater is hazardous for environment, in this process as bleaching is not done. So extra chemicals do not add on as effluent.
4. If process stages are increase more than require amount of energy will also be more. In the bleaching process need huge amount energy to operate the machine. Here bleaching operation is totally ignored. So, it saves sufficient amount of energy. That makes the process easier, safe and cost effective.

2. MATERIALS AND METHODS

2.1 Materials

2.1.1 Raw materials

Table 1: Information of used cotton fiber

Table 2: Fabric specification

2.1.2 Dyes and chemicals:

Table 3: Name of used dyes

Table 4: Name of used chemicals

2.1.3 Machineries

Table 5: Specification of used machineries

2.2 Methods:
Method followed: Exhaust Method

2.2.1 PROCESSES FOLLOWED IN LABORATORY TRIAL:

A. Pretreatment:

Table 6: Recipe for pretreatment

Sequence followed in scouring & bleaching:

Sequence followed in scouring without bleaching:

Working procedure:
All the chemicals were taken according to recipe. 10% stock solution of caustic soda was prepared. Then the samples were given in scouring bath. The program was set for 40 min at 105⁰c. After unloading of the samples normal wash were done for 5 minutes. Then peroxide killer was used in conventional way for removing H₂O₂ from the fabric at 80⁰c for 15-20 min. After that acid wash was done for the both samples for 10 min. Then hot wash was performed with detergent for 10 min at 80⁰c. Finally, cold wash was done.

B. Dyeing:

Table 7: Recipe for lab dyeing (0.5% shade)

Working procedure:

Stock solution preparation: During the lab dip, little amount of dyes and other chemicals were required. 1 gm of dye has been taken in 100 ml of warm water and was made as 1% stock solution of dye. Similarly, 20% of Na₂CO₃ (Sodium carbonate) and 20% of Gluber salt solution have been prepared. The formulae below were exercised to get the accurate amount of dyes and chemicals.

Sample preparation: The pretreated fabric had been cut and made sample of 5 gm by electronic balance. The sample size was required as rectangular to assess rubbing fastness test. Then all the samples were soaked in distilled water for few minutes and squeezed well which then got ready for dyeing.

Dyeing: All the auxiliaries, salt and dyes were placed in dye bath from stock solution and water was taken to maintain 1:10 liquor ratio. Then fabric was added in dye bath at room temperature and run for 5 minutes. Temperature was gradually increased (2⁰/min) up to 60^oC. At this temperature the system was run for 15 min and soda dosing was performed for 45 min. After Completing dyeing the dye liquor was drained out.

After treatment: Normal wash was done. Then hot wash was performed at 80^oC with detergent for 10 min. Finally, cold wash has been done for 5 min followed by drying at 100^oc for 20 min.

Sequence followed in laboratory dyeing:

2.2.2 PROCESS FOLLOWED IN BULK TRIAL:

Specification of used machineries:

• Machine name-MCS
• Origin-Italy
• Machine capacity-1500 kg
• Maximum capacity for single jersey-1000 kg
• Maximum Temperature 1300⁰c
• Maximum water capacity-11200 liter
• No. of nozzle-06

A. Pretreatment:
Recipe for 1000 kg knitted (S/J) Fabric:

Table 8: Recipe of pretreatment process for bulk production

Working procedure:

B. Dyeing:
Recipe:

Table 9: Recipe for dyeing and after treatment

Working procedure:
Sequence followed in dying:

Sequence followed in after treatment:

2.2.3 PROCESS FOLLOWED IN TESTING

1. Color fastness to wash
   Method followed: ISO 105 C03
2. Color fastness to rubbing /crocking
   Method followed: EN ISO 105×12
3. Color fastness to perspiration:
   Method followed: ISO105E02 h

RESULTS AND DISCUSSIONS

3.1 Color Measurement Committee (CMC) pass/fail values:

Table 10: CMC pass/fail values for different shade %

The above result shows that dyeing without bleaching is possible upto 0.5% red, 0.5% blue and 0.1% yellow shades and also for specific combination shades (0.5%)

3.2 Images of dyed fabric:

3.3 Results of color fastness to wash test:
a. Results for Red shade: 

With the help of this graph, it can be concluded that both the results are about same for all fibers except wool fiber. In case of wool, the wash fastness ratings with peroxide treatment is 4, generally defined as good but without peroxide treatment the value is greater than 4 but less than 5 which represents better than good.

b. Result for Blue shade:

From the graph, it can be stated that both results almost same for all fibers except wool fiber. In case of wool, the wash fastness ratings without peroxide treatment is 4, generally defined as good but with peroxide treatment the value is greater than 4 but less than 5 which represent better than good.

c. Result for Yellow shade:

The graph shows that with bleaching and without bleaching both of the test results are same for all fibers.

d. Result for Combined shade:

From the graph, it can be stated that both the results are almost same for all fibers except polyamide fiber. In case of polyamide, the wash fastness ratings without peroxide treatment is 4, generally defined as good but with peroxide treatment the value is greater than 4 but less than 5 which represent better than good.

3.4 Color fastness to rubbing:
a. Result for Red shade:

The above graph is shows that dry rubbing fastness test ratings are same for both process but wet rating fastness test ratings are fair to good for without peroxide treatment whereas with peroxide process test rating is good.

b. Result for Blue shade:

The above graph shows that dry and wet rubbing fastness test ratings are same for both treated fabrics.

c. Result for Yellow shade:

From the graph, it can be stated that dry and wet rubbing fastness test ratings are same for both the treated fabrics.

d. Result for Combined shade:

The above graph shows that dry and wet rubbing fastness test ratings are same for both the treated fabrics.

3.5 Color fastness to perspiration:
a. Result for Red shade:

From the graph it can be stated that with bleaching and without bleaching both the perspiration test result is fair for cotton and good for acetate, polyamide, polyester, acrylic and wool.

b. Result for Blue shade:

From the graph it can be stated that with bleaching and without bleaching both the perspiration test result is good for all fibers.

c. Result for Yellow shade:

From the graph it can be stated that with bleaching and without bleaching both the perspiration test result is good for all fiber.

d. Result of Combined shade:

Above figure shows that with bleaching and without bleaching both perspiration test results are fair for cotton and good for acetate, polyamide, polyester, acrylic and wool.

4. COST ANALYSIS

4.1 Graphical representation of chemicals distribution:

Graph shows that with bleaching process needs 9 types of chemicals and without bleaching process needs only 5 types of chemicals. So, process without bleaching saves extra 4 chemicals.

4.2 Cost of chemicals (Source: Purchasing department of PPC)

Table 11: Cost in chemicals saves without bleaching process

From the table it is clear that process without Bleaching saves 1093Tk/1000kg (approx.) fabrics.

4.3 Graphical representation of amount of time

The graph showed that process with bleaching needs 255 min and process without bleaching needs 188 min. So, process without bleaching saves 67 min. As a result, process without bleaching provides following benefits:

1. Production will be increase
2. Labor cost will be decrease
3. Product can be delivers to the buyer within certain time. So, buyer will satisfy to the company’s authority.
4. Save machine running cost. i.e. electricity, gas, and power cost.

4.4 Energy cost calculation for MCS dyeing machine [3]

1kw hour = 1 unit of electricity

1-unit cost = 5.5Tk (Approximately)

Dyeing machine is 60 KW capacity

So it consumes 60×1=60 unit per hour

Cost =60×5.5 =330Tk/hr

Since process without bleaching save 67 minutes, so it saves 67×5.5=368.5Tk (approx.) energy cost.

4.5 Graphical representation of required water for pretreatment process

From the graph it can be stated that in conventional pretreatment process 30000lt water is required; whereas without bleaching pretreatment process required 24000lt. So proposed process saves extra 6000lt of water.

4.6 Required cost for extra water [4]

a. Cost in WTP:

Table 12: Cost for water treatment plant

So, for 6000 lt of water process without bleaching saves 6×5.415 = 32.49Tk(approx.)

b. Cost in ETP:

Table 13: Cost for effluent treatment plant

So, for 6000Lt of water process without bleaching saves 6×18.66 = 111.96Tk (approx.)

Total cost for 6000lt water=32.49+111.96=143.97Tk
= 144Tk (approx.)

4.7 Total saving in cost

Table 14: Total saving in cost

So proposed process saves 1605.5Tk/1000kg (approx.) and 67 min duration.

5. CONCLUSION
Detailed experimental data were manipulated through the research work. As the elimination of bleaching results the grayness retaining in cotton fabric. So CMC pass/fail comparison with conventionally treated fabric were investigated. Consequently, color fastness to wash, rubbing and perspiration have been tested. During this experiment dyeing of cotton knit goods is performed for shade percentages of 2, 1.75, 1.5, 1.25, 1.00, 0,75, 0.50, 0.25, 0.10 with bleaching and without bleaching for Red, Yellow, Blue and combination sheds. For Red, Blue and combination color up to 0.5% shade has been passed in data color result but below 0.5% the result in data color did not pass. It was passed up to 0.1% shade in case of yellow color. Besides, samples passed in data color results have been shown good color fastness (washing, rubbing and perspiration) values. Some bulk dyeing has been performed in factory after successful completion of laboratory trials. Experiments were done on two different combination shades % i.e. 2% and 2.5% and the results have been derived successfully. It can be concluded that dyeing with red (0.5%), blue (0.5%) and yellow (0.1%, 0.25%, 0.5%) colors, excluding bleaching process passed at data color 650 (CMC pass/fail) with conventional (including bleaching) dyeing process. In case of specific combination shade, it was found that 0.5% shade is possible without bleaching operation. Cost analysis displays that 1605Tk (approx.) was saved per 1000 kg fabric dyeing through the proposed way.

5.1 Limitations:

• Due to insufficient laboratory facilities all testing parameters could not be performed.
• Due to Limitations in factory accessibility and financial support, it was not possible to follow all laboratory trials in bulk production below 2% shades.

5.2 Future scopes:
Wet processing is responsible for wasting lots of water and energy, now the time came to increase performance of existing utility and to save more to reduce the production cost to stay in a tremendous competitive market. There are lots of scopes to work on the same topic to find out the more acceptable zone in combined shade area to avoid the bleaching process; hence benefit will come on two ways, one is saving environment and another is reduction of production cost. From this experiment we can forecast that dyeing can be performed in bulk production below 2% of single shade. Another research can be made by implementing this research result on different kinds of fabrics.

6. References

1. http://www.fibre2fashion.com/industry-article/4/316/cost-effectiveness-in-textile-processing1.asp
2. Hasan, Md. Rakibul, “Scopes of Improvisation in Knit-Dyeing process of Cotton in Bangladesh to optimize the process-time”, Bangladesh Textile Today, March-April 2010.
3. Interview from Mr. Sehk Asadullah Tareq, Head of the department of Maintenance. Padma Poly Cotton & Knit Fabrics Ltd.
4. Interview from Sahida Sultana, Manager of the department of ETP and WTP. Padma Poly Cotton & Knit Fabrics Ltd.

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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