Methods for Removing Colour from Polyester and

Cotton Blended Textile Waste

Commissioned by IKEA

Bachelor Thesis

Written by Hedvig Magnusson & Adina Löthwall

Thesis for the Degree of Master in Textile Technology with a major in

Textile Product Development and Entrepreneurship

The Swedish School of Textiles

Report number: 2020.12.01

Date 7th of June 2020

Contacts:

Hedvig Magnusson: hedvig.e.magnusson@gmail.com

Adina Löthwall: adina.lothwall@icloud.com

Bachelor Thesis

Subject: Literature review and interviews

University of Boras

School of Textiles

SE-501 90 BORAS

Telephone +46 033 435 4640

Examiner: Supervisors’ names: Carina Kauppi

Supervisors’ contact information: carina.kauppi@hb.se

Abstract

The textile industry is developing at a fast pace, and is constantly changing. It is

constantly evolving new methods for recycling and further research is important for

future needs. The ability to recycle a textile blended material is a step towards a more

sustainable industry. There are however different difficulties around the various

processes that have to be removed for recycling. The purpose of the study is to find

methods for removing dyes from polyester and cotton blended textile waste for

recycling. To investigate the subject, a literature study combined with interviews with

experts was performed. The results of the study shows that it is possible to remove

dye from cotton and polyester individually.

To remove dye from cotton chlorine and hydrogen peroxide are used. Another method

is to use a reducing agent hydrosulphite and after use together with lye. There are

several ways to remove colour from polyester, although it will almost always have a

residue of colour left. One can either melt the pigment into the fibre by using heat.

Another method is to use chemicals which increase the amorphous areas in the fibres

and the colour will be penetrated. Finally, when investigating a method for removing

dye from a polyester and cotton textile blend. The study has highlighted the need of

developing new methods without destroying the quality of the fibres.

By this study it has been concluded removing dye from fibres are difficult but can be

achieved with certain chemicals and processes. It is concluded in the study, removing

dye from polyester and cotton individually can be succeed. However, removing

colour from a blended fabric is rather difficult. The study has focus on discussing the

difficulties when decolouring a blended textile.

Keywords

Recycle, textile waste, polyester, cotton, colour, dyeing, decolouration.

Acknowledgments We would like to address a great thank you to Anna Palmberg and Marius Lehadus at

IKEA for taking their time guiding us during the study with their knowledge and

kindness. To have been given the opportunity have been a rewarding and exciting

journey. We would also like to thank our supervisor Carina Kauppi for helping us

with the report writing and also for your availability.

Finally, a great thank you to all the interviewing participants for taking your time and

contributing with your knowledge.

Table of Content 1. Introduction………………………………………………………….………….. 1

2. Background………………………………………………………………….….. 1-4

2.1 IKEA………………………………………………………………..………. 2

2.2 Textile Waste………………………………………………………..……… 3

2.3 Recycling……………………………………………………………....…… 3-4

3. Problem statement…………………………………………………………..….. 4

4. Purpose of the Study……………………………………………………………. 4

5. Research Questions……………………………………………………...……… 4

6. Delimitations……………………………………………………………………. 4

7. Methods…………………………………………………………………...…….. 5-7

7.1 Research Strategy…………………………………………………...………. 5

7.2 Collection of Theory and Data………………………………………..…….. 5-6

7.3 The Design of Interviews………………………………………………….... 6

7.4 Selection of Interview Participants…………………………………………. 6

7.5 Validity and Reliability………………………………………………………6-7

7.6 Data Analysis Method………………………………………………..………7

8. Theoretical Framework…………………………………………………….…… 7-11

8.1 Cotton Properties……………………………………………………………. 7

8.1.1 Dyeing of Cotton…………………………………………….……… 8

8.1.2 Removing Colour from Cotton…………………………....………… 8

8.2 Polyester Properties…………………………………………………….....…. 9

8.2.1 Dyeing of Polyester…………………………………………......…… 9

8.2.2 Removing Colour from Polyester……………………………………. 9-10

8.3 Dyeing a Blended Polyester and Cotton Material………………………...…. 10-11

9. Results………………………………………………………………………...…. 11-13

9.1. Methods Used to Remove Dyes from Cotton and How the Process is

Accomplished……………………………………………………………….…… 11

9.2 Methods Used to Remove Dyes from Polyester and How the Process is

Accomplished……………………………………………………………………. 11-12

9.3 Methods Used to Remove Dyes from a Cotton and Polyester

Blended Fabric………………………………………………………………..…. 12-13

10. Discussion…………………………………………………………………..…… 13

11. Conclusion…………………………………………………………………….… 14-15

11.1 Contribution to Area of Informatics…………………………………..…… 14

11.2 Evaluation of Method…………………………………………………..….. 14

11. 3 Further Research……………………………………………………..……. 15

12. List of References…………………………………………………………..…… 16-18

13. Appendix………………………………………………………………….…….. 19

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1. Introduction Approximately 77,5 million kilograms textile waste are disposed each year in Sweden.

This means on a yearly basis 7,5 kg per person. Today, textile waste is used in landfills,

padding or in worst case burned. If these textiles could be brought back in the life cycle it

would contribute to a more sustainable industry.

The textile industry is one of the most polluted and resource-intensive industries. The

production of fibres to textile waste has a negative environmental impact in

manufacturing, on climate and in terms of water consumption, chemical use and

transportation. Fortunately, the attitude towards textile waste has dramatically changed

over the past few decades. Since the 1970s, a greater awareness of reuse and recycling

waste has been developed in society. It is considered important to use the already existing

resources instead of producing new. By reusing textile waste and removing colour, the

material will have a longer and circular life cycle. This study aims to find a method for

removing colour from a composition of cotton and polyester blended fabric for a

recycling purpose.

1. Background The industrial textile colouring process has its origin in the industrial revolution. In this

time the craftsmanship of colouring were changed to a large industry (Rehnby, 2010).

Colouring is a way to refine a textile material, to create an additional attraction between

the product and the consumer. There are several ways to dye a material, in the state of a

fibre, yarn or fabric. Based on which fibre, the expected quality and field of application,

different methods and dyes are used. Water-soluble substances are called dyes, another

insoluble substance is called pigment. Auxiliary chemicals are used when colouring for

attachment to the fibre (Rehnby, 2007).

The earth's resources are being used in a high pace. The natural resources of raw material

are limited and must be reduced (European environmental agency, 2016). To recycle a

textile, it must be as similar to the original fibre as possible. Therefore, it is important to

remove dye, pigment and finishing products before recycling. Cotton and polyester fibres

are the most consumed fibres in the world, consequently the study is focusing on these

two. Below, statistics of the global fibre consumption 2018 is presented as an overview

(Figure 1).

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Figure 1: Global Fibre Consumption (Lenzing, 2018)

2.1 IKEA IKEA is a global furnishing company founded in Sweden 1943 by Ingvar Kamprad. The

business idea is to offer a wide range of functional well designed home furnishing

products in the low price segment (IKEA, 2019). According to IKEA’s Sustainability

Strategy - People and Planet Positive, the environmental initiatives, is to design products

in a circular principle. In the long-term the company only wants to use renewable and

recycled fibres. IKEA is committed to turn waste into resources. Transforming secondary

materials by reusing or recycling materials, the company will take the lead into clean

resources. Further IKEA consciously implements sourcing and producing recycled and

renewable materials (IKEA, 2018). Developing a method for removing dye from a

blended textile waste material would create opportunities to develop new sustainable

solutions for a more sustainable production process for IKEA textiles.

Two years ago only 10% of the polyester IKEA used was recycled. Today 60% of the

PET used is recycled. The majority of the recycled polyester is from PET-bottles, only a

fraction is residues from textile production. According to Nils Månsson, the reason is the

absence of technical solutions for large scale chemical recycling of old textiles. Therefore,

IKEA is also searching on recycling textiles to textiles (Obminska, 2019).

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2.2 Textile Waste

Waste in various forms, is one of the most important issues facing the world today. Our

inadvertency of the problems generated by waste will have an impact on our children´s

lifetime, resulting in a legacy our generation will not be proud of. Problems regarding

waste has grown exponentially with the industrial and petrochemical revolution. With a

growing population and greater consumption, the way individuals are thinking needs to

change. Advances in reduction of hazards and waste have encouraged a technological

optimism, even though the amounts continue to threaten society. Waste is an indication of

inefficiency of energy and expensive (Letcher & Vallero 2011). As much as half of the

textile products used by consumers, both new products and second hand, are discarded as

waste. This means a total amount of 145 000 tonnes in Sweden, Denmark and Finland and

the majority are incinerated or used in landfills (Tojo, 2012). Recycling the waste

removes it from the waste stream and brings it back to the market. The waste can arise

from various textile industries and manufacturers (Hawley, 2006).

To prevent textile waste it is considered important to reduce both the quantity of waste

and the harmful substances in materials. This because it creates qualitative problems in

the end of a products lifetime (Tojo, 2012). 95% of all textiles produced have the potential

to be reused or recycled. Currently only 15% are recycled and this disproportionate rate is

because of the lack of awareness among individuals (Center for Ecotechnology, 2020).

2.3 Recycling

The production of fibres are increasing and the reason is the rising in the population and a

better standard of living. The main fibres used are synthetic fibres and natural fibres.

When producing synthetic fibres non-renewable natural resources is utilized. Recycling is

a way to use the already existing resources and reuse them. Although it seems like an

obvious choice, it is a difficult process.

Cotton can be mechanically recycled, though the quality of the fibre is significantly worse

after this process. The cotton fibre will be considerably shorter and is therefore mixed

together with virgin cotton to receive a better quality. New methods to recycle cotton is

under development. One method is to dissolve the cotton fibre and regenerate the fibre to

viscose or lyocell fibres. Re:newcell is the company that is working with this method, the

first step is to shred the textiles of cellulose and then add the solution which decolourise

the material and then resolve the cellulose material (Donaldson, T. 2017).

The fibre of polyester is extensively recycled and creates significantly less environmental

pollution compared with virgin polyester fibres made from new raw materials. For

example, air pollution may be reduced by as much as 85%. The challenges of producing

recycled polyester includes achieving appropriate levels of purity of the polymer and

improve spinning methods to make new fibres with good quality. Methods to bleach dyed

or printed fabrics may improve the recyclability of polyester interior and furniture textiles

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(Textiles, 2014). To recycle a cotton and polyester blend an alkaline hydrolysis is used

without a catalyst, this depolymerize the polyester fibre. The study's result showed the

polyester with a temperature of 90 degrees with 10% sodium hydroxide concentration

with a time on 390 minutes is depolymerize, and then the two fibres are separated

(Björkqvist, 2017).

3. Problem Statement This study is addressing the problem of removing dye before recycling, in an examination

to find methods of removing colour from a polyester and cotton blended textile. The result

will create new aspects regarding the recycling process of decolouring a textile waste

material. The study is relevant for a more sustainable recycling process. A literature study

will be conducted with additional interviews to receive a result and define a conclusion.

4. Purpose of the Study The purpose of the study is to find methods for removing dyes from polyester and cotton

blended textile waste for recycling.

5. Research Questions 5.1 What method is used to remove dyes from cotton and how is the process

accomplished?

5.2 What method is used to remove dyes for polyester and how is the process

accomplished?

5.3 Is there a method for removing dyes from a cotton and polyester blended fabric? How

is the process accomplished and in what readiness level?

6. Delimitations The study will not focus on any other fibres besides cotton and polyester, which means

only direct dyes, reactive dye and disperse dyeing are selected. This means that vat and

sulphur dyes will not be examined. Possible treatments or finishing processes of the

material are excluded from the study. To gather theory and data, the report will only

contain a literature study supplemented with semi-structured interviews.

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7. Methods The methodology chapter aims to provide a transparent description of the research

process and starts by discussing the choice of research strategy. Further, it is described

how information was gathered by interviews.

7.1 Research Strategy

The study includes a deductive method including a literature study with semi-structured

interviews (Figure 2). A literature study is a systematic, methodical and critical review of

literature based on a scientific purpose. The literature reviewed consists of scientific

literature, scientific publications, such as dissertations and articles in scientific journals

(Göteborgs universitet, 2015). The advantage of using a literature study is the results of

several scientific studies can compared with others. However, it is important in a literature

study to review the information from a critical perspective. In addition, to assess the

quality of the facts presented it is important to remain objectively to reduce subjectivity

(Willman, A et al. 2006).

A semi-structured interview is a qualitative strategy of collection of data where the

researchers asks a series of open-ended predetermined questions. In this case the

researcher has control over the interviewing topics, the respondent has more freedom to

answer the question. This because there is none specific order of responses to each

question (The SAGE Encyclopaedia of Qualitative Research Methods, 2008). It is

considered easier to accomplish an analysis of the collected material if frames if designed

in advanced (Bell, 2000). However, there is a risk of misinterpreting and missing

information during semi-structured interviews (Bryman, Bell 2005).

(Figure 2)

7.2 Collection of Theory and Data

The method for processing and analysing the references has been performed by

researching articles on the subject. It has gathered theories and facts to get an overview,

by searching for relevant articles. The collection of data and theory has been made by

using keywords when searching sources in Diva portal. The information has been limited

to the keywords: recycled, textile waste, polyester, cotton, colour, dyeing and

decolouration. The interviewed experts possessed information about sources that could be

6

relevant for the study about decolouring and colouring. A part of the selected articles has

been recommended by the interview participants, who are experts in the subject.

7.3 The Design of Interviews

A questionnaire has been designed for qualitative interviews with experts in various

fields. The structure of the questions is semi-structured interviews which means the

interview was based on certain predetermined questions, but had the advantage of being

more adaptable. This created a personal conversation where the questions could be

adapted to the respondent’s expert knowledge. It resulted in a deeper understanding of the

different parts of the process from dyeing to decolouring. First, the questionnaire was

created to get to know the respondent and his working life experiences and slowly delve

deeper into the subject. Secondly, to gain a greater understanding of how to remove

colour from a cotton and polyester blended textile. It was important to understand how the

colour got linked to the material from the beginning. During this phase, the fibres cotton

and polyester was separated for better understanding of each fibre. To summarize when

coming to the end of the interview, the focus directed on discussing if there is any method

for removing colour from a blended textile material. The questionnaire is attached in the

appendix.

7.4 Selection of Interview Participants

The five interview participants was chosen by their expertise in the area of colouring and

treatments. The majority were teachers and researchers from The Swedish School of

Textiles and have been recommended by the supervisor of the study. Their knowledge

about different processes and aspects in the area contributes with information from

multiple points of views. The interviews has been performed by zoom interaction or

telephone.

7.5 Validity and Reliability

To create a reliable study experts in the field have been used by conducting interviews.

During the interviews open questions were used, the open questions did not have an

underlying valuation. The interviews were performed one by one. This means the

participants wasn't affected by each other, and the experts were given the opportunity to

be anonymous which means the answers will be honestly. Relevant scientific articles are

used in the study. The articles used in the study are recommended by experts in the area

and these are written by scientist and professionals. The study is based on relevant

information used in substantial order. By conducting the study by interviewing experts

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and using a literature study, the information is collected and processed in a systematic

way which lead to a result.

The fact the interview participant are anonymous affect the reliability because of the

unknown experts. The reader do not have the ability to draw conclusions according to the

interviewed participant’s competence. There is a great responsibility by the authors to not

distort the information and facts.

7.6 Data Analysis Method

To examine the collected data and analyse the information the authors have used the

method of first reading abstract and conclusion to gain an understanding of the article.

The collected data from the literature study have been reviewed and examined critically.

To analyse data from the interviews, these have been transcript. The information from the

interviews has been analysed and evaluated based on the relevance of the study. When the

interviews was analysed the differences and similarities was examined. The responses

from the various interviews were coded to provide an overview of the question which

made it easier to analyse.

8. Theoretical Framework

In this chapter, earlier research on the subject will be presented. The focus will be directed

towards the two fibres of cotton and polyester and its ability to be coloured and

decolorized.

8.1 Cotton Properties

Cotton is today one of the most common renewable fibres to use in interior textiles. What

makes the cotton fibre usable are the characteristics of durable properties. It can be

washed with high temperatures and easily absorb moisture as well as being soft (NE n.d.).

The cotton fibre is a staple fibre and is approximately 12-60 millimetres. The longer the

fibre is, the stronger and better quality it has. When growing cotton the quality is

classified by colour and purity, fibre length and strength (NE n.d.). The original colour of

the fibre is white with a hint of yellow. The fibre can be naturally coloured when

cultivating cotton (Sourcing Journal, 2017). The great interest of the environment has

made natural coloured cotton popular. Although, the quality of the fibre is not as good as

the pure white and twice as expensive as cotton (Textiles, 2014).

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8.1.1 Dyeing of Cotton

When colouring the cellulose fibre a reactive or direct dye bath is used. The colours are

water-soluble, therefore a help chemical is used. Salt will make the reactive or direct

colour create a covalent bond to the cotton fibre instead of remaining in the water bath.

The difference between direct and reactive dyes is the way they fixates on the fibre.

Direct dyes creates an attractive force between the dye and the fibre. With this method the

washing resistance is reduced. Reactive colour fixates on the fibre better compared with

direct colour by creating chemicals bonds to hydroxyl in the fibre (Rehnby, 2007).

8.1.2 Removing Colour from Cotton

By 2020 the cellulosic fibre will have a large gap of approximately five million tonnes.

This deficiency could be reduced if the resources produced can be reused or recycled. A

study was made to find how to chemically recycle and remove reactive dyes from a cotton

fabric treated with a wrinkle free finish, was the alkaline bleach the answer to how to

remove reactive dyes. With the recycling method described in the study, the cotton fibre

is regentated to a viscose fibre (Niit et al, 2018 a). The process includes 3 steps to remove

the dye and finish. The first step is made in an alkaline condition and the second with an

acidic condition. These two processes are made to remove the reactive dye. The third

process is made to hydrolyse the wrinkle free finish (Niit et al, 2018 b). The conclusion of

the study was that in order to recycle the cotton the reactive colour and the wrinkle free

finish has to be removed in a pre-phase to be able to process the cotton fibre to viscose. It

was concluded the alkaline bleach was successful in removing the finish and reactive

colour (Niit et al, 2018 a). The physical properties of the regenerated fibre was evaluated

to be worse comparing with the original fibre. Although a working method of removing

reactive colour and wrinkle free finish was the result of the study (Niit et al, 2018 b).

There is a project called Vividye who are developing a commercial method for removing

and redye textiles without using any bleach or deteriorating the quality of the fabric.

Through this method, a bath with positively charged ions will allow the old colour to

remove. The dye is separated away and can be used again. The coloured garment can now

be re-coloured instead of disposed. This method is only working in labs. One of the

founders Johanna Nissén Karlsson describes that the process, so far, only can be applied

to cellulosic fibres such as cotton and viscose (Forne, 2020).

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8.2 Polyester Properties

Polyester is the most widely used synthetic fibre and its filament is extremely versatile.

Common properties for synthetic fibres is that they are heat-sensitive, resistant to most

chemicals, has a low moisture absorbency, is oleophilic and has a good strength. Polyester

as a fibre has the properties of resilient in both wet and dry state, dimensional stability,

durable, sunlight- and abrasion-resistant. Polyester fibres are white and normally do not

need to be bleached. However, optical whiteners can be added to the fibre-spinning

solution. The fibres absorbency is about 0,4 to 0,8 percent, which is quite low. To bleach

the fibre either chlorine or oxygen bleach works since the fibre is resistant to acids and

alkalis (Textiles, 2014).

8.2.1 Dyeing of Polyester

Polyester is dyed with disperse dyes which is water insoluble. The fibre does not swell in

water which means high temperature is needed for colouring. The amorphous areas of the

fibre molecules become larger in high temperatures to allow the colour to enter the fibre.

Because the dyes are fasten inside the fibre, the colour cannot be washed out. The

temperature of the colouring bath is depending on the fixation method and can be

complemented with printing if the dyeing bath has low temperature. In this case, 130

degrees is enough for the colour to attach and a discontinuous colouring process is used

where the fabric gets time to absorb the colour from the dye bath. Another method is to

place disperse colour on the fabric going into a foulard and then fixing it in a high

temperature heating chamber, for example at 200 ℃. The dye is sublimated from liquid to

gas, penetrates and dissolves within the fibre (Rehnby, 2010).

However, there is a method for dyeing polyester by using a hybrid solvent such as carbon

dioxide, CO2, to replace aqueous solutions. This method means no auxiliary chemicals

are needed, because the colour is atomized in the solvent by increased pressure and the

solvent can be reused (Andersson Drugge & Svensson, 2016, see Chavan 2011).

8.2.2 Removing Colour from Polyester

There are several studies describing how to remove colour from a polyester material. In a

candidate essay from the Swedish School of Textiles, it has been investigated how this is

implemented based on two previous patents with an experimental method. In the study a

controlled dyeing was made of a 100% polyester knit fabric with dispersion dye

containing only a chromophore group, Disperse blue 56. The fabric who had a weight of

7,5 grams was cut in 2*2 cm and placed in decolourized solvent who had the temperature

of 93-95 ℃. The solvent bath had a constant stirring of 100 rpm with the bath ratio 1:20.

The solvent used in the study was 1,3 dimethyl-2-imidazolidione 98% which is 150

grams, abbreviated DMI. After 10 minutes the textile and solvent bah was filtered and

separated. The filtered textile was poured into 37.5 grams of pure DMI and rinsed

10

manually in a glass container. Then the textile was again filtered using a strainer and

rinsed and washed in 150 grams of cold ethanol. The fabric pieces were filtered again and

excess ethanol was squeezed out of the fabric. The textile pieces were then dried for at

least 12 hours. The result showed the possibility of decolourisation from a textile. It also

indicated how the time in the solvent bath impacted how much colour was removed. The

best result was obtained when the textile was placed in a solvent bath in pure DMI for 15

minutes (Andersson Drugge & Svensson, 2016).

As earlier mentioned, in order for the colour molecules to penetrate between the polymers

in the polyester fibre, the amorphous areas need to open up by adding high temperature

and pressure. After it can be closed by cooling down which can be accomplished in a bath

or by supercritical carbon dioxide (Rehnby 2010). In the two different patents it is

discussed if the fibres can swell again by exposing the polymers to heated solvents and

thereby allowing the dyes to migrate into the bath. This could be compared with a reverse

dyeing (Andersson Drugge & Svensson, 2016, see Sidebotham, Shoemaker & Young

1978, Walker 2016)

8.3 Dyeing a Blended Polyester and Cotton Material

Classification of the methods for dyeing a polyester and cotton blended fabric with

disperse and reactive dyes are either a discontinued- or continued method. The

discontinued method is exhaust dyeing method or batch dyeing method, and can be

classified as following three groups. Either, two bath dyeing, one bath one step dyeing or

one bath two step dyeing. Two bath dyeing includes two dyeing solutions which the fabric

passes discontinued, the different dyes reactive and disperse are separated in each bath.

One bath one step dyeing is explained as a method where the both dyes are in the bath.

One bath two step dying has the following steps. During the first stage the temporarily

solubilised disperse dye sticks to the polyester with a temperature of 130 °C for 1 h. The

second stage is to add alkali in the colors bath, then the uptake of the temporarily

solubilised reactive colors for cotton is successful. The dyeing bath for the blended fabric

was found to be highly dependent on the initial pH, optimum results being obtained at pH

5 (J J Lee, et al, 2006).

The continued method is thermosol dyeing and can be classified as following in two

groups, both can be single bath or double bath. One is called continuous dyeing and has

the principle of colouring the fabric in full width during a short period of time. The textile

are immersed in the dyeing bath and the leftovers are compressed. In addition, another

method is pad batch process which is semi-continuous. When dyeing a cotton and

polyester blend it is important the fibres withstand each other’s process conditions. The

fabric is immersed in the first foulard in a dyeing bath with both reactive and disperse

colour. In following step, the fabric is dried and heat fixed for the disperse dyes to be

fixated to the polyester. The fabric proceeds in to a foulard bath containing alkali and salt,

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which attaches the reactive colour to the cotton fibre. Further in the process, a steam

chamber is used for fixating the reactive dye and after this step both fibres are coloured

(Rehnby, 2010).

9. Results

The result will present the collected data of the methods for decolourise the various fibres

of polyester and cotton. To reach the purpose of the study by describing the methods for

removing colour from a blended textile waste, this will be discussed as an summarize later

in this chapter.

9.1 Methods Used to Remove Dyes from cotton and How the Process is

Accomplished

Pursuant to the interviews and the literature in the study, there are methods to remove

dyes from cotton. According to a former university lecturer in dyeing the previous

treatments made on the cotton are important. To decolourise the fibre one need to know

what treatments the material have been treated with. One method to decolourize cotton is

to use chlorine and hydrogen peroxide according to the former university lecturer. It is

found that an alkaline bleach is successful to remove colour from cotton. The first step in

this process was made in an alkaline condition, the second with a acidic condition. These

two processes are made to remove the reactive dye.

According to an expert in colouring and its chemicals it is important to know which

colour class is used for cotton decolourisation. With reactive and direct colour, there is no

major problem. When removing reactive colour the bleach hydrogen peroxide can be

used, the fibre may not be entire white but close. The ability to remove colour also

depends on what reactive colours are used, some are harder to remove and some are easier

according to the expert. Another method is to use a reducing agent hydrosulphite and after

it is used together with lye. With this method, the expert adds, you often get a better

bleach.

9.2 Methods Used to Remove Dyes from Polyester and How the Process is

Accomplished

According to the accumulated sources of information there are different methods for

removing colour from a polyester material. In the study “Additives in polyester textile”

believe a decolourized solvent bath with dimethyl-2-imidazolidione washed with ethanol,

is the most beneficial method since it is based on previous patents. The study also discuss

12

the patents meaning of swelling the fibres again by exposing the polymers to heat solvent.

This would allow the dyes to migrate into the bath and be compared with a reverse

dyeing.

A majority of the interviewed remarked the following fact. To find a method for removing

the colour from a textile it is of great importance to know exactly what dyes and dyeing

method used from the beginning. Therefore, one cannot find a common method for the

polyester fabric, as well as the cotton or blended fabric.

An interviewed participant has expertise within the subject of colour, dyeing and

chemicals. The expert explained how the colour is strongly attached to the polyester fibre

and hard to remove. When colouring a polyester textile one can either melt the pigment

into the fibre using heat, or use chemicals which increase the amorphous areas in the

fibres and the colour can be penetrated. This is why the polyester fibre is difficult to

decolourize. The respondent also clarifies how the fibre never will have its original

colour, but the removal will partly decolour the fabric because it may get a shade of

yellow or grey. The respondent recommended the method of breaking down the polyester

fibre by using chemicals as reducing agents, hydrosulphite and lye which is the same for

cotton. Carriers are also used to open up the fibre.

Since the polyester fibre is a thermoplastic polymer it can be melted. Another way to

remove the colour is to dissolve the fibre completely by using chemicals and it becomes a

liquid like solution. Centrifuged can be added and one can separate the dyestuff and the

liquid fibre. In the next step of the process the solution can be spun into new fibres

according to an assistant university lecturer at a university in Sweden with an expertise in

polymers.

9.3 Methods Used to Remove Dyes from a Cotton and Polyester Blended

Fabric

After interviewing experts who contributed with their expertise through different aspects

within the subject, the perspective of the study broadened. Jointly, the interviewed

participants believed this is a difficult subject and still unexplored. There is a deficiency

of knowledge and the interest for such study is found at several companies because of its

importance. However, the cost ineffective aspect probably is the reason for the

unexplored issue regarding removal of colour from a blended textile waste of cotton and

polyester.

An expert interviewed, former university lector in dyeing explains there is no effective,

already developed method for removing both reactive dyes and disperse dyes without

destroying the quality of the fibres. High temperatures and hazardous chemicals will

probably be used in this case to break down the fibres. The respondent adds the thought of

transparency within the industry for knowing which preparations, treatments and finishing

13

processes the material has passed. This is important to know before decolourizing since it

can affect the methods end result. The expert in colouring and its chemicals means in the

field of dyeing there is an existing method. The problem lays with the polyester, when

coloured the fibre will never go back to white there will be a residue left often a yellowish

colour or greyish.

When dying a textile material the focus are on how to improve the adhesion between the

colour and the textile. When talking about recycling, one need to remove such connection

by finding a mechanicalism how to cancel such reinforcement, otherwise it will not

disappear. Nevertheless, two materials blended are already a challenge. Especially if you

do not know the composition, according to an assistant university lecturer at a university

in Sweden with an expertise in polymers. After the study, it has been found the method of

decolourization does not occur in large scale production, only in laboratory. Although, the

process is not financially defensible, the money spent in recycling fibres exceed the costs

of buying new.

10. Discussion

The area of decolouring a blended textile of cotton and polyester is still undeveloped and

unexplored. Therefore, the theory of finding a method for removing colour is difficult.

The fact that companies do not want to mention or share to much information about their

progress within this field creates distance. The industry would improve in a sustainability

perspective if the company's shared their findings when it comes to techniques and

methods. Transparency would lead to a more effective process when searching for a

solution for removing colour from a fabric. However, every fining revolves around the

economical aspect and therefore the transparency is unattainable.

As mentioned in the result chapter, one of the greatest challenges when decolourizing is

the fact of a blended fabric. This means the fibres has two distinct properties and cannot

be damaged by the other fibres processes or chemicals. To find a method it is needed to

view the problem from another perspective. One concept that has been discussed is to use

a binder who can be dissolved. This is a similar principle as Vividye (Forne, 2020). In this

case, colour could attach to the binder instead of the textile fabric. This method could be

compared with removing nail polish with acetone where the colour do not break down but

the binder does. When removing colour it is important to keep in mind that the fact the

fabric will have a residue of colour when decolouring, often a shade of grey or yellow.

Therefore it is considered important to take into account and adapt the colour of dying

with the original colour. For example if the original colour is black, after decolouring, the

fabric will not be able to be white because of the residue.

Regarding the readiness level the reason for the pilot scale is there is no method who is

economically defensible and the limited research. The cost of virgin fibres are less than

14

producing recycled. This could be a reason for the lack of information and research on the

subject. A lot of hazardous chemicals and impurities are used when removing colour from

the blended textile. In addition, is it even environmentally justifiable to add chemical

processes to remove colour from a fabric compared to producing new? How long can one

continue to refine a material without destroying the quality and properties before it

exceeds the sustainability aspects?

To summarize, to succeed in removing colour from a polyester and cotton blended textile

waste, a reversed dyeing process must be implemented. This means one have to define

every step of the dyeing process to know exactly which previous treatments are used.

11. Conclusion Below, the concerns regarding the topic of removing colour from a blended textile of

polyester and cotton will be discussed.

11.1 Contribution to Area of Informatics

By this study it has been concluded removing dye from fibres are difficult but can be

achieved with certain chemicals and processes. It is concluded in the study, removing dye

from polyester and cotton individually can succeed. However, removing colour from a

blended fabric is rather difficult. The study has the focus of discussing the difficulties

when decolouring a blended textile.

11.2 Evaluation of Method

After conducting the study it is concluded the results of the method would have been

strengthened by an experimental part. Due to the defective data the interviews have a

great part of the study's results and discussion. It also contributed with new perspectives

and thoughts around the subject. The literature study was necessary to create a knowledge

base. This helped to analyse the discussion during and after the interviews, and establish

conclusions. The interviews contributed with the knowledge that did not exist in

literature, at least in large scale. It also gave the study new perspectives of viewing the

problems based on their expertise.

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11.3 Further Research

The study is describing a problem which can contribute to a more sustainable textile

industry with greater environmental responsibility. Further research will have a great

impact on textile- and dyeing development and create a circular raw material chain. To

investigate the subject even more detailed, an experimental method is needed for a

quantifiable result. Today, the removal of colour only take place in pilot scale. Therefore,

it would be interesting for future research to find a method for industrial use and make

conclusions from the economical perspective. Is the method economically defensible?

There are several perspectives which can be discussed with a broader study. For example

finding such method for removing colour from other fibres besides cotton and polyester.

This also means other dye classes will be included. Another fact the study have proved is

the awareness of the fabrics earlier treatments. Is it possible to remove these effectively

before removing the colour. Lastly, it is interesting to investigate which dyeing machines

and processes are the most resource efficient?

This is a subject with great potential for future research where the findings will have an

enormous impact on the industry of textiles.

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12. List of References

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Bell, J. (2000). Introduktion till forskningsmetodik. Lund: Studentlitteratur.

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polyester textiles. Magisteruppsats, Institutionen Biblioteks- och informationsvetenskap.

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13. Appendix The transcription of interviews are in Swedish. All respondents are anonymous and therefore

the transcribed interviews can be found by authors. Because of requests for anonymity, they

are not attached to the essay.

Interview Questions - Methods for Removing Colour from Polyester

and Cotton Blended Textile Waste

1. What is your profession when it comes to textiles?

2. What are your experience when it comes to colouring in textiles?

3. What are your thoughts about recycling textiles?

4. How does a blended material of cotton and polyester get coloured?

5. Have you heard about methods for removing colour from a polyester and cotton blended

fabric?

6. What kind of method is it? Can you describe details/process?

7. If not, do you think it is possible?

8. What are the complications? Where are the difficulties?

9. What method is used to remove colour from a polyester waste textile material?

10. What method is used to remove colour from a cotton waste textile material?

11. How do you view this methods from a sustainability, environmental perspective and

Technology Readiness Level? which scale is it

12. How do you view this methods from an economic perspective?

13. What method is used for removing colour from a mixed cotton and polyester waste

material?

14. What are your thoughts about textile waste?

15. What do you think will be possible form a waste point of view in the future in regards to

removing dyes?

16. Do you have any advice on some relevant scientific articles that would be beneficial for

our study?

17. Do you have any other contacts you think would be helpful for our study?