ABSTRACT FEI, XIUZHU. Towards Closed Loop

ABSTRACT

FEI, XIUZHU. Towards Closed Loop Recycling of Polyester Fabric. (Under the direction of Dr. Harold S. Freeman and Dr. David Hinks).

Polyethylene terephthalate (PET) is extensively used in various types of apparel, home textiles, and outdoor products that are regularly placed in landfills after use. But unlike natural fibers,

PET is not readily biodegradable. In view of sustainability, research regarding the recycling of textiles derived from PET fibers is of interest, and effective color removal has been recognized as a crucial step towards recycling of colored PET fabrics. To this end, a decolorization process was developed using sodium formaldehyde sulfoxylate (SFS) as the reducing agent. Disperse dye decolorization studies were conducted in water and acetone media, and an optimized combination of treatment time (30 min), water to acetone ratio (1:2),

SFS concentration (10g/L), temperature (100oC), and liquor ratio (1:50) was found effective for decolorizing various commercial disperse dyes as well as basic dyes. Results in terms of intrinsic viscosity of decolorized PET showed that the optimized SFS decolorization method has no significant effect on fiber strength.

The goal of this work was to study the recyclability of bath and fabric after decolorization, investigate the ecotoxicity of the decolorization process, study the life cycle assessment of the closed-loop recycling process, characterize dyes from commercial fabrics and study their decolorization properties.

Fabric decolorization using the optimized SFS method followed by re-dyeing using Disperse

Yellow 42, Disperse Orange 30, Disperse Red 60, and Disperse Blue 79 was conducted on cationic dyeable PET. It was found that fabrics containing nitro and anthraquinone dyes,

Disperse Yellow 42 and Disperse Red 60, respectively, have better decolorization efficiency than those containing azo Disperse Orange 30 and Disperse Blue 79 dyed fabrics.

Bearing in mind that ecotoxicity testing is of increasing importance in the screening of newly developed substances or treatment processes, solutions of six high volume disperse dyes and one basic dye were decolorized using SFS, and the resultant solutions were tested with

Daphnia similis and Parhyale hawaiensis to observe the acute toxicity to the two species. The control sample, which is the SFS solution without dyes, showed that EC50 to Daphnia similis is 1.83%, and LC50 to Parhyale hawaiensis is 9.0%. EC50 and LC50 were expressed in percentage of dye solution. Decolorized dye solutions differed in the toxicity, however, the differences were not significant. The toxicity observed in the acute tests is probably mainly related to SFS decolorization medium. Converting EC50 and LC50 of decolorized solution to equivalent concentration, the effluents were considered relatively harmful to Daphnia similis.

Control SFS solution and decolorized Disperse Blue 56 were moderately toxic to Parhyale hawaiensis, whereas decolorized Disperse Orange 30 was relatively nontoxic to Parhyale hawaiensis.

A closed loop recycling of PET fabric was proposed beginning with collection of post- consumer PET fabrics/garments, followed by chemical decolorization, mechanical reprocessing, and ending with production of recycled PET fibers. A life cycle assessment was conducted to compare the innovative closed loop recycling process and virgin PET production process. Results suggest that recycled PET production has less environmental impacts than the virgin system in six categories, namely, exotoxicity, eutrophication, human health- carcinogenics, human health-non-carcinogenics, ozone depletion, and respiratory effects, but

also shows higher impact results in four categories, which are acidification potential, global warming potential, photochemical ozone formation potential, and fossil fuels resource depletion. Contribution analysis shows higher impacts in those four categories result from the consumption of acetone. Sensitivity analysis also shows that overall impact is sensitive to acetone consumption, which means environmental benefits of the recycling method are highly dependent on the acetone consumptions. This life cycle assessment is conducted based on a hypothetical closed-loop scenario. Further work on obtaining specific data in innovative recycling processing for more reliable analysis would be beneficial.

All Rights Reserve Towards Closed Loop Recycling of Polyester Fabric

by Xiuzhu Fei

A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Fiber and Polymer Science

Raleigh, North Carolina

2018

APPROVED BY:

______Dr. David Hinks Dr. Harold S Freeman Co-chair of Advisory Committee Co-chair of Advisory Committee

______Dr. Nelson Vinueza Dr. Joseph DeCarolis ii

DEDICATION

I dedicate my dissertation work to Dr. Harold S. Freeman and Dr. David Hinks for their guidance and support over the years.

I also dedicate this work to my parents, my sister, brother in law, and my beloved, Ju Dong.

iii

BIOGRAPHY

Xiuzhu Fei was born in Shaoxing, Zhejiang Province of China in 1991. Shaoxing is a medium size city that relied heavily on textile industry 15 years ago. Many of her relatives were working for textile companies. However, due to the increasing regulations and restrictions, the traditional labor-intensive textile plants and mills lost their competitiveness in recent years.

She chose the Dyeing and Finishing Engineering as her major in Jiangnan University, because she wanted to learn more about textiles and bring some benefits to her hometown. Later she was enrolled to North Carolina State University in August 2013 as a master student majoring in Textile Chemistry. Afterwards she was enrolled in the Fiber and Polymer Science Program to pursue a PhD degree. She believes sustainable textiles are the future of the textile world.

ACKNOWLEDGMENTS

Writing this note of thanks is the finishing touch on my dissertation. It has been several years of learning in North Carolina State University, Raleigh, not only in the scientific area, but also on a personal level. I would like to express my sincere acknowledgements to the people who have supported and helped me so much throughout this period.

I would first like to thank Dr. David Hinks for founding me throughout my research career. I have never imaged I could study abroad before I received an offer letter from Dr. Hinks 5 years ago. I am deeply grateful for the opportunity. He covered me all the time so I could focus on the research. Without his support, this PhD work would not have been achievable.

My greatest appreciation goes to Dr. Harold S. Freeman for all the guidance, instruction and encouragement he gave me during the time I spent at the NC State. He is a very patient and responsible professor. I will always keep every piece of hand-written feedback he gave to me about my thesis and manuscripts. He pointed me to the right direction so that I can successfully complete my dissertation. He is also a considerate person which inspires me a lot in my personality.

I would also like to thanks Dr. Nelson Vinueza and Dr. Joseph DeCarolis for their excellent cooperation as kindly being my committee members. I sincerely appreciate the helpful suggestions and comments I received from them.

A very special thanks to previous and current group members in Dr. Hinks’s and Dr. Freeman’s research group, especially Dr. Malgorzata Szymczyk, for their help in the lab work and for their companionship in my life. v

Finally, many thanks go to my parents, sister and brother in law, for believing in me and supporting me all the time; to all my dear friends for bringing me happiness and joy; and to my dear boyfriend Ju, for his selfless love.

TABLE OF CONTENTS

LIST OF TABLES ...... x

LIST OF FIGURES ...... xii

1. INTRODUCTION ...... 1

2. LITERATURE REVIEW ...... 3

2.1 Polyethylene terephthalate ...... 3

2.1.1 Introduction to polyethylene terephthalate ...... 3

2.1.2 Properties of polyesters ...... 5

2.2 Coloration of polyester ...... 7

2.2.1 Disperse dyes ...... 8

2.2.2 Basic dyes ...... 14

2.3 Dye characterization ...... 16

2.3.1 Ultraviolet-visible spectroscopy ...... 16

2.3.2 Chromatography ...... 17

2.3.3 Mass spectrometry ...... 18

2.4 Toxicity ...... 19

2.7.1 Dye structure property relationships ...... 20

2.4.2 Methods used ...... 25

2.5 Decolorization treatment ...... 29

2.5.1 Wastewater decolorization treatment ...... 29

2.5.2 Decolorization of textiles ...... 37

2.6 Recycling method ...... 40

2.6.1 Conventional polymer recycling ...... 41

2.6.2 Fabric reuse ...... 42 vii

2.7 Preliminary study - development of SFS decolorization method ...... 45

2.7.1 Effect of treatment conditions on fabric decolorization ...... 48

2.7.2 Fabric strength assessment ...... 57

2.7.3 Conclusions from preliminary study...... 58

3. PRESENT RESEARCH ...... 59

3.1 Objectives ...... 59

3.2 Rational ...... 59

4. REUSE OF DECOLORIZATION BATH AND DECOLORIZED FABRICS ...... 61

4.1 Introduction ...... 61

4.2 Experimental ...... 64

4.2.1 Material ...... 64

4.2.2 Batch fraction distillation ...... 65

4.2.3 Application of disperse dyes to decolorized fabrics ...... 65

4.2.4 Decolorization of laboratory-dyed fabrics using acetone distillate ...... 66

4.2.5 Color evaluation ...... 66

4.2.6 Fabric strength evaluation ...... 67

4.3 Results and discussion ...... 67

4.3.1 Solvent recovery and reuse ...... 67

4.3.2 Re-dyeing decolorized cationic dyeable PET ...... 68

4.3.3 Burst pressure measurement ...... 74

4.4 Conclusion ...... 74

5. THE ECOTOXICITY OF SODIUM FORMALDEHYDE SULFOXYLATE DECOLORIZATION MEDIUM ...... 75

5.1 Introduction ...... 75

5.2 Experiment ...... 80 viii

5.2.1 Materials and organisms ...... 80

5.2.2 Decolorization of commercial dyes ...... 80

5.2.3 Ecotoxicity testing ...... 81

5.3 Results ...... 81

5.3.1 SFS decolorization of commercial dyes...... 81

5.3.2 Daphnia similis test ...... 85

5.3.3 Parhyale hawaiensis test ...... 88

5.4 Conclusion ...... 91

6. LIFE CYCLE ASSESSMENT OF CLOSED-LOOP RECYCLING OF PET FABRICS ...... 92

6.1 Goal and scope ...... 92

6.2 Introduction ...... 93

6.3 Methodology ...... 95

6.3.1 Goal and scope, functional unit and system boundary ...... 95

6.3.2 Data collections and assumptions ...... 98

6.3.3 Weight and normalization ...... 100

6.4 Closed-loop recycling of polyester fabric ...... 103

6.5 Life-cycle assessment results ...... 104

6.5.1 Comparative analysis ...... 104

6.5.2 Contribution analysis ...... 106

6.6 Sensitivity and uncertainty analysis ...... 109

6.7 Conclusion ...... 111

7. COMMERCIAL BLACK DYE COMPOSITION AND THEIR DECOLORIZATION PROPERTIES ON POLYESTER FABRIC ...... 112

7.1 Introduction ...... 112 ix

7.2 Experimental ...... 114

7.2.1 Materials ...... 114

7.2.2 Decolorization of commercial black fabrics ...... 115

7.2.3 Fabric color evaluation...... 115

7.2.4 Chemical analysis ...... 115

7.2.5 Preparation of disperse dyes ...... 117

7.2.6 Decolorization of commercial dye solutions ...... 119

7.3 Results and discussion ...... 119

7.3.1 Analytical results ...... 119

7.3.2 Comparison with synthesized disperse dyes ...... 128

7.3.2 Decolorization results ...... 130

7.4 Conclusion ...... 134

8. FUTURE WORK ...... 135

9. REFERENCES...... 138

10. APPENDIX ...... 157

LIST OF TABLES

Table 1. Relationship between polyester molecular weight and spinnability 3...... 5

Table 2. Abrasion resistance of polyester and other synthetic fibers...... 7

Table 5. Absorption of visible light and color seen ...... 16

Table 6. Disperse dyes considered a health risk to consumers...... 21

Table 7. Interpretation of LC50 values...... 27

Table 6. K/S values of commercial PET fabrics before and after SFS (40g/L) treatment in acetone/water (1:1) at 100°C...... 47

Table 7. Intrinsic viscosity (IV) Vs viscosity-average molecular weight for control PET fabric and PET fabric after SFS (40g/L) treatment in acetone/water (1:1) at 100 ˚C...... 57

Table 8. C.I. names, classes, and structures of dyes used in this study...... 64

Table 9. Acetone recovery percentage from lab-scale fractional distillation...... 67

Table 10. K/S values from lab-dyed cationic dyeable PET fabrics using virgin and recovered acetone for SFS (40g/L) decolorization in water/acetone (1:2) at 100 °C...... 68

Table 11. Color difference values of cationic dyeable PET fabrics between once decolorized fabrics and virgin white fabrics dyed by corresponding original colors...... 69

Table 12. Color difference values of cationic dyeable PET fabrics between twice decolorized fabrics and virgin white fabrics dyed by corresponding original colors...... 71

Table 13. Color difference values of cationic dyeable PET fabrics between three-time decolorized fabrics and virgin white fabrics dyed by Disperse Yellow 42...... 73

Table 14. C.I. names, classes, and structures of dyes used in this study...... 79

Table 15. EC50 (%) values of SFS decolorized solution tested with Daphnia similis...... 87

Table 16. Global harmonized system criteria for classification of a substance in acute categories ...... 88

Table 17. LC50 (%) values of decolorized solutions tested with Parhyale hawaiensis...... 89 xi

Table 18. Physico-chemical parameters of Parhyale hawaiensis acute toxicity test...... 89

Table 19. Globally harmonized system criteria for classification of hazardous to the aquatic environment...... 91

Table 20. Basis of the comparative life cycle assessment study...... 97

Table 21. Data source of this study...... 101

Table 22. Impact categories and TRACI normalization factors (US 2008) used in LCA analysis ...... 102

Table 23. Normalized LCA results for producing 1 metric ton of PET fiber by virgin and recycled fiber production methods...... 105

Table 24. Processes contributing to acidification potential in recycled PET fiber production ...... 107

Table 25. Processes contributing to acidification potential in virgin PET fiber production ...... 107

Table 26. Retention time, area, and percentage area of peaks ...... 122

Table 27. Identification of disperse dyes...... 125

Table 28. H-NMR spectral results of the Orange, Blue1 and Red dyes...... 128

Table 29. K/S values and WI of commercial black fabrics before and after SFS (10g/L) treatment in acetone/water (2:1) at 100°C...... 131 xii

LIST OF FIGURES

Figure 1. Simplified two-step PET manufacturing process...... 4

Figure 2. Structure of cationic dyeable polyester...... 5

Figure 3. Structures of various chromophores...... 9

Figure 4. General structure of aminoazobenzene disperse dye...... 10

Figure 5. Disperse dye structure based on aminoazobenzene...... 11

Figure 6. Structural skeleton of most anthraquinone disperse dyes...... 12

Figure 7. Disperse dye structure based on anthraquinone...... 13

Figure 8. Chemical structure of two heterocyclic disperse dyes...... 14

Figure 9. Colorless compound liberated from reaction of basic dye with alkali...... 15

Figure 10. Structure and color index specification of some basic dyes...... 15

Figure 11. Chemical structures of some bladder carcinogens...... 20

Figure 12. Chemical structure of 6BT and 4PhDAB...... 23

Figure 13. Electrophilic nitrenium ion from amino-containing compounds...... 24

Figure 14. Carcinogenic CI Disperse Orange 11 and CI Disperse Blue 1, and mutagenic CI Disperse Violet 1...... 24

Figure 15. Metabolic pathway for polycyclic aromatic hydrocarbons...... 25

Figure 30. Proposed initial pathway for degradation of commercial DR1 dye by photo- Fenton oxidation35...... 28

Figure 17. Production of reactive species in hydrogen peroxide (1), ...... 31

Figure 18. Proposed degradation pathway for the dye RB 171 by ozonation53...... 33

Figure 19. Chemical structures of some important reducing agent...... 34

Figure 20. Reductive degradation of azo dye under anaerobic condition...... 35

Figure 21. General overview of the fate of azo dyes during anaerobic-aerobic treatment. .. 36

Figure 22. Reduction of aromatic aldehyde to alcohol by SFS in aqueous media72...... 39 xiii

Figure 23. Reductive dehalogenation of phenacyl halide in ethanol medium by SFS...... 40

Figure 24. SFS decomposition reaction upon heated...... 40

Figure 25. Preparation of benzothiazole from BHET (a) and synthesis of dyes (b)81...... 44

Figure 26. Color photographs of polyester fabric dyed with synthesized dyes...... 45

Figure 27. Changes in the UV-visible spectrum of (A) Disperse Blue 56, (B) Disperse Orange 30, (C) Disperse Yellow 42, and (D) Basic Yellow 28 after SFS (25g/L) treatment in water/acetone (1:1) medium...... 46

Figure 28. Commercial PET fabrics before and after SFS (40g/L) treatment in acetone/water (1:1) at 100°C...... 48

Figure 29. Effect of (a) treatment time, (b) water to acetone ratio, (c) SFS concentration, (d) Temperature, and (e) liquor ratio on K/S value of black commercial fabrics after decolorization...... 54

Figure 30. Visualized effect of (a) treatment time, (b) water to acetone ratio, (c) SFS concentration, (d) Temperature, and (e) liquor ratio on K/S value of black commercial fabrics after decolorization...... 55

Figure 31. Diagram of experimental device for lab-scale fractional distillation. (1) Digital hot plate, (2) round-bottom flask, (3) condenser used as fractionating column, (4) two-way adapter, and (5) condenser...... 65

Figure 32. Cationic dyeable PET fabrics showing the color difference between virgin (left) and once decolorized fabrics (right) after dyeing in the same bath. (a) Disperse Red 60, (b) Disperse Orange 30, (c) Disperse Yellow 42, and (d) Disperse Blue 79...... 70

Figure 33. Cationic dyeable PET fabrics showing the color difference between virgin (left) and twice decolorized fabrics (right) after standard dyeing in same bath...... 71

Figure 34. Disperse Yellow 42 on three-time decolorized cationic dyeable PET fabrics originally dyed by (1) virgin-standard, (2) Disperse Yellow 42, (3) Disperse Orange 30, (4) Disperse Red 60, and (5) Disperse Blue 79...... 73

Figure 35. Preparation of sodium formaldehyde sulfoxylate through (1) reaction of formaldehyde with dithionite, and (2) reaction of bisulfite and formaldehyde with zinc...... 75

Figure 36. Reduction of aromatic aldehyde to alcohol by SFS in aqueous media72...... 76

Figure 37. Reductive dehalogenation of phenacyl halide in ethanol medium by SFS...... 77 xiv

Figure 38. SFS decomposition reaction upon heated...... 78

Figure 39. UV-Vis absorption spectra of commercial dyes (100mg/L) and SFS decolorized (SFS=10g/L, 95 °C, 45min) solutions...... 83

Figure 40. Comparison of decolorization percentage after SFS decolorizaton treatment (10g/L, 95 °C, 45min)...... 85

Figure 41. EC50 (%) values and confident intervals of SFS decolorized solution tested with Daphnia similis...... 87

Figure 42. LC50 (%) values and confident intervals of SFS decolorized solutions tested with Parhyale hawaiensis...... 90

Figure 43. Cradle-to-gate system boundaries of virgin PET fiber production system (left), and recycling PET fibers from waste PET textile products (right)...... 98

Figure 44. The closed-loop recycling process...... 104

Figure 45. Comparison of environmental impacts for producing 1 metric ton of PET fiber by virgin (Black) and recycled (Red) fiber production system using TRACI method...... 106

Figure 46. Sensitivity of the acetone consumption to acidification, global warming, photochemical ozone formation, and resource depletion...... 110

Figure 47. Disperse Black 9 formation inside textiles...... 113

Figure 48. TLC analysis of black fabric extract using chloroform: acetone (19:1)...... 120

Figure 49. UV-vis spectra of orange, blue1, red and blue2 fractions in chloroform/acetone (19/1, v/v) obtained by UV-vis spectroscopy...... 120

Figure 50. Chromatographic separation of the sample extracted from commercial black fabric at 515 nm...... 122

Figure 51. UV-vis spectra obtained by photodiode array detection of peak 1 obtained at 3.167 min, peak 2 at 3.383 min, peak 3 at 4.133 min, and peak 4 at 5.483 min...... 123

Figure 52. High resolution mass spectra and possible structures characterizing commercial black dye components (Orange, Blue, and Red Dye)...... 126

Figure 53. High-resolution mass spectrum of synthesized orange disperse dye...... 129

Figure 54. High-resolution mass spectrum of synthesized blue disperse dye...... 129 xv

Figure 55. TLC chromatogram compassion of A: black fabric extraction; B: synthesized orange disperse dye; and C: synthesized blue disperse dye using hexane/ethyl acetate (1/20)...... 130

Figure 56. Commercial black fabric before and after SFS (10g/L) treatment in water/acetone (1:2) at 100 ˚C for 30 min...... 131

Figure 57. Commercial disperse dye solution of SFS (10g/L) treatment in water/acetone (1:2) at 100 ˚C in different treatment times: A=0 min, B=5 min, C= 10 min and D=15 min...... 133

Figure 58. Absorption spectra changes during the SFS decolorization ([SFS] =10g/L, water/acetone=1/2, 100 ˚C) of black dye mixture solution...... 133

Figure 60. SEM pictures of SFS decolorized polyester fabrics...... 136

Figure 61. Microscopic pictures of (a) blue fiber and (b) decolorized blue fiber...... 137

Figure 62. Full 1H-NMR spectrum of synthesized orange disperse dye...... 158

Figure 63. Full 1H-NMR spectrum of synthesized blue disperse dye...... 159 1

1. INTRODUCTION

Polyethylene terephthalate (PET) fiber, commonly known as polyester fiber, has become the fiber of choice within textile industry due to its unique set of advantages. The overall demand for polyester fiber is increasing year-by-year. The low price of the virgin polyester fiber accounts significantly for this growing trend. One major application of polyester fiber is the production of fabrics, which are extensively used in all kinds of apparel, home furnishings, and other finished textile goods that are regularly disposed and ended in landfills. However, disposing PET products in landfills creates significant environmental issues, because of the durability of the polymer involved. In addition, the manufacture of PET is an energy-intensive process requiring large amounts of crude oil. One-time use of PET fabric is regarded as a waste of valuable polymer derived from non-renewable petroleum resources. Efforts have been devoted to recycle PET beverage bottles and liquid containers. However, methods that have been developed to recycle PET bottles are not applicable to recycle PET fabrics due to the presence of dyes.

Removing dyes from textile wastewater has been widely studied in recent years. Physical methods, including adsorption and membrane filtration, chemical methods, such as bleaching and ozonation, and biological methods have been reported. However, there is no systematic study on removing dyes from fabric in order to achieve fabric recycling. Bearing this in mind, an innovative approach is proposed in this work to decolorize dyes from fabrics.

This project will achieve the following objectives:

(1) Develop an efficient decolorization method for removing dyes from PET fabrics.

(2) Determine the scope of disperse dyes that can be removed by the decolorization

method.

(3) Study the recyclability of the decolorized fabric.

(4) Study the ecotoxicity of the decolorization process.

(5) Understand the Life Cycle Assessment (LCA) of the recycling process.

2. LITERATURE REVIEW

2.1 Polyethylene terephthalate

2.1.1 Introduction to polyethylene terephthalate

Polyethylene terephthalate, commonly abbreviated PET, is the most common form of polyester used commercially. PET has wide range of applications. It is spun into fibers for the production of fabric, blow-molded into disposable beverage bottles, and extruded into photographic film and magnetic recording tape. The history of polyester fiber dates back to the early 1940s when British scientists Whinfiled and Dickson firstly synthesized PET from a combination of terephthalic acid and ethylene glycol and found it was well suited for forming fiber. The first marketed polyester fiber was patented as Terylene by Imperial Chemical

Industries Ltd, and later DuPont manufactured another polyester fiber using modified nylon technology, which they named Dacron. Subsequent to the development of Terylene and

Dacron, a whole range of trademarked products as Kodel and Mylar were rapidly produced during 1960s and 1970s 1.

When carboxylic groups from terephthalic acid react with OH groups from ethylene glycol, esterification occurs at the ends of the bifunctional compounds and PETs with a liner structure are produced2. In large-scale practice, a two-step process, transesterification followed by polycondensation reaction using dimethyl terephthalate and excess ethylene glycol with the aid of catalysts, has achieved some importance on a production basis. This manufacturing process is based on the original patent of Whinfield and Dickosn. Figure 1 shows the linear structure of PET and the simplified two-step reaction process.

Figure 1. Simplified two-step PET manufacturing process.

According to Carothers, the pioneer of thermoplastic polyesters, PET used in the production of fibers must possess a certain molecular weight range and must be capable of orientation when stretched. Table 1 gives the results achieved by Carothers and Van Natta3 in their investigation of the relationship between the molecular weight of polyester and its fiber formation including spinnability. Observations obtained by Meehan 4 are consistent with this results. In general, polyester with a number average molecular weight of 15,000 ~ 20,000 shows good spinnability, as well as other mechanical properties.

Table 1. Relationship between polyester molecular weight and spinnability 3.

Molecular weight Spinnability Extensibility Fiber Strength (number average) (kg/mm2) 780 None N/A N/A 4,170 None N/A N/A 5,670 Short fibers None N/A 7,330 Long fibers None Minute 9,330 Long fibers Possible Minute 16,900 Good Good 13.1 20,700 Difficult Good 12.3

Apart from the conventional polyester fiber, there are cationic dyeable polyesters (CDP) that also became popular. CDP is a special polyester having anionic sites in the main chain5. The schematic structure of CDP is shown in Figure 2. It is worth mentioning that in a CDP polymer chain, the number of sections containing anionic sites are much less than the number of normal ester sections.

Figure 2. Structure of cationic dyeable polyester.

2.1.2 Properties of polyesters

Many new synthetic fibers have been developed within the last decades, including rayon, acetate, spandex, etc., but it is still hard to claim that polyester has been replaced by other fibers

6 in the textile market. In fact, in 2014, world production of polyester reached 46.1 million tons, which is greater than production of all the other synthetic fibers6. Distinguished properties of

PET take credit for its success. The presence of aromatic rings in the main chain gives PET notable stiffness and strength. When heated above its glass-transition temperature, PET turns from a rigid glass-like form into a rubbery elastic state, where the polymer molecular chain can be stretched and aligned in one direction to form polyester fibers7. Polyester fibers exhibit high elastic modulus, which indicates that polyester fibers possess superb elastic recovery8.

This capacity of recovering rapidly imparts polyester fibers with excellent crease resistance and very good dimensional stability. When used in textiles, PET also has many other attractive properties, like good abrasion and heat resistance9. Abrasion is an undesirable but inevitable effect of exposure to normal use. The abrasion of resistance of PET fiber is not as excellent as polyamide fibers, but almost equals to or surpasses the values of viscose and acetate fibers10.

Table 2 presents a comparison. Good thermal stability of PET is attributed to the presence of aromatic phenyl groups as well. The recorded glass transition temperature (Tg) ranges from

11 67 to 81 °C, and the experimental melting temperature (Tm) is between 255-260 °C .

Therefore, polyester textile products can withstand treatment at 170-180 °C without any damages. Polyester fibers exhibit good resistance to combustion and flammability. When a polyester fiber is contacted with a flame, the end of the fiber will contract and melt with formation of a droplet or a pill that is difficult to ignite12. It is interesting that when polyesters are blended with other readily flammable fibers that promote combustion, such as cotton, they become flammable as well and will continue to burn together with the other fibers12. In addition, polyester shows good resistance to atmospheric and biological agents13, due to the orientation and high crystallinity of polyester fibers. In accordance with the chemical structure

7 of PET, the ester linkages should undergo hydrolysis attacked by acids and alkalis. However, polyester fiber shows chemical resistance better than expected. Because the attack of these chemical agents is limited essentially to the surface, since water-soluble acids and alkalis cannot diffuse insider the nonpolar polymer phase. For the same reason, polyester fibers show an outstanding resistance to oxidants and reducing agents. CDP, the modified polyester, possesses similar properties with fibers of normal PET. However, the meta substitution in the anionic section increases segmental mobility, resulting in lower glass transition temperature and lower thermal stability of the CDP14. Also the CDP is more readily hydrolyzed.

Table 2. Abrasion resistance of polyester and other synthetic fibers.

Type of fiber Number of rubs up to breaking point Dry Wet Polyester 1980 1870 Polyamide 8800 3890 Polyacrylonitrile 135 139 Viscose 880 28 Acetate 409 58

2.2 Coloration of polyester

Due to the lack of water solubilizing group in polymer chain, polyester has limited affinity, especially at low temperatures, towards most of the water-soluble dyes, such as reactive and acid dyes15. Hence, polyester requires the use of disperse dyes, which are non-ionic chemicals with sparing solubility in water. Upon dyeing of polyesters, disperse dye particles are dissolved in the fiber material. A diffusion equilibrium is established between fiber and liquor until saturation concentration is attained16,17. However, due to the hydrophobicity and the

8 compact structure of polyester fibers, only pale to medium shades can be obtained under atmospheric conditions. For darker shades it is necessary to employ various carriers or raise dyeing temperature to increase the disperse dye diffusion. Cationic dyeable polyester fibers is a special polyester fiber that can be dyed with both disperse dye and cationic dye.

2.2.1 Disperse dyes

The name of disperse dye was derived for its sparing water-soluble properties and the need to apply it from a fine aqueous dispersion. Dyes are transferred in the molecular state from bath to fiber through a process of surface adsorption and diffusion. For the sake of efficient diffusion inside the fiber, disperse dye particles should be as small as possible, typically ranging from 0.5-2.0 micron, which necessitated designing disperse dye comprising low molecular weight in the range of 250-60015. Based on their unique sublimation fastness and dyeing properties, disperse dyes can be classified into four categories, named A to D. In dyes

A to D, the molecular weight increases along with the sublimation fastness, whereas ease of dyeing decreases18. Category A contains dyes that have excellent dyeing properties due to their molecular size but poor sublimation fastness. These dyes usually find use on acetate and nylon fiber. Category B dyes possess excellent carrier-dyeing behavior and moderate sublimation fastness. These dyes are suitable for the dyeing of texturized polyester fabric and yarn, on which they can provide a degree of heat fastness adequate for the mild heat setting treatments used on these materials. Dyes in category C have higher sublimation fastness than category B, and moderate carrier-dyeing properties and good high-temperature dyeing properties. Category D dyes have very high sublimation fastness and poor carrier-dyeing properties. They are used in cases when the highest standard of heat fastness is required, e.g.

9 for permanent press finishing treatments. They are not generally suitable for the carrier dyeing of polyester at the boil. From a dye chemist’s perspective, a classification by chromophore is very useful. The Color Index listed around 1,150 disperse dyes in 1992 by chemical class, and the categories include but not limit azo (1), anthraquinone (2), nitrodiphenylamine (3), methine

(4), quinoline (5), coumarin (6), and aminoketone (7). The corresponding chemical structures of the chromophores are demonstrated in Figure 3.

Figure 3. Structures of various chromophores.

Azo dyes are by far the most important class and account for more than 50% of the total commercialized disperse dyes in the world. The general method used to make an azo dye requires a coupling component and a diazo component. Therefore, various combinations of coupling components and diazo components should give an enormous range of possible dyes.

In theory, azo dyes can supply a complete range of rainbow colors, from yellow to blue-green and even black hues. However, commercially azo disperse dyes tend to supply more yellows, oranges and reds instead of dark hues. There are mono-azo, and disazo structures. However, in order to facilitate satisfactory molecular size, mono-azo structures are exceptionally

10 important. Aminoazobenzene is a typical structure in mono-azo disperse dye, which is presented by the structure in Figure 4. The characteristics of the product is controlled by the chemical nature of the substituents.

Figure 4. General structure of aminoazobenzene disperse dyes.

In this structure, X, Y, and Z are usually ring deactivating groups, such as, -NO2, -CN, -Br, and CF3. R1 to R4 include groups such as –CH3, -C2H5, -OCH3, -OC2H5, -C2H4CN, and

C2H4OCOCH3. Different combinations of substituents result in enormous numbers of aminoazobenzene based disperse dyes, creating colors from yellows to reds, and in some conditions, blues. In general, the greater the tendency of groups X, Y and Z to accept electrons and the groups R1 to R4 to donate electrons, the further the hue of the molecule will lie along the line from yellow, orange, red, violet, to blue19. Movement along the line in the direction yellow to black is an increase in the maximum absorption wavelength of the dye, which in a precise term is called a bathochromic shift. Figure 5 shows how the substituents affect the color of azo disperse dyes. The dyes from (8) to (11) are presented in a bathochromic series.

Other than the benzonoid mono-azo structures, heterocyclic diazo components are also used in preparation of azo disperse dyes to produce brighter and greener shades of yellow.

Figure 5. Disperse dye structure based on aminoazobenzene.

There are some deficiencies in azo dyes, which dye chemist should pay attention to during application, such as duller shades and lower light fastness than anthraquinone dyes, and the potential to breakdown into carcinogenic amines derived from the cleavage of the azo linkage20. However, the cost effectiveness compensates for the drawbacks mentioned above, which makes azo dyes still the largest class of synthetic organic dyes.

Another important group of disperse dyes are anthraquinone derivatives, accounting for 25% of the commercialized disperse dyes. Complementing the colors produced by the azo chemical class, anthraquinone disperse dyes often generate reds, violets, blues and blue-greens. While yellow and orange colors can be synthesized based on anthraquinone structure, they have been proved to be less competitive with yellows and oranges based on other chromophores20. Figure

6 presents the general structural of most anthraquinone disperse dyes.

Figure 6. Structural skeleton of most anthraquinone disperse dyes.

Like azo dyes, substituents R1 to R6 have wide range of options. The hue is largely controlled by substituents R1, R4, R5 and R6, rather than R2 and R3, and these groups are usually hydroxyl, amino and secondary amino groups, -NHR. The –R in the secondary amino groups also has various possibilities, such as –CH3, -C2H4OH, a benzene ring (Ar), and a benzene ring that is itself substituted by other groups. The more powerful the effect of the electron donor substituents, the further the hue of the dye will lie in the bathochromic shift direction. The approximate order of electron donating effect follows the list: -NHAr > -NHAlk > NH2 > OH, while substitution in both rings is more powerful than substitution in only one. Substituents in the R2 and R3 positions have less effect on the color of the anthraquinone disperse dyes.

Because they are less likely to form intramolecular hydrogen bonding with carbonyl group.

19 However, R2 and R3 can have a significant effect on the fastness properties of the product .

The effects of different substituents are shown in Figure 7.

Figure 7. Disperse dye structure based on anthraquinone.

Generally, anthraquinone dyes give brighter colors than azo dyes, and have better light fastness and wash fastness properties. They also have advantages such as good stability in dyeing and levelling. On the other hand, they are expensive to synthesize and pose the potential to cause pollution problems, which make them gradually replaced by other type of disperse dyes, except for some bright pinks and blues17. Newer disperse dyes are increasing based on the use of heterocyclic components; i.e., aromatic rings containing five or six membered atoms which include nitrogen, sulfur and oxygen in place of one or more of the normal carbon atoms. These heterocyclic components may appear at either side of the azo chromophore. Examples are CI

Disperse Green 9 and CI Disperse Yellow 8, which are shown in Figure 8.

Figure 8. Chemical structure of two heterocyclic disperse dyes.

2.2.2 Basic dyes

Concerning cationic dyeable polyesters, it literally means that they can be dyed by a cationic dye, which is also known as basic dye. Meanwhile, being dyeable by basic dyes does not prevent them being dyeable by disperse dyes as well. The consumption of CDP accounts for less than 10% of the polyester market, and they are often blended with other fibers to achieve certain properties. For example, when CDP is blended with polypropylene, the resulting mixed fiber shows reduced crystallinity, which favors the dyeability of the fibers21.

Basic dyes also have various chemical classes defined by their chromophores. Figure 10 shows structure and color index specification of several important basic dyes belonging to various classes.

Compared to disperse dyes, basic dyes have larger molecular extinction coefficients and higher build-up property, so they can give brighter and deeper colors, and some dyes even exhibit fluorescent properties. Basic dyes are very sensitive to alkali and upon hydrolysis produce colorless substances15. An example is illustrated in Figure 9. Therefore, acids should be added for the sake of storage. In addition, dyes form a sticky mass on storage posing difficulty in solubilization, adding a little acid can facilitate solubilization in water. Basic dyes possess

15 advantages like wide shade range, good brightness and relatively economical. However, they also have marked disadvantages, such as poor shade stability, very poor light fastness, high acid content, and color backwaters, making them not as wide spread as disperse and other dyes.

Figure 9. Colorless compound liberated from reaction of basic dye with alkali.

Figure 10. Structure and color index specification of some basic dyes.

2.3 Dye characterization

2.3.1 Ultraviolet-visible spectroscopy

Color of a substrate is determined by the light reflected from the surface of a solid or passing through a liquid. Sunlight has uniform white color, but it is actually composed of a broad range of wavelengths in the ultraviolet (UV), visible and infrared (IR) portions if the spectrum.

Visible wavelengths cover a range from approximately 400 to 700 nm, among which the shortest is violet and the longest is red. When a beam of sunlight or other white light is illuminated at a red dye, a portion of mixed wavelengths is absorbed, leaving the red light to be reflected. The remaining red light is the complementary color to the wavelengths absorbed.

Ultraviolet-visible (UV-Vis) spectrophotometer is used to measure the absorbed light22. The relationship between the wavelength absorbed, colored absorbed and the color seen by human eye is demonstrated in Table 3.

Table 3. Absorption of visible light and color seen

Wavelength Absorbed (nm) Color Absorbed Color Seen 400-435 Violet Yellow-Green 435-480 Blue Yellow 480-490 Green-Blue Orange 490-500 Blue-Green Red 500-560 Green Purple 560-580 Yellow-Green Violet 580-595 Yellow Blue 595-605 Orange Green-Blue 605-700 Red Blue-Green

For dye solution, other than measuring the absorbed wavelength of the sample, concentration of the dye solution can also be obtained by UV-Vis measurement. Because the absorption of light by a dye in solution is directly proportional to its concentration; i.e., the greater the concentration of the dye, the greater of the amount of light is absorbed. The equation for the absorption is known as Beer-Lambert Law, which is:

� = ��

Where A is the observed absorption, b is the path length of the sample cell, c is the concentration of the sample, and ε is the absorptivity or molar extinction coefficient, which is specific for each species23. Typical ε values for mono-substituted anthraquinone disperse dyes are in the range of 4,000-7,000, and for di-substituted anthraquinone disperse dyes are about

10,000-17,000.

2.3.2 Chromatography

The concept of chromatography was firstly introduced by Michael Tswett24. It is an analytical technique for the separation of a mixture. There are many types of chromatography, such as thin layer chromatography, column chromatography, and high performance liquid/gas chromatography, but all of these follow the same basic principles. The mixture is dissolved in a solvent called the mobile phase, which carries it through a fixed material called the stationary phase. From the same initial zone, different components in the mixture shows varying migration rates, causing them to separate. In another word, the separation is based on the different partition coefficient of the solute between the mobile and stationary phases. The mobile phase may be either a liquid or a gas, and can be manipulated to accommodate a variety of chemical compositions. Stationary phase can be either a solid or a liquid with different

18 choice of materials, e.g. cellulose, silica, alumina, inert gas, etc. High performance liquid chromatography (HPLC) is an improved form of column or thin layer chromatography. It uses material with very small particle size for column packing, which gives a larger surface area for interactions between the stationary phase and the molecules flowing through it. Moreover, there are two phases in use in HPLC depending on the relative polarity of the solvent. One is normal phase, the column of which is filled with polar materials as same as normal thin layer chromatography. The other is reversed phase HPLC. In this case, the column is filled with modified silica gels to make it non-polar. Although it is described as “reversed”, it is the most commonly used form of HPLC. In addition, the detection method is also improved by using highly automated and extremely sensitive technologies.

2.3.3 Mass spectrometry

Mass spectrometry is a highly sensitive technique used to detect and identify molecules based on their mass-to-charge ratios (m/z)25. In order to measure the characteristics of individual molecules, they are converted to ions so that they can be sorted and separated by external magnetic fields according to their mass-to-charge ratios. The ions are then detected and analyzed electronically by mass analyzer. The analytes can be ionized by various methods, such as electrons, photons, excited atoms, or electrostatically charged droplets. Harsh method results in more fragmentation patterns of the analyte, while soft method allows less fragmentation during ionization. It is common to couple HPLC to a mass spectrometer. When the detector from HPLC is showing a peak, the substance passing through the detector at that time is transferred to a mass spectrometer, at which it will finally be analyzed for its m/z and give a mass ion pattern for the sample. It can be compared against a computer database of

19 known patterns or other referrals, which means LC-MS can identify a wide range of compounds without having to know their retention times.

2.4 Toxicity

Toxicology is the study of adverse effects of chemicals on living organisms and their environment. Before the discovery of the first synthetic dye in 1856, people obtained colorants from nature, mainly from plants and some portion from insects and molluscs. It was relative safe for workers to produce dyes from nature. However, the efficiency was below expectation because large amounts of raw materials were required in order to just obtain a tiny amount of impure dyes. Since the historical development in 1856, dyes, chemical intermediates, and later pigments were produced on a large scale with less labor intensity. Unfortunately, several years later, the incidence of bladder cancer became higher between workers who involved in the manufacture of certain dyes and intermediates26, such as CI Basic Violet 14, CI Basic Yellow

2, benzidine and 2-naphthylamine (see Figure 11), which drew researchers’ attention to study the toxicity and structure-carcinogenic relationship of synthetic dyes and their intermediates.

Later it was proved that both benzidine and 2-naphthylamine are indeed bladder carcinogens in humans. Nowadays, for registration of a textile dye, the toxicological studies and eco- toxicological studies are required in the registration package.

Figure 11. Chemical structures of some bladder carcinogens.

2.7.1 Dye structure property relationships

The toxicological aspects of textiles dyes can be divided into acute, also known as short-term effects and chronic, or long-term effects. Acute toxicity is a result from an acute exposure to potential toxic dyes through oral ingestion, inhalation, skin and eye irritation, and skin sensitization. Caliskaner27 studied a case of a 35-year-old woman who was referred for a recurred lesion over the incision scar of right total hip replacement surgery. They found out that Disperse Blue 106 and Disperse Blue 124 from her dark-colored synthetic panties were the potential cause of the contact dermatitis. Textile dermatitis is actually not uncommon.

Other than the aforementioned two disperse blue dyes, which are the two mostly reported dye allergens, dermatologists also have reported textile-related skin reactions thought to be caused by Disperse Blue 1, Disperse Yellow 3, Disperse Orange 1, Disperse Orange 3, Disperse Red

1 and Disperse Red 1728, listed in Table 4.

Table 4. Disperse dyes considered a health risk to consumers.

C.I. Name Chemical structure Disperse Blue 106

Disperse Blue 124

Disperse Blue 1

Disperse Yellow 3

Disperse Orange 1

Disperse Orange 3

Disperse Red 1

Disperse Red 17

The sweat-fastness properties of the dyes are important as to whether an allergic response is caused or not. Disperse dyed polyester is not problematic since the sweat-fastness is high.

However, polyamide or cellulous acetate dyed with disperse dyes poses problems since the low sweat-fastness allows the dyes to migrate to the skin, which increases the sensitizing

22 potential. Besides, disperse dyes containing anthraquinone or azo structures are more likely to cause contact dermatitis28.

Certain reactive dyes have been implicated in causing acute effects on plant workers who manufacture or handle the dyes29. Reactive dyes for cotton are water-soluble and readily hydrolyzed. Once the dye has been used to color the cotton fabric, the dye structure is modified, i.e., a covalent bond is formed between the dye and the hydroxyl group in the fiber.

Any reactive dye left on the surface should be hydrolyzed in the wet dyeing process and can be easily removed through washing and rinsing. That is the reason why reactive dyes should poses no problems in consumers but mainly in plant workers.

Genotoxicity is the major long-term potential health hazard of certain textile dyes. Genotoxic chemicals include mutagens, carcinogens and teratogens. Some azo dyes have been found to be both mutagenic and carcinogenic, e.g., 6-dimethylaminophenylazobenzothiazole (6BT) is a potent carcinogen and mutagen in rat following dietary administration30. In stark contrast, some other azo dyes are neither mutagenic nor carcinogenic, e.g., 4’-phenyl-4- dimethylaminozaobenzene (4PhDAB) shows low azoreductase activity in the Salmonella bacterial tester assay in the presence of an induced rat-liver S9 mix31. Teratogens are agents that cause malformation of an embryo. Teratogenicity is very uncommon in textile dyes and will not be discussed.

Figure 12. Chemical structure of 6BT and 4PhDAB.

The underlying principle for dyes to induce genotoxic effects on living organisms is that the dyes need to penetrate the cell membranes and attack the DNA function. Therefore, physical factors of dyes such as solubility and molecular size are essential in determining whether the dye penetration occurs. In general, molecules with small size are more readily transported across the cell membranes than larger molecules. Above a certain molecular size, MW > 800, chemicals become too large to transport across the membranes. Thus, producing dyes with large molecular size is a potential way to prevent genotoxic effects. Indeed, this approach was adopted to produce non-toxic food dyes. Solubility is also of importance in determining the toxicity of dyes. Majority of pigments are non-carcinogenic because the nature of large pigment particles does not allow them to pass the cell membranes. Dyes with high water solubility are often non-carcinogenic. Because water-soluble molecules are generally excreted rapidly, bioaccumulation of such dyes is less likely to occur in a living organism32.

The active species of carcinogens or mutagens should be an electrophile, E, since the DNA is a nucleophile compound. The ultimate attack forms a covalent bond between the E and DNA.

Therefore, molecules containing electron-deficient carbon, nitrogen, or oxygen atom are possible to be genotoxic. Such molecules may be the dyes themselves, or may be metabolites of the dyes. Carcinogens related with textile dyes are most chemicals possessing one or more electron-deficient nitrogen atom, among which the most important type is the amino-

24 containing dye. Figure 13 shows the general process for these compounds to produce an ultimate electrophilic nitrenium ion33. This pathway occurs at primary or secondary amino groups, and at methylamino- or dimethylamino-groups via oxidative demethylation. As earlier mentioned, half of these compounds increasing the bladder cancer incidence are large depots for the nitrenium ion. Anthraquinone structure does not contain azo bond, but also follows the similar reaction mechanisms. Anthraquinone dyes having one or more primary amino- or methylamino- groups tend to be genotoxic. For instance, in Figure 14, CI Disperse Orange 11, and CI Disperse Blue 1 are carcinogens, and CI Disperse Violet 1 is a mutagen. Cationic dyes have been reported to be carcinogenic, such as CI Basic Violet 14 and CI Basic Yellow 14, as shown in Figure 11.

Figure 13. Electrophilic nitrenium ion from amino-containing compounds.

Figure 14. Carcinogenic CI Disperse Orange 11 and CI Disperse Blue 1, and mutagenic CI Disperse Violet 1.

Carcinogens from carbon and oxygen electrophiles are not as common as nitrogen electrophiles. However, they are encountered in the synthesis or chemical modification of dyes. They are usually chemicals containing alkyl substituents bearing a leaving group, such as chlorine and bromine, or a strained small ring system, which open to generate an electrophilic center. Some agents used in the synthesis of dyes produce electrophilic carbon by the polarization induced by the electron-withdrawing group. Typical examples are vinyl chloride, acrylamide and acrylonitrile. Many compounds having four or more fused benzene rings are believed to be carcinogenic. Because they tend to generate an electrophilic carbon center via epoxide formation, as illustrated in Figure 1534.

Figure 15. Metabolic pathway for polycyclic aromatic hydrocarbons.

2.4.2 Methods used

Whether dyeing and finishing or decolorization treatment, textile activities are often wet processes, thus generating considerable amount of effluent discharged to the environment.

Therefore, studying the effects of compounds to organisms living in the water, which is also known as aquatic toxicity, is of extreme importance. Toxicity tests are based on the principle that the response of living organisms to the exposure of the toxic agents is dependent upon the exposure level (dose) of the toxic agent. Therefore, aquatic toxicity tests are designed to demonstrate a dose-response relationship, referred to as the dose-response curve when the

26 measured effect is plotted graphically with the concentration. The endpoint for acute toxicity is usually survival, whereas endpoints for chronic studies are sub-lethal effects such as growth, reproduction, behavior.

2.7.2.1 Acute toxicity tests

Acute toxicity is the toxicity elicited immediately following short-term exposure to a chemical.

It may be the result from a single exposure or from multiple exposure in a short period, and the adverse effects should occur within 24- to 96-hour period. There are standard guides on how to perform acute toxicity tests published by the American Society for Testing and Material

(ASTM), Environment Canada, and the U.S. EPA. Particular species are used for different tests, environmental compartments, and regulations. The relationship is generally established by exposing groups of organisms to various concentrations of the chemical. A well-defined concentration-response curve should select concentrations that elicit >0% effect but <100% effect during the course of the experiment. Then it can be used to calculate the LC50 for the toxicant, which is defined as the exposure concentration of the toxicant that is lethal to 50% of the exposed population. Clearly, the LC50 value is not indicative of an acceptable level of the chemical in the environment, rather the LC50 is just an indicator of relative acute toxicity. LC50 values are often interpreted as follows, shown in Table 5. Besides, EC50 is also used to characterize the acute toxicity, which is defined as the concentration of a toxicant at which

50% if its maximum response is observed. The response may be lethal or sub lethal effects.

Table 5. Interpretation of LC50 values.

LC50 (mg/L) Toxicity rating >100 Relatively nontoxic 10-100 Moderately toxic 1-10 Very toxic <1 Extremely toxic

Much research has been conducted to investigate the ecotoxicity of some commercially available disperse dyes and their main degradation products by either reduction or oxidation.

For example, ecotoxicity of Disperse Red 1 (DR1), an azo dye, and the degradation products generated during photo-Fenton degradation has been assessed by measuring acute toxicity with microcrustacean Daphnia similis35. The tests were performed with Daphnia similis in 48 h, and EC50 values were reported. By real-time monitoring the photo-Fenton degradation process, it was found that toxicity increased after 10 min as a consequence of generation of degradation products of higher toxicity than DR1. After 45 min reaction, acute toxicity of DR1 azo dye to

Daphnia similis was completely removed. LC/MS results detected most of the intermediates formed in the reaction. A possible degradation mechanism was proposed and is depicted in

Figure 16. The attack of hydroxyl radical, which is a very reactive species generated by photo-

Fenton reaction, includes the hydroxyl addition to an aromatic ring and cleavage of the azo bond.

Figure 16. Proposed initial pathway for degradation of commercial DR1 dye by photo-Fenton oxidation35.

2.7.2.2 Chronic toxicity tests

Aquatic chronic toxicity study is used to assess potential hazards to aquatic species resulting from prolonged and repeated exposure over a significant portion of the organism’s life span, typically one tenth or more of the organism’s lifetime. Chronic studies evaluate the sub-lethal effects of toxicants on reproduction, growth, and behavior due to physiological and biochemical disruptions. Effects on survival are also evaluated, but they are not always the main objective of a chronic study. Aquatic toxicity studies often conducted on species includes brook trout, fathead and sheepshead minnow, daphnids, oligochate, midge, freshwater amphipod, zebrafish, and mysid shrimp36. Algal species reproduce so rapidly that several

29 generations are exposed during a typical study, and therefore chronic tests should not use these species. As acute toxicity tests, chronic toxicity tests also have standard testing methods regulated by environmental agencies. Important information derived from the concentration- response curve tells the NOEC (no observable effect concentration), LOEC (lowest observable effect concentration), and MATC (maximum allowable toxicant concentration) values of the chemical.

2.5 Decolorization treatment

According to the treatment object, decolorization can be classified into two categories: decolorization of solid phase and decolorization of liquid phase. The latter is well known as wastewater decolorization treatment. Decolorization of solid phase, which means stripping colors from a solid substrate, has been less investigated.

2.5.1 Wastewater decolorization treatment

Over the past two decades, manufactures and users of synthetic colorants have faced increasing stringent regulations regarding the safety our environment, which promoted tremendous research programs and technologies to comply with the regulations. A significant portion of the research was conducted to analyze and remove priority pollutants from wastewater effluents. Wastewater from the textile industry contains unfixed dyes along with other components like salts, acids, surfactants and even metals. In terms of its environmental impact, wastewater discharged is polluting to some extent. Colorful textile effluent also causes aesthetic issues. In general, the composition of a particular wastewater, in addition to site- specific conditions, dictates the most appropriate wastewater treatment method. Huge successes have been achieved to remove colors from wastewater37–44. However, the research

30 on the decolorization of textile dyes has mainly been focused on water-soluble dyes, while decolorization of disperse dyes has received only scant attention.

2.5.1.1 Chemical methods

Chemical decolorization methods use chemical agents to break down dye structure through oxidation or reduction reactions. In view of oxidation technologies, hydrogen peroxide and hypochlorite are reported as widely used oxidation agents. Hydrogen peroxide (H2O2) has low environmental impact and is relatively economic. Owing to its mild nature, H2O2 is heavily used as the bleaching agent to remove yellowish colors from cotton fabric. However, it may fail or take an extremely long time to decolorize dark hues. Chlorine-containing substances such as sodium hypochlorite, calcium hypochlorite, chlorine and chlorine dioxide are also well known bleaching agents for cellulosic fabric. The equipment required for hypochlorite decolorization is simple and the treatment process can be finished in a short time scale. On the other hand, they are of relatively high toxicity compared with other decolorization agents, and generate large amount of salt as secondary contamination. Ozone is also reported effective for azo disperse dyes decomposition in textile wastewaters38. Ozone fading of dyes occurs by the oxidative cleavage of the conjugated system of the dye molecule. The ozonization of molecules, such as azobenzene, phenylazonaphthalene, and azonaphthalene dyes, is very complicated so that the products have not been fully identified. Decolorization of Disperse

Blue 3 on nylon carpet via ozone fading has been reported to give phthalic acid45. It is suggested that aromatic rings are more reactive toward ozone than an azo linkage46. Ozone was used to decolorize wastewater containing Acid Red 158, a bisazo acid dye47. Results confirmed that ozone decolorization is an effective color removal method, and the rates of

31 ozone reaction are not sensitive to pH and only mildly affected by temperature. In that study, researchers also found that ozone does not react preferentially with uncolored organic compounds. In practice, ozone alone is usually utilized for the treatment of drinking water.

At present, Advanced Oxidation Process (AOP) 39,48–52 has been developed to oxidize organic compounds to harmless products with high reaction rate as well as low environmental emissions. The AOP is mainly a catalyst-driven process, using UV light or metal catalyst with an oxidizer such as H2O2 and/or ozone to generate highly reactive hydroxyl radicals, which can attack organic compounds non-selectively. For example, Fenton’s reagent, which is a combination of H2O2 and an iron catalyst, is able to generate free radicals automatically without UV light or heating42. Equation (1) in Figure 17 is the process of conventional hydrogen peroxide releasing reactive species HOO-. Equations (2) and (3) show how the hydroxyl radicals are produced from Fenton’s reagent, and how the ferric iron is reduced back to ferrous ion, indicating Fe2+ can be recycled after treatment.

Figure 17. Production of reactive species in hydrogen peroxide (1), and Fenton’s reagent (2), (3)

Szpyrkowicz et al. 42 made a comparison study on oxidation of disperse dyes (mixture of

Disperse Yellow 126, Disperse Red 74, and Disperse Blue 139) by chemical oxidation using ozone, hypochlorite, Fenton’s reagent and electrochemical oxidation. They found that the least

32 satisfactory result was obtained by hypochlorite oxidation, while the best treatment result was obtained with Fenton process, and the performance of ozone and electrochemical oxidation are between the two extremes, as judged by color removal and chemical oxygen demand (COD) removal.

Namata and co-workers53 reported a study regarding the decolorization of Reactive Blue 171

(RB 171) using ozonation and UV/H2O2. The found RB 171 with 50 mg/L can be completely decolorized using ozonation by modifying operational conditions such as pH, temperature, and concentration of the oxidants, while UV/H2O2 showed poor decolorization efficiency. Based on the GC-MS analysis, they proposed a possible fate of metabolism of intact RB 171 molecular by ozone, which is demonstrated in Figure 18. They assumed that the dye molecular was attacked by OH·, leading to an asymmetric cleavage and yielded intermediate a, and another reactive intermediate (1). Compound (1) was further attacked by OH· giving two intermediates b and (2), which the author described as an azo bond cleavage process. However, it seems other reactions occurred since the intermediates lost an -SO3Na group in b and an –

NH2 group in (2). These compounds were detected in (3) as other fragments. Oxidation cleavage between N and C of the triazine ring in (2) led to the formation of c and (4).

Figure 18. Proposed degradation pathway for the dye RB 171 by ozonation53.

For many dyes, particularly azo dyes, chemical reduction is an effective decolorization technique, and options for reducing agent are less complicated. Most reducing agent used in textile applications are compounds that can slowly decompose and release sulfur dioxide under specific conditions. These agents belong to the group of hydroxyl- and aminoalkanesulfinates

(rongalite, thiourea dioxide, and their analogs, see Figure 19). The reducing properties of these

2- compounds are mainly due to the cleavage of C-S bond and the formation of intermediate SO2

- 2- 54,55 anions of sulfoxylic acid, radical ions SO2 , and S2O4 dithionite ions .

Figure 19. Chemical structures of some important reducing agent.

When evaluating the reduction of dyes in wastewater, it is also important to investigate the potential reversal of the reaction upon exposure to oxygen, since color may reappear when the treated wastewater is discharged to the environment. A study was conducted to evaluate the effectiveness of three reducing agents in decolorizing Navy 106 (a mixture of three azo dyes)56.

In this study, the reduction process was the chemical pretreatment, followed by aerobic biological treatment. Three reducing agents were evaluated: 225 ppm sodium hydrosulfite,

225 ppm thiourea dioxide, and 150 ppm sodium borohydride. The chemical pretreatments were effective in removing color. However, they were not effective in removing BOD, and did not enhance the biodegradation when used in tandem with aerobic biological treatment.

2.5.1.2 Biological methods

Biological decolorization treatment is a complex process at the intersection of biology and biochemistry. Biological methods rely on microorganisms, such as white rot fungi, bacteria, nematodes, yeast and so on, to break down organic wastes. Due to the complex structure of dyes and their molecular design, many dyes are difficult to decolorize and decompose through simple exposure to biological agents. Aerobic biological treatment used to be very popular to

35 treat wastewater generated from textile dyeing operations. However, the ineffectiveness of aerobic biological treatment in reducing color has caused aesthetic issues. Azo disperse dyes, for example, are highly resistance to biodegradation under aerobic conditions. It has been reported that azo dyes undergo reductive splitting of the azo bond relatively easily under anaerobic microbial conditions, resulting in the formation of aromatic amines. The anaerobic treatment takes place in the absence of oxygen and converts various organic compounds to methane and carbon dioxide57. This process is considered to be microbiologically a nonspecific process, as presented in Figure 20.

Figure 20. Reductive degradation of azo dye under anaerobic condition.

However, some of the resultant aromatic amines have been demonstrated to be carcinogenic and mutagenic to aquatic life and even to mammals37. Therefore, the aerobic treatment seems to be a more practical and safe method for the biodegradation of textile dyes. In fact, sequential anaerobic-aerobic biological treatment has been reported capable of decolorizing textile

58–60 dyes . Regarding azo dyes, anaerobic-aerobic treatment (Figure 21) may generate CO2,

H2O, and NH3 as the final products.

Figure 21. General overview of the fate of azo dyes during anaerobic-aerobic treatment.

Textile wastes containing reactive, disperse and vat dyes were reported successfully decolorized and detoxified in a full scale combined anaerobic-aerobic system60. This study showed that the color derived from reactive and disperse dyes was largely removed in the pre- acidification basin and the anaerobic reactor. Anthraquinone vat dyes were also anaerobically decolorized, indicating that this system is capable of effective removing the color both soluble and insoluble dyes with various structures. The effluent after sequential anaerobic-aerobic treatment showed no toxicity towards Vibrio fisheri. In yet another report, the two-stage system was employed on decolorization of azo reactive dye, CI Reactive Black 5 (RB5), and its analog61. It has been reported that an overall color removal of 65% was found for both fully and partially hydrolyzed RB5 dyes. One metabolite (substituted hydroxylnaphthalene) remained in the aerobic stage effluent, causing the effluent to be colored even though no RB5 was present. Study on degradation of azo dye Disperse Red 1 in a pilot scale anaerobic-aerobic reactor has also been reported62. The results confirmed the capacity of the anaerobic-aerobic system to degrade azo dyes, as judged by 80% dye decolorization and 92% COD removal. In addition, both toxicity and mutagenicity were reduced significantly. Overall, the idea that

37 dyestuffs undergo anaerobic reduction generating organic amines that are more amenable to aerobic biodegradation than the original dyes is supported by these results.

2.5.1.3 Other methods

There are also other wastewater treatment methods that have been widely discussed, such as physical and physical-chemical wastewater treatment methods. Physical methods may not be dye-specific, but can be used to remove undissolved chemicals and particulate matter present in wastewater. Adsorption, for example, is one of the most effective, economically feasible techniques to remove textile dyes. Carbon-based adsorbent materials have been used for adsorption of various types of dyes, ranging from acid, direct, basic, and reactive to disperse dyes63,64. In general, low adsorption has been observed for acid and reactive dyes with low molecular weight, whereas high adsorption occurs with basic and direct dyes which are usually of higher molecular weight, and medium to high adsorption for disperse dyes which are hydrophobic in nature57. A major disadvantage of activated carbon adsorption is its high price, which calls for regeneration. Carbon adsorption is considered as neither an efficient nor economical decolorization treatment method. Therefore, it is recommended as a finishing and polishing step after a chemical or biological process65. Ion exchange, coagulation-flocculation, and membrane technologies are also reported for textile wastewater treatment66,67. However, they have disadvantages either high cost or secondary salt and sludge formation, which make them not a promising application for commercial treatment.

2.5.2 Decolorization of textiles

Many reactive dyes, basic dyes and disperse dyes used for textiles were designed to be stable to high temperature and UV light. In this case, decolorization of textile fiber will require strong

38 chemical agents to decompose the dye structure. There are limited efforts on fiber and fabric decolorization specifically. Hydrogen peroxide was patented to bleach hair fibers68.

Reduction clearing of disperse on the surface of polyester fabric may also be considered as a decolorization process. Disperse dyes adsorbed on surfaces are broken down into smaller and more water-soluble fragments by reduction clearing agents, usually made up of sodium dithionite and sodium hydroxide. Oxidative clearing of polyester fabric, is an alternative method to remove disperse dyes from polyester surface. Comparable wash fastness results to conventional reduction clearing and lower chemical oxygen demand values were reported by oxidative clearing process using hydrogen peroxide or ozone as the oxidation agent69.

SFS and its analog zinc formaldehyde sulfoxylate (ZFS) were largely used in discharge resist printing on polyesters fabrics70. SFS, also known as Rongalit (Rongal-registered trademark of

+ - BASF), is represented by the chemical formula Na HOCH2SO2 ·2H2O. Discharge printing is realized through destroy the background color by discharging agent, usually reducing agent such as SFS/ZFS, stannous chloride, and thiourea dioxide. Thus, compared to direct printing, discharge printing can print lighter colors on deeper background. Besides, SFS was also used to bleach dyed hair fibers and decolorize blue dyed denim fabric71. SFS has found applications in many other branches of industry of science, such as the paper industry and the organic synthesis, due to the excellent reducing properties of SFS. Like aforementioned sulfur- contained reducing agent, the reactions involving SFS occur through cleavage of C-S bond and

2- the formation of SO2 anions of sulfoxylic acid, which shows potential to selectively reduce aromatic aldehydes, benzils, ketones, and other carbonyl compounds without destroying the

72 - carbon frame . In addition, HOCH2SO2 anion also possesses relative reduction potential.

2- Aromatic carbonyl compounds can be destroyed by nucleophilic attack of either SO2 anions

- (Path A in Figure 22) or initial HOCH2SO2 anions (Path B in Figure 22). Considered that the reduction rate of some carbonyl compounds by sodium dithionite is more rapid than that by

SFS, Path B seems to be more favored.

Path A Path B

Figure 22. Reduction of aromatic aldehyde to alcohol by SFS in aqueous media72.

SFS also serves as an efficient reagent for the reductive dehalogenation of aldehydes and ketones. In Figure 23, a phenacyl halide was reduced in ethanol medium slowly (24 h) at room temperature or rapidly (<1 h) at reflux temperature to achieve the corresponding product73.

2- Addition of SO2 anion to ketone was also proposed as another possible mechanistic pathway.

- However, the nucleophilic displacement of halide by HOCH2SO2 anion, followed by loss of formaldehyde and SO2, was still more favored, because of the pronounced tendency of α- haloketones to undergo halogen displacement.

Figure 23. Reductive dehalogenation of phenacyl halide in ethanol medium by SFS.

Regarding physical properties, SFS is readily soluble in water, but is not stable in aqueous solution at high temperature. It contains large, transparent, and tubular crystals. It is a heavily hygroscopic substance and should be stored in a dry, cool and dark place, protected from moisture. SFS is odorless or possesses a faint leek smell. The loss of reactivity is indicated if a fishy smell is produced. It liberates toxic gases (H2S and SO2) upon heated, as the equation in Figure 24 shows74. Nevertheless, SFS is a powerful reducing agent, is inexpensive and commercially available, and can be handled without any special precautions, which make it a great candidate for decolorizing polyesters.

Figure 24. SFS decomposition reaction upon heated.

2.6 Recycling method

Many polymers like PET are inexpensive and durable materials, which can readily be converted to variety of products that find use in a range of applications. Current levels of polymer usage and disposal generate several environmental problems. Recycling is an

41 important action to reduce these impacts. Recycling provides opportunities to reduce oil usage and the quantities of landfilling wastes.

2.6.1 Conventional polymer recycling

Currently, recycling technologies for polymers including PET can be divided into primary, secondary, tertiary, and quaternary approaches75. Primary recycling approach only applies mechanical methods to achieve products with equivalent properties. It involves the re- introduction of clean products. From the textile perspective, primary recycling is simply reusing wearable polyester clothes that are donated to others who need them. Secondary recycling approach involves mechanical processes resulting in products with lower properties, therefore secondary recycling is often referred to as downgrading recycling. Examples are absorption composites recovered from polyester and polypropylene nonwoven selvages76, molded automotive carpets recovered from recycled fibers from PET bottle wastes77. In the former case, polyester and polypropylene nonwoven selvages were shredded, mixed, and compressed by molding techniques to produce functional sound absorption composites. While in the latter case, reclaimed PET bottles were melting extruded into fibers and further molded into automotive carpet. Both examples involve mechanical processes, but no chemical treatment. Tertiary recycling is the depolymerization process to convert polymers into constituent monomers or into oligomers that may be suitable for reforming original polymers.

Depolymerization of PET has been studied for many years. The initial patents78,79 regarding the depolymerization of PET by glycolysis in an excess diol, such as ethylene glycol and propylene glycol, were aimed to industrially produce polyols and unsaturated polyesters.

Satish and Wong initially developed the chemical recycling application of the reclaimed PET

42 for the purpose of sustainability. In their work, post-consumer soft-drink bottles were depolymerized by excess ethylene glycol in the presence of a metal acetate as catalyst. The resulting monomers and oligomers could be used as raw material to synthesize PET. Since then, the research of recycling PET bottles has been achieved significant progress. There are commercial approaches that have been well-established to recycle the PET bottles, either chemically or mechanically. However, recycling technology for dyed PET fabrics is limited, making incineration the predominant method of textile waste processing excluding landfilling.

Incineration, which is a way of quaternary recycling, only involves energy recovery and poses potential environmental problems, such as toxic ash emissions. Energy recovery from polymer wastes requires complete or partial oxidation of the material, producing heat, power and/or gaseous fuels, oils and chars. Each method provides a unique set of advantages that make it particularly beneficial for specific locations, applications or requirements.

2.6.2 Fabric reuse

Fabric reuse is different from primary recycling, which is a simply donating and transferring process. It involves chemical decolorization and re-dyeing the fabrics, producing products with new colors. Since polyester is a durable material, it is hard to damage the clothes by normal use. Decolorizing old-fashioned fabric and re-dyeing seem to be a good option to meet the continuously changing fashion markets and extend the life cycles of polyester fabrics.

Unfortunately, there is little literature regarding this type effort. When referring to fabric reuse, it is more likely to be quilting, re-purposing, and donating.

Guan et al. conducted a decolorization study of PET fabric using Fenton’s reagent80, which is known to be effective for wastewater decolorization. In their work, a full factorial design was

43 conducted to optimize the PET decolorization using Fenton’s reagent, and the optimal conditions involved using FeSO4 (0.18mM), H2O2 (1235mM), in water/acetone mixture

(1:1,v/v), at 120°C for 15 min. They found the use of acetone as a co-solvent with water was the key factor in providing efficient PET fabric decolorization. The efficiency of the optimized method was examined for a variety of disperse dyes, including azo dyes (Disperse Orange 30 and Disperse Blue 79), nitrodiphenylamine dyes (Disperse Yellow 42 and Disperse Yellow

86), anthraquinone dyes (Disperse Blue 56 and Disperse Red 60), a quinoline dye (Disperse

Yellow 54), and a basic dye (Basic Yellow 28). Result showed that PET fabric dyed by such colorants differ in ease of decolorization by Fenton’s reagent. Disperse Blue 79, Disperse Blue

56, Disperse Red 60 and Disperse Yellow 54 were successfully decolorized using the optimum conditions, while Disperse Orange 30, Disperse Yellow 42 and Disperse Yellow 86 were not fully decolorized using the same method.

An interesting study has been published by Shukla and co-workers for converting PET fabric waste into hydrophobic textile dyestuffs81. In their study, PET waste was chemically depolymerized using excess ethylene glycol, giving the product bis(2-hydroxyethylene terephthalate) (BHET). BHET was reacted with p-nitrobenzoyl chloride, which was prepared from p-nitrobenzoic acid, to give compound 2. Compound 2 was reduced to the amino derivative, and then reacted with bromine and potassium thiocyanate to get a benzothiazole derivative, which is the compound 4 shown in Figure 25 (a). Using the 2 diazo components,

2 disperse dyes were synthesized, which are the bright orange disperse Dye A and dull orange disperse Dye B in Figure 25 (b). These dyes were applied to polyester fabrics by standard dyeing, and depth of dyeing, levelness, and performance characteristics were found to be promising, which is shown in Figure 26.

(a)

(b)

Figure 25. Preparation of benzothiazole from BHET (a) and synthesis of dyes (b)81.

Figure 26. Color photographs of polyester fabric dyed with synthesized dyes.

2.7 Preliminary study - development of SFS decolorization method

Before the design of experiment, solutions of three disperse dyes and one basic dye with different types of chromophores (anthraquinone, azo, nitro, and methine) were treated with

SFS in water/acetone (1:1) medium and color changes were monitored by absorption spectroscopy. The anthraquinone dye (Disperse Blue 56) was not completely decolorized whereas the azo dye (Disperse Orange 30), nitro dye (Disperse Yellow 42) and methine dye

(Basic Yellow 28) underwent a much greater color loss. The changes of the four samples in

UV-visible spectra are displayed in Figure 27. The spectrum of Disperse Blue 56 showed a decrease in intensity at λmax and the color of the solution underwent a considerable hypsochromic shift, exemplified by a shift from 630 nm to 525 nm.

2.5 2.5 2 2 1.5 1.5 1 1 Absorbance Absorbance 0.5 0.5 0 0 330 430 530 630 730 330 430 530 630 730 Wavelength Wavelength

0 min 30 min 0 min 30 min

A B

2.5 3 2 2.5 2 1.5 1.5 1 1 Absorbance Absorbance 0.5 0.5 0 0 330 430 530 630 730 330 430 530 630 730 Wavelength Wavelength

0 min 30 min 0 min 30 min

C D

In addition, several commercial fabrics were decolorized using SFS in water/acetone (1:1) solution. Kebelka-Munk (K/S) values were measured to characterize color remaining on treated fabrics. In these examples, the treated fabrics possessed only a faint amount of their original color. The color value of each sample was measured before and after treatment, the results of which are summarized in Table 6. The untreated samples were all deeply dyed, which

47 was reflected in their high K/S values, except for the grey sample. Dyes used for the commercial fabrics were not revealed to us. Results from decolorization of the commercial fabrics were coincident with that from decolorization of disperse dye solutions. After treatment, their colors were reduced dramatically and only a small amount of color remained on the fabric, as shown in Figure 28. The fluorescent yellow sample became slightly grey after

SFS reduction. The grey and blue fabrics samples possessed a beige tint. The black fabric was also well decolorized, becoming off-white. Decolorization of the red sample was somewhat less effective than the others, with a red stain left on the treated fabric. The green sample was decolorized efficiently, becoming nearly white.

Table 6. K/S values of commercial PET fabrics before and after SFS (40g/L) treatment in acetone/water (1:1) at 100°C.

K/S Values Fabric Color Before Treatment After Treatment Yellow 53.6 1.6 Grey 13.2 1.6 Blue 41.8 2.5 Black 532.6 6.1 Red 240.6 2.8 Green 220.7 1.9

Both from the visual assessment of these samples and statistical measurement of K/S values, it was clear that SFS decolorization is a promising method for treating dyed PET fabrics as well as dye solutions, since most of these fabrics and solutions were decolorized to a high degree.

Yellow Grey Blue

Before After Before After Before After

Black Red Green

Before After Before After Before After

Figure 28. Commercial PET fabrics before and after SFS (40g/L) treatment in acetone/water (1:1) at 100°C.

2.7.1 Effect of treatment conditions on fabric decolorization

2.7.1.1 Treatment time

Having confirmed that disperse dyes could be decolorized by SFS in solution and in PET fibers, the next set of experiments pertained to optimizing the decolorization process using a commercial garment fabric. Figure -(a) shows the effects of SFS treatment time on K/S values of the commercial black fabric, over the 5-60 min timeframe, and Figure 30-(a) shows samples of the treated PET fabrics themselves. It can be seen that longer treatment time gives better decolorization performance. To help establish the lower limit of the treatment time, 5 min and

10 min SFS treatment were considered. However, from the K/S values, it is clear that more

49 color persisted at both time intervals. In general, the sample treated for 30 min appears to have a comparable decolorization level to the one treated for 60 min.

2.7.1.2 Water to acetone ratio

The treatment procedure was the same as used to investigate the effects of treatment time, except for using baths of different water to acetone ratios, and the temperature was lowered to

110oC. If the reaction vessel was heated to 120oC, the pressure inside beaker led to significant bumping. With this in mind, the treatment temperature was lowered to 110oC.

The effects of water to acetone ratio on the depth of shade (K/S) of decolorized polyester fabric are illustrated in Figure -(b) and Figure 30-(b). The results show that decolorization took place in all media but higher ratios of water to acetone (4:1 and 3:1) had a negative effect on decolorization efficiency. It can be concluded that the higher proportion of water is unfavorable for the extraction of sparingly water soluble disperse dyes from PET fabric to the reducing medium. However, significantly increasing the amount of organic solvent (acetone) reduced decolorization efficiency as well. This is because SFS is soluble in water, but not in acetone. Solubility of reducing agent decreases as acetone content increases, which results in a decrease in decolorization performance. In summary, the most acceptable decolorization resulted when the ratio of water to acetone was 1 to 2.

2.7.1.3 SFS concentration

Results from assessing the effects of SFS concentration on fabric decolorization are illustrated in Figure -(c) and Figure 30-(c), and can be divided into three parts. First, the K/S value decreased when increasing SFS concentration from 5 to 10g//L, which indicates that more dye

50 was reduced by increasing the amount of reducing agent. Then K/S increased as SFS concentration increased further, and reached a peak at 30g/L. Subsequently, K/S value dropped back to a low level when SFS concentration was increased to 40g/L. These results suggest the conversion of initially uncolored products or intermediates to secondary colors followed by secondary color degradation. A large excess of SFS (40g/L or more) does not improve dye degradation. Sufficient decolorization performance can be achieved with concentrations as low as 10 g/L.

2.7.1.4 Temperature

Results from this set of experiments are presented in Figure -(d) and Figure 30-(d) where a strong temperature relationship on PET decolorization is observed, which means temperature is a very important parameter that will have a significant influence on decolorization. At 80˚C, little dye was extracted and decolorized, with decolorization at 100 ˚C and 110˚C much more effective. This emphasizes that SFS decolorization involves dye transfer from PET fibers to the liquid medium (extraction), and after dye arrives in the medium, it will be more readily decolorized, and thus driving more dye out of fiber. In the dyeing process, disperse dye molecules can only penetrate the amorphous region, and the diffusion of dye molecules from the fibers surface into the body of polymer can only occur when temperature is above the glass transition temperature (Tg) of polyester. When enough heat is applied, polyester changes from rigid structure to a flexible structure. Then the dye molecules have the opportunity to slip between the movable chain segments into the pores of the fiber. By the same token, decolorization takes place more effectively at elevated temperatures. As an energy conservation measure, 100 ˚C was deemed suitable for this decolorization process.

2.7.1.5 Liquor ratio

Liquor ratio is an important parameter in batch process, and is defined as the weight of ratio between the total dry material and the bath volume. The effects of the liquor ratio on the K/S values of decolorized polyester fabric were investigated. The amount of SFS was constant as liquor ratio changed. The results obtained are shown in Figure -(e) and Figure 30-(e), which show that K/S decreased with increasing liquor ratio. The difference of decolorization performance between various liquor ratios was not significant, and 1:50 gave substantial color removal in the Ahiba lab dyeing machine. The relative higher K/S value at low liquor ratio

(1:10 or 1:20) is likely due to insufficient coverage of fabric samples, resulting in poor dye extraction and therefore decreased decolorization performance. However, the minimum liquor ratio needed differs greatly between machine types. Mechanical factors of wet processing equipment, such as bath and fabric turnover rate, turbulence and physical/flow characteristics could influence the liquor ratio significantly. Using low-liquor ratio equipment, the weight of bath used to dye and/or decolorize a given weight of goods can be reduced as a result.

Temperature=120°C (a) Water: acetone=1:1 [SFS]=40g/L Liquor ratio=50:1

Temperature=110°C Time=30min [SFS]=40g/L Liquor ratio=50:1 (b)

Figure 29. Effect of (a) treatment time, (b) water to acetone ratio, (c) SFS concentration, (d) Temperature, and (e) liquor ratio on K/S value of black commercial fabrics after decolorization.

Temperature=110°C Water: acetone=1:2 (c) Time=30min Liquor ratio=50:1

Time=30min Water: acetone=1:2 [SFS]=10g/L (d) Liquor ratio=50:1

Figure 29 (continued).

Temperature=100°C (e) Water: acetone=1:2 [SFS]=10g/L Time=30min

Figure 29 (continued).

5 10 15 20 30 40 50 60

(a)

4:1 3:1 2:1 1:1 1:2 1:3 1:4

(b)

g/L 5 10 15 20 25 30 35 40

(c)

80 ˚C 90 ˚C 100 ˚C 110 ˚C

(d)

1:10 1:20 1:30 1:40 1:50

(e)

Figure 30 (continued).

2.7.2 Fabric strength assessment

To determine whether fiber degradation occurred when dye PET fabrics were subjected to SFS decolorization at elevated temperature, intrinsic viscosity was measured using an Ubbelohde viscometer and viscosity-average molecular weight was calculated using the Mark-Houwink equation:

[η] = 3.72×10-4 M0.73

In this investigation, the control was untreated 100% PET warp knit fabric, while the test samples were decolorized PET fabrics that had been dyed by C.I Disperse Orange 30 and C.I

Disperse Blue 60. Intrinsic viscosity and molecular weight results from these three fabrics are recorded in Table 7, where it can be seen that these properties were essentially unchanged.

Although this analysis did not provide information pertaining to the shapes of the molecular weight distribution, it gave us a general indication that degradation of PET fibers did not occur during SFS treatment.

Table 7. Intrinsic viscosity (IV) Vs viscosity-average molecular weight for control PET fabric and PET fabric after SFS (40g/L) treatment in acetone/water (1:1) at 100 ˚C.

Fabric IV (dL/g) MW Untreated 0.50 19,400 Decolorized Orange 30 0.50 19,300 Decolorized Blue 60 0.50 19,350

2.7.3 Conclusions from preliminary study

As an initial step in the recycling of PET-based textiles, it has been shown that sodium formaldehyde sulfoxylate (SFS) can be used to decolorize dyed PET in water/acetone media.

While a treatment time of 60 min gives better decolorization, 30 min is sufficient. A water to acetone ratio of 1:2 gives the best decolorization performance, as higher levels of water or acetone reduce decolorization effectiveness. Sufficient decolorization can be achieved with an SFS concentration as low as 10 g/L and there is a significant temperature dependence for decolorizing polyesters but 100oC is deemed suitable. On a laboratory scale, the best liquor ratio is 1:50, which gives substantial color removal. Organic solvent used during decolorization process can be efficiently recovered and reused. It is also clear that SFS decolorization does not affect the mechanical properties of PET fibers. This method has other advantages. It is very easy, a one-step process, and only one chemical (sodium formaldehyde sulfoxylate) is needed. Secondly, it is applicable to regular PET and cationic dyeable PET.

3. PRESENT RESEARCH

3.1 Objectives

The present work had following objectives:

(1) Study the recyclability of the decolorization bath and the decolorized fabrics. Solvent-

based decolorization bath should be recovered and reused in order to reduce the effluent

emission. Decolorized fabrics should be re-dyed as virgin PET fabrics with acceptable

color differences.

(2) Characterize the dye compounds in commercial fabrics by UV-vis, TLC, HPLC, and

MS.

(3) Investigate the toxicity of the decolorized solution. Azo, anthraquinone, and nitro

disperse dyes are decolorized by SFS, and the toxicity data of the remaining solution

should be obtained.

(4) Conduct a life cycle assessment of the closed loop recycling process, and compare with

the life cycle assessment impacts of virgin PET production system.

3.2 Rational

In 2011, Aizenshtein predicted that the PET fiber production would be twice as high as the annual cotton harvest in a few years, making it the main and most reliable raw material base within the global textile industry82. It is a synthetic material derived from non-renewable petroleum sources and its hydrophobic nature and high resistance to biodegradation make disposing worn-out PET textiles in land field sites a potential environmental problem. Further, continuous disposal of PET following a single lifetime of use is a waste of valuable resources.

With environmental stewardship in mind, an efficient approach to recycling colored polyester textiles has come to the forefront in the textile industry. Many studies have been conducted to investigate the recycling of PET bottles. However, the recycling of PET fabrics is limited.

PET bottles are usually clear and transparent but PET apparel contains various dyes. The dyes inside the fiber will reduce the degree of polymerization of the fiber during recycling process.

Besides the remaining dyes in the recycled PET will cause uniformity issues. In this regard, it seems clear that dye removal from colored products is a crucial step in the recycling process.

This study involved the selection of a group of structural diverse and widely used dyes to develop an efficient PET decolorization method. Dyes chosen included azo, anthraquinone, quinoline, and nitro disperse dyes, and sodium formaldehyde sulfoxylate was used as the decolorizing agent. A medium containing an organic solvent combined with water facilitated simultaneous dye extractraction and decolorization. Considering sustainability, a toxicity study and life cycle assessment were conducted.

4. REUSE OF DECOLORIZATION BATH AND DECOLORIZED FABRICS

4.1 Introduction

The worldwide production of polyethylene terephthalate (PET) was around 49 million tons in

2008, having overtaken cotton since 2002, and a majority (79%) of the PET produced was used in the textile industry 82,83. PET fabrics are extensively used in a wide variety of apparel, home furnishings and automotive products, which find their way to landfills at the end of their useful life84. As a semicrystalline thermoplastic polyester, PET has high mechanical strength and low permeability to gases, which means it has high resistance to atmospheric and biological agents

13. Disposing the slowly degradable PET fabrics in landfills is creating a significant environmental concern 85. In addition, the manufacture of PET is an energy-intensive process, requiring large amounts of crude oil 86. Thus, a one-time use of PET fabric can be regarded as a waste of a valuable polymer derived from non-renewable petroleum resources. Although a fraction of PET bottles are recycled 88, the technology needed to reuse the PET fabrics is limited.

Currently, recycling technologies for PET and other polymers can be divided into primary, secondary, tertiary, and quaternary approaches 89. Primary recycling approach applies mechanical methods to achieve products with equivalent properties. From the textiles perspective, primary recycling is simply reusing wearable polyester clothes that are donated to others who need them. Secondary recycling approach involves mechanical processes resulting in products with lower properties, therefore secondary recycling is often referred to as downgrading recycling. Examples are sound absorption composites recovered from polyester and polypropylene nonwoven selvages 76, molded automotive carpets recovered from recycled

62 fibers from PET bottle wastes 77. Tertiary recycling is the depolymerization process to convert polymers into constituent monomers or into oligomers which may be suitable for reforming original polymers 90. Depolymerization of PET has been studied for many years. The initial patents78,91 regarding the depolymerization of PET by glycolysis in an excess diol, such as ethylene glycol, propylene glycol, were aimed to industrially produce polyols and unsaturated polyesters. The chemical recycling application of the reclaimed PET with the purpose of sustainability was initially developed by Satish and Wong79. In their work, post-consumer soft-drink bottles were depolymerized by excess ethylene glycol in the presence of a metal acetate as catalyst. The resulting monomers and oligomers can then be used as raw material to synthesize PET again. PET can be depolymerized to the corresponding monomers by hydrolysis, aminolysis 92, methanolysis, and glycolysis 81,90. Ever since then, the research of recycling PET bottles has been achieved significant progress. There are commercial approaches that have been well-established to recycle the PET bottles, either chemically or mechanically87,93. However, these approaches are not suitable for recycling most PET based textiles due to the presence of dyes. Disperse dyes are used to dye PET fabric and basic or disperse dyes are employed to dye cationic dyeable PET, which is a specialty fiber produced by adding small amounts of the sodium salt of dimethyl ester of 5-sulfoisophthalic acid when manufacturing PET94. If disperse dyes are not removed before recycling the fabric, their presence could cause a reduction in degree of polymerization during the melting process 95, as well as uniformity issues. Since recycling technology for dyed PET fabrics is limited, making incineration the predominant method of textile waste processing excluding landfilling96.

Incineration, which is a way of quaternary recycling, only involves energy recovery and also poses potential environmental problems, such as toxic ash emissions 97.

While solvent extraction methods can be used to remove dyes from textiles, the dye concentration inside and outside the fibers will eventually reach a thermodynamic equilibrium.

In another words, extraction cannot make the textiles fully colorless, without removing the dyes from the solvent medium continuously. Physical methods, including adsorption using granular activated carbon 98 and membrane filtration99, chemical methods such as bleaching

100, ozonation 101 and Fenton oxidation102, and biological methods 103 have been reported for decolorizing dyes from textile wastewater but normally not from dyed textiles.

The presence of colorful dyes makes PET fabric attractive, but brings about challenges when it comes to recycling. With this in mind, a decolorization method was developed in our previous studies to remove disperse dyes from PET fabric for enhanced recyclability. Sodium formaldehyde sulfoxylate (SFS) was employed as the reducing agent to help remove disperse dyes. The decolorization process was carried out in water/acetone mixture solution since disperse dyes are hydrophobic and cannot be substantially extracted using water as the only solvent. Elevated temperature is required to increase desorption of the dyes by reducing cohesion between polymer chains. The decolorization behavior is strongly influenced by SFS concentration, treatment time, and liquor ratio. By considering the decolorization performance as well as the cost effectiveness, the optimized procedure was found to be water/acetone media

(v/v=1:2) at elevated temperature (100˚C) with the liquor ratio of 50:1 using SFS (10g/L) for

30 min. This method was effective for decolorizing a variety range of colorants104.

In the present work, SFS decolorization was further investigated. The goal was to reduce acetone consumption without decreasing decolorization performance. In addition, the strength of the decolorized fabric was tested using a standard method, burst pressure measurement, and

64 the re-dyeability of decolorized PET fabrics was assessed. Dyes used in this study included those listed in Table 8.

Table 8. C.I. names, classes, and structures of dyes used in this study.

Color Index Name Chemical Class Molecular Structure Disperse Orange 30 Azo

Disperse Blue 79 Azo OC2H5 Br

N N(CH2CH2OCOCH3)2 O2N N HN NO 2 COCH3 Disperse Yellow 42 Nitro

Disperse Red 60 Anthraquinone O NH2 OC6H5

O OH

4.2 Experimental

4.2.1 Material

Dyed commercial polyester knit leisure wear and white cationic dyeable polyester fabric were kindly donated by Nike, Inc. (Beaverton, OR, USA). Reducing agent sodium formaldehyde sulfoxylate dihydrate (SFS) was purchased from Arcos Organics, and HPLC grade acetone was purchased from Fisher Scientific. The disperse dyes and dyeing auxiliaries were obtained from our internal pilot plant inventory. All chemicals were used without further purification.

4.2.2 Batch fraction distillation

After each fabric decolorization, the treatment bath (47~48 mL of acetone/water) was collected. Lab-scale fractional distillation apparatus was assembled (Figure 31). The bath was transferred to a 100-mL round-bottom flask containing a boiling stone. Heat was applied from a digital hot plate and maintained for a distillation rate of one drop per second. When the liquid stopped boiling, heat was removed and the distillate was re-used in decolorization experiments.

4.2.3 Application of disperse dyes to decolorized fabrics

A stock solution (1g/L) of each disperse dye was prepared, with the addition of 1 mL of the dispersing agent Novadye NT 9. The dyebath consisted of stock solution at a 1% (o.w.f.) level, and glacial acetic acid (50 µL). Tap water was used to bring the bath to final volume needed for a liquor ratio of 20:1. Dyeing was conducted in an Ahiba lab dyeing machine. The dyebath was increased from room temperature to 130 ˚C at a ramp rate of 4˚C/min. The bath was held at 130 ˚C for 30 min and allowed to cool for 30 min. The fabric was rinsed with water,

66 reduction cleared using sodium dithionite (0.5 g/L) and sodium hydroxide (0.5 g/L), rinsed again with water, and allowed to air-dry.

4.2.4 Decolorization of laboratory-dyed fabrics using acetone distillate

The collected acetone distillate from section 4.2.2 was used to decolorize cationic dyeable PET fabrics that were dyed using Disperse Blue 79, Disperse Yellow 42, and Disperse Red 60 at

1% (o.w.f.). Water and distilled acetone were mixed at the ratio of 1:2. For each run, 1 g of fabric was treated in 50 mL of the solvent medium. SFS (0.5 g) was used as the reducing agent. The bath chamber was sealed and heated to 100 ˚C at rate of 4°C/min, and held for 30 min. The bath was cooled, and fabrics were removed, rinsed with running tap water for 2 min, and allowed to air-dry.

4.2.5 Color evaluation

A calibrated Datacolor Spectraflash 600X Reflectance Spectrophotometer equipped with iMatch software from X-Rite was used to determine the K/S and Whiteness Index values of the PET fabrics. The software was set to use illuminant D65 with the UV light included, and the CIE 10-degree supplemental standard observer. The sample being tested was folded twice and measured two times by rotating the sample at 90 degrees between measurements. The average value was recorded. The K/S value of each sample was calculated by adding the K/S value of each 10 nm from 400 nm to 700 nm as follows:

��(�/�) = (�/�)

4.2.6 Fabric strength evaluation

Burst pressure measurements were performed with a diaphragm bursting tester TruBurst

Model 810 machine on commercial black fabrics and decolorized commercial fabrics. Fabrics tested were clamped over a rubber diaphragm by means of an annular clamping ring.

Increasing pressure was applied until each fabric failed or the machine reached its limit, and the corresponding pressure was recorded.

4.3 Results and discussion

4.3.1 Solvent recovery and reuse

The decolorization method worked best in an aqueous medium containing acetone due to the hydrophobicity of disperse dyes. Although acetone has been removed from the Toxic Release

Inventory (TRI) 105, its discharge into wastewater would still need to be addressed appropriately since acetone is extremely flammable 106. This aspect of the study explored the recovery and reuse of acetone by distilling it from an aqueous mixture to save cost as well as increase sustainability. A condenser was used as a fractionating column. Table 9 lists the yields of recovered acetone from a set of 5 experiments, which shows that 73-90% recovery occurred. The average acetone recovery percentage was 82.0%, as shown in Table 9.

Table 9. Acetone recovery percentage from lab-scale fractional distillation.

Batch Decolorization bath Acetone Distillate Recovery (Water/Acetone=1:2; mL) (mL) Percentage #1 45 27 90.0% #2 45 24 80.0% #3 46 27.5 89.7% #4 43 22 76.7% #5 47 23 73.4% Average 45.2 24.7 82.0%

The recovered acetone was used to decolorize PET fabrics again. Decolorization performance in recovered and virgin acetone were compared, which was characterized by K/S values. Table

10 results show that the K/S values dropped significantly after SFS decolorization. The difference between the K/S values of PET decolorized in virgin and recovered aqueous acetone are negligible, which means the distillate from fractional distillation can be readily reused. In the case of SFS decolorization, the organic solvent is not required to be extremely pure since it will eventually be mixed with water in the decolorization process.

Table 10. K/S values from lab-dyed cationic dyeable PET fabrics using virgin and recovered acetone for SFS (40g/L) decolorization in water/acetone (1:2) at 100 °C.

K/S Values Dyes and Shade Depths Used Before Recovered Virgin Acetone decolorization Acetone Disperse Red 60, 1.0% (owf) 48.33 0.24 0.27 Disperse Blue 79, 1.0% (owf) 81.02 1.12 1.04 Disperse Yellow 42, 1.0% (owf) 16.80 0.22 0.30

4.3.2 Re-dyeing decolorized cationic dyeable PET

To help assess the recyclability of the decolorized fabrics, re-dyeability of the fabrics was examined. For this aspect of our study, Disperse Red 60, Disperse Yellow 42, Disperse Blue

79 and Disperse Orange 30 were chosen as representatives of the major chemical types of disperse dyes, providing anthraquinone, nitro, and azo chromophores. Cationic dyeable PET fabrics dyed by these colorants were initially decolorized using SFS. The resulting fabrics possessed low K/S values and high Whiteness Index values, making them comparable to virgin

69 white polyester fabrics. Thus the decolorized fabrics were re-dyed to their original color. For example, a piece of cationic dyeable PET fabric containing Disperse Orange 30 was decolorized using SFS and the decolorized fabric along with a piece of white cationic dyeable

PET fabric were dyed using Disperse Orange 30 in a same bath. Colors dyed on virgin white fabrics were considered as standards, and were measured to obtain their colorimetric attributes.

Colorimetric attributes of the samples that were the decolorized fabrics re-dyed by their original color, were measured and compared with the standard to attain the statistical color difference values (ΔEcmc), the results of which are listed in Table 11 . Figure 32 contains pictures of the corresponding cationic dyeable PET fabrics that were used for direct visual assessment.

Table 11. Color difference values of cationic dyeable PET fabrics between once decolorized fabrics and virgin white fabrics dyed by corresponding original colors.

Dyes L* ΔL* a* Δa* b* Δb* ΔEcmc Disperse Orange 30 57.45 -2.72D 39.13 1.81R 53.02 -0.81B 2.25 (No Pass) Disperse Blue 79 36.99 -1.79D -0.76 -2.02G -18.41 0.16Y 2.35 (No Pass) Disperse Yellow 42 88.91 -0.74D 0.40 -0.12G 59.25 0.01Y 0.28 (Pass) Disperse Red 60 60.36 -1.20D 56.96 0.28R -1.40 0.26Y 0.56 (Pass) L*a*b*=colorimetric attributes of virgin polyester fabric Δ=once decolorized fabric-virgin fabric

Commission International de I’Eclairage (CIE) L*a*b* color space was used to identify color differences. L* indicates lightness, a* is the red/green coordinate, and b* is the yellow/blue coordinate. In all sets of comparison, the ΔL* values are negative, which means the re-dyed decolorized fabrics are darker than the standards. The value of Δa* is either positive or

70 negative, which indicates the trial is either redder or greener than the standard. A negative value of Δb* means the trial fabric is bluer than the standard, otherwise the fabric is yellower.

The ΔL*, Δa*, and Δb* are caused by the different whiteness levels of decolorized fabrics and virgin white fabrics. Among them, two azo dyes Disperse Orange 30 and Disperse Blue 79 did not match the color of the standards (ΔEcmc>1), while the nitro dye Disperse Yellow 42 and the anthraquinone dye Disperse Red 60 passed the color matching assessment (ΔEcmc<1).

By looking at each picture in Figure 32, it can be seen that the color difference between the re- dyed and virgin fabrics are not significant, except for Disperse Blue 79. An darker blue color was perceived on the re-dyed fabric. The difference between Disperse Orange 30 is noticeable, but not as significant as Disperse Blue 79. However, they have the same ΔEcmc values. The color differences in the sets of Disperse Red 60 and Disperse Yellow 42 are visually negligible.

(a) (b)

(c) (d) Figure 32. Cationic dyeable PET fabrics showing the color difference between virgin (left) and once decolorized fabrics (right) after dyeing in the same bath. (a) Disperse Red 60, (b) Disperse Orange 30, (c) Disperse Yellow 42, and (d) Disperse Blue 79.

To further study the recyclability of the cationic dyeable PET fabric, the re-dyed fabrics were decolorized again using SFS reduction method, and the twice decolorized fabrics were dyed

71 again by their original colorant together with virgin white fabrics. The color differences were compared, which are demonstrated in Table 12 and Figure 33.

Table 12. Color difference values of cationic dyeable PET fabrics between twice decolorized fabrics and virgin white fabrics dyed by corresponding original colors.

Dye ΔL* Δa* Δb* ΔEcmc Disperse Orange 30 -4.41D 2.15R 0.85Y 2.39 (No Pass) Disperse Blue 79 -8.74D -1.53G 0.58Y 4.92 (No Pass) Disperse Yellow 42 -0.02D -0.51G -1.81B 0.72 (Pass) Disperse Red 60 -0.73D 0.14R 0.25Y 0.76 (Pass) Δ=twice decolorized fabric-virgin fabric

Figure 33. Cationic dyeable PET fabrics showing the color difference between virgin (left) and twice decolorized fabrics (right) after standard dyeing in same bath.

Again all the twice re-dyed fabrics were darker than the dyed virgin white fabrics. Δa* and

Δb* values vary but are not predictable. Re-dyeing of Disperse Yellow 42 and Disperse Red

60 still passed the color matching assessment, but Disperse Orange 30 and Disperse Blue 79

72 did not. All of the ΔEcmc values were obviously increased this time. It indicates that the twice decolorized fabrics have darker shades than the once decolorized fabrics. In the case the

ΔEcmc values of Disperse Blue 79 and Disperse Orange 30 were 4.92 and 2.39, and visual assessment of the fabrics are provided in Figure 33.

The investigation of fabric recyclability was not limited to examining the re-dyeing properties of the decolorized fabric using the original color, but included the study of re-dyeability using other colors. In this instance, the aforementioned re-dyed fabrics were decolorized a third- time using the SFS method, and Disperse Yellow 42 was applied to re-dye each of the three- time decolorized cationic dyeable PET fabrics. Yellow is a relative light color compared with orange, red and blue. Therefore, it requires high degree of whiteness of the base fabric, since colored impurities cannot be covered easily by the yellow color. Table 13 and Figure 34 list the colorimetric and visual assessment results, respectively. ΔEcmc values of the four samples show that the three-time decolorized Disperse Yellow 42 and Disperse Orange 30 fabrics can be successfully re-dyed by a yellow color with acceptable color differences. Decolorized

Disperse Orange 30 and Disperse Blue 79 fabrics did not pass the color matching assessment, especially for the three-time decolorized Disperse Blue 79. It can be seen from Error!

Reference source not found. that the sample (5) may contain residual blue dye in the base fabric.

Table 13. Color difference values of cationic dyeable PET fabrics between three-time decolorized fabrics and virgin white fabrics dyed by Disperse Yellow 42.

Fabric ΔL* Δa* Δb* ΔEcmc Decolorized Disperse Yellow 42 -1.73D 0.45R 0.48Y 0.71 (Pass) Decolorized Disperse Orange 30 -2.63D 0.72R -0.68B 1.08 (No Pass) Decolorized Disperse Red 60 -1.55D 0.92R 1.22Y 0.91 (Pass) Decolorized Disperse Blue 79 -6.13D -5.89G -7.31B 5.09 (No Pass) Δ=three-time decolorized fabric-virgin fabric

It was confirmed from the results that SFS method is an effective decolorization method for disperse dyes on PET. Fabrics treated by this method have acceptable recyclability in terms of re-dyeability. Among them, decolorized Disperse Yellow 42 and Disperse Red 60 dyed fabrics have better recyclability than decolorized Disperse Orange 30 and Disperse Blue 79 dyed fabrics, which may indicate that azo dyes are harder to decolorize thoroughly than the nitro and anthraquinone dyes.

4.3.3 Burst pressure measurement

To study whether the strength of PET fabric was adversely influenced or not when fabrics were subjected to SFS decolorization at relative high temperature, burst pressure was measured on diaphragm bursting tester TruBurst Model 810. The control was untreated 100% PET warp knit commercial black fabric, while the variable was the decolorized commercial PET fabric.

The strength of both control and variable samples exceeded the maximum pressure that the machine can reach, which was a good indicator that the fabric strength was not significantly reduced. This result is also consistent with previous intrinsic viscosity measurements indicating that SFS decolorization has no significant effect on fabric strength.

4.4 Conclusion

Fractional distillation using a simple apparatus is useful for acetone recovery following SFS decolorization in acetone: water, and the recovered solvent can be used to achieve comparable decolorization performance. Reuse of decolorized cationic PET fabrics was achieved for three rounds of decolorization and re-dyeing. The decolorized fabrics can be re-dyed the same or different colors with acceptable color differences, without significant effects on fabric strength.

However, the recyclability of fabric can have a dye-structure dependence on good ΔEcmc color differences.

5. THE ECOTOXICITY OF SODIUM FORMALDEHYDE SULFOXYLATE

DECOLORIZATION MEDIUM

5.1 Introduction

Sulfur containing chemicals, such as sodium dithionite, and thiourea dioxide, have been used in chemistry and chemical technology as reductants for a long time 107. Due to the instability of sodium dithionite in aqueous solution108 , which is the first well-known sulfur containing reductant widely used since 1854, researchers attempted to develop chemicals combining high reducing power with stability in aqueous media109. A key member of this group of compounds is sodium formaldehyde sulfoxylate (SFS). SFS, also known as Rongalite, has the chemical

- + formula HOCH2SO2 Na . Other names for this salt include formaldehyde sodium bisulfite adduct, formaldehyde desulfoxylic acid sodium salt, and sodium hydroxylmethanesulfinate.

Rongalite, which means discharge in French, is largely used in discharge resist printing on polyester fabrics 70, bleaching dyed hair fibers and decolorizing blue dyed denim jeans68. It also has found applications in many other branches of industry of science, such as paper industry110, organic synthesis111, reduction of graphite oxide, and metallization of fibers112, due to the excellent reducing properties of SFS. It can be prepared through reaction of formaldehyde with dithionite, or reduction of a mixture of bisulfite and formaldehyde with zinc 109, shown in Figure 35 respectively.

Figure 35. Preparation of sodium formaldehyde sulfoxylate through (1) reaction of formaldehyde with dithionite, and (2) reaction of bisulfite and formaldehyde with zinc.

2- The reduction involving SFS occur through cleavage of C-S bond and the formation of SO2 anions of sulfoxylic acid, which shows potential to selectively reduce aromatic aldehydes, benzils, ketones, and other carbonyl compounds without destroying the carbon frame72. In

- addition, HOCH2SO2 anion also possesses relative reduction potential. Aromatic carbonyl

2- compounds can be destroyed by nucleophilic attack of either SO2 anions (Path A in Figure

- 36) or initial HOCH2SO2 anions (Path B in Figure 36). Considered that the reduction rate of some carbonyl compounds by sodium dithionite is more rapid than that by SFS, Path B seems to be more favored.

Path A Path B

Figure 36. Reduction of aromatic aldehyde to alcohol by SFS in aqueous media72.

SFS also serves as an efficient reagent for the reductive dehalogenation of aldehydes and ketones. In Figure 37, a phenacyl halide was reduced in ethanol medium slowly (24 h) at room temperature or rapidly (<1 h) at reflux temperature to achieve the corresponding product73.

2- Addition of SO2 anion to ketone was also proposed as another possible mechanistic pathway.

- However, the nucleophilic displacement of halide by HOCH2SO2 anion, followed by loss of

77 formaldehyde and SO2, was still more favored, because of the pronounced tendency of α- haloketones to undergo halogen displacement.

Figure 37. Reductive dehalogenation of phenacyl halide in ethanol medium by SFS.

Polyester, which is widely used in textile application, is usually dyed by a class of dyes known as disperse dyes. Modified polyester, cationic dyeable polyester, for example, also can be dyed by cationic dyes or basic dyes. Azo dyes account for more than 50% of the commercialized disperse dyes worldwide. Anthraquinone derivatives are another important type of disperse dyes, accounting for 25% of the commercialized disperse dyes. Due to the excellent reducing power, SFS was chosen in previous work to decolorize polyester fabrics.

SFS is readily soluble in water. It is not stable in aqueous solution at high temperatures. It

74 liberates toxic gases (H2S and SO2) upon heated, as the equation in Figure 38 shows .

According to the International Uniform Chemical Database, SFS is is not readily

113 biodegradable . Aquatic toxicity of SFS in terms of EC50 value to daphnia magna is 20 mg/L, LC50 to leuciscus idus is 10000 mg/L. Besides, the toxicological assessment of SFS has not been reported. There is no data related to formaldehyde sulfoxylate anion found in surface water downstream from wastewater treatment plants in the US.

Figure 38. SFS decomposition reaction upon heated.

The ecotoxicity and genotoxicity of certain disperse dyes have been investigated, such as

Disperse Red 1 80, Disperse Red 13 62 and Disperse Yellow 7 114, but there have been few studies about the ecotoxicity of disperse dye decolorized compounds arising from SFS treatment. In this study, six high volume disperse dyes and one basic dye were decolorized by

SFS, and the media containing their reduction products were tested with Daphnia similis and

Parhyale hawaiensis to observe the ecotoxicity. SFS media without dyes was also investigated as the control experiment. From a quantitative standpoint, these effects are measured as EC50 and LC50 values. LC50 represents the concentration of the test substance that causes mortality of the organism in 50% of the exposed population. EC50 is the concentration estimated to immobilize 50% of the exposed population within a defined exposure period. In this case, immobilization is defined as the loss of the ability for daphnia similis to swim within 15 seconds after gentle agitation of the test vessel 35. Dyes used in this study were those in Table

14.

Table 14. C.I. names, classes, and structures of dyes used in this study.

Color Index Name Chemical Class Molecular Structure C.I. Disperse Orange 30 Azo

C.I. Disperse Blue 79 Azo OC2H5 Br

N N(CH2CH2OCOCH3)2 O2N N HN NO 2 COCH3 C.I. Disperse Blue 56 Anthraquinone

C.I. Disperse Red 60 Anthraquinone O NH2 OC6H5

O OH C.I. Disperse Yellow 42 Nitro

C.I. Disperse Yellow 86 Nitro

C.I. Basic Yellow 28 Methine

5.2 Experiment

5.2.1 Materials and organisms

Sodium formaldehyde sulfoxylate dihydrate (SFS) was purchased from Arcos Organics. The disperse dyes and dyeing auxiliaries were obtained from our internal pilot plant inventory. All chemicals were used directly without further purification.

The organisms used in the test were Daphnia similis neonates (<24h old) and Parhyale hawaiensis neonates (7 days old) from Faculty of Technology laboratory (UNICAMP/Brazil).

5.2.2 Decolorization of commercial dyes

Solutions (100 mg/L) of seven commercial dyes were prepared using tap water. Each solution

(100mL) was mixed with SFS (1g, 10g/L) in beakers. Control solution was prepared by dissolving 1 gram of SFS in 100 mL of tap water. The temperature of the various solutions was raised to 95˚C using an oil bath and held for 45 min. After cooling, the solutions were analyzed using a UV-Vis spectrometer. The decolorization level in percentage for all the dyes was determined, according to the equation 115

Decolorization (%) = × 100%,

where � is the initial absorbance of untreated dye solution at the maximum absorption wavelength and � is the absorbance of dye solution after SFS decolorization treatment.

5.2.3 Ecotoxicity testing

The SFS decolorization products were evaluated for acute toxicity to Daphnia similis according to ABNT116 and OECD 202 guidelines117. The group of decolorized dye solutions were diluted in aqueous medium at 20 ± 2 °C, pH in the range of 7.0-7.6, hardness between

40-48 mg/L as CaCO3. Concentrations selected were 0.03, 0.1, 0.3, 1, 3, 10 % of original treated solution. Five neonates (<24 h old) were placed in each concentration of test solution, and four replicates were performed. Exposures were performed in vials (10mL) for 48 h at 20

± 2 °C, under a photoperiod of 16:8 light/dark, without feed. The number of immobile organisms was recorded. The results were statically analyzed using the trimmed Spearman-

118 Karber ; the EC50 was expressed in percentage of dye solution.

Decolorized Disperse Orange 30, Disperse Blue 56 and SFS solution were tested for acute toxicity using neonates of Parhyale hawaiensis (7 days old), in 96-well microplates, containing

200 µL of sample and 1 neonate each well. Twenty replicates were conducted for each sample.

Tests were performed for 96 h, at temperature of 24 ± 2 °C and photoperiod of 1:1 light/dark.

At the end of the test, number of dead organisms were recorded, and pH and salinity were analyzed. The LC50 values were calculated using a statistical analysis method trimmed

Spearman-Karber118; the values were expressed in percentage of dye solution.

5.3 Results

5.3.1 SFS decolorization of commercial dyes

UV-Vis results from decolorization of 6 disperse dyes and 1 basic dye are shown in Figure 39.

Due to the lack of a water-solubilizing group in disperse dye structure, it actually forms fine

82 dispersion instead of solution when dissolved in water. Therefore, disperse dyes were dissolved in acetonitrile for better analysis. The visible spectrum of Disperse Yellow 42 dissolved in acetonitrile is characterized by the band with λmax at 411 nm. After decolorization, the media was also dissolved in acetonitrile, and the spectrum showed that the band in visible region disappeared, indicating that the yellow color was fully removed, and no secondary color was generated. The maximum absorption wavelength for Disperse Blue 56 is 621 nm. After SFS decolorization, the absorption at lmax was reduced dramatically, which means the blue dye structure was substantially changed. However, there was an absorption in the visible range, indicating secondary color was generated. From Figure 40, it can be seen that the nitro and methine dyes used in this study, which are Basic Yellow 28, Disperse Yellow 42, and Disperse

Yellow 86, are easier to decolorize using SFS than the azo dyes (Disperse Orange 30 and

Disperse Blue 79). Among the dye categories studied in this work, the anthraquinone structures are the most resistant to SFS reduction, judging from the decolorization result of

Disperse Red 60 and Disperse Blue 56. However, these results do not disqualify any of the dyes from use when to be decolorized using SFS.

Figure 39. UV-Vis absorption spectra of commercial dyes (100mg/L) and SFS decolorized (SFS=10g/L, 95 °C, 45min) solutions.

Figure 39 (continued).

Figure 40. Comparison of decolorization percentage after SFS decolorizaton treatment (10g/L, 95 °C, 45min).

5.3.2 Daphnia similis test

Acute toxicity results for decolorized dye solutions and SFS control solution to D. similis are summarized in Table 15. In the present study, toxicity was evaluated in percentage of decolorized dye solution, which can be roughly converted to equivalent concentrations through calculation. For example, SFS control solutions was treated with the decolorization process

(95 °C, 45min), and the resultant solution was tested with Daphnia similis and the EC50 was obtained to be 1.83% of the decolorized solution. The density of solution was assumed to be

1g/mL. Therefore, in terms of equivalent concentration, EC50 can be described as 18.3 mg/L.

In the SFS control solution testing, no immobility was observed at 0.03%, 0.3%, and 1%

86 solution. 10% and 85% immobility was observed in 0.1% and 3% solution, respectively. At

10%, the highest concentration tested, a 100% immobility of daphnia was observed at 48-h.

The EC50 was calculated to be 1.83% through trimmed Spearman-karber calculation. It can be seen from Figure 41 that SFS decolorized Disperse Orange 30 and Disperse Blue 56 solutions were more toxic than SFS control, whereas other decolorized dye solutions afforded less toxic than the control solution. Decolorized Basic Yellow 28, which is a methine dye, gave the lowest toxicity. The highest toxicity came from the decolorized Disperse Blue 56 solution, which is an anthraquinone dye. However, the difference between the control solution and other reduced dye solutions was not significant, which indicated that the toxicity may come from the

SFS decolorization medium but not from the dyes. The globally harmonized system (GHS) criteria for classification of a substance in acute categories is listed in Table 16. According to this classification, decolorized dye solutions and SFS control solution are in the Acute III category after converting EC50 percentage to EC50 equivalent concentration. Solutions after decolorization treatment was considered harmful to daphnid similis, with a 48-h EC50 of between 10 to 100 mg/L of the equivalent concentration.

Table 15. EC50 (%) values of SFS decolorized solution tested with Daphnia similis.

Decolorized dye solution EC50 (%) CI* SFS 1.83 1.44-2.34 Disperse Orange 30 1.63 1.46-1.83 Disperse Blue 79 4.35 3.49-5.43 Disperse Blue 56 1.51 1.23-1.86 Disperse Red 60 2.74 2.08-3.63 Disperse Yellow 42 1.94 1.57-2.41 Disperse Yellow 86 2.30 1.72-3.10 Basic Yellow 28 4.88 4.18-5.70 *CI: 95% confidence interval.

Figure 41. EC50 (%) values and confident intervals of SFS decolorized solution tested with Daphnia similis.

Table 16. Global harmonized system criteria for classification of a substance in acute categories

Category Acute toxicity (48 h EC50) Note Acute I £1 mg/L Very toxic to aquatic life Acute II 1-10 mg/L Toxic to aquatic life Acute III 10-100 mg/L Harmful to aquatic life

5.3.3 Parhyale hawaiensis test

Since sodium formaldehyde sulfoxylate is a salt that is largely consumed in the decolorization process, the acute toxicity of the decolorized solution to freshwater organism Daphnia similis may be attributed to the salinity of solution. Therefore, Parhyale hawaiensis testing was conducted to study the acute toxicity of the decolorized Disperse Blue 56, Disperse Orange 30 solutions and the control solution. The amphipod Parhyale hawaiensis is a small crustacean found in intertidal marine habitats worldwide, which is thought to represent a species complex119, making it a promising model organism to evaluate acute toxicity of substances with certain salinity. Results are summarized in Table 17, and Table 18 lists the physico- chemical parameters of the tests. The initial salinity of 100% solutions is around 3.5 to 4 g/kg, which is lower than the typical living salinity of Parhyale hawaiensi, 28-32 g/kg120. Therefore, at 100% concentration, a 100 % level of immobility was observed in both decolorized dye solutions and SFS control solution. In the diluted solution, for example, 1% and 10% of the

SFS control solution, salinity is controlled within 28-32 g/kg, and 30% and 40% of immobility was observed, respectively. The results show that the LC50 of the SFS control solution was calculated to be 9.0%, and decolorized Disperse Blue 56 solution is more toxic than SFS

89 control, whereas the decolorized Disperse Orange 30 is less toxic to Parhyale hawaiensi, which is compared in Figure 42. The observed toxicity is probably related to decomposed chemicals, and the reaction products of dyes and SFS alter the toxicity of the solution.

Table 17. LC50 (%) values of decolorized solutions tested with Parhyale hawaiensis.

Dye solution (%) LC50 (%) Confident interval (%) SFS 9.0 1.84-44.12 O30 11.5 3.30-40.36 B56 3.12 0.55-17.65

Table 18. Physico-chemical parameters of Parhyale hawaiensis acute toxicity test.

Parameters pH Salinity Dye Conc. (%) Initial Final Initial Final SFS 1 7.86 7.82 31.04 28.40 10 7.86 7.52 28.43 26.72 100 8.30 7.87 3.58 3.47 O30 1 7.86 7.84 30.92 30.35 10 7.96 7.49 28.25 26.64 100 6.15 8.56 3.38 3.32 B56 0.1 7.83 7.79 30.55 30.16 0.3 7.84 7.96 30.44 30.36 1 7.77 7.80 30.27 30.11 3 7.45 7.45 29.81 29.44 10 6.66 4.56 27.85 27.51 100 9.13 7.94 3.84 3.57

Figure 42. LC50 (%) values and confident intervals of SFS decolorized solutions tested with Parhyale hawaiensis.

Table 19 lists the GHS criteria for classification of a substance to the aquatic environment in acute categories. According to this classification, control solution SFS and decolorized

Disperse Blue 56 solution are in category 3, which are moderately toxic to aquatic environment, and decolorized Disperse Orange 30 is in category 4, which means relatively nontoxic, after converting the LC50 in percentage to equivalent concentration.

Table 19. Globally harmonized system criteria for classification of hazardous to the aquatic environment.

Category Acute toxicity (96 h LC50) Note Category 1 £1 mg/L Extremely toxic Category 2 1-10 mg/L Very toxic Category 3 10-100 mg/L Moderately toxic Category 4 ³100 mg/L Relatively nontoxic

5.4 Conclusion

Sodium formaldehyde sulfoxylate is a strong reducing agent that can be used to decolorize various types of commercial disperse dyes. Judging from the decolorization percentage, the reducing efficiency of SFS varies among dyes, based on their initial color and chromophore.

The acute toxicity results from Daphnia similis and Parhyale hawaiensis tests have been used only as models to extrapolate the toxicological impacts that may result from SFS decolorization of commercial dyes. The toxicity observed in the acute tests is probably related to SFS decolorization process. Reaction products of SFS and dyes may also alter the toxicity of the solutions. Converting EC50 and LC50 of SFS decolorized solution to equivalent concentration, the effluent was considered relatively harmful to Daphnia similis. Control SFS solution and decolorized Disperse Blue 56 are moderately toxic to Parhyale hawaiensis whereas decolorized Disperse Orange 30 is relatively nontoxic to Parhyale hawaiensis.

6. LIFE CYCLE ASSESSMENT OF CLOSED-LOOP RECYCLING OF PET

FABRICS

6.1 Goal and scope

Purpose An approach towards recycling colored PET fabrics into PET fibers was investigated, beginning with a new decolorization process, followed by a mechanical recycling procedure.

The primary purpose of this study was to compare the environmental impacts associated with the SFS decolorization-mechanical recycling method to the environmental impacts associated with virgin PET fiber production system.

Methods The study followed the LCA methodology that has been standardized by the

International Organization for Standardization ISO 14040 (2006). A life cycle inventory (LCI) for the virgin and recycled PET fiber production system was developed, and a contribution analysis was performed to identify the significant processes and parameters affecting impacts of interest. The emissions released by the product systems to the environment were converted into environmental impact categories using the TRACI (Tool for the Reduction and

Assessment of Chemical and Other Environmental Impacts) LCIA method, since this methodology is developed specifically for the United States using input parameters consistent with U.S. locations. The environmental impact categories chosen for the analysis were global warming, ozone depletion, acidification, eutrophication, ecotoxicity, photochemical ozone formation, human health-carcinogenics, human health-non-carcinogenics, resource depletion

– fossil fuels and respiratory effects.

Results and Discussion Within the system boundaries of this study, it was found that recycling has higher impacts on global warming potential, acidification potential, photochemical ozone formation potential, and fossil fuel resource depletion; whereas in ecotoxicity, eutrophication, ozone depletion, respiratory effects, human health carcinogenics and non-carcinogenics categories, virgin PET production has higher emissions. A sensitivity analysis based on the acetone consumption was performed, and result shows that reducing the acetone consumption led to a substantial reduction on overall impacts.

Conclusion SFS decolorization method followed by mechanical recycling process to treat the worn-out PET fabrics is a hypothetical scenario under research level. This comparative study shows that recycled PET fiber production causes lower environmental impacts than virgin PET production in six out of total ten categories. The environmental benefits of the recycling method are highly dependent on the acetone consumptions. Further work on obtaining specific data in innovative recycling processing for more reliable analysis would be beneficial.

Keywords Life cycle assessment, PET recycling, polyethylene terephthalate fabric, decolorization, environmental impact

6.2 Introduction

With the fast pace in globalization and improvements in living standards, it is becoming possible for companies to produce textile products at an increasing rate with lower prices 82.

The thermoplastic polyester PET has become the most common type among the fiber family.

According to a Textile Exchange Preferred Fiber Marketing Report, the global polyester consumption in 2015 goes up to 55% of total global mill fiber consumption, which is more than double that of cotton121. PET has high mechanical strength and low permeability to gases,

94 which means it has high resistance to atmospheric and biological agents13. It is believed that

PET-based textiles are the biggest source of microplastic pollution in the ocean122. Thus, there is a well-established recycling system to reclaim post-consumer PET bottles. The recycling processes consist of bottle collection, sorting, grinding, washing, density separation, drying, and then reconstituting the reclaimed material to textile products123. However, recycling technology of colored PET fabrics is limited, resulting in considerable amount of PET fabrics disposed of every year. According to the U.S. EPA, 85% of post-consumed textile wastes go to landfills, and only 15% are recycled mainly in terms of incineration for energy recovery124.

The large variety of colors used in fabrics are considered limiting factor in PET textile recycling, given that it challenges the sorting process and decrease the quality of recycled materials during reconstitution77. Even in the PET bottle recycling, the color consistency is also difficult to achieve, since the base color of the recycled polyester chips vary from white to creamy yellow even to green125,126. In previous study, an innovation decolorization step was developed to remove colors from textiles, therefore the decolorized fabrics can be further recycled to ideally improve the environmental sustainability. With many products or processes claiming to be or sustainable, properly implementing a Life Cycle Assessment

(LCA) practice can help to determine if those terms are used appropriately. A comparative life cycle assessment was conducted to estimate the environmental impacts associated with virgin

PET fiber production, and to evaluate the environmental impacts of a hypothetical PET fiber recovery scenario in which PET fabrics were initially decolorized by SFS decolorization method, followed by a mechanical recycling procedure. The outcomes of this study can provide support information to researchers, manufacturers and decision makers in the textile industry, and even to consumers with a strong eco-conscious.

6.3 Methodology

This study followed the LCA methodology that has been standardized by the ISO 14040127.

6.3.1 Goal and scope, functional unit and system boundary

By developing a method that is able to efficiently remove the dye inside PET fibers, it will be possible to recycle the PET fabric wastes instead of landfilling or incineration. A new decolorization method was developed that uses sodium formaldehyde sulfoxylate and solvent based medium. The purpose of this LCA study was to assess the environmental impacts of recycled PET fiber compared with virgin PET fiber, both of which were assumed to be produced in the US. The functional unit was defined as one metric ton of fiber produced as a current facility in the US.

In this study, the scenario of virgin PET fiber production system was a cradle-to-gate system.

It included the extraction of raw material feedstock, which are crude oil and natural gas in this case, production of primary PET resin, fiber manufacturing and transportation consumptions associated with the transportation between each facility122,84. In addition, the chemical synthesis of PET polymer was also considered, which is produced from ethylene glycol and dimethyl terephthalate at high temperature. In the hypothetical closed-loop recycling system, the environmental impacts were assessed from the moment when the collected textile waste enters the recycling facilities until the recycled polyester fibers are manufactured. Thus this was a gate-to-gate system. The environmental impacts associated with post-consumer textile collection and transportation to the treatment facilities were not included, because they were expected to be insignificant if in-store collection and same truck back-loading is employed128.

The chemical decolorization applied during recycling was developed by previous work, and

96 was assumed to take place in current dyeing facilities. After decolorization, the treated fabric should reach a certain level of Whiteness Index (WI), i.e. WI>70. This step not only involved the decolorization process but also included the residual and effluent treatment process.

Organic solvent used as a medium during decolorization should be collected by fractional distillation, which requires heat to run. Water phase of the solution is discharged to a wastewater treatment plant. After decolorization, mechanical recycling technology of textile substrates was assumed to be applied for fiber production based on current PET bottle recycling technology. This method is referred as the “cut-off” method, under this approach, a boundary was drawn between the initial use of the polyester fabric and subsequent recycling of the material. Therefore, the virgin products carry all virgin production burden, and the recycled products were not assigned any virgin burdens, which means there were no shared burdens.

The goal, scope, functional unit and target audience of the this LCA study have been defined and summarized in Table 20. The boundaries of the two systems have been summarized and shown in Figure 43. This research was performed using openLCA Version 1.4.2 and ecoinvent

3.2 package. The emissions released by the two product systems to the environment were converted into ten environmental impact categories using TRACI (Tool for Reduction and

Assessment of Chemical and Other Environmental Impacts) LCIA method. The TRACI method was selected for use to evaluate the results for multiple reasons. First, the assumed geographic system boundary for this study is the United States, and TRACI is specifically developed for the United States, which means TRACI methodology uses input parameters consistent with U.S. locations. Second, TRACI 2.1 converts the impact results to ten categories, therefore a more comprehensive analysis may be conducted and environmental

97 trade-offs among the categories may be analyzed129. Further, the result of TRACI scores can be normalized to person equivalent and weighted in terms of relative importance if necessary, which provides a better understanding of the environmental impacts. The ten impact categories chosen from TRACI for analysis were global warming potential, ozone depletion potential, acidification potential, eutrophication potential, ecotoxicity potential, photochemical ozone formation, human health-carcinogenics, human health-non-carcinogenics, resource depletion

– fossil fuels and respiratory effects.

Table 20. Basis of the comparative life cycle assessment study.

To quantify the environmental impacts associated with recycled PET fiber production system and virgin PET fiber Goal production system; To make a comparison of the environmental impacts of the two systems. Production of 1 metric ton of PET fiber at a current textile Functional unit facility in the US. For recycling system, the fiber should reach an acceptable level of Whiteness Index (WI>70). The recycling system covered from the generation of post- consumer PET fabric as a waste to the point that they become Scope the recycled fiber; The virgin system covered from the drilling of the crude oil to the fiber production process. Textile waste management professionals in academic, industrial Target audience and policymaking roles.

Figure 43. Cradle-to-gate system boundaries of virgin PET fiber production system (left), and recycling PET fibers from waste PET textile products (right).

6.3.2 Data collections and assumptions

The accuracy of the study is directly related to the quality of input data. PET was first patented in 1941130, and it has become the best-known synthetic material in recent years, which means the production line for the primary PET polymer and polyester fiber is quite mature. Generally, the cost-advantaged procedures of virgin PET polymer are located in the Middle East and Asia,

99 such as China and India. However, the geographic boundary based on the goal and scope of this study only covers the United States. Therefore, the virgin PET fiber produced in the US was chosen as the preference. The LCI data of virgin PET fiber is from ecoinvent v3.2 database modified by the average technology in Nan Ya Plastic Corporation and PolyQuest Incorporated.

Because PET is petroleum-based material, data about the crude oil extraction, refinery and raw materials production also should be included. In the scenario with innovative recycled PET fiber production, three types of data are employed. First, production data related with the reducing agent used in the decolorization is calculated from a similar proxy. Sodium

- + formaldehyde sulfoxylate (HOCH2SO2 Na ) has a similar molecular weight and chemical property with sodium sulfite (Na2SO3). Therefore, manufacturing data about sodium sulfite from ecoinvent v3.2 is used as a proxy in this case. Second, data from on-going research and previously published literatures47,60 are used to determine the decolorization condition in terms of chemical usage, temperature, water and electricity consumption. Last but not least, background processes and product flows are modeled in openLCA using ecoinvent v3.2. Data sets in Ecoinvent were updated as necessary by comparing with published articles. For example, amorphous polyethylene terephthalate spinning process for market was modified based on the literature84.

There is an argument among researchers regarding the waste fabric collection data. Some hold the opinion that the data is insignificant if the post-consumer textiles are collected in-store and transported by the same truck for distribution128. Others believe that worn-out polyesters collection is more complicated than that. They can be collected with other household wastes before they are sorted manually, or via textile drop-off curbside93. However, it is commonly agreed that energy consumption related to sorting, bailing and compacting is very small

100 compared to the energy requirement of the following recycling process90. In this study, we assumed that the energy requirements associated with post-consumer textile collection were negligible. Table 21 summarizes the data and assumptions used in this study.

6.3.3 Weight and normalization

In life cycle impact assessment, the life cycle inventory data, which represent all emissions released by the product system to the environment and all raw material requirements, are converted into environmental impact categories by TRACI 2.1 methodology. Normalization was used to assist in the interpretation of the LCIA results by adjusting the characterization result to common unit: dividing the LCIA result by a normalization factor of the reference area.

This reference situation could be one person’s share of all emission and resource use in the world during one year. The normalization factor used in this study is presented in Table 22.

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Table 21. Data sources for this study.

Data Source Notes Polyester decolorization Lab-scale experiments, NCSU Research level process Effluent treatment – acetone Lab-scale experiments using lab- Laboratory level recovery assembled apparatus, NCSU Effluent treatment – water Ecoinvent v3.2 Wastewater phase wastes Modified from Deep River Dyeing treated as normal Company, Randleman, NC, US textile effluent Energy and electricity Lab-scale experiments, NCSU, Scaling up consumption of recycling wet Published literatures 47,60 process Electricity, grid Ecoinvent v3.2 US-specific Road transportation Ecoinvent v3.2 3.5-7.5 metric ton lorry for road transportation,US Amorphous PET manufacture Ecoinvent v3.2 US-specific Published literatures130 Nan Ya Plastic Corporation PolyQuest Incorprated Energy use for spinning Evoinvent v3.2 US-specific process

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Table 22. Impact categories and TRACI normalization factors (US 2008) used in LCA analysis

Impact Category Normalization factor Normalized unit

Acidification 91.0 Kg SO2 eq/yr/capita Ecotoxicity 11076.0 CTUe/yr/capita Eutrophication 22.0 Kg N eq/yr/capita

Global warming 24000.0 Kg CO2 eq/yr/capita Human health – carcinogenics 5.05E-5 CTUh/yr/capita Human health – non-carcinogenics 0.001037 CTUh/yr/capita Ozone depletion 0.16 Kg CFC-11 eq/yr/capita

Photochemical ozone formation 1400.0 Kg O3 eq/yr/capita Resource depletion – fossil fuels 17000.0 MJ surplus/yr/capita Respiratory effects 24.0 Kg PM2.5 eq/yr/capita

Weighting is an optional step in life cycle impact assessment after normalization. Weighting entails multiplying the normalized results of each of the impact categories with a weighting factor that expresses the relative importance of the impact category. Thus, the weighted results have the same units and can be added up to create one score for the environmental impact of a scenario. However, each impact assessment method has its own approach for determining the weight factors. The choice of weighting factors can have a significant effect on the results and conclusions of the LCA. According to e ISO 14044, the leading standards for LCA, it has been specified that weighting should not be used for comparative assertions. In this study, therefore, weighting was not conducted.

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6.4 Closed-loop recycling of polyester fabric

Figure 44 shows the material flow of the closed-loop recycling system. The first step in this hypothetical system is raw material acquisition, which includes material collection, sorting, compacting and transportation. In this case, customers are invited to return used-up clothing to the store, therefore, the same transport lorry can be loaded to deliver the retired garments to a fiber manufacturer. Thus, the transportation is negligible in this step. By referring to used-up clothing, it means the stuff has no longer wear and life in it, which indicates the garment cannot be reused or handed-down any more. The closed-loop recycling is the final destination to produce products that have identical properties with virgin PET products. There is no existing model to accurately identify and sort returned products. After the garments arrive the collection facility, they are sorted manually for different material groups, since many commercial clothing are made from PET/non-PET blend. Buttons, zippers and snaps are also removed manually for further recycling. Overall, capital, equipment maintenance and labor are outside this study’s system boundaries. The material flow for the acquisition step is considered to be negligible. The material manufacture step, which is also known as production step, includes SFS decolorization, tap water rinsing, which are research level wet processes, and air drying, which requires zero energy. Wastewater was generated during decolorization and rinsing. Finally, the decolorized garments are assumed to be transported to a pellet plant and mechanically recycled. Then the fabric is transformed into pellets and then converted into fiber and further products.

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Figure 44. The closed-loop recycling process.

6.5 Life-cycle assessment results

6.5.1 Comparative analysis

Within the system boundaries, assumptions and methodology used in this study, the estimated environmental impacts for producing 1 metric ton of PET fiber are shown in Table 23. It can be easily calculated that recycling using post-consumer PET fabric for fiber production is

39.82% lower in exotoxicity, 57.76% lower in eutrophication, 10.78% lower in human health- carcinogenics, 44.0% lower in human health- non- carcinogenics, 76.4% lower in ozone depletion, and 16.4% lower in respiratory effects than the impacts for fiber production using

PET. However, the recycled system has a 33.4% higher acidification potential, 25.5% higher global warming potential, 34.4% higher photochemical ozone formation potential, and 50% higher fossil fuels resource depletion. Figure 45 shows the comparison of characterized impacts of different systems.

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Table 23. Normalized LCA results for producing 1 metric ton of PET fiber by virgin and recycled fiber production methods.

Impact Category Reference Unit Virgin Recycled Acidification kg SO2 eq/yr/capita 0.50405 0.67242 Ecotoxicity CTUe/yr/capita 4.0252 2.42242 Eutrophication kg N eq/yr/capita 4.60425 1.94454 Global warming kg CO2 eq/yr/capita 0.44454 0.55777 Human health - carcinogenics CTUh/yr/capita 13.36481 11.92302 Human health - non-carcinogenics CTUh/yr/capita 1.7976 1.00603 Ozone Depletion kg CFC-11 eq/yr/capita 0.00982 0.00231 Photochemical kg O3 eq/yr/capita 0.36692 0.49302 Resource depletion MJ surplus/yr/capita 1.24028 1.86057 Respiratory effects kg PM2.5 eq/yr/capita 0.69503 0.58057

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Figure 45. Comparison of environmental impacts for producing 1 metric ton of PET fiber by virgin (Black) and recycled (Red) fiber production system using TRACI method.

6.5.2 Contribution analysis

In recycled PET fiber production, there are several processes that contribute to the resource depletion – fossil fuels, among which the top three key processes are listed in Table 24: acetone production, petroleum and gas production, and hard coal mine operation. The top three key processes for virgin PET production are listed in Table 25 for comparison. Although crude oil is the raw material for making PET and its precursor, PET is not the major outcome for the oil refinery production. Therefore, the impact of resource depletion in virgin PET system is offset

107 by the generation of other useful byproducts. Acetone is an organic solvent that is only consumed in the recycled system but not in the virgin PET production. Even though an acetone recovery method was developed in previous work. Large amount of acetone is still consumed to produce 1 metric ton of PET fiber due to the limitation of recovery efficiency. Similarly, global warming potential, photochemical ozone formation and acidification potential impacts are also mainly attributed to acetone production. Therefore, decolorized and recycled PET fiber production system produces higher emissions in those categories.

Table 24. Processes contributing to acidification potential in recycled PET fiber production

Contribution Process Amount Unit 90.17% Acetone production, liquid | acetone liquid | 28518.6 MJ surplus conseq. long-term, U -Row 3.1% Petroleum and gas production, on-shore | 982.6 MJ surplus petroleum | conseq. long-term, US 1.08% Hard coal mine operation | hard coal | 246.3 MJ surplus conseq. long-term, U-RME

Table 25. Processes contributing to acidification potential in virgin PET fiber production

Contribution Process Amount Unit 34.82% Petroleum and gas production, on-shore | 7339.6 MJ surplus petroleum | conseq. long-term, US 21.8% Xylene production | xylene | conseq. long- 4595.5 MJ surplus term, US 5.99% Ethylene production, average | ethylene, 1262.9 MJ surplus average | conseq. long-term, U-RoW

Particulate matter, which is a collection of small particles in ambient air, is the key source for respiratory effects. In the two systems, particulate matter (PM<2.5 µm) is mainly generated from electricity production, and dust particles from roads and fields during transportation. Due

108 to the geographical boundary, both systems have comparable electricity and transportation consumptions. For this reason, the difference of the respiratory effect between the two systems is not significant. The most significant difference occurs between the ozone depletion impacts of the two production systems. The primary emissions accounting for the ozone depletion effects are methane and ethane, which are heavily released during the petroleum and gas production. These processes are avoided in the recycled system. Thus, the impact is substantially reduced in this category through recycling.

Wastewater treatment, which is either generated by oil refinery in virgin PET system or textile wet processing in recycled PET system, contributes significantly to ecotoxicity, eutrophication, human health-carcinogenics, and human health-non-carcinogenics. Water consumption is oil refineries is huge and so is the wastewater generation. The major contaminants in wastewater from oil refinery are petroleum hydrocarbons, ammonia, and organic sulfur131. Wastewater in recycled system is mainly from decolorization process and other cleaning processes. Contaminants are mainly nitrogen contained degraded dye compounds, inorganic salts, organic surfactants, and uncovered acetone. However, the emissions from textile wastes seem friendlier than those from oil refinery wastes. Therefore, the virgin PET production system has higher impacts in these four categories than the recycled system.

Among those processes mentioned above for contribution analysis, a lot of them were not created with the system boundary; however they were drawn from EcoInvent as the upstream or downstream components of the created processes. This is reasonable; for example, since acetone is an essential input material in PET fabric decolorization, acetone production as the

109 upstream process should not be neglected. For the same reason, treatment of wastewater, which is the downstream process of oil refinery and decolorization, should also be analyzed in this study.

6.6 Sensitivity and uncertainty analysis

Through contribution analysis, it can be concluded that acetone production is a key process contributes to several impact categories in the recycled PET system. Sensitivity of acetone consumption was conducted to demonstrate how impacts can change with variation in parameter. Acetone was reduced to 10% of the baseline value, and its sensitivity to resource depletion – fossil fuel, acidification, global warming potential and photochemical ozone formation is presented in Figure 46. The emission associated with acetone production was reduced. Consequently, the overall impact of the recycling system decreases. In resource depletion – fossil fuel category, for example, the impact reduced 82.0% compared with previous recycled system, and reduced 73% compared with the virgin system. The impacts in acidification, global warming, and photochemical ozone formation, decreased 51.8%, 51.4% and 53.1% respectively, compared with the baseline acetone consumption system. It can be concluded that the overall impact is substantially sensitive to the acetone consumption.

Therefore, an optimum acetone recovery method should be developed to increase the recovery rate, to reduce the acetone loss in each decolorization application. Further, a more efficient and environmental responsible acetone production method should be developed to reduce the emission.

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Figure 46. Sensitivity of the acetone consumption to acidification, global warming, photochemical ozone formation, and resource depletion.

There are several uncertainties in this study. In the closed-loop recycled PET system, the upstream process of the crucial chemical SFS is unavailable in the EcoInvent database. It was replaced by other common chemical (sodium sulfite), which has a similar molecular weight and structure as SFS. Such substitution may be inaccurate and cause uncertainty in impact analysis. In addition, material flow associated with post-consumer fabric collection was considered negligible in this study. In pactice, worn-out fabric collection is not well established, and the collection rate is highly depended on public behavior. Simply neglecting

111 this process may cause uncertainties as well. The closed-loop recycling system using a mechanical method to re-process the PET fabric is only a hypothetical scenario, not employed in reality yet. Decolorization step is under search level, and fiber re-processing after decolorization treatment is assumed from literatures/patents involving PET bottle recycling process. PET bottles are capable of turning into PET flakes/chips, which can be easily extruded to fibers. However, PET fabrics are not suitable for extrusion based on current technology. In addition, PET fabric contains certain levels of chlorine, sulfur, and heavy metals, which may lead to the difficulty in extrusion75. Therefore, the differences between bottle and fabric recycling process will cause uncertainty of the results.

6.7 Conclusion

In this study, a comparative life cycle assessment was conducted to assess the environmental impacts of virgin PET fiber production process from crude oil and closed-loop fabric-to-fiber recycling process. Recycled PET production has less environmental impacts than virgin system in six categories, but also shows higher impact results in four other categories.

Sensitivity analysis shows that overall impact is sensitive to acetone consumption. When acetone was reduced to 10% of the baseline consumption, environmental impacts are lower in every category than the virgin PET production. However, based on current data and research level, it cannot be concluded directly whether PET fabric-to-fiber recycling offers important environmental benefits over single-use virgin PET fiber or not. Further work to obtain data associated with the production of SFS and collection/transportation of PET fabric wastes would be beneficial to increasing the accuracy of further LCA studies.

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7. COMMERCIAL BLACK DYE COMPOSITION AND THEIR

DECOLORIZATION PROPERTIES ON POLYESTER FABRIC

7.1 Introduction

Textile dyes are colored organic substances that have affinity for fibers and are able to absorb certain wavelengths of visible light. Due to the hydrophobicity of polyethylene terephthalate

(PET) fiber, PET has limited affinity towards water-soluble dyes. Hence polyester requires the use of disperse dyes, which are non-ionic chemicals with sparingly low solubility in water.

Disperse dyes have been available for almost 95 years132. Originally introduced for the coloration of cellulose acetate, now they are mostly used for dyeing polyesters17. The only exception is the use of basic dyes to dye the cationic dyeable polyester14, which accounts for a small percentage of the polyester market. With different combination of chromophores and auxochromes, disperse dyes are capable of giving broad range of colors to polyesters19.

According to AATCC Buyer’s Guide133, the majority of disperse dyes, which are produced under more than 200 Color Index names, are blues, ca. 30%; reds, ca. 25% and yellows, ca.

20%. Oranges and violets both account for ca. 8% and browns account for ca. 3%. By mixing different dyes, it is possible to create more colors and achieve certain technical properties.

Black is the darkest color and maybe one of the most popular colors in the leisure wear space.

It can be obtained from a single dye, such as Disperse Black 9, which is actually a brownish color but becomes black after it has been diazotized and developed134, as shown in Figure 47.

Black disperse dyes, which are readily available, are usually mixtures of three components: a blue, a red or rubine and a yellow or orange20. However, the composition of components in the commercial fabric was not disclosed135

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Figure 47. Disperse Black 9 formation inside textiles.

With an increasing application of polyesters, closed loop recycling of textiles derived from polyester fibers becomes a new topic for the purpose of sustainability, which offers benefits such as reducing wastes in landfills and increasing supply chain for recycled PET (rPETe).

Efficient color removal has been recognized as a crucial step toward recycling, since dyed products highly limit the recycling process. Upon coloring polyesters, disperse dyes are dissolved in fiber matrix, which are considered highly stable. An effective decolorization method has been developed using sodium formaldehyde sulfoxylate (SFS) as the reducing agent, acetone/water as the medium to efficiently decolorize disperse dyes from polyester fabrics.

Azo and anthraquinone dyes account for a significant portion of commercial disperse dyes134.

Many studies have been conducted to characterize those dyes using microspectrophotometry,

UV-visible spectroscopy (UV-Vis), thin layer chromatography (TLC), flash column chromatography, high performance liquid chromatography – mass spectrometry (LC-MS),

Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy

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(NMR)136–141. Detection and characterization of commercial dyes with unknown source is becoming increasing important, which provides significant information not only to the textile industry and environmental protection142, but also to forensic science143 and even antiquarian research144. In the present study, the nature of dyes from commercial black fabric was investigated. Major dye components in the commercial black fabric were separated by TLC and flash column chromatography. Each component was identified using UV-Vis, LC-MS and NMR.

The decolorization property of each component in solution was investigated by SFS reduction, and decolorization result was characterized by UV-Vis spectra. The SFS decolorization method was employed to treat the post-consumer polyester black fabric. Decolorization of the fabric was characterized by the reduction of color strength (K/S) values.

7.2 Experimental

7.2.1 Materials

Commercial black knit fabrics were kindly donated by Nike, Inc. (Beaverton, OR, USA).

Sodium formaldehyde sulfoxylate (SFS) was purchased from Arcos Organics. Acetone (ACS grade), dimethylformamide (DMF, HPLC grade), and chloroform (HPLC grade), were obtained from Fisher Scientific. CDCl3 purchased from Cambridge Isotope Laboratory Inc. was used in NMR analysis. The reagents acetic acid, nitrosyl sulphuric acid and potassium carbonate, and dye precursors were sourced from Sigma Aldrich. All chemicals and solvents were used directly without further purification.

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7.2.2 Decolorization of commercial black fabrics

Black knit fabric was cut into 1g square pieces. Water and acetone, mixed at the ratio of 1:2, was used as the medium for decolorization. Reducing agent SFS (0.5 g) was dissolved in the water/acetone media (50 mL), 1 g of cut fabric was added to the bath. In laboratory dyeing machine (Ahiba Spectradye Plus), the sealed bath was heated to 100°C at the ramp rate of

4°C/min and held for 30 min. The bath was cooled, and the fabric was removed, rinsed with room temperature water for 2 min, and allowed to air-dry.

7.2.3 Fabric color evaluation

Color strength and Whiteness Index were measured on a calibrated Datacolor Spectraflash

600X Reflectance Spectrophotometer equipped with iMatch software from X-Rite. The software was set to use illuminant D65 with the UV light included, and the CIE 10-degree supplemental standard observer. The sample being tested was folded twice and measured two times by rotating the sample at 90 degrees between measurements. The average value was recorded. The K/S value of each sample was calculated by adding the K/S value of each 10 nm from 400 nm to 700 nm as follows:

��(�/�) = (�/�)

7.2.4 Chemical analysis

Before chromatographic analysis, disperse dyes were extracted from 2 g of commercial black knit fabric using 40 mL of DMF/water (v/v: 50/50) in a sealed beaker. The solvent was heated to 100 °C and held for 15 min. A Buchi R-210 Rotavapor with V-850 vacuum controller and

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F-105 Recirculating Chiller (Buchi, Switzerland) was used to dry the extracts, and 0.1227 g of black dye mixture was obtained.

Preparative thick layer chromatography was employed to separate the colored components in the black mixture, using 19 chloroform/1 acetone as the mobile phase and silica gel 60 as the stationary phase. Four fractions were observed from top to bottom on the thick layer plate: an orange, a dark blue, a red and a light blue, with Rf values 0.90, 0.70, 0.47, and 0.17, respectively.

High performance liquid chromatography analyses were conducted in a Waters 2695

Separations Module apparatus coupled with a Waters 2996 photodiode array detector. The chromatograms were investigated within visible range. HPLC analysis was performed on a reversed-phase column XBridge C18 (4.6 × 150 nm). A mobile phase acetonitrile/water 75:25

(v/v), flow rate 0.8 mL/min, and analysis time 8 min were used as the isocratic method.

A flash column was developed using silica gel 60 A, and same mobile phase used in TLC was used to isolate the dyes. Solutions of each fraction were rotatory evaporated. The extracts were then kept in open beakers at room temperature (22-24 °C) prior to use in further experiments.

Agilent Technologies 1260 liquid chromatography coupled to an Agilent Technologies 6520

Quadrupole-Time-of-Flight (Q-TOF) mass spectrometry with an electrospray ionization (ESI) source was used to analyze the four components. Ionization was carried out in positive ionization mode. The LC eluent used was 30% water and 70% acetonitrile. The flow rate was

0.5 mL/min, the total run time was 5 min, and the equilibration time between each sample was

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1 min. MS conditions were: gas temperature: 350 °C; Drying gas flow: 10L/min; nebulizer pressure: 30 psig; capillary voltage: 3500 V; and Fragmentor voltage: 175V.

NMR spectra were recorded on a Varian Inova 400 MHz NMR spectrometer (H at 700 MHz) in solvent CDCl3 solutions.

7.2.5 Preparation of disperse dyes

7.2.5.1 Synthesis of orange dye

Nitrosyl sulfuric acid (3.5 g 40%) was cooled below 20°C, and 2.07 g 2,6-dichloro-4- nitroaniline (0.01 mol) was added. The mixture was stirred at 5-10°C for 2 h. Then 25 g ice,

20 ml water and 5 ml acetic acid were added. N,N-bis(2-acetoxyethyl)aniline (0.0105 mol,

2.78g) was added slowly to the resulting mixture, while maintaining the temperature below

5°C. After stirring the coupling reaction overnight, the mixture was neutralized to pH=7.0 with caustic soda (0.15 ml, 40%), heated to 90°C and held for 1 h. The dye was filtered and

1 washed with tap water. H NMR (500 MHz, CDCl3): δ 8.15 (s, 2H), 7.80 (d, J = 8.8 Hz, 2H),

6.77 (d, J = 8.9 Hz, 2H), 4.20 (d, J = 5.8 Hz, 4H), 3.75 (d, J = 5.7 Hz, 4H), 1.97 (s, 6H).

7.2.5.2 Synthesis of blue dye

Nitrosyl sulfuric acid (3.5 g 40%) was cooled below 20°C, and 1.89 g 3,5-dinitro-2- thiophenamine (0.01 mol) was added to the solution. The diazonium mixture was stirred at 5-

10°C for 1.5-2 h, and then added to a solution of N,N-bis(2-acetoxyethyl)aniline (0.0105 mol,

2.78g) in 20 g ice, 15 ml water and 8 ml acetic acid. The mixture was stirred overnight and then neutralized to pH=7.0 with caustic soda (0.15 ml, 40%), heated to 90°C and held for 30

1 min. The dye was filtered and washed using tap water. H NMR (500 MHz, CDCl3): δ 8.33

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(s, 1H), 7.93 (d, J = 9.1 Hz, 2H), 6.87 (d, J = 8.9 Hz, 2H), 4.29 (t, J = 6.0 Hz, 4H), 3.78 (t, J =

6.1 Hz, 4H), 2.01 (s, 6H).

7.2.5.3 Synthesis of red dye

3-Amino-N-acetylaniline (0.55g, 0.0037 mol) was dissolved in 15 ml of toluene at room temperature. Methyl chloroacetate (1 g, 0.0092 mol) and potassium carbonate (1.38 g, 0.01 mol) were added to the solution. Then the mixture was heated under reflux for 48 h with stirring. The resultant mixture was filtered and washed using tap water. After air drying, yellow compound Y was obtained. 2-Cyano-4-nitroaniline (0.54 g) was added to 1.18 g nitrosyl sulfuric acid at temperature below 20°C. Following the addition of 5 ml acetic acid, the amine was diazotized for 2-3 h at 0-5°C. Yellow compound Y was added to the diazonium solution with 5 ml water and 5 g ice over a period of 0.5 h. The liquor was stirred overnight to complete the coupling and was then adjusted by caustic soda (0.03 ml, 40%) to neutral pH and heated to 90°C for 1 h. The separated dye was filtered, washed and allowed to air dry.

Scheme 1. Synthetization of compound Y.

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7.2.6 Decolorization of commercial dye solutions

Solutions (100mg/L) of each commercial black dye component were prepared using 1 water/

2 acetone media. Each solution (50 mL) was mixed with SFS (0.5 g) in a sealed beaker. The temperature of the solution was raised to 100˚C and held for 30 min. The solution was cooled down in water bath and measured under UV-Vis spectrometer.

7.3 Results and discussion

7.3.1 Analytical results

After DMF/water extraction of 4 g commercial black fabric, 0.1227 g of dye was obtained.

Then the depth of shade in terms of on weight of fabric (%o.w.f.) was calculated to be at least

%�. �. �. = . × 100% = 3.16%, . which is within the typical range of 3% to 6%, for intensely colored black145. Thin layer chromatography was employed to examine the composition of the dye mixture. Four components were observed, including an orange, a red and two blues (one weak), as shown in

Figure 48. However, the Blue2 dye has very low intensity.

Flash column chromatography was used isolate larger amount of dyes with the mobile phase chloroform/acetone (19/1, v/v). The same four components were collected, and UV-Vis spectra were recorded. The maximum absorption wavelength (λmax) of Orange, Blue1, Red and Blue2 were 420, 598, 515, and 615 nm, respectively. It can be seen that the Blue2 has a higher λmax than Blue1, which means even though Blue2 looks lighter in TLC plate than

Blue1 but it is more bathochromic than Blue1.

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Orange Blue1

Red

Blue2

Figure 48. TLC analysis of black fabric extract using chloroform: acetone (19:1).

420 598

515 615

Figure 49. UV-vis spectra of orange, blue1, red and blue2 fractions in chloroform/acetone (19/1, v/v) obtained by UV-vis spectroscopy.

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A high performance chromatographic separation was obtained for the sample extracted from commercial fabric, which is presented in Figure 50. According to the preliminary TLC result, as can be expected, four peaks were identified based on the retention time. Characteristic UV- vis spectra obtained by the photodiode array detection are reported in Figure 51, which were compared with the UV-Vis spectra of the pure sample of each component, and then afterwards were used to identify the each species. The result confirms that the black color is a mixture of four disperse dyes. The sample tested in HPLC was dissolved in water/acetone (1/2, v/v) medium, therefore the maximum absorption wavelength of each peak differs with that in chloroform/acetone (19/1, v/v) medium. Comparing the UV-Vis spectra, it can be established that peak 1 at retention time 3.173 is the Red dye, peak 2 at RT 3.387 is the Blue2, peak 2 at

RT 4.131 is the Blue1, and peak 4 at RT 5.481 is the Orange dye. Table 26 lists the peak area percentages, which were used to analyze the percentage of each compound among the detectable samples. In the detection wavelength of 515 nm, four peaks of compounds were found. Among them, the Blue2 dye, which is corresponded to peak 2, accounts for 4.84 % of total detectable constituents.

The amount of Blue2 collected in flash column chromatography was not sufficient for NMR analysis. Since Blue2 dye has low composition in the black sample, this dye was not further analyzed.

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Figure 50. Chromatographic separation of the sample extracted from commercial black fabric at 515 nm.

Table 26. Retention time, area, and percentage area of peaks

Peak # RT Area % Area Assigned dye 1 3.173 128975 15.31 Red 2 3.387 40820 4.84 Blue2 3 4.131 490887 58.26 Blue1 4 5.481 191870 21.59 Orange

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Figure 51. UV-vis spectra obtained by photodiode array detection of peak 1 obtained at 3.167 min, peak 2 at 3.383 min, peak 3 at 4.133 min, and peak 4 at 5.483 min.

Orange, Blue1, and Red dyes were characterized in LC-MS and 1H-NMR. They were considered the major components of the black color, because black is invariably a mixture of appropriate proportions of blue, red and yellow or orange.

In the LC-MS results, signals due to dyes were recognized by their absorption of visible light

(DAD spectrum), and the corresponding mass spectra were selected on the basis of the retention time. A molecular formula prediction tool (mMass, version 5.5) was used to find the chemical formula corresponding to a given mass. Among all candidates generated by the tool,

124 the most plausible formula was selected based on the general knowledge of disperse dyes. In this work, the molecular compositions of the Orange, Blue1 and Red dyes were judged to be

C20H20Cl2N4O6, C18H19N5O8S, and C21H20N6O7, respectively. The chemical structures were discenned by searching within public databases, such as the Colour Index, patents and literatures. Dyes that were not in the databases required a more advanced search. This search was based on mass and chemical formula of the dye and comparison of mass and formula to dyes in the database. This step was helpful as certain differences led to potential structures.

For example, if the chemical formula difference was C2H2O, it was deemed likely to correspond to conversion of –OH and –OCOCH3, which is often seen in the pendant chain of the coupling component of azo dyes to improve the fastness properties. Combining information from databases and derived molecular composition, structures of the three major components from disperse black fabric have been identified. Their chemical structures are listed in Table 27, and high resolution mass spectra of the isolated colored components are presented in Figure 52. The orange dye was identified to be ethanol, 2,2'-[[4-[2-(2,6-dichloro-

4-nitrophenyl)diazenyl]phenyl]imino]bis-, 1,1'-diacetate, which is registered as C.I. Disperse

Orange 78. This is not a high volume commercial dye but has been found in several patents146–

149. This dye has been found as an important component in black dye mixture in dyeing of hydrophobic materials, such as automobile seats148, with good light fastness, good luster, good abrasion fastness, wash fastness, and sublimation fastness147. The Blue1 was identified as a monoazo heterocyclic dye synthesized from a thiophene diazo component. This dye was initially reported by Choi, et al in 1999 in the search for colorants of high fastness and reduced environmental impact150. Later it was used for dyeing and printing of hydrophobic materials, such as polyester and spandex151,152. It was also found in several patents to produce black or

125 navy blue composite with advantages of high dye uptake, large dyeing depth, and good level dyeability153–156. The Red dye was found very popular in China as a dye product having excellent color fastness for hydrophobic fabrics. This Red dye is an essential compounds found in Chinese 72 patents to produce disperse dye commercial composite157–159.

Each mass spectrum contained M+H, M+Na, and M+K peaks that corresponded to the exact mass of the possible dye. In addition, unknown signals of other compounds were contained in the mass spectra. They may be background ions as present in the matrix, or chemicals other than dyes extracted from commercial fabrics, which however are considered irrelevant to the mass peaks caused by the dyes of interest.

Table 27. Identification of disperse dyes in black fabric extract.

Dye Observed Chemical Chemical Structure Erro exact mass formula r (M+H) ppm Orange, 483.0828 C20H20Cl2N4O6 1.56 Rf=0.9

Blue, 466.1016 C18H19N5O8S 2.2 Rf=0.7

Red, 469.1459 C21H20N6O7 1.79 Rf=0.47

126

Figure 52. High resolution mass spectra and proposed structures characterizing commercial black dye components (Orange, Blue, and Red Dye).

127

Figure 52 (continued).

The three dyes were structurally characterized by proton NMR. Results are shown in Table 28.

The signals appeared in the region of 6.69-8.66 δ ppm are assigned to the protons of the aromatic rings. Due to the difference of electron negativity of substituent groups, the chemical shift varied in different positions. The 1H-NMR signals were in accordance with the proposed structures of the dyes.

128

Table 28. H-NMR spectral results of the Orange, Blue1 and Red dyes.

Dye 1H-NMR (δ, ppm) Aromatic H Aliphatic H N-H Solvent

Orange 8.41 (2H, s), 7.96 (2H, d), 4.29 (4H, t), 3.85 (4H, t), CDCl3 6.82 (2H, d) 1.58 (6H, s)

Blue1 8.41 (1H, s), 7.99 (2H, d), 4.42 (4H, t), 3.91 (4H, t), CDCl3 6.94 (2H, d) 2.06 (6H, s)

Red 8.66 (1H, s), 8.50 (1H, d), 4.58 (4H, s), 3.90 (3H, s), 9.79 (1H, s) CDCl3 8.07 (1H, d), 7.90 (1H, d), 2.06 (3H, s) 7.17 (1H, s), 6.69 (1H, d) Abbreviations: s=singlet; d=doublet; t=triplet

7.3.2 Comparison with synthesized disperse dyes

The three dyes extracted from black fabric were identified by modern analytical techniques. It was deemed worthwhile to compare them with synthesized dyes to validate the proposed structures. The structure of synthesized orange and blue dyes were confirmed by 1H-NMR and

LC-MS. Figure 53 and Figure 54 show the LC-MS spectra of synthesized dyes, in which the peak corresponding to [orange dye + H] was found as 483.0824, and the [blue dye + H] peak was 466.1013, which are very close to the peaks found from the extracted orange and blue samples, 483.0828 and 466.1016 respectively. In a TLC plate shown in Figure 55, it can be seen that the orange and blue dyes from commercial extraction have identical Rf values with synthesized orange and blue disperse dyes.

However, the synthesis of red dye was not possible due to the lack of the required coupling component.

129

Figure 53. High-resolution mass spectrum of synthesized orange disperse dye.

Figure 54. High-resolution mass spectrum of synthesized blue disperse dye.

130

Figure 55. TLC chromatogram comparison of A: black fabric extraction; B: synthesized orange disperse dye; and C: synthesized blue disperse dye using hexane/ethyl acetate (1/20).

7.3.2 Decolorization results

Commercial black fabrics were decolorized using SFS reduction method, and color strength

(K/S) values were measured in order to characterize the color differences. Whiteness Index of the decolorized fabric was also recorded. The efficiency of SFS decolorization method is illustrated in Table 29 and Figure 56, by low K/S values after treatment and acceptable

Whiteness Index. Color strength was substantially reduced after decolorization, and the fabric became almost white. High whiteness of decolorized fabric is of extreme importance for further recycling, since color uniformity and color matching in re-dyeing are best achieved when the base fabric has high whiteness.

131

Table 29. K/S values and WI of commercial black fabrics before and after SFS (10g/L) treatment in acetone/water (2:1) at 100°C.

Black fabric Before decolorization After decolorization K/S value 262.16 2.04 Whiteness Index N/A 68.9

Before After

Figure 56. Commercial black fabric before and after SFS (10g/L) treatment in water/acetone (1:2) at 100 ˚C for 30 min.

Decolorization of dye solution and decolorization of colored fabric may have different outcomes. Therefore, the same SFS reduction method was employed to examine the decolorization performance of commercial dye solutions, and the real-time color change of the solution was monitored by UV-Vis spectroscopy. Black dye mixture extracts were dissolved in water/acetone (1/2, v/v) solvent. As time progressed, the color of the solution changed gradually, and only after 10 min, the color disappeared completely (C in Figure 57). It can be concluded that the decolorization of dye solution is faster than the decolorization of fabric,

132 which is probably due to the accessibility of the reducing agent to the dyes. Dyes in the solution are readily accessed by SFS, but dyes inside the fiber have to be transferred from the fabric to the solution, which takes longer. Figure 58 shows the UV-Vis spectra of the dye solution after various treatment time. The black color of the solution at 0 min was not the result of complete absorption of visible light. Instead, it absorbed a pair of opposite colors, which have the absorption peaks at 436 and 625 nm, to produce the black. The absorption wavelength of the sample at 625 nm disappeared immediately after 5 min treatment, and only one peak was observed at 432 nm. Therefore the color of the sample is considered having a significant hypsochromic shift. The maximum absorbance at 432 nm also disappeared after

10 min. This means all the chromophores of the dyes have been reduced by SFS treatment in water/acetone aqueous phase. However, the absorbance was still non-zero as treatment time increased further. The solution became almost colorless, but it was not transparent.

Results from decolorization on black fabric and black dye solution draw a promising conclusion that commercial black dye, which is a mixture of orange, red and blue, can be completely decolorized by SFS reduction method in aqueous media. Therefore, the decolorized fabric can be recycled and re-dyed in the closed-loop recycling procedures. At the same time,

SFS decolorization method offers a potential approach to treating wastewater generated by the

Orange, Blue1 and Red dyes for efficient color removal.

133

A B C D

Figure 57. Commercial disperse dye solution from SFS (10g/L) treatment in water/acetone (1/2) at 100 ˚C in different treatment times: A=0 min, B=5 min, C= 10 min and D=15 min.

Figure 58. Absorption spectra changes during the SFS decolorization ([SFS] =10g/L, water/acetone space=1/2, 100 ˚C) of black dye mixture solution.

134

7.4 Conclusion

In this study, disperse dyes were extracted from post-consumer polyester fabrics using

DMF/water (50/50, v/v). The extracted mixture was separated into four components, including an orange, a red and two blue dye. The Orange, Blue1 and Red dyes were characterized as the major components in that black mixture, and analyzed by UV-Vis, HPLC, LC-ESI-MS, and H-NMR. The Orange dye was identified as C.I. Disperse Orange 78; Blue1 dye is ethanol,

2,2'-[[4-[2-(3,5-dinitro-2-thienyl)diazenyl]phenyl]imino]bis-, 1,1'-diacetate; and Red dye is glycine, N-[3-(acetylamino)-4-[2-(2-cyano-4-nitrophenyl)diazenyl]phenyl]-N-(2-methoxy-2- oxoethyl)-, methyl ester. The results from black polyester fabric and disperse dye solution decolorization suggest that these dyes can be successfully decolorized by SFS reduction method. The decolorized fabric achieves acceptable Whiteness Index and low color strength

(K/S), which provides a promising approach to the closed-loop recycling of polyester fabric.

The decolorized solution became almost colorless, which means this method can be potentially used in wastewater treatments.

135

8. FUTURE WORK

In a closed-loop recycling of polyesters, the recycled material should be competitive with virgin polyester fabric in all terms. In the life cycle assessment, a hypothetical scenario was analyzed in which decolorized fabric was mechanically processed to polyester fiber as used for PET bottle recycling. Microscopic and Scanning Electron Microscopic (SEM) pictures of decolorized fabric were recorded, which are shown in Figure 59 and Figure 60. The SFS chemical treatment has no significant effect on the fiber integrity. There are particles attached on the fiber surface. Decolorization of dyes by SFS method occurs not only on the surface of the fiber but also inside the fiber. Other than these features, it would be beneficial to study the recyclability of the decolorized fabric to confirm that if it can be successfully re-processed to fibers. It would also increase the utility of future LCA analysis.

136

Figure 59. SEM pictures of SFS decolorized polyester fabrics.

137

Figure 60. Microscopic pictures of (a) blue fiber and (b) decolorized blue fiber.

To promote the closed-looped recycling of polyester fabric, scaling up the lab experiment to larger scales would be necessary.

138

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10. APPENDIX

158

1H-NMR spectra of synthesized orange disperse dye and synthesized blue disperse dye are shown in Figure 61 and Figure 62.

Figure 61. Full 1H-NMR spectrum of synthesized orange disperse dye.

1H NMR (500 MHz, ) δ 8.15 (s, 2H), 7.80 (d, J = 8.8 Hz, 2H), 6.77 (d, J = 8.9 Hz, 2H), 4.20 (d, J = 5.8 Hz, 4H), 3.75 (d, J = 5.7 Hz, 4H), 1.97 (s, 6H).

159

Figure 62. Full 1H-NMR spectrum of synthesized blue disperse dye.

1H NMR (500 MHz, ) δ 8.33 (s, 1H), 7.93 (d, J = 9.1 Hz, 2H), 6.87 (d, J = 8.9 Hz, 2H), 4.29 (t, J = 6.0 Hz, 4H), 3.78 (t, J = 6.1 Hz, 4H), 2.01 (s, 6H).