GREEN METHOD OF INDIGO DYEING USING
ORGANIC REDUCING AGENTS
Group No. 15
Batch: 2016-2017
Name
Seat No.
Alisha Abdul Majid
Rafay Umam
Sheikh Muhammad Omar
Muhammad Salman Khan
TE-16042
TE-16058
TE-16072
TE-16076
Internal Advisors:
Dr. Quratulain Mohtashim
(Asst. Professor)
DEPARTMENT OF TEXTILE ENGINEERING
NED UNIVERSITY OF ENGINEERING&TECHNOLOGY
Department of Textile Engineering
CERTIFICATE
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ACKNOWLEDGEMENT
We would like to express our sincere gratitude to our project advisor, Dr. Quratulain
Mohtashim, Asst. Professor at NED University of Engineering and Technology for her
ongoing guidance, time and support. We would not have been able to accomplish all the
goals and priorities of this project without her guidance. We would also like to appreciate
the facilities available in Textile Dyeing Laboratory as well as the Textile Wet Processing
and Physical Testing Laboratory at NEDUET for our project experimentation and sample
testing and evaluation.
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ABSTRACT
Indigo dyeing cannot proceed without the reduction process, because it is insoluble in
water, therefore it is reduced using sodium dithionite (Na2S2O4). This compound
produces a lot of harmful by-products (such as sulphate and sulphite) when they are
discharged into waste water they cause environmental pollution. To overcome the
harmful environmental effects that this compound causes, a new reduction process
should be introduced using organic reducing agents which reduces the dye and is less
hazardous to the environment. This work is based on natural reducing agents like
monosaccharides (glucose and fructose) and artificial sweeteners (sucral and canderel),
for this work glucose is used as the reducing agent, which will reduce indigo dye and its
effects will be compared against sodium dithionite (Na2S2O4) by performing different
tests of colour fastness and evaluating different colour fastness properties, colour
strength (K/S).
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TABLE OF CONTENTS
Chapter 1
Introduction .................................................................................................. 1
1.1. BACKGROUND ..................................................................................................... 1
1.1.1. Natural Source .................................................................................................. 2
1.1.2. Chemical Source ............................................................................................... 2
1.1.3. Reduction of Indigo .......................................................................................... 3
1.1.4. Sodium dithionite ............................................................................................. 4
1.2. PROBLEM STATMENT ........................................................................................ 4
1.3. OBJECTIVES ......................................................................................................... 5
1.4. Scope And significance of work ............................................................................. 5
Chapter 2
Literature Review ......................................................................................... 7
2.1. Green methodS for indigo dyeing ........................................................................... 7
2.1.1. Electrochemical reduction of indigo ................................................................. 7
2.1.2. Enzymatic technologies for reduction .............................................................. 8
2.1.3. Fruit peel or extracts ......................................................................................... 9
2.1.4. Bokbunja sludge ............................................................................................... 9
2.1.5. Environmentally friendly 3-hydroxybutanon ................................................... 9
2.1.6. Synergetic Effect of α-Hydroxycarbonyl mixture in indigo reduction........... 11
2.1.7. Organic reducing sugars ................................................................................. 11
2.2. Fixing agent ........................................................................................................... 14
2.2.1. Cationic Fixing Agent..................................................................................... 14
2.2.2. General Properties and fields of application ................................................... 14
Chapter 3
Methodology and calculations ................................................................... 15
3.1. General method of indigo dyeing .......................................................................... 15
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3.2. Proposed recipe (DYEING) .................................................................................. 15
3.2.1. Pre-wetting...................................................................................................... 15
3.2.2. Dye bath preparation....................................................................................... 15
3.2.3. Dyeing parameters .......................................................................................... 15
3.3. Proposed recipe (Fixing) ....................................................................................... 16
3.3.1. Direfix SD Liquid ........................................................................................... 16
3.3.2. Lava Fix FF .................................................................................................... 16
3.3.3. Achifix FF-429 ............................................................................................... 16
3.4. preparation of dye bath .......................................................................................... 16
3.5. Fabric for dyeing ................................................................................................... 17
3.6. CHEMICALS FOR DYEING ............................................................................... 17
3.6.1. Denisol Indigo Blue 30L ................................................................................ 17
3.6.2. Sodium Dithionite........................................................................................... 17
3.6.3. NaOH (50% conc.) ......................................................................................... 17
3.6.4. RDT Glucose powder ..................................................................................... 17
3.7. CHEMICALS FOR FIXING ................................................................................ 18
3.7.1. Direfix SD Liquid ........................................................................................... 18
3.7.2. Lava Fix FF .................................................................................................... 19
3.7.3. Achifix FF-429 ............................................................................................... 19
3.7.4. Machine and parameters ................................................................................. 20
3.8. PROCEDURE OF DYEING ................................................................................. 20
3.9. PROCEDURE OF APplying fixing agent ............................................................ 21
3.9.1. Direfix SD Liquid ........................................................................................... 21
3.9.2. Lava Fix FF .................................................................................................... 21
3.9.3. Achifix FF-429 ............................................................................................... 22
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3.10. Methods of performance ..................................................................................... 22
3.10.1. Initial Method ............................................................................................... 22
3.10.2. New Method ................................................................................................. 22
3.10.3. Dyed Fabrics ................................................................................................. 24
3.11. TESTING AND evaluation of dyed fabric ......................................................... 26
3.11.1. Color fastness tests ....................................................................................... 27
3.11.2. Evaluation method ........................................................................................ 27
Chapter 4
RESULTS AND DISCUSSION ................................................................ 28
4.1. observations (Old) ................................................................................................. 28
4.1.1. Trial 0.............................................................................................................. 28
4.1.2. CIE L* a* b* Values (D65 10 Deg) ............................................................... 28
4.1.3. Color fastness results ...................................................................................... 29
4.1.4. Trial 1.............................................................................................................. 29
4.1.5. CIE L* a* b* Values (D65 10 Deg) ............................................................... 30
4.1.6. Color fastness results ...................................................................................... 30
4.1.7. Trial 2.............................................................................................................. 31
4.1.8. CIE L* a* b* Values (D65 10 Deg) ............................................................... 31
4.1.9. Color fastness results ...................................................................................... 31
4.1.10. Trial 3............................................................................................................ 32
4.1.11. CIE L* a* b* Values (D65 10 Deg) ............................................................. 32
4.1.12. Color fastness results .................................................................................... 32
4.2. observations (NEW) .............................................................................................. 33
4.2.1. Standard Samples (Sodium Dithionite) .......................................................... 34
4.2.2. Batch Samples (Glucose) ................................................................................ 36
4.2.3. Fixer Samples ................................................................................................. 38
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4.3. discussion on results .............................................................................................. 40
Chapter 5
Conclusion ................................................................................................. 41
5.1. CONCLUSION ..................................................................................................... 41
5.2. Future work ........................................................................................................... 41
References ........................................................................................................................ 42
LIST OF FIGURES
Figure 1-1 (Reduction of indigo into leuco-indigo form) [4] ............................................ 3
Figure 1-2 (Sodium Hydrosulphide Structure) .................................................................. 4
Figure 2-1 [Effect of the alkalinity on the bath exhaustion E (%) and the color yield
parameter (K/S)] [10] ....................................................................................................... 10
Figure 2-2 [Effect of the reducing temperature on the bath exhaustion E (%) and the color
yield parameter (K/S)] [10] .............................................................................................. 10
Figure 2-3 (Oxidation of glucose in alkaline solution) [6] .............................................. 12
Figure 2-4 (Redox potential of indigo dyebath as a function of reduction time at 50 C
using different reducing sugars) [6] ................................................................................. 13
Figure 3-1 (Dyebath solutions using glucose and sodium dithionite) ............................. 16
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LIST OF TABLES
Table 3-1 (Progression of trials and their parameters)..................................................... 23
Table 3-2 (Dyed samples from Sodium Dithionite)......................................................... 24
Table 3-3 (Dyed samples from Glucose) ......................................................................... 25
Table 3-4 (Dyed glucose samples with fixers applied) .................................................... 26
Table 4-1 CIELAB Values (Trial 0) ................................................................................ 28
Table 4-2 Color Fastness Results (Trial 0) ...................................................................... 29
Table 4-3 CIELAB Values (Trial 1) ................................................................................ 30
Table 4-4 Color Fastness Results (Trial 1) ...................................................................... 30
Table 4-5 CIELAB Values (Trial 2) ................................................................................ 31
Table 4-6 Color Fastness Results (Trial 2) ...................................................................... 31
Table 4-7 CIELAB Values (Trial 3) ................................................................................ 32
Table 4-8 CIELAB Values (Trial 3) ................................................................................ 32
Table 4-9 Sample Distribution ......................................................................................... 33
Table 4-10 Color Strength Values (K/S) of standard samples ......................................... 34
Table 4-11 Color Fastness results of standard samples ................................................... 35
Table 4-12 Color Strength Values (K/S) of batch samples .............................................. 36
Table 4-13 Color Fastness results of batch samples ........................................................ 37
Table 4-14 Color Strength Values (K/S) of batch fixer samples ..................................... 38
Table 4-15 Color Fastness results of batch fixer samples ................................................ 39
Table 4-16 Comparative Results Table............................................................................ 40
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CHAPTER 1
INTRODUCTION
1.1. BACKGROUND
Indigo dye is an organic compound with a distinctive blue color, it is supplied in markets
in a form of blue crystalline powder. It is amongst the oldest dyes to be used in textile
dyeing and printing, the oldest known fabric which was dyed with indigo was dated back
to 6000years ago. [1]
The indigo dye has been used since old civilizations and it was popular in Mayan,
Egyptian, Indian and Japanese cultures. When the trade of indigo dye made its way to
Greek and Rome, it found a name of the pigment ‘indikon’ which means ‘from India’ and
it was considered as a valuable item. As it was a high value trade, so it got the name of
‘blue gold’ [2].
After some time the demand of natural indigo dye was outstripped, and now these days
the consumers demand sustainable production with no harm to the environment therefore
indigo has gone quietly back on the radar because of the development of synthetic
alternatives which were relatively cheaper [2].
Indigo Dye can be used on several materials but especially it is good for cotton, but it is
also used for linen, leather, wool, and silk. Indigo was the first dye which was used to dye
the blue jeans.
The indigo dye can be naturally extracted and can also be made synthetically. In 1865,
German chemist Adolf von Baeyer started working on the synthetic development of indigo
and in 1878 he gave his first synthesis which was from the chemical isatin, and then he
gave his second synthesis in 1880 which was from 2-nitrobenzaldehyde.
So basically there are two sources of indigo dye:

Natural source

Chemical source
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1.1.1. Natural Source
Historically indigo was extracted naturally from many plants but mostly the leaves of
indigofera tinctoria (which bloom in hot humid places) were the main source of production
of natural indigo. A common alternative was used in colder subtropical locations which
was the most important blue dye in east-Asia until the arrival of ‘indigoferra’ species.
Several plants contain indigo such as coffee beans and cacao which are grown in perfect
soil conditions and perfect temperature, but the problem is that in these plants the blue dye
is in low concentration which makes it difficult to work with, leaving to a greenish tinge.
Indigo contains ‘indican’ which is a colorless water soluble derivative of the amino acid
tryptophan obtained from the plant’s leaves which contains around 0.2-0.8% of the
compound. To obtain indigo form them, the leaves of indican are dipped in water and then
fermented so that the glycoside indican converts into indigotin which is the blue insoluble
chemical that is the end point of the indigo dye. All of this is done by oxidation process.
[3]
1.1.2. Chemical Source
Indigo can be prepared synthetically by many methods. The first method of preparing
indigo was an ‘aldol condensation’ of O-nitrobenzaldehyde with acetone after which the
cyclization and oxidative dimerization is done to form indigo. This procedure of making
indigo dye was very useful on laboratory scale but it was not possible for industrial scale
synthesis. Eventually ‘Johannes pfleger’ came up with a new idea of industrial masssynthesis. This process involved the treatment of N-phenylglycine with a molten mixture
of sodium hydroxide, potassium hydroxide and soda mide, this is a highly sensitive melt
which produces indoxyl which is then oxidized in air to form indigo. The variations of
this process are still used. Another method involves heating N-(2-Carboxyphenyl) glycine
to 200degree Celsius with sodium hydroxide in an inert atmosphere. This method was
found to be easier than Pfleger method but the substances involved in this method are
more expensive than Pfleger method. According to Baeyer-Drewsen route, the preparation
of indigo dye is practiced in small scale laboratories. [1]
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1.1.3. Reduction of Indigo
The reduction of indigo dye is a necessary step, as the vat dyes have a conjugated
dicarbonyl system which makes them water insoluble. So therefore it is required to convert
the Indigo in water-soluble form which is called leuco-indigo. For this reduction process
of indigo a reducing agent is used which makes the dye water soluble. Different reducing
agents can be used (both organic and inorganic) for reduction process. But mainly sodium
dithionite (Na2S2O4) is used for the reduction of indigo dye on a commercial basis
Depending on the pH of the dyebath, the dye can undergo two-step ionization from the
non-ionic form to mono-ionic or di-ionic form. The mono-ionic form is preferred form for
the cellulosic fibres which is obtained when the pH is maintained around 11.5, while the
di-ionic form is obtain when pH crosses the 12 mark, di-ionic form does not give proper
results on cellulosic fibers. [3]
Figure 1-1 (Reduction of indigo into leuco-indigo form) [4]
Basically the process of reduction is to give negative charge (by adding electron) to the
indigo molecule which then converts the indigo into leuco-indigo water soluble form. In
this way the indigo is made to dissolve in water thus enabling it for the dyeing process.
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1.1.4. Sodium dithionite
Sodium dithionite (Na2S2O4) is also called sodium hydrosulphite, it has always been a
major reducing agent in the industrial reduction of indigo dye to its chemical properties
as well was economic advantages. It causes frequent reduction of indigo enabling very
short fixing times during dyeing and also provides levelness during continuous dyeing.
The problem with Sodium dithionite is that it is not recyclable from the waste water and
it very easily oxidized by air. The oxidation of byproducts of sodium dithionite can lead
to the generation of sulfate (SO42-) and sulfite (SO32-) ions which can cause harmful effect
on the environment due to their level of toxicity [4].
Figure 1-2 (Sodium Hydrosulphide Structure)
1.2. PROBLEM STATMENT
The process of indigo dye involves a major step of reduction of indigo dye, as the dye is
not soluble in water, thus it is required to be reduced into leuco indigo form in order to
make it water soluble, for this purpose sodium dithionite (Na2S2O4) is used in dye bath for
indigo blue extraction, which then stays in the dye bath and cannot be extracted back, later
on it causes environmental pollution in many ways as this reducing agent and its
derivatives are a major source of pollutants in textile industry.
Sodium dithionite is also listed on the “hazardous substance list” by Department of
Transportation (DOT) and National Fire Protection Association (NFPA) [4] because
sodium dithionite causes severe health issues, such as, when it is inhaled it causes irritation
in nose, throat and lungs which causes coughs and wheezes and shortness of breath,
ingestion symptoms which causes nausea, vomiting and abdominal pain, it’s exposure
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causes asthma-like allergy, eye symptoms such as redness and pain, along with several
other health issues. So considering all these environmental threats, either its consumption
must be reduced or it should be replaced completely by an eco-friendly compound. [4]
1.3. OBJECTIVES
In our work we will try different approaches to reduce indigo dye by using organic
reducing agents instead of sodium dithionite (Na2S2O4), as it is hazardous for the
environment, without losing much of the dye quality. The criteria for selecting the
alternative reducing agent will be based on the following factors:
1. The stability it provides during the dyeing process
2. The redox potential it maintains during the dyeing process
3. It should be easily available
4. It should be eco-friendly
Based on these criteria’s we chose ‘reducing sugars’ as our base reducing agents which
included monosaccharides (glucose and fructose) and disaccharides (sucrose). And to
extend our research we have also decided to perform dyeing by using the artificial
sweeteners (canderel and sucral) as our reducing agent. But due to the pandemic which
caused shortage of time, we decided to stay on glucose as our main reducing agent while
trying to improve its results from calibrating the process parameters and by applying
different fixing agents onto our fabric (with glucose as reducing agent) and to do
comparative study on their results.
Glucose is known for its stability in dyeing and giving good rubbing fastness results in
comparative to sodium dithionite.
The results of reducing agents will be tested and evaluated on the basis of K/S (color
strength) values along with the color fastness results against sodium dithionite (Na2S2O4).
1.4. SCOPE AND SIGNIFICANCE OF WORK
Every year, around 15billion meters of denim fabric is produced globally, around
66,000tons of indigo powder is needed for this level of production, and for the reduction
of this much amount of dye a lot of reducing agent is required, the commercial reducing
agent used for indigo dyeing is not favorable towards the environment, and mostly the
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waste water effluent is discharged into the environment without any kind of treatment.
This can cause various health issues when subjected to physical contact or exposure. The
health of workers working in the industries is also affected if proper health and safety
measures are not taken into account. The denim dyeing process has been amongst the
major source of pollution problems within textile industry [5].
The scope of our work is to reduce the consumption of this harmful chemical (sodium
dithionite) on a commercial scale. It may not be possible to completely replace it on a
technical level, but with proper methodology and moderate parameters we can
substantially reduce the amount of sodium dithionite required for the reduction of indigo
dye on a commercial level, by using the natural organic reducing agents sources from
natural resources.
Organic reducing agents may not be perfect in terms of results as compared to the sodium
dithionite because of their long term stability during the dyeing process and weaker color
yield, but with appropriate methodology, one can produce better results as well.
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CHAPTER 2
LITERATURE REVIEW
This chapter covers the overview of indigo dyeing and the alternative steps taken to
reducing the usage of sodium dithionite for the reduction process of the dyeing. This
chapter will cover various reduction methods that have been performed during the years,
along with the result comparisons. The chapter also give an insight of problems in shifting
towards the organic reducing agents.
2.1. GREEN METHODS FOR INDIGO DYEING
Because of the increasing awareness of the environmental issues, the interest of ecofriendly processing is also increasing in the textile industry, in the case of indigo dyeing,
the reducing agent (sodium di thionite) that is being commercially used, is
environmentally unfavorable [6]. Several experiments have been done and many
methods have been devised to replace the harmful reducing agent (sodium dithionite)
with a less harmful and eco-friendly alternative by using organic reducing agents.
Although the organic reducing agents are environmentally friendly, but they are quite
difficult to handle during the dyeing process as they can have variations [7]. The major
problem in the organic reducing agents is the redox potential, which in case of indigo
dyeing must be lower than -700mV throughout the dyeing process. Most of the Organic
reducing agents have shown fluctuating values of the redox potential resulting in poor
dye results. The main factors in judging an organic reducing agent is by analyzing the
results of dyeing, by measuring K/S and L* a* b* values and comparing them to the
results of the sodium dithionite, it came to a conclusion that sodium dithionite is still
better with regards to stability and process control [5].
2.1.1. Electrochemical reduction of indigo
The purpose of electrochemical reduction is to minimize the consumption of chemicals
and also to control the redox potential for monitoring the process. This can be done by
direct election chemical reduction by radical process or it can be done on graphite
electrodes, however this process requires a large amount of electrical energy and
electrodes with large surface area, thus this is not economically favorable process [8].
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2.1.2. Enzymatic technologies for reduction
Enzymatic technologies can be used in place of standard chemical reduction and oxidation
processes, it is also economical because of the reduction in the water treatment cost of
effluent. The advantage of this procedure is the moderate temperatures of processing and
the absence of by-products, most of the enzymatic processes are considered to be ecofriendly, but the problem with such method is the activation of enzymes, which work on
very specific temperature and pH, also regarding to these properties some enzymes can be
toxic as well. However there is still no possibility of replacing the standard reduction
process in the indigo dyeing by a system that has a biological approach [9].
2.1.2.1. Enzymes for dye reduction in indigo dyeing of polyamide
Another process of indigo reduction is the use of NADH dependent reductases along
with redox mediators. The dyeing of decitex polyamides 6 and 6, 6 was studied at 60 °C,
and at a pH of7 and 11. The color fastness properties were evaluated and compared to
chemically indigo-dyed sample. The results showed that the dyeing properties were
dependent on the pH, time and polyamide type. Which resulted in better color depth of
polyamide 6, 6 dyed at pH 11 for 90 minutes. The alkaline fastness and acid perspiration
fastness were relatively good, but the dyeing displayed poorer fastness of 3-4 to light
and wash. Use of enzyme successfully was confirmed. [10]
2.1.2.2. Enzyme mediated reaction
In an enzyme-mediated reaction, substrate molecules are changed, and product is
formed. The enzyme molecule is unchanged after the reaction, and it can continue to
catalyze the same type of reaction over and over.
2.1.2.3. What is NADH
NADH is a co-enzyme. The NAD+ is an oxidizing agent, which accepts electrons from
other molecules and is reduced, forming NADH, this can be used as a reducing agent to
donate electrons. NAD is mostly responsible for the electron transfer function.
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2.1.3. Fruit peel or extracts
Several different fruits and their parts like date palm, banana peel, apple and ripe banana
have been previously tested as reducing agents in indigo dyeing. The reduction systems
using such natural products and by-products is claimed to be more eco-friendlier.
However the basic problem with this reducing method is the variation and inconsistency
of the material composition can cause problems in reproducing the results [11].
2.1.4. Bokbunja sludge
Bokbunja (Rubus coreanus Miq.) is a kind of wild berry, whose growth is limited to the
south-east Asian countries, along with some parts of Korea, China and Japan. While
sludge is a semi-solid slurry that can be produced from a range of industrial processes.
Bokbunja is recently being used to manufacture jellies, jams, juices and beverages. By
using it a lot of health-promoting products are being developed as well. The sludge of
bokbunja is produced about 20% on the weight of the fruit in processing it. It contains
large amount of effective components including sugars and phenolics. For indigo dyeing,
the bokbunja sludge is extracted by using water and ethanol, and is then used as natural
organic reducing agent for dyeing, and the reducing power of this extract was evaluated
by measuring reduction potential and color yield. The utilization of Bokbunja sludge as a
reducing agent was investigated, the extract was effective in reducing the indigo dye, but
at an elevated temperature of 80 C, and also the maximum color yield was reached in one
or two days. The reduction potential was also higher than -700mV at around -500 ~ -600
mV depending on it concentration [12].
2.1.5. Environmentally friendly 3-hydroxybutanon
Ecologically friendly 3-hydroxybutanone (C4H8O2) can also be used as reducing agent in
the indigo dyeing process, and evaluation was performed by measuring the effect of
alkalinity and reducing temperature on the reduction power of 3-hydroxybutanone in the
presence of indigo. In this case the cotton has to be modified so it is pretreated using
Denitex BC 200% in order to improve the quality of the exhaustion of dyeing process.
[12]
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The reduction temperature in this process played an important role in lowering the redox
potential, the higher the temperature the more reduced the redox potential gets. Thus
effecting the E (%) and K/S values as well. [12]
The effect of alkalinity on the reduction power was also taken into consideration as it was
as same as the effect of temperature, the higher its concentration is the better the redox
potential values. Following is the graph showing the effect of alkali in the bath exhaustion
on E (%) and K/S values
Figure 2-2 [Effect of the reducing temperature on the bath
exhaustion E (%) and the color yield parameter (K/S)] [10]
Figure 2-1 [Effect of the alkalinity on the bath exhaustion E
(%) and the color yield parameter (K/S)] [10]
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In order to achieve best dyeing conditions with 3-hydroxybutanon, higher reducing
temperatures (>90 C), along with higher concentration of alkali (up to 12 g/l) are
required, also the modification of cotton by Denitex BC 200% is required in order to
achieve better results [13].
2.1.6. Synergetic Effect of α-Hydroxycarbonyl mixture in indigo reduction
In this method α-hydroxycarbonyl have been suggested as environmentally friendly
alternatives to reduce indigo, a mixture design of experimental (DOE) methods was used
to determine the optimum combination of α-hydroxycarbonyl to be applied in the indigo
reduction process since α-hydroxycarbonyl alone in the reducing indigo process would
not achieve the same dyeing performances offered by the conventional reduction
process. Therefore, we propose the use of a mixture of only some selected αhydroxycarbonyl. α-hydroxycarbonyl compounds used in this method are: acetol,
acetoin and glucose.
It is observed that synergy between α-hydroxycarbonyls leads to a better reducing power
then when using each one alone. Thus, such mixture would have great importance on
improving the reducing process, and the synergy attained, and even to improve the
dyeing performances offered by conventional reduction methods.
2.1.6.1. Mixture Design Model (DOE)
Mixture design model (DOE) A three component constrained simplex lattice mixture
design was used. The mixture consisted of acetol (A), acetoin (B) and glucose (C).
Component proportions were expressed as fractions of the mixture with a sum (A + B +
C) equal to one.
2.1.7. Organic reducing sugars
Reducing sugars like monosaccharides (glucose and fructose) and disaccharides have
been used as reducing sugars in indigo alkaline reduction. They are capable of being
used as reducing agents because they have a free aldehyde group or a free ketone group
which allows them to perform reducing process. [8]
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Glucose and Fructose are a preferable alternative amongst the reducing sugars, as they
do not require high elevated temperatures to be stable as they give almost the highest
reduction potential amongst the other reducing sugars (maltose, lactose, and galactose).
Figure 2-3 (Oxidation of glucose in alkaline solution) [6]
During the process of reduction of indigo, the aldehyde group of glucose is oxidized to
carboxylic acid, while the indigo is reduced to leuco indigo form. NaOH is used for the
maintaining the pH (11.5-12), with elevated temperatures and the mixture of glucose and
NaOH, the dyebath conditions are stable. The redox potential is negative enough to keep
the reduced indigo in its reduced form. Glucose is an eco-friendly, non-toxic,
biodegradable and inexpensive as well. [8]
Figure 2.3 (Dyeing profile of indigo on cotton fabrics) [8]
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In the case of glucose and fructose, the dyeing was carried out at 50 C for 60mins,
during which the reduction potential was recorded, the reduction potential for both the
sugars was below -700mV, which is enough to reduce the indigo dye. Among the both,
fructose gave the highest negative redox potential value at -716.3mV while glucose
staying around -703.9mV, as fructose belong to the ketose group, so there is no aldehyde
group present within the molecule. This leads to rapid reduction of the indigo. Most dyes
Figure 2-4 (Redox potential of indigo dyebath as a function of
reduction time at 50 C using different reducing sugars) [6]
baths reached the mark around -650 to -700 mV within 10mins. And the dye bath was
stable throughout the 60min experiment at 50 C. Amongst the sugars, the fructose
reached the highest negative redox potential within 5mins, and stayed stable for 60mins.
2.1.7.1. Significance on technical scale
On a technical scale, glucose has two major drawbacks, first being the high pH required
for reduction, and at such a high pH, the indigo is in its di-anion form, and from context,
mono-ionic form has much higher sorption of indigo on cotton than the di-anion form.
Thus we can conclude that reducing sugars out of other reducing agents and methods are
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considered to be most convenient when it comes to stability and consistency of dyeing at
moderate temperature and alkalinity [8].
2.2. FIXING AGENT
Fixing agent is one of the important textile auxiliaries in dyeing and printing industry,
which can improve the color fastness of dye in fabric. On the fabric, it can form
insoluble colored material with dye, thus to improve the color of washing, perspiration
fastness, and sometimes can improve its sun fastness.
2.2.1. Cationic Fixing Agent
Mainly through the cation and dye molecules in the anion group formation of ionic
bonding, thereby sealing the water-soluble groups, to improve the wet treatment
fastness. This kind of fixing agent can be divided into following types (according to its
surface activity):

Surface Active fixing agent

Non-Surface active fixing
2.2.2. General Properties and fields of application

Appearance: Light yellow to deep yellow or white viscous liquid

Ionicity: Cationic

pH: 3-5

Solubility: Easily soluble in water

Stability: Stable to acid, alkali, electrolytes and hard water

Negligible shade fades to efficiently prevent low stripping and shade change.

Obviously improves rubbing, soaping and perspiration fastness.

Outstanding alkali resistance that makes mercerization available after fixing.

Free of formaldehyde that complies with environmental requirements.

Resistant to chlorine bleaching
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CHAPTER 3
METHODOLOGY AND CALCULATIONS
This chapter covers the method of dyeing of indigo onto the cotton fabric, along with the
proposed recipe and the details of the chemicals used in them. Moreover, the parameters
of the process and the method of evaluation is also covered in this chapter.
3.1. GENERAL METHOD OF INDIGO DYEING
Indigo dyeing can be done using the batch, semi-continuous and continuous method.
The method we elected for the dyeing process is semi-continuous ‘Pad-Batch’ process.
For this process first the dyebath is prepared, meanwhile the fabric samples are cut of
the required size and then it is pre-wetted. After that the machine parameters are set and
the prepared solution is poured into the padder. Then the fabric is fed into the machine to
be dyed. After the fabric has been dyed it is exposed to air for a particular time in order
to oxidize the fabric which is then washed in hot water followed by washing at room
temperature and then the fabric is left for drying.
3.2. PROPOSED RECIPE (DYEING)
3.2.1. Pre-wetting


WASH
WASH
60 C
Room Temperature
3.2.2. Dye bath preparation





Denisol Indigo 30liq.
Sodium dithionite
Glucose
NaOH (50 %)
pH
0.5 – 4
0.2 – 0.5
10
2 – 2.2
11.5 – 12
g/L
g/L
g/L
g/L
(4g/l selected)
(0.5g/l selected)
(10g/l selected)
(2.2g/l selected)
3.2.3. Dyeing parameters



Number of dips
Dipping time
Airing Time
4 – 12
20 sec
90 sec


WASH
WASH
60 C
Room Temperature

DRY
Room Temperature
15
(4 dips selected)
Department of Textile Engineering
3.3. PROPOSED RECIPE (FIXING)
3.3.1. Direfix SD Liquid

Direfix SD Liq.
15-20

Pick-up
70-80%

Temperature
Cold
g/L
(20g/L selected)
(Room Temperature)
3.3.2. Lava Fix FF

Liquor Ratio
3-5% o.w.f

Pre-run
3-5mins

Temperature
60C
(Treat for 10-15mins)
(40g/L selected)
3.3.3. Achifix FF-429

Achifix FF-429
20-40g/L

Temperature
Room Temperature
3.4. PREPARATION OF DYE BATH
The dyeing was performed with two different reducing agents, one being sodium
dithionite and the other being glucose. Firstly both of the dyebaths are prepared in 100ml
of water, then the indigo dye (0.4g) along with the chemicals like caustic soda (NaOH)
(0.22g), sodium dithionite (0.05g) /glucose (1g) was added to the dye bath.
When the solution is being prepared the pH has to be maintained at around 11.5-12, which
is done by adding NaOH gradually and checking the pH using the pH strips provided [8],
to ensure that the indigo stays in mono-ionic form which helps in better absorption of dye
onto the cotton fabric.
Figure 3-1 (Dyebath solutions using
glucose and sodium dithionite)
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3.5. FABRIC FOR DYEING
Two types of fabrics were used for this project. Both were 100% cotton bleached fabric
with the difference of their weaves. One was 1x1 plain weave light cotton fabric while the
other was 2x1 twill weave denim fabric.
3.6. CHEMICALS FOR DYEING
3.6.1. Denisol Indigo Blue 30L
The new aniline-free indigo dye ‘Denisol Pure Indigo 30liq’ made by archroma which
reduces the risk of aniline discharge into the water which can cause environmental and
health hazards.
Therefore it is possible to produce indigo dyed denim without high levels of aniline
impurities. Denisol pure indigo is a pre-reduced dye in liquid form which helps in
consistent reduction process and reduces the consumption of the reducing agent used [14].
3.6.2. Sodium Dithionite
Sodium dithionite (Na2S2O4) is a whitish to light yellow crystalline solid having a smell
of sulfur dioxide. The reduction of NaHSO3 with zinc metal produces sodium dithionite.
Na2S2O4 has many industrial uses, including reduction of organic compounds, primarily
in the dyeing industry [15]. Sodium dithionite is known for its excellent results as well as
economic advantages.
3.6.3. NaOH (50% conc.)
Basically NaOH 50% is a strong alkali solution of 50% concentration. It is used to
maintain the pH of the solution when preparing the dye, around 11.5-12, which is very
important to keep the dye in mono-ionic reduced form [16]. If the pH is beyond 12 so that
dye will not stay in the desired mono-ionic form but is rather converted into di-ionic form
which results in improper absorbency onto the cotton fabric and the inconsistency of dye.
3.6.4. RDT Glucose powder
All monosaccharides are reducing sugars because all monosaccharides have an aldehyde
group (if they are aldoses). The glucose powder comes as white powder [17].
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3.7. CHEMICALS FOR FIXING
3.7.1. Direfix SD Liquid
It is formaldehyde-free fixative agent for improving wash fastness properties of fabrics
dyed with Diresul Sulphur dyestuffs. is especially suitable as fixing agent The product
can also be used as fixing agent in other type of processes such as cationic fixation of
Diresul Black dyes for very high repetitive washing fastness, as well as after fixation
agent for all Diresul dyes dyed by conventional processes when improving wet fastness
is required. Direfix SD liq has no influence on the light fastness of the dyeing.
3.7.1.1. Properties

Aspect:
White liquid dispersion

Ionic character:
Cationic

Aspect:
White liquid dispersion

Ionic character:
Cationic

Density at 20ºC:
1.25

pH (undiluted):
7.0

Stability to storage:
Good in closed containers between 0ºC and 50ºC.

Solubility in water:
275 g/l in hot (60ºC) water
3.7.1.2. Stability

To acid products:

To alkaline products: Possibility of precipitation.

To salts:
Good at normally used concentrations.
May precipitate at high concentrations of phosphates and
sulphates
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3.7.2. Lava Fix FF
It is fixing agents whose function specifically is to fix indigo on to cellulosic fibers.
3.7.2.1. Properties

Appearance:
Yellowish Liquid

pH: approx.:
3

Ionic character:
Cationic

Density:
1.04kg/l

Shelf life:
3months at 20C
3.7.2.2. Chemical Characteristics

Fixation of indigo improves rub fastness by 1-2 grades

Less abrasion during stone-washing

Liquid, dosable

Good affinity for the fibers because of its cationic nature

Cross-Links with the fiber when exposed to heat
3.7.3. Achifix FF-429
It is made up of macromolecular compound with dye and synchronously combined with
fiber to prevent dyeing releasing hence improve wet treatment fastness of fabric. It can be
used for fixing reactive dyed fabrics as cotton, linen, silk and direct dyed fabric.
3.7.3.1. Properties

Appearance:
Colorless to yellowish transparent liquid

pH: approx.:
7.0-8.5

Ionic character:
Cationic

Solubility:
Can be diluted with water by any ratio
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3.7.3.2. Chemical Characteristics

Has no formaldehyde, no peculiar smell, and no irritation to skin (according to
eco request.)

Can obviously improve soaping fastness and fastness to perspiration of reactive
and direct dyed fabrics

Restraining migration of hydrolyzed reactive dyes during drying

Can be mixed with cationic and nonionic softener in one bath
3.7.4. Machine and parameters

Speed
=
2m/min

Pressure
=
2bar

Direction
=
Forward
3.8. PROCEDURE OF DYEING

The samples are cut according to the working width of the padder

The amount of dye, caustic and reducing agents is calculated according to the bath
volume.

The dye bath solution is prepared by adding the calculated amounts of chemicals
into the beaker containing water.

The padder is set onto the following parameters:
o The pressure of padding rollers is set at the required value by using the air
pressure gauge
o The speed of padder rollers is also set by using the speed adjusting knob
o The rotation director for the rollers is set by using the direction control
selector
o The nip is closed by using the nip close selector
o The start button is then pressed to start the machine

The solution is poured between the nip of padding rollers throughout its width

The fabric is inserted in between of the padding rollers

The padded sample is grabbed as it comes out of the rollers

The fabric is given 12 dips
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
The fabric is given 90sec of aeration time after every dip

The liquor is drained using the drain valve

The freshly made liquor is poured again into the machine for next dip

The dipping process is continued until the subsequent number of dips are achieved

The machine and compressor is then turned off

The fabric is washed in hot water at 60 C for 2 mins

The fabric is washed again in cold water at room temperature and dried
3.9. PROCEDURE OF APPLYING FIXING AGENT
3.9.1. Direfix SD Liquid

The samples are cut according to the padder width

The fixer bath is prepared with the respective recipe

The padder is adjusted such that 70-80% pick-up is achieved

The solution is poured in between the padder rollers

The fabric is inserted in between the padder rollers

The fabric is then taken out from the other side

The fabric is then dried
3.9.2. Lava Fix FF

The sample is cut with respect to machine

The liquor ratio of 10:1 is set in the machine at 30C temperature

The fixer solution is then prepared which is to be put into the machine

The solution is poured into the machine

The machine is pre-run for 3 to 5mins

Then the fabric is place in the machine

The temperature is raised to 60C

The machine is ran for further 10 to 15mins

The machine is stopped and fabric is taken out

The fabric is then dried
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3.9.3. Achifix FF-429

The sample is cut according to the padder width

The fixer solution is prepared according to the recipe

The solution is poured in between the padder rollers

The fabric is then inserted between the padder rollers

The fabric is taken out from the other side of the padder

The fabric is then dried
3.10. METHODS OF PERFORMANCE
3.10.1. Initial Method
This method was used in first four trials of the project, which was comprised of dipping
the fabric in the same bath for 4 to 12 times, the fabric used was 1x1 plain weave light
fabric. This lead to the following observations:

One dye bath for all 12 dips leading to poor dyeing results

No oxidation time in between dips leading to poor dye results

Dye gets hydrolyzed after some time

Lump formation within dye bath after some time

Poor color pickup on fabrics

Light shade on fabrics

Variation in color throughout the fabric
It was very clear that the method that was initially used was not the correct way of dyeing
the fabric. Also minor errors in the padding machine (poor washing, dye residue on the
rollers etc.) caused a lot of issues on our light plain weaved cotton fabric.
3.10.2. New Method
The previous method was improved in all aspects. Firstly the parameters for the machines
were checked at different values and settled down to only one parameter (2bar , 2.2m/min)
firstly only 2 dye baths were used for 12 dips (6dips per dyebath), Fresh dye bath was
used after every 6 dips. It was made sure that each fabric got 20 seconds of dipping time
in the dye bath (as stated in the proposed recipe). Also 90secs of aeration time was given
to the fabric after every dip so that the dye on the fabric gets oxidized. After the
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observation, the number of dye baths were increased to the point that each dip was given
in a fresh dye bath (12 baths for 12 dips). The plain weave fabric had good depth of color
but due to problems in padder resulted in uneven dyeing results so it was changed with
denim fabric to observe the results. The following is the table of the methods that were
used.
Trial
Machine
Type of
No. of
No. of
Observation of
No.
Parameters
Fabric
Dye baths
Dips
Results
T1
T2
T3
T4
T5
T6
T7
T8
T9
1.5bar
Plain Weave
2m/min
Cotton Fabric
2bar
Plain Weave
1.5m/min
Cotton Fabric
2bar
Plain Weave
2m/min
Cotton Fabric
2bar
Plain Weave
2.2m/min
Cotton Fabric
2bar
Denim Fabric
2.2m/min
(RTD)
2bar
Denim Fabric
2.2m/min
(RTD)
2bar
Denim Fabric
2.2m/min
(RTD)
2bar
Denim Fabric
2.2m/min
(RTD)
2bar
Denim Fabric
2.2m/min
(RTD)
1
12
Very light shade
Uneven poor dyeing
1
12
Very light shade
Uneven poor dyeing
1
12
Slightly better shade
Uneven poor dyeing
2
12
Better shade
Uneven poor dyeing
2
12
Better shade
Even & better dyeing
4
12
Darker shade
Even & better dyeing
6
12
More darker shade
Even & better dyeing
12
12
Very dark shade
Even & better dyeing
12
12
Very dark shade
Even & better dyeing
Table 3-1 (Progression of trials and their parameters)
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3.10.3. Dyed Fabrics
The twill weaved denim fabric held up to the results quite well, given good depth of
shade and even dyeing, Thus the fabrics were then dyed on the same recipe and
procedure with the newly decided method. At padder pressure set to 2bar and roller
speed set to 2.2m/min. To give the fabrics 12 dips, 12dyebaths were prepared and fabrics
were given appropriate aeration time between the dips. After that the fabrics were
washed and dried.
3.10.3.1. Sodium Dithionite Samples (Standard)
Some fabrics were dyed with the recipe that included sodium dithionite as reducing
agent. All fabrics were dyed, washed and dried and then the best one amongst them was
set as a benchmark for comparison for all the batch samples which were going to be
made using glucose as reducing agent.
Sample Parameters
Name
S1
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S2
2bar & 2.2m/min Dips = 6 Dip time = 10sec
S3
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S4
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S5
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S6
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S7
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S8
2bar & 2.2m/min Dips = 6 Dip time = 20sec
S9
2bar & 2.2m/min Dips = 12 Dip time = 20sec
S10
2bar & 2.2m/min Dips = 12 Dip time = 20sec
Table 3-2 (Dyed samples from Sodium Dithionite)
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3.10.3.2. Glucose Samples (Batch)
Some fabrics were dyed with the recipe that included glucose as reducing agent. All
fabrics were dyed, washed and dried, all the fabrics were then evaluated and compared
against the standard selected sample of sodium dithionite.
Sample Parameters
Name
G1
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G2
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G3
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G4
2bar & 2.2m/min Dips = 6
G5
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G6
2bar & 2.2m/min Dips = 6
G7
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G8
2bar & 2.2m/min Dips = 12 Dip time = 20sec
G9
2bar & 2.2m/min Dips = 6
Dip time = 10sec
G10
2bar & 2.2m/min Dips = 6
Dip time = 20sec
G11
2bar & 2.2m/min Dips = 6
Dip time = 20sec
Dip time = 10sec
Dip time = 20sec
Table 3-3 (Dyed samples from Glucose)
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3.10.3.3. Fixer Samples (Batch)
Three more glucose samples were prepared, on which the fixing agents were to be
applied respectively. The two fixer (Achifix & Direfix) were applied on the padder
machine as prescribed in their respective fixer recipes. The last fixer (Lava Fix FF) was
applied onto the fabric in the IR Machine with its respective recipe.
Sample
Parameters
Name
F1(achifix FF)
2bar & 2.2m/min
Dips = 1
Dip time = 5sec
F2(direfix SD)
1.5bar & 1.5m/min Dips = 1
Dip time = 5sec
Pickup = 70-80%
F3(lavaFF)
Pre-run at 30C for 10mins
Treatment for 15mins at 60C
Table 3-4 (Dyed glucose samples with fixers applied)
3.11. TESTING AND EVALUATION OF DYED FABRIC
The dried fabric samples were then tested on the spectrophotometer to calculate the results
of the CIE values, %reflectance and color strength values (K/S). Spectrophotometer is a
very powerful tool used in both the biological and chemical sciences yet operates by
simply shining a beam of light, filtered to a specific wavelength (or very narrow range of
wavelengths), through a sample and onto a light meter. The software used for this purpose
was ‘Datacolor TOOLS’. Datacolor is an important quality control application for
industries where the application of color accuracy is crucial, it helps in objective analysis
and visualization of accurate color results [18].
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3.11.1. Color fastness tests
The tests for color fastness are also done on the dyed samples. For this purpose the testing
samples were cut out of the dyed fabrics in order to perform the tests on them.
3.11.1.1. Color fastness to washing (ISO 105 CO6 A2S)
The sample (10x4cm) to be tested is cut from the fabric and attached with an adjacent
white fabric. A solution is prepared of the following recipe:
Water
150ml
Detergent
4g/L
Steel balls
10
Temperature 40 C
This container is closed and placed in the laundrometer, at first it is pre-ran in order for
the solution to achieve the temperature then the fabric is placed in the container and is ran
for 30mins. After the process the specimen is removed from the container, washed and
dried and then evaluated for shade change and staining.
3.11.1.2. Color fastness to crocking (AATCC 08)
The fabric to be tested is placed on the bottom holder, the exposed area of the fabric is
135 x 50mm, while the crocking cloth is 2x2in, and the machine is set to 10cycles. For
dry crocking test the fabric was placed on the base of crock meter with the help of holder.
The crocking cloth was fixed of the finger with the help of a clip. Then the sliding arm
was dragged downward and the machine was started by pressing the start button. After
10cycles the machine stopped automatically. The crock cloth was removed and assessed
by the grey scale. For wet crocking water was added to the crocking cloth with the help
of dropper by 65times to its dry weight, the excessive water was removed.
3.11.2. Evaluation method
The k/s values were extracted from spectrophotometer while the color fastness to washing
evaluation was done in light box under D-65 light.
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CHAPTER 4
RESULTS AND DISCUSSION
This chapter covers the detailed explanation of the results of the dyed fabrics which were
evaluated on the spectrophotometer and color assessment box. This chapter also contains
detailed comparison of the values of color fastness and color strength (K/S) of both
fabrics.
4.1. OBSERVATIONS (OLD)
Earlier four trials of dyeing done, each trial consisted of two samples one being the
standard to be compare with, while other being the batch sample. There were two dye
baths prepared for the dyeing each of the samples, one was made from sodium dithionite
(standard sample) and other from glucose (batch sample) as reducing agents. The samples
were dyed from the same recipe and procedure as mentioned earlier.
4.1.1. Trial 0
The first trial was referred as a test trial to get used to the working with the padder and the
process handling. The pH was maintained at around 12 (tested with pH strips) and the
fabric was not pre-wetted before the dyeing process, thus leading towards inconsistent and
uneven dyeing with patches and spots on the sample fabrics.
4.1.2. CIE L* a* b* Values (D65 10 Deg)
Standard
Batch
Differences
L*
73.37
73.32
-0.05
a*
-4.12
-4.73
-0.61
b*
-9.43
-11.78
-2.35
C*
10.29
12.70
2.41
h
246.41
248.14
0.34
DE*
2.43
Table 4-1 CIELAB Values (Trial 0)
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4.1.3. Color fastness results
COLOR FASTNESS TO CROCKING
Standard
Batch (Trial 0)
Dry
4-5
4-5
Wet
3-4
4-5
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade Change
4
3-4
COLOR FASTNESS TO WASHING (STAINING)
Staining
4-5
4
Table 4-2 Color Fastness Results (Trial 0)
4.1.4. Trial 1
In the second trial. The pH was maintained at around 12 and the fabric was pre-wetted for
10mins in warm water before the dyeing process, in order to open up the fibers and
increase the absorbency of dye onto the fabric. With this method the dyeing was consistent
with slight unevenness, the dye shade was still at the lighter side. The possible reason of
lighter shade and poor absorbency of the dye onto the fabric is the pH value which
supposedly got beyond the “12” mark leading towards the conversion of dye into its diionic form which is not suitable for cellulosic fibers.
The L* a* b* values for these samples were very low due to the poor shade depth of the
dye.
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4.1.5. CIE L* a* b* Values (D65 10 Deg)
Standard
Batch
Differences
L*
61.86
57.56
-4.29
a*
-4.36
-4.12
0.24
b*
-16.56
-16.47
-0.91
C*
16.16
16.98
0.82
h
254.36
255.97
0.47
DE*
4.40
Table 4-3 CIELAB Values (Trial 1)
4.1.6. Color fastness results
COLOR FASTNESS TO CROCKING
Standard
Batch (Trial 1)
Dry
3-4
3-4
Wet
2-3
2-3
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade Change
4
3-4
COLOR FASTNESS TO WASHING (STAINING)
Staining
4-5
3-4
Table 4-4 Color Fastness Results (Trial 1)
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4.1.7. Trial 2
Amongst the other two trails, this came out to be the best in results. In this trial, the pH
was maintained at 11.5 to ensure the mono-ionic form of the dye, and his fabric was also
pre-wetted in warm water. The dye bath solutions were given 10mins of rest time in order
for them to achieve their desirable redox potential values (below -700mV). So far the trial
gave the most desirable results, with better shade depth and result values.
4.1.8. CIE L* a* b* Values (D65 10 Deg)
Standard
Batch
Differences
L*
46.40
53.70
7.29
a*
-3.49
-4.44
-0.95
b*
-22.24
-19.16
3.08
C*
22.51
19.67
-2.84
h
261.09
256.96
-1.52
DE*
7.97
Table 4-5 CIELAB Values (Trial 2)
4.1.9. Color fastness results
COLOR FASTNESS TO CROCKING
Standard
Batch (Trial 2)
Dry
2-3
2-3
Wet
2-3
2-3
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade Change
4
4
COLOR FASTNESS TO WASHING (STAINING)
Staining
5
3
Table 4-6 Color Fastness Results (Trial 2)
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4.1.10. Trial 3
This trial was performed on a different fabric (Heavy GSM denim fabric) to test the results
on a different weave. In this trial, the pH was maintained at 11.5, and his fabric was prewetted in with NaOH and wetting agent. The results were again poor due to the less
penetration of dye into the fabric, thus the shade was very light.
4.1.11. CIE L* a* b* Values (D65 10 Deg)
Standard
Batch
Differences
L*
71.17
68.30
-2.87
a*
-3.79
-4.53
0.17
b*
-11.85
-14.30
-2.46
C*
12.78
15.03
2.25
h
247.97
252.07
0.99
DE*
3.78
Table 4-7 CIELAB Values (Trial 3)
4.1.12. Color fastness results
COLOR FASTNESS TO CROCKING
Standard
Batch (Trial 2)
Dry
4-5
4-5
Wet
3-4
4
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade Change
4
4-5
COLOR FASTNESS TO WASHING (STAINING)
Staining
5
4-5
Table 4-8 CIELAB Values (Trial 3)
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4.2. OBSERVATIONS (NEW)
The newly dyed samples which followed the new devised method and procedure, were
evaluated as same as previous trials. The L* a* b* values were not considered this time as
the shade and hue change between standard and batch samples were very minor. The
newly dyed samples are divided into following categories.
SodiumDithionite
Glucose Samples
Fixer Samples
S1
G1
F1 (Achifix FF-429)
S2
G2
F2 (Direfix SD Liq)
S3
G3
F3 (Lava Fix FF)
S4
G4
S5
G5
S6
G6
S7
G7
S8
G8
S9
G9
S10
G10
Samples
G11
Table 4-9 Sample Distribution
The results of these samples will the compared with the standard sample which will be of
sodium dithionite. The comparison between standard and more of sodium dithionite
samples will be done then glucose samples will be compared against the standard sample.
And lastly the comparison between standard and fixer samples will be done.
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4.2.1. Standard Samples (Sodium Dithionite)
4.2.1.1. Color Strength Values (K/S)
The color strength values of all the sodium dithionite samples were observed and the best
value was taken as the standard for comparison of all other samples. The color strength
values for all these samples are relatable to actual values of indigo dyed fabrics, showing
that the dyeing results were satisfactory
COLOR STRENGTH (K/S)
Sample Name
K/S
S1 (Standard Sample)
19.49
S2
16.3
S3
14.59
S4
16.8
S5
17.9
S6
16.8
S7
16.8
S8
14.49
S9
16.4
S10
18.3
Table 4-10 Color Strength Values (K/S) of standard samples
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4.2.1.2. Color fastness results
The standard sodium dithionite samples were all evaluated for their color fastness values,
and as on paper they all performed significantly well. The CF to staining for all the
samples was near perfect. The standard sample performed the best amongst all other
samples. While some samples performed well, few of them also performed lesser than
others.
COLOR FASTNESS TO CROCKING
S1
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
Dry
3-4
3-4
3-4
3-4
3
3-4
3-4
3-4
3-4
3-4
Wet
3-4
3
3
3
3
2-3
2-3
3
2-3
2-3
4-5
4-5
5
5
Std
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade
5
4-5
4-5
4-5
4-5
4
4-5
4-5
Change
COLOR FASTNESS TO WASHING (STAINING)
Staining
5
4-5
4-5
4-5
4-5
Table 4-11 Color Fastness results of standard samples
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4.2.2. Batch Samples (Glucose)
4.2.2.1. Color Strength Values (K/S)
The color strength values of glucose samples were then observed against the chosen
standard sample. All of the glucose samples showed acceptable results, while only a few
of them were able to come closer to the standard sample value.
COLOR STRENGTH (K/S)
Sample Name
K/S
Standard Sample
19.49
G1
16.83
G2
16.7
G3
16.5
G4
12.6
G5
17.06
G6
13.7
G7
14.3
G8
15.1
G9
14.03
G10
14.07
G11
13.34
Table 4-12 Color Strength Values (K/S) of batch samples
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4.2.2.2. Color fastness results
The batch glucose samples were all evaluated for their color fastness values, their results
were compared against the standard color fastness values. From the observation most of
the glucose samples performed similar to the sodium dithionite samples, but the glucose
samples showed poor results in wet crocking.
COLOR FASTNESS TO CROCKING
Std
G1
G2
G3
G4
G5
G6
G7
G8
G9
G
G
10
11
Dry
3-4
3-4
3-4
4
3
3
3-4
3-4
3-4
3-4
3-4
3
Wet
3-4
2-3
2
2
2-3
2
3
3
2-3
3
3
2-3
3-4
3
4-5
4-5
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade
5
4
4-5
3-4
4
3-4
3-4
4
4
4
Change
COLOR FASTNESS TO WASHING (STAINING)
Staining
5
5
5
4-5
4-5
4-5
Table 4-13 Color Fastness results of batch samples
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4-5
4-5
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4.2.3. Fixer Samples
4.2.3.1. Color Strength Values (K/S)
The fixers which were applied onto the glucose samples were then evaluated for their
color strength values, by observing the results of these fixers it was clear that the effect of
fixer on the color strength of the sample is near to minimum.
COLOR STRENGTH (K/S)
Sample Name
K/S
Standard Sample
19.49
F1 (Achifix FF-429)
16.43
F2 (Direfix SD Liq)
16.43
F3 (Lava Fix FF)
16.93
Table 4-14 Color Strength Values (K/S) of batch fixer samples
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4.2.3.2. Color fastness results
The fixers which were applied onto the glucose samples were evaluated for their color
fastness values. The fixers took over the poor result of previous glucose samples and
overcame the places where glucose performed worse (wet crocking). This made the results
of the glucose samples come closer to the actual standard sample
COLOR FASTNESS TO CROCKING
Standard
F1 (ACHIFIX)
F2 (DIREFIX)
F3 (LAVAFIX)
Dry
3-4
3-4
4
3-4
Wet
3-4
3-4
3-4
3-4
COLOR FASTNESS TO WASHING (SHADE CHANGE)
Shade
5
4-5
4-5
4-5
Change
COLOR FASTNESS TO WASHING (STAINING)
Staining
5
5
5
Table 4-15 Color Fastness results of batch fixer samples
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4.3. DISCUSSION ON RESULTS
The results mentioned showed the strengths and weaknesses of both standard and batch
samples. The standard sample performed outstanding while the batch sample lacked in
some aspects. Previously in ‘Old method’ of performance, the samples showed poor
staining results in few cases, which is now not the case as the oxidation of our dye in new
samples are done the correct way. Main weaknesses of glucose is performing worse than
sodium dithionite in terms of CF to dry and wet crocking and CF to shade change. This
was countered by the use of cationic fixing agents onto the glucose samples which
improved the results of the batch in both dry and wet crocking thus making the results
come more near to the standard sample.
Standard
CF to washing
Glucose Samples
Fixer Samples
Best
Better
Better
Best
Best
Best
Best
Near to Best
Improved
Best
Better
Improved
(Shade
Change)
CF to washing
(Staining)
Crocking
(Dry)
Crocking
(Wet)
Table 4-16 Comparative Results Table
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CHAPTER 5
CONCLUSION
5.1. CONCLUSION
From the result of all the samples and comparative study of them, dictates that the
possibility of replacing the harmful reducing agent in indigo dyeing (sodium dithionite)
with an eco-friendly reducing agent is quite high. The reducing sugars (glucose in this
case) hold great similarities in results compared to sodium dithionite in terms of color
strength (K/S) and color fastness values. The following conclusions can be made out of
this project:

Parameters of dyeing process greatly affect the end result of the dyed fabric

Glucose powder is cheaper and abundantly available, same as sodium dithionite

The consumption of glucose for dyeing process was observed to be 20times more
than the sodium dithionite

The glucose held great similarities in terms of results against sodium dithionite

The use of fixing agent greatly improved the color fastness properties of our
batch samples making them more comparable against sodium dithionite

All three of the fixing agents showed effective performance in improving the
results
5.2. FUTURE WORK
The goal of this project was to achieve complete replacement of the harmful chemical
reducing agent used in the indigo dyeing process. For this project glucose was the major
part of the research, as for further future work different reducing sugars are to be further
researched, such as Fructose and Galactose. The combination of reducing sugar with
sodium dithionite can also be studied to insure less consumption of the harmful
chemical, such that the best alternative method/chemical could be found amongst them.
Artificial sugars are also seen as a possibility to explore, along with reducing sugars,
different reduction methods can also be studied, but in the end the selected alternative
must be economical and less environmentally harmful than Sodium Dithionite also are
practical to implement on industrial scale.
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