Management of PET Plastic Bottles Waste Through Recycling in Khartoum State

Home , Bottle recycling, PET bottle recycling, Plastic bottle

Sudan Academy of Science

Engineering Research And Industrial Technology Council

Management of PET Plastic Bottles Waste Through Recycling In Khartoum State

A Thesis submitted in partial fulfillment of the requirement for the degree of Master of Science in Cleaner Production

By: Nabeel Bedawi Ismail Fadlalla B.Sc(hon),chem.. Eng-U of K. 1975

Supervisor : Dr.Kamal Eldin Eltayb Yassin October 2010 Acknowledgement

I would like to express my gratitude to my friend and supervisor Dr. Kamal Eldin Eltayeb Yassin, who encouraged me to undertake this study. This study could not have been successful without the valuable input of the various stakeholders. I would like to thank them all for sparing their valuable time to participate in the meetings and interviews. I would like to appreciate the efforts of my friends Awad Eltom and Mohamed Yahia in providing me with the need contacts and access to Sudan Bank and Customs Authorities. A special thanks to my family my parents and wife for their encouragement and thanks also extended to my sons Mohamed and Ahmed for their assistance. Abstract

Abstract

This study has been carried out to assess the general waste management in Khartoum State and effectively manage the PET plastic bottles by identifying practical means and introducing recycling as cleaner production tool to achieve sustainable development goals.

The information/ data were gathered during the period June - July 2010 through questionnaires, interviews, meetings and visits to various sites, in addition to the official information and documents collected from reliable sources, mainly Sudan Central Bank, Customs Authorities, Ministry of Industry, soft drink and water bottling factories.

The data were presented in tables, graphs and charts by applying Windows Excel Program and also applying Eview Package for the future forecast. Analysis of data shows a rising consumption in PET bottles and the forecasted PET consumption in year 2015 estimated to be 60000Tons, twice the estimate in the year 2010. This situation will create serious environmental problems that require much more effort to be exerted by all stakeholders to look for scientific and practical solutions for the disposal of plastic waste through recycling.

Based on the analysis and findings recommendations have been made that ensure on recycling of PET plastic bottles by mechanical method that depends mainly on collection, segregation, cleaning and processing. Further studies and researches on other recycling methods have been recommended in the future.

II Arabic Abstract

ﻣ ﺴﺘ ﺨﻠ ﺼ ﻦ

ﺗﻬﺪ ف ﻫﺬه اﻟﺪرا ﺳﺔ إﻟ ﻰ اﻗﺘﺮا ح آﻟﻴﺔ ﻳﻤﻜﻦ ﺑﻬﺎ إدارة اﻟﻨﻔﺎﻳﺎ ت اﻟﺒ ال ﺳﺘﻴﻜﻴﺔ ﺑﻮ الﻳﺔ اﻟﺨﺮﻃﻮم

وﺑﺸﻜﻞ أﺧ ﺺ ﻋﺒﻮا ت T J 'PE اﻟﺒ ال ﺳﺘﻴﻜﻴﺔ ودرا ﺳﺔ إﻣﻜﺎﻧﻴﺔ إ ﻋﺎدة ﺗﺪوﻳ ﺮﻫﺎ ﻛﻮ ﺳﻴﻠﺔ ﻣﻦ وﺳﺎﺋﻞ

ا إلﻧﺘﺎ ج ا ألﻧ ﻈ ﻒ ﺣ ﻤﺎﻳ ﺔ ﻟﻠﺒﻴﺌ ﺔ و ﺗ ﺤﻘﻴ ﻘﺎ ال ﻫ ﺪا ف اﻟﺘﻨ ﻤﻴ ﺔ اﻟ ﻤ ﺴﺘ ﺪا ﻣ ﺔ.

ﺗ ﻢ ﺟ ﻤ ﻊ اﻟﺒﻴﺎﻧﺎ ت و اﻟ ﻤ ﻌﻠ ﻮ ﻣﺎ ت اﻟ ﺨﺎ ﺻ ﺔ ﺑ ﻬ ﺬ ه اﻟ ﺪ را ﺳ ﺔ ﻋ ﻦ ﻃ ﺮﻳ ﻖ ا إل ﺳﺘﺒﻴﺎﻧﺎ ت و

اﻟ ﻤﻘﺎﺑ ال ت اﻟ ﺸ ﺨ ﺼﻴ ﺔ وا إل ﺟﺘ ﻤﺎ ﻋﺎ ت واﻟ ﺰﻳﺎ را ت ﻟﻠ ﻤ ﻮاﻗ ﻊ اﻟ ﻤ ﺨﺘﻠﻔ ﺔ ﺑﺎ ال ﺿﺎﻓ ﺔ اﻟ ﻰ اﻟ ﻤ ﻌﻠ ﻮ ﻣﺎ ت و اﻟ ﻮﺋﺎﺋ ﻖ

اﻟ ﺮ ﺳ ﻤﻴ ﺔ اﻟ ﺼﺎ د ر ة ﻋ ﻦ ﻋ ﺪة ﺟ ﻬﺎ ت ﻣ ﺮ ﺟ ﻌﻴ ﺔ أ ﻫ ﻤ ﻬﺎ ﺑﻨ ﻚ اﻟ ﺴ ﻮ دا ن اﻟ ﻤ ﺮ ﻛ ﺰ ى وا إل دا ر ة اﻟ ﻌﺎ ﻣ ﺔ ﻟﻠ ﺠ ﻤﺎ ر ك

و و زا رﺗ ﻰ ا ﻟ ﻤ ﻨ ﺎ ﻋ ﺔ و ا إل ﺳﺘﺜ ﻤﺎ ر و ﺷ ﺮ ﻛ ﺔ ﻧ ﻈﺎﻓ ﺔ و الﻳ ﺔ اﻟ ﺨ ﺮ ﻃ ﻮ م و ﻣ ﺤﻠﻴﺎﺗ ﻬﺎ و ﻣ ﺼﺎﻧ ﻊ اﻟ ﻤ ﺸ ﺮ وﺑﺎ ت

اﻟﻐﺎزﻳﺔ واﻟﻌ ﺼﺎﻧﺮ و اﻟﻤﻴﺎه اﻟﻤﻌﺪﻧﻴﺔ واﻟﺘﻰ أﺧﺬت ﻛﻌﻴﻨﺔ وﻫ ﻰ ا ألﻛﺜﺮ اﺳﺘﺨﺪاﻣﺎ ﻟﻌﺒﻮا ت ال •PE T• PET

ﺗﻢ رﺻﺪ اﻟﺒﻴﺎﻧﺎت و ﻋ ﺮ ﺿ ﻬﺎ ﻓﻰ ﺟﺪاول ورﺳﻮﻣﺎت ﺑﻴﺎﻧﻴﺔ ﺑﺎﺳﺘﺨﺪام ﺑﺮﻧﺎﻣﺞ وﻧﺪوز آﻛﺴﻞ

Excel واﻳ ﻀﺎ ﺑﺮﻧﺎﻣ ﺞ Eview إلﺳﺘﻘﺮاﺀ اﻟﺘﻮﻗﻌﺎ ت اﻟﻤ ﺴﺘﻘﺒﻠﻴﺔ اﻟﺘ ﻲ أﺛﺎ ر ت اﻟ ﻰ زﻳﺎدا ت ﻣ ﻀﻄﺮﺑﺔ

ﻓ ﻰ إ ﺳﺘ ﻬ ال ك PETJ' ﻗ ﺪ ﻧ ﻤ ﻞ إﻟ ﻰ م0 م 60 ﻃ ﻦ ﻣﺘ ﺮ ي ﺑ ﺤ ﻠ ﻮ ﻟ ﻌ ﺎ ﻣ ﻘ ﻞ 20 أ ي ض ا ال ﺳﺘ ﻬ ال ك

اﻟ ﻤﺘ ﻮﻗ ﻊ ﻟ ﻌﺎ م 2010 . ﻣ ﻤﺎ ﻳ ﺸ ﻜ ﻞ ﺧ ﻄ ﺮا ﺑﻴﻨﻴﺎ ﻳ ﺴﺘﻠ ﺰ م ﺗ ﻀﺎﻓ ﺮ اﻟ ﺠ ﻬ ﻮ د ﻣ ﻦ ﺟ ﻤﻴ ﻊ اﻟ ﺸ ﺮ ﻛﺎ ﺀ ﻟ ﻮ ﺿ ﻊ

اﻟ ﺤﻠ ﻮ ل اﻟ ﻌ ﻤﻠﻴ ﺔ اﻟ ﻤﻨﺎ ﺳﺒ ﺔ ﺣ ﻔﺎ ﻇﺎ ﻋﻠ ﻰ اﻟﺒﻴﺌ ﺔ و ذﻟ ﻚ ﺑﺈ ﻋﺎ د ة ﺗ ﺪ وﻳ ﺮ ﻫﺬه اﻟ ﻤ ﺨﻠﻔﺎ ت اﻟﺒ ال ﺳﺘﻴ ﻜﻴ ﺔ واﻟﺘ ﺨﻠ ﺺ وا

١' ن ﺑﻄﺮق ﻋﻠﻤﻴﺖ

ﻃ ﻰ ﺿ ﻮ ﺀ اﻟﻨﺘﺎﺋ ﺞ واﻟﺘ ﺤﻠﻴ ال ت ﻟﺘﻠ ﻚ اﻟﺒﻴﺎﻧﺎ ت ﺗ ﻢ و ﺿ ﻊ اﻟ ﻤﻘﺘ ﺮ ﺣﺎ ت واﻟﺘ ﻮ ﺻﻴﺎ ت ﻋﻠ ﻰ

إﻋﺎدة ﺗﺪوﻳﺮ ﻋﺒﻮا ت PET،J' اﻟﺒ ال ﺳﺘﻴﻜﻴﺔ ﺑﺎﻟ ﻄ ﺮﻳﻘﺔ اﻟﻤﻴﻜﺎﻧﻴﻜﻴﺔ واﻟﺘ ﻲ ﺗﻌﺘﻤﺪ ﻓ ﻲ ا الﺳﺎ س ﻋﻠﻰ آﻟﻴﺔ آ

اﻟﺘ ﺠ ﻤﻴ ﻊ واﻟﻔ ﺮ ز واﻟ ﻄ ﺤ ﻦ واﻟﻨ ﻈﺎﻓ ﺔ واﻟﺘ ﺼﻨﻴ ﻊ ﻣ ﻊ د را ﺳ ﺔ ا ﻣ ﻜﺎﻧﻴ ﺔ ﺗ ﻄﺒﻴ ﻖ اﻟ ﻄ ﺮ ق ا ال ﺧ ﺮ ى اﻟ ﻜﻴ ﻤﻴﺎﺋﻴ ﺔ

وإﺟﺮاﺀ ﺑﺤﻮ ث إ ﺿﺎﻓﻴﺔ ﻓ ﻰ ﻫﺬا اﻟﻤﺠﺎل ﻛﻤﻘﺘﺮ ﺣﺎ ت ﻣ ﺴﺘﻘﺒﻠﻴﺔ Table of Content

Table of Contents

Acknowledgment I

Abstract II

Arabic Abstract III

Content IV

List of Tables VII

List of Figures VIII

ABBREVIATIONS IX CHAPTER ONE: INTRODUCTION 1.1 General 1 1.2 Objectives 3

CHAPTER TWO: LITERATURE REVIEW 2.1 Background 4 2.2 Common Thermoplastics 6 2.2.1 Polyethylenes 9 2.2.2 Polypropylene 13 2.2.3 Poly(Vinyl Chloride) 16 2.2.4 Polystyrene 18 2.3 Poly(Ethylene Terephthalate) 21 2.3.1 General 21 2.3.2 Uses 23 2.3.3 Intrinsic Viscosity 24 2.3.4 Drying 25 2.3.5 Copolymers 26 2.3.6 Crystals 27 2.3.7 Degradation 28 2.3.8 Antimony 29 2.3.9 Bottle Processing Equipment 29 2.4 Thermoplastic Products Manufacture 30 2.4.1 General 30

IV Table of Content

2.4.2 Extrusion Processing 32 2.4.3 Injection Molding 33 2.4.4 Blow Molding 36 2.4.5 Extrusion Blowing of Film 37 2.5 Polyester and PET Recycling Industry 39 2.5.1 General 39 2.5.2 PET Bottle Recycling 41 2.5.3 Impurities and Material Defects 42 2.5.4 Processing Examples for Recycling Polyester 44 2.5.4.1 Simple Re-pelletizing 44 2.5.4.2 Manufacture of PET-pellets 45 for Bottles (B-2-B) 2.5.4.3 Direct Conversion of Bottle Flakes 45 2.5.5 Recycling Back to the Initial Raw Materials 47 2.5.5.1 Glycolysis and Partial Glycolysis 47 2.5.5.2 Hydrolysis 48 2.5.5.3 Methanlysis 48 2.5.6 Practices in Collection& Rcycling of PET 49 2.5.6.1 Collection 49 2.5.6.2 Recycling PET bottles 51 2.5.6.3 Designing Community PET Recycling Program 52

CHAPTER THREE: MATERIALS & METHODS

3.1 The Study Area 54 3.1.1 Khartoum State Map 55 3.2 Sources and Methods of Data Collection 55 3.3 Statistical Analysis Methods 56

CHAPTER FOUR: RESULTS & DISCUSSION

4.1 Results 58 Table of Content

4.1.1 Excel Presentation 59 4.1.2 Eview Package Application 68 4.1.3 Soft drink &Water bottling Factories Survey 69 4.2 Discussions 70

CHAPTER FIVE: CONCLUSION&RECOMMENDATIONS

5.1 Conclusions 71 5.2 Recommendations 72

REFERENCES 74 List of Tables

List of Tables

Table (4.1) Imported Plastic Resin/ PET Preform &commodity During 2005 - 2009 Table (4.2) Annual increment of imported PET preform during period 2005-2010 Table (4.3) Forecast of PET Preform (bottles) to Year 2015

VII List of Figures

Figure (2.1) Common polymers derived from crude oil &natural gas Figure (2.2) Stress strain graph of thermoplastic material. Figure (2.3) Schematic representation of levels of chain branching in different types of polyethylenes Figure (2.4) Simplified flow diagram of Unipol process. Figure (2.5) Flow diagram for suspension or polymerization of vinyl chloride. Figure (2.6) Simplified flow diagram for solution polymerization of styrene. Figure (2.7) Flow diagram illustrating components of plastics industry Figure (2.8) Main features of a simple single-screw extruder Figure (2.9) Diagram of a simple injection-molding machine Figure (2.10) Injection-molded piece. Figure (2.11) Blow molding of plastic bottles Figure (2.12) Schematic representation of extrusion blowing of plastic film Figures (4.1a)&(4.1b) Virgin plastic resin imports quantity/value Figures (4.2a)&(4.2b) PET preform imports quantity/value Figures (4.3a)&(4.3b) Plastic products imports quantity/value Figures (4.4a)&(4.4b) Relationship between Virgin resin, PET and Plastic products imported quantities. Figures (4.5a)&(4.5b) Relationship between virgin resin, PET and Plastic products imported values Figures (4.6a)&(4.6b) Ratio of PET preform imports against Virgin Resin quantity/value Abbreviations

TSW Total solid waste MSW Municipal solid waste LDPE Low Density Polyethylene LLDPE Linear Low Density Polyethylene HDPE High Density Polyethylene PP Polypropylene PVC Polyvinyl Chloride PS Polystyrene PET Polyethylene Terephthalate PMMA Polymethylmetha crylate ipp Isolated polypropylene BOPP Biaxially oriented PP VCM Vinyl Chloride Monomer pPVC Plasticized PVC FDA Food & Drug Administration ABS Acrylonitrile - Butadiene - Styrene SAN Styrene - Acrylonitrile - copolymer SMA Styrene - Maleic - Antriydride SBR Styrene with Butadiene copolymer CFC Chlorofluoro carbon IV Intrinsic Viscosity CHDM Cyclohexane di-methanol SBM Stretch blow molding

PTA Purified Terephthalic Acid DMT Dimethyl Terephthalate EG Ethylene Glycol

IX Chapter One

* Introduction Introduction Chapter 1

1 Introduction

1.1 General:

Total solid waste (TSW) is every thing that people throw away each day. Total solid waste comes from agriculture , mining , industry and municipal solid waste .Municipal solid waste (MSW) is the garbage that people produce in their homes and where they work which is operated and controlled by local officials such as city or governments. (MSW) contains all kinds of garbage including papers, yard waste, plastics, old appliance, household garbage, used furniture and any thing that people throw away at homes , schools and business. Sustainable solid waste management is crucial problem not only for developing countries but for the developed countries as well. However, the plastic waste as significant portion and component of the municipal solid waste is a quite problematic for its non biodegradability and therefore can stay in the environment for a considerable length of time carrying all sorts of problems. *

There are two major categories of plastics include thermoplastics and thermosets. .Thermoplastics refer to plastic materials that can be formed into other products by re-melting or processing into different shapes by the application of heat and pressure. These are easily recyclable into other products. These thermoplastics include polyethylene, low and high density (LDPE, HDPE) polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET) etc Thermoset plastics contain alkyd ,epoxy ,ester ,melamine formaldehyde, polyurethane ,etc .which are cross linked on curing and will not soften with heat to allow these to be formed into different shapes.

Polyethylene terephthalate (PET) is widely used in several key products ,as fiber for textile applications and into backing materials for audio and video tapes .Biaxially oriented polyester film is used for packaging and as thermoformed sheets in frozen meal trays for microwave ovens . Pet films are used in electric devices as well.

- 1 - e------

■ Introduction Chapter 1

The best known product made from aromatic polyester (PET),however is the blow molded water and soda bottles for soft drinks and other household and consumer products . PET is a relatively new packaging resin .. Soft drink bottles remain the biggest user of PET resin .'consumer' bottles are used for other products such as ,salad dressing ,peanut butter and jullies ,H alf of the polyester carpet made in united states is made from recycled PET bottles .The rise of use of custom bottle and the increased consumption of water and soft drinks away from home have created challenges for increasing the PET recycling rate .PET use has reduced the size o f the waste stream because PET has replaced heavier steel and glass containers.

One of the approaches to solution of the plastic waste problem is through recycling for its numerous benefits justifying the aim of this study that essentially meant to contribute to sustainable consumption and production of PET bottles in particular. Recycling of plastics should be carried in such a manner to minimize the pollution level during the process and as a result to enhance the efficiency of the process and conserve the energy. Plastics recycling technologies have been historically divided into four general types -primary, secondary, tertiary and quaternary.

Primary recycling involves processing of a waste/scrap into a product with characteristics similar to those of original product.

Secondary recycling involves processing of waste/scrap plastics into materials that have characteristics different from those of original plastics product.

Tertiary recycling involves the production of basic chemicals and fuels from plastics waste/scrap as part of the municipal waste stream or as a segregated waste.

Quaternary recycling retrieves the energy content of waste/scrap plastics by burning/incineration.

-2 - Introduction Chapter 1

1.2 Objectives of the Study :

Major objective

TO assess the general plastic waste management in Khartoum state and to effectively manage the PET plastic bottles by identifying practical means to introduce cleaner production tools mainly recycling in order to achieve sustainable development goals.

Specific objectives

■ To collect and study available data on plastic and PET plastic bottles in particular. ■ To effectively manage the PET plastic bottles waste and minimize the volume (industrial / domostic). ■ To identify ways and methods for collectio of PET bottles waste. ■ To recommend on what to be done to support the growth of PET bottle recycling. Chapter Two Literature Review Literature Review Chapter 2

2 Literature Review

2.1. Background

The first totally man-made polymer to be synthesized was the phenol formaldehyde resin (called Bakelite at the time) made by Leo Baekeland in his garage in Yonkers, New York, back in 1907.1 It was an immediate success not only as a replacement for shellac in electrical wiring (the primary reason for its invention) but also in numerous consumer uses including the body of the old black dial telephones and in early electrical fittings. Since that time, plastics have grown rapidly and have now become an indispensable part of everyday life. The exponential growth of plastics and rubber use, essentially over a short period of half a century, is a testimony to the versatility, high performance, and cost effectiveness of polymers as a class of materials.

Polymers derive their exceptional properties from an unusual molecular architecture that is unique to polymeric materials, consisting of long chainlike macromolecules. While both plastics as well as elastomers (rubber-like materials) are included in polymers, discussions on environment-related issues have mostly centered around plastics because of their high visibility in packaging and building applications Many of the common thermoplastics used today, however, were developed after the 1930s; and a few of these even emerged after World War II. Among the first to be synthesized were the vinyl plastics derived from ethylene.. But the now common rigid PVC used in building was a postwar development that rapidly grew in volume to a point that by the early 1970s the demand for vinyl resin was close to that for polyethylene! Polyethylene, the plastic used in highest volume worldwide, was discovered at Imperial Chemical Industries (ICI) research laboratories in 1933. This high-pressure polymerization route was exclusively used to commercially produce low-density polyethylene (LDPE) for nearly two decades until the low-pressure processes for high-density polyethylene (HDPE) were developed in 1954. Linear low-density copolymers of ethylene (LLDP), intermediate in structure and properties between the HDPE and LDPE, followed even more recently in the 1970s. In the last decade yet another new class of polyethylene

4 Literature Review Chapter 2 based on novel metallocene catalysts has been developed. Polypropylene manufacture started relatively late in the 1950s only after the stereospecific Ziegler-Natta catalysts that yielded high-molecular-weight propylene polymers became available. While a range of copolymers of ethylene is also commercially available, the homopolymer of propylene enjoys the highest volume of use. Polyethylene, polypropylene (and their common copolymers) are together referred to as polyolefins.

Several other common thermoplastics emerged about the same time as LDPE in 1930s. Polystyrene, for instance, was first produced in 1930 and by 1934 plants were in operation producing the commercial resin in both Germany and the United States. Poly(methylmethacrylate) (PMMA) was developed by ICI about the same period. Carothers’s discovery of nylons (introduced in 1939 at the World’s Fair in New York) yielded a material that particularly served the allied war effort.

The millions of metric tons of polymer resins manufactured annually • worldwide are predominantly derived from petroleum and natural gas feedstock, but other raw materials such as coal or even biomass might also be used for the purpose. In regions of the world where natural gas is not readily available, petroleum or coal tar is in fact used exclusively as feedstock. About half the polyolefins produced in the United States today is based on petroleum, the remainder being derived from natural gas. The crude oil is distilled to separate out the lighter components such as gases, gasoline, and kerosene fractions. Cracking is the process of catalytically converting the heavier components (or “residues” from this distillation) of crude oil into lighter more useful components. About 45% of the crude oil reaching a refinery is converted to gasoline.

Ethylene from cracking of the alkane gas mixtures or the naphtha fraction can be directly polymerized or converted into useful monomers. (Alternatively, the ethane fraction in natural gas can also be converted to ethylene for that purpose). These include ethylene oxide (which in turn can be used to make ethylene glycol), vinyl acetate, and vinyl chloride. The same is true of the propylene fraction, which can be converted into vinyl chloride and to ethyl benzene (used to make styrene)..

5 For the purpose of this study, this chapter is subdivided into common thermoplastics, polyethylene terephthalate (PET), thermoplastic products manufacture , plastic and PET recycling .

2.2. Common Thermoplastics

A thermoplastic, also known as thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers (Bakelite) in that they can be remelted and remoulded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene.

6 Literature Review Chapter 2

Fig 2.2 Stress strain graph of thermoplastic material.

Thermoplastics are elastic and flexible above a glass transition temperature specific for each one— the midpoint of a temperature range in contrast to the sharp melting point of a pure crystalline substance like water. Below a second, higher melting temperature, Tm, also the midpoint of a range, most thermoplastics have crystalline regions alternating with amorphous regions in which the chains approximate random coils. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity, as is also the case for non thermoplastic fibrous proteins such as silk. (Elasticity does not mean they are particularly stretchy; e.g., nylon rope and fishing line.) Above Tm all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above Tm, viscosity gradually decreases without any distinct phase change.

Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC. Generally, amorphous thermoplastics are less chemically resistant and can be subject to stress cracking. Thermoplastics will crystallize to a certain extent and are called "semi-crystalline" for this reason. Typical semi-crystalline thermoplastics are PE, PP, PBT and PET. The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque. Semi-crystalline thermoplastics become less brittle above Tg. If a plastic with otherwise desirable properties has too high a T%, it can often be lowered by adding a

7 Literature Review Chapter 2 low-molecular-weight plasticizer to the melt before forming (Plastics extrusion; molding) and cooling. A similar result can sometimes be achieved by adding non reactive side chains to the monomers before polymerization. Both methods make the polymer chains stand off a bit from one another. Before the introduction of plasticizers, plastic automobile parts often cracked in cold winter weather. Another method of lowering Tg (or raising Tm) is to incorporate the original plastic into a copolymer, as with graft copolymers of polystyrene, or into a composite material. Lowering T% is not the only way to reduce brittleness. Drawing (and similar processes that stretch or orient the molecules) or increasing the length of the polymer chains also decrease brittleness.

Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. This quality makes thermoplastics recyclable. The processes required for recycling vary with the thermoplastic. The plastics used for soda bottles are a common example of thermoplastics that can be and are widely recycled. Animal horn, made of the protein a-keratin, softens on heating, is somewhat reshapable, and may be regarded as a natural, quasi-thermoplastic material.

Although modestly vulcanized natural and synthetic rubbers are stretchy, they are elastomeric thermosets, not thermoplastics. Each has its own and will crack and shatter when cold enough so that the crosslinked polymer chains can no longer move relative to one another. But they have no Tm and will decompose at high temperatures rather than melt. Recently, thermoplastic elastomers have become available.

A comprehensive introduction to common polymers and their manufacture within this study is impractical and is not the present objective. Therefore, this chapter is limited to a discussion of the common thermoplastic materials that are produced in large volume and therefore of particular environmental significance.. For the present purpose “common” plastics include the high-volume commodity resins polyethylene, polypropylene, poly(vinyl chloride), polystyrene, and thermoplastic polyester. Literature Review Chapter 2

2.2.1. Polyethylenes

Polyethylenes, the most widely used class of plastics in the world, include several copolymers of ethylene in addition to the homopolymer. The polyethylene homopolymer has the simplest chemical structure of any polymer. —CH2— CH2— CH2— CH2— CH2— CH2— CH2— CH2— The commercially available resins, however, have far more complicated structures with branched chains and semi crystalline morphologies not indicated in this simple representation. Depending on their copolymer composition and the polymerization process used, commercial polyethylenes display a wide range of average molecular weights, molecular weight distributions (polydispersity), and chain branching in the resin. These molecular parameters affect the ability of the macromolecules to pack closely into a dense matrix and also control the extent of crystallinity in the material. Because of their semicrystalline nature, polyethylenes do not display their theoretical density o f 1.00 g/cm3 (or the theoretically expected melting point o f about 135°C) but show a surprisingly wide range of physical properties, Based on these, particularly the bulk density, the resins are divided into three basic types: • Low-density polyethylenes (LDPE) • High-density polyethylenes (HDPE) • Linear low-density polyethylene (LLDPE)

High-density polyethylene has the simplest structure and is essentially made of long virtually unbranched chains of polymer (somewhat representative of the simple structure shown above). These chains are able to align and pack easily; HDPE therefore has the highest degree of crystallinity in a polyethylene. Its molecular weight is high enough (and the chain branching minimal) to obtain a degree of crystallinity as high as 70-95% (and a correspondingly high density in the range of 0.941-0.965 g/cm3). Low-density polyethylene on the other hand has extensive chain branching in its structure. Both long- and short-chain branching are usually present, and this results in a comparatively lower material density of 0.910-0.930 g/cm3 and a crystallinity of only 40-60% . LDPE has a melting temperature range of 110-115°C. The amount of crystallinity and the melt temperature of the resin can even be further

9 Literature Review Chapter 2 reduced by incorporating a small amount of a suitable co-monomer. When the branches on polymer chain are mostly short chains, a linear low-density polyethylene with a density range of 0.915-0.940 g/cm3 and a higher degree of crystallinity of 40- 60% is obtained. Figure 2.3 shows a schematic of the nature of chain branching in the three varieties of polyethylene. Since its introduction in 1968 the LLDPE resin has been extensively used in packaging films, particularly in products such as grocery bags and garbage sacks where high clarity is particularly not important. LLDPE with short branches yield exceptional strength and toughness; LDPE packaging film can often be replaced with an LLDPE film of only about a third of the thickness. Given the cost effectiveness of LLDPE, it is likely to be used increasingly (mainly at the expense of LDPE) in future packaging applications. [3]

10 Literature Review Chapter

Figure 2.3 Schematic representation of levels of chain branching encountered in different types of polyethylenes.

Ethylene for the manufacture of polyethylene is derived from cracking various components of petroleum oil such as the gasoline fraction, gas oil, or from hydrocarbons such as ethane. While petroleum remains the predominant source of the monomer at the present time, it can also be produced using biomass. In fact ethylene has been commercially derived from molasses, a by-product of sugar cane industry, via the dehydration o f ethanol.

11 Literature Review Chapter 2

The polymerization of ethylene might be carried out in solution or in a slurry process. But these processes are complicated by the need for a separation step to isolate the resin product from solution. The newer installations favor the gasphase process that can produce both the low- and high-density resins. Older plants lack this versatility and are able to produce only either the high-density or the low-density type of polyethylene. In the older process, LDPE resin was produced under high pressure (15,000-22,500 psi at 100°C-300°C) in stirred autoclave or tubular-type reactors, where the liquefied ethylene gas is polymerized via a free radical reaction initiated by peroxide or by oxygen. CH2=CH2------» — [— CH2— CH2—]n—

The reaction is highly exothermic (22 kcal/mol) and therefore requires careful control of the temperature, especially in autoclave reactors. The product generally has a high level of long chain branching from chain transfer to polymer. Short-chain branches are methyl or alkyl groups formed by the active growing chain end abstracting a hydrogen atom from another part of the chain via “back-biting” reactions. [4]

Gas-phase polymerization represents an important advance in the manufacturing technology for polyolefins. In the Unipol (gas-phase) process ethylene and any comonomers (usually other olefins such as oct-1-eping or handling viscous polymer solutions and the solubility of the resin product. The solid polyethylene is directly removed from the reactor with any residual monomer being purged and returned to the bed. The gas-phase reactors are able to take advantage of the new metallocene catalysts with little engineering modification. A schematic diagram of a Unipol-type reactor is shown in Figure 2.4 [5]

12 Literature Review Chapter 2

Blower

Figure 2.4 .Simplified flow diagram of Unipol process.

2.2.2. POLYPROPYLENE

Polypropylene is typically manufactured by the direct polymerization of propylene in a low-pressure process employing Ziegler-Natta catalyst systems (typically aluminum alkyls and titanium halides with optional ether, ester, or silane activators). The process can be carried out in liquid or slurry in conventional manufacturing or in the newer gas-phase stirred-bed or fluidized-bed reactors. The polymerization generally yields an is tactic index (generally measured as the percent insolubles in heptane) of 85-99. The isotactic form of the polymer with a high degree of crystallinity (40-60% ) is preferred for most practical applications.

Isotactic polypropylene (iPP), the principal type used by the polymer processing industry, has a density of about 0.92-0.94 g/cm3. The weight-average molecular weight of polypropylene from these processes is in the range of 300,000- Literature Review Chapter 2

600,000 with a polydispersity index of about 2-6 [7]. Some atactic polypropylene results as a by-product9 of the process and has found limited practical use [8]. The atactic form is mostly amorphous and has a density of only about 0.85-0.90 g/cm3. Small amounts of the syndiotactic form of polypropylene (where the methyl groups on repeat units are located on alternate sides of the chain on adjacent units) are made commercially using the single-site metallocene catalyst and are being evaluated in various applications. The syndiotactic resin has lower crystallinity (30^40%) and are softer, tougher, stronger (higher impact strength and elastic modulus), and relatively more transparent than the isotactic resin. Propylene monomer is produced by catalytic cracking of petroleum fractions or the steam cracking of hydrocarbons during the production of ethylene. Conventional processes in liquid phase and in slurry use stirred reactors and a diluent such as naphtha, hexane, or heptane. The reaction takes place typically at a temperature of about 60-80°C and at 0.5-1.5 MPa, and the final product is obtained as a solid suspension of polypropylene in the liquid phase. Isolation of the resin requires a separation step (such as centrifugation) followed by washing the resin free of residual diluent and drying.

The manufacturing process for polypropylene has undergone many changes since 1957 when the first facility went on stream. In the 1960s the Novolon gas phase process and the Phillips process for polymerizing liquid propylene were introduced. These processes had the advantage of not using any diluents, but they generally suffer from relatively poorer catalyst performance and some limitations on the stereoregularity of resins. In 1975 with the introduction of improved third-generation catalysts that facilitate the reaction at the same temperature but at the slightly higher pressure of 2.5-3.5 MPa, both optimum yield and stereoregularity could be achieved. These catalysts introduced, by Montedison and Mitsui, could be used with liquid monomer systems in the new gas-phase reactors.

The latter technology modeled after the already successful Unipol polyethylene process went on stream in 1985. The flow diagram for the process for polyethylene production, shown in Figure 2.5, applies equally well for polypropylene. Polymerization-grade propylene (usually at a purity of at least 99.8%)

14 Literature Review Chapter 2

is used in place of the ethylene monomer feed. A suitable co-monomer (usually ethylene) is also generally used. Most of the advantages of gas-phase processes cited for polyethylene also apply to the production of polypropylene [6]. Over a third of the polypropylene produced in the United States is ultimatel processed into useful products by injection molding. A wide range of resins spanning a melt flow index (MFI) range of 2 to >70 g/10 min is available for this purpose. In North American markets a majority of the polypropylene is injection molded into products or spun into fibers for use in various textile applications. The latter includes sacks made of woven polypropylene strips cut from oriented sheets used for packaging agricultural products. The common molded products include closures, containers, bottles, jars, and crates. A relatively small fraction of the polypropylene (about a tenth) is extruded into film. In applications involving low-temperature use (as with refrigerated packages), the copolymers are preferred over the homopolymer. Both biaxially oriented film (BOPP) and nonoriented packaging films of polypropylene are used in food packaging. The former is used as a barrier film, usually with a surface coating. Nonoriented films are used in general-purpose applications such as apparel bags, bandages, diaper linings, and in sanitary products. Blow molding of polypropylene is also common, and is used in the production of bottles and containers.

15 Literature Review Chapter 2

Dewatering and drying of product

Figure 2.5 Flow diagram for suspension or emulsion polymerization of vinyl chloride.

2.2.3. POLY(VINYL CHLORIDE)

Poly(vinyl chloride) (PVC), the second widely used resin in the world (after polyethylene) is made by the polymerization of vinyl chloride monomer (VCM). In theory the chemical structure of the polymer is simple, consisting of the same structure as for polyethylene with one hydrogen in every other — CF12— group being replaced by a chlorine atom — CH2— CHC1— CH2— CHC1— CH2— CHCL However, as the repeat unit is asymmetrical because of the presence of only a single chlorine atom, two types of linkages, head to tail and head to head, are possible:

CH2— CHC1— CH2CHC1 CH2— CHC1— CHC1— CH2 Head to tail Head to head In general, however, the head-to-tail linkages are predominant (nearly 90%) in the resin. The weight-average molecular weight Mw of

16 Literature Review Chapter 2 commercial PVC resins ranges from about 100,000-200,000 and the polydispersity index is about 2.0. The resin has a glass transition temperature of 75-85°C and a crystalline melting point of 120-210°C. The crystallinity in PVC is due to syndiotactic sequences in the polymer and amount to about 7-20% in commercial resins. Resins with higher levels of crystallinity can be obtained by polymerization under specific conditions.

The polymer is susceptible to both photo- and thermal degradation; and, for products intended for outdoor use, the resin has to be compounded with light stabilizers.Such formulations typically contain other additives (such as a thermal stabilizer package to protect the resin during processing), fillers, and lubricants. The compounds not containing any plasticizers or the rigid PVC materials (also referred to as uPVC) are used extensively in building products such as pipes, fittings, siding, window frames, and rainwater products. In unplasticized formulations of PVC intended for outdoor use, an opacifier,' usually rutile titania, that effectively absorbs the damaging ultraviolet (UV-B) radiation is incorporated in the formulation to protect the surface from UV-induced degradation.

PVC resin can also be made into a versatile soft pliable rubbery material by incorporating plasticizers such as organic phthalates into the compound. Plasticized PVC (also referred to as pPVC) is used widely as packaging film, roofing membranes, belting, hoses, and cable covering. With pPVC, calendering is employed to produce films and sheets. The resin is also used as a coating on paper or fabric and is made into numerous household products. A small amount of the plasticized film is used in packaging, for instance, in meat wraps where it is approved by the Food and Drug Administration (FDA) for food-contact use..

In suspension polymerization the vinyl chloride monomer is dispersed in water using a protective colloid or a surfactant to control the final particle size (usually between 130 and 165 pm) and a monomer-soluble initiator (usually an azo compounds or a peroxide) is used. Gelatin, soaps, glycols, and pentaerythritol or their mixtures can be used as dispersing agents in the reaction mixture. The polymerization is usually carried out in a glass-lined reactor with controlled agitation, at a Literature Review C h ap ter 2 temperature of 50-75°C and at a pressure of about 0.7 MPa. Oxygen is usually excluded from the reaction vessel to prevent interference with the free-radical polymerization reaction. Vinyl chloride monomer is volatile with a boiling point of -13.4°C and is a hazardous air pollutant. (The reactants are usually maintained under pressure during the process to keep the VCM in a liquid state). Figure 2.6 shows aschematic representation of the manufacturing process [10].

Styrene and solvent r recovery Styrene

Solvent

Devolatilizer V.J

v y \\ ‘ / / Polystyrene to cutter Reactors Extruder

Figure 2.6 .Simplified flow diagram for solution polymerization of styrene.

2.2.4. POLYSTYRENE

General-purpose polystyrene (also called crystal polystyrene because of the clarity of resin granules) is a clear, hard, glassy material with a bulk density of 1.05 g/cm-3. These desirable physical characteristics, as well as easy moldability, low water absorbancy, and good color range in which the resin was available, made it a popular general-purpose resin. Its brittleness, which limited the range of products in which the resin could be used, was soon overcome when the highimpact toughened grades of polystyrene containing rubber became available. The resin is available as a

18 Literature Review Chapter 2

general-purpose grade, high-impact resin, high-molecularweight resin (for improved strength), high-heat grades with a higher softening point, and easy flow grades for sophisticated molding applications. High-heat resins are high-molecular-weight resins with melt flow rates o f 1.6 g/10 min. The medium and easy flow grades contain 1—4% added mineral oil or other lubricant to obtain higher flowrates of about 7.5 and 16 g/10 min, respectively. Impactgrade resin accounts for about half of the demand for polystyrene and is widely used in injection molding of consumer products. Some copolymers such as (acrylonitrile- butadiene-styrene) copolymers (ABS), styrene-acrylonitrile copolymers (SAN), and styrene-maleic anhydride copolymers (SMA) are also commercially available [11], Copolymer of styrene with butadiene (SBR) is an important elastomer widely used in passenger tire applications.

The first commercial production of polystyrene (PS) was carried out in the early 1930s by the Farben Company(Germany) and was soon followed in 1937 by the Dow Chemical Company introducing in the United States a grade called “Styron.” Styrene monomer is mainly produced by the dehydrogenation of ethylbenzene made by reacting ethylene and benzene in a Friedel-Crafts reaction using a catalyst system containing aluminum chloride [12]. Yields in excess of 98% are common in this process. The thermal cracking reaction that produces the dehydrogenation is carried out at 630°C in the presence of a catalyst, commonly a mixture of Fe203, C r203, and K 2C03. The reaction yields a mixture of products, but the process conditions can be controlled to obtain about 80% conversion.

The styrene is separated from the product mix, which also contains unreacted ethylbenzene and other impurities, by vacuum distillation. The monomer can easily autopolymerize into a hard solid and is therefore inhibited from polymerization during storage by mixing in a few parts per million of a free-radical reaction inhibitor (generally /-butyl catechol). A relatively small amount of styrene is also made by the oxidation o f ethyl benzene in a process introduced by Union Carbide. The ethylbenzene hydroperoxide formed by oxidation is reacted with propylene to form propylene oxide and 2-phenyl ethanol. The latter compound is dehydrated to obtain styrene.

19 Literature Review Chapter 2

While bulk or emulsion polymerization can also be used for the purpose, the commercial manufacture of polystyrene is mostly carried out in a solution process using a free-radical initiator. The solvent, typically ethylbenzene, used at a level of 2- 30%, controls the viscosity of the solution. High-impact-grade polymer used in injection-molding and extrusion is modified with butadiene rubber incorporated during polymerization. The solvent and residual monomer in the crude resin is removed by flash evaporation or in a devolatilizing extruder (at about 225°C). Figure 2.6 is a schematic of the polymerization process.

Since this study is mainly concentrating on PET for its value as a recyclable resin ,more elaboration is considered in the following subchapter . Literature Review Chapter 2

2.3. POLY (ETHYLENE TEREPHTHALATE)

2.3.1. GENERAL

Polyethylene terephthalate

Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P), is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber.

Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline material. The semicrystalline material might appear transparent (particle size < 500 nm) or opaque and white (particle size up to a few microns) depending on its crystal structure and particle size. Its monomer (bis-B-hydroxyterephthalate) can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct, or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct. Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/transesterification) with ethylene glycol as the byproduct (the ethylene

glycol is directly recycled in production).

The majority of the world's PET production is for synthetic fibers (in excess of 60%) with bottle production accounting for around 30% of global demand. In discussing textile applications, PET is generally referred to as simply "polyester" whiJe "PET" is most o/ccn to refer to packaging applications.

Some of the trade names of PET products are Dacron, Diolen, Tergal, Terylene, and Trevira fibers, Cleartuf, Eastman PET and Polyclear bottle resins, Literature Review Chapter 2

Hostaphan, Melinex, and Mylar films, and Amite, Ertalyte, Impet, Rynite and Valox injection molding resins. The polyester industry makes up about 18% o f world polymer production and is third after polyethylene (PE) and polypropylene (PP).

PET consists of polymerized units of the monomer ethylene terephthalate, with repeating CioHsCU units. PET is commonly recycled, and has the number "1" as its recycling symbol.

PET

Molecular formula (CioH804)n

Density amorphous 1.370 g/cm3

Density crystalline 1.455 g/cm3

Young's modulus (E) 2800-3100 MPa

Tensile strength('of') 55-75 MPa

Elastic limit 50-150%

notch test 3.6kJ/m 2

Glass temperature 75 °C

melting point 260 °C

Vicat B 170 °C

Thermal conductivity 0.24 W/(m-K)

linear expansion coefficient (a) 7xlO_:7K

Specific heat (c) 1.0 kJ/(kg-K)

Water absorption (ASTM) 0.16

Refractive Index 1.5750

Price 0.5-1.25 €/kg source: A.K. van der Vegt & L.E. Govaert, Polymeren, van keten tot kunstof, ISBN 90-407-2388-5

22 2.3.2. USES

PET can be semi-rigid to rigid, depending on its thickness, and it is very lightweight. It makes a good gas and fair moisture barrier, as well as a good barrier to alcohol (requires additional "barrier" treatment) and solvents. It is strong and impact- resistant. It is naturally colorless with a high transparency

PET bottles are excellent barrier materials and are widely used for soft drinks (see carbonation). For certain specialty bottles. PET sandwiches an additional polyvinyl alcohol to further reduce its oxygen permeability When produced as a thin film (biaxially oriented PET film, often known by one of its trade names, "Mylar"), PET can be aluminized by evaporating a thin film of metal onto it to reduce its permeability, and to make it reflective and opaque (MPET). These properties are useful in many applications, including flexible food packaging and thermal insulation, such as "space blankets". Because of its high mechanical strength, PET film is often used in tape applications, such as the carrier for magnetic tape or backing for pressure sensitive adhesive tapes.

Non-oriented PET sheet can be thermoformed to make packaging trays and blisters. If crystallizable PET is used, the trays can be used for frozen dinners, since they withstand both freezing and oven baking temperatures.

When filled with glass particles or fibers, it becomes significantly stiffer and more durable. This glass-filled plastic, in a semi-crystalline formulation, is sold under the tradename Rynite, Arnite, Hostadur, and Crastin.

While most thermoplastics can, in principle, be recycled, PET bottle recycling is more practical than many other plastic applications. The primary reason is that plastic carbonated soft drink bottles and water bottles are almost exclusively PET, which makes them more easy to identify in a recycle stream. PET has a resin identification code of 1. One of the uses for a recycled PET bottle is for the manufacture of polar fleece material. Among its many uses, companies, such as English Retreads use the PET material to line their products. It can also make fiber for polyester products.

23 Literature Review Chapter 2

Because of the recyclability of PET and the relative abundance of post consumer waste in the form of bottles, PET is rapidly gaining market share as a carpet fiber. Mohawk Industries released everSTRAND in 1999, a 100% post-consumer recycled content PET fiber. Since that time, more than 17 billion bottles have been recycled into carpet fiber Pharr Yarns, a supplier to numerous carpet manufacturers including Looptex, Dobbs Mills, and Berkshire Flooring, produces a BCF (bulk continuous filament) PET carpet fiber containing a minimum of 25% post-consumer recycled content.

PET, as with many plastics, is also an excellent candidate for thermal disposal (incineration), as it is composed of carbon, hydrogen, and oxygen, with only trace amounts of catalyst elements (but no sulfur). PET has the energy content of soft coal. PET was patented in 1941 by the Calico Printers' Association of Manchester. The PET bottle was patented in 1973 by Nathaniel Wyeth.

2.3.3. Intrinsic viscosity

One of the most important characteristics of PET is referred to as intrinsic viscosity (IV) The intrinsic viscosity of the material, measured in deciliters per gram (dC/g) is dependent upon the length of its polymer chains. The longer the polymer chains, the the more entanglements between chains and therefore the higher the viscosity. The average chain length of a particular batch of resin can be controlled during polycondensation.

The intrinsic viscosity range of PET

Fiber grade

0 .4 0 -0 .7 0 dC/g Textile 0.72 - 0.98 dC/g Technical, tire cord

Film grade

0.60 - 0.70 dC/g PET film (biaxiallv oriented) 0.70 - 1.00 dt/g Sheet grade for thermoforming

24 Literature Review Chapter 2

Bottle grade

0.70 - 0.78 d£/g Water bottles (flat) 0.78 - 0.85 dC/g Carbonated soft drink grade

Monofilament

1 .0 0 -2 .0 0 dC/g

2.3.4. Drying

PET is hygroscopic, meaning that it naturally absorbs water from its surroundings. However, when this 'damp' PET is then heated, the water hydrolyzes the PET, decreasing its resilience. This means that before the resin can be processed in a molding machine, as much moisture as possible must be removed from the resin. This is achieved through the use of a desiccant or dryers before the PET is fed into the processing equipment.

Inside the dryer, hot dry air is pumped into the bottom of the hopper containing the resin so that it flows up through the pellets, removing moisture on its way. The hot wet air leaves the top of the hopper and is first run through an after cooler, because it is easier to remove moisture from cold air than hot air. The resulting cool wet air is then passed through a desiccant bed. Finally the cool dry air leaving the desiccant bed is re-heated in a process heater and sent back through the same processes in a closed loop. Typically residual moisture levels in the resin must be less than 5 parts per million (parts of water per million parts of resin, by weight) before processing. Dryer residence time should not be shorter than about four hours. This is because drying the material in less than 4 hours would require a temperature above 160 °C, at which level hydrolysis would begin inside the pellets before they could be dried out.

25 Literature Review Chapter 2

PET can also be dried in compressed air resin dryers. Compressed air dryers do not reuse drying air. Dry, heated compressed air is circulated through the PET pellets as in the desiccant dryer, then released to the atmosphere.

2.3.5. Copolymers

In addition to pure (homopolymer') PET, PET modified by copolymerization is also available.

In some cases, the modified properties of copolymer are more desirable for a particular application. For example, cyclohexane dimethanol (CHDM) can be added

to the polymer backbone in place of ethylene glycol. Since this building block is much larger (6 additional carbon atoms) than the ethylene glycol unit it replaces, it does not fit in with the neighboring chains the way an ethylene glycol unit would. This interferes with crystallization and lowers the polymer's melting temperature. Such PET is generally known as PETG (Easljnan Chemical and SK Chemicals are the only two manufacturers). PETG is a clear amorphous thermoplastic that can be injection molded or sheet extruded. It can be colored during processing.

A- O-

£3 Replacing terephthalic acid (right) with isophthalic acid (center) creates a kink in the PET chain, interfering with crystallization and lowering the polymer's melting point. Another common modifier is isophthalic acid, replacing some of the 1,4- (para-) linked terephthalate units. The l,2-(ortho-) or l,3-(meta-) linkage produces an angle in the chain, which also disturbs crystallinity.

Such copolymers are advantageous for certain molding applications, such as thermoforming, which is used for example to make tray or blister packaging from PETG film, or PETG sheet. On the other hand, crystallization is important in other applications where mechanical and dimensional stability are important, such as seat Literature Review Chapter 2 belts. For PET bottles, the use of small amounts of CHDM or other comonomers can be useful: if only small amounts of comonomers are used, crystallization is slowed but not prevented entirely. As a result, bottles are obtainable via stretch blow molding ("SBM"), which are both clear and crystalline enough to be an adequate barrier to aromas and even gases, such as carbon dioxide in carbonated beverages.

2.3.6. Crystals

Crystallization occurs when polymer chains fold up on themselves in a repeating, symmetrical pattern. Long polymer chains tend to become entangled on themselves, which prevents full crystallization in all but the most carefully controlled circumstances. PET is no exception to this rule; 60% crystallization is the upper limit for commercial products, with the exception of polyester fibers.

t PET in its natural state is a crystalline resin. Clear products can be produced by rapidly cooling molten polymer to form an amorphous solid. Like glass, amorphous PET forms when its molecules are not given enough time to arrange themselves in an orderly fashion as the melt is cooled. At room temperature the molecules are frozen in place, but if enough heat energy is put back into them, they begin to move again, allowing crystals to nucleate and grow. This procedure is known as solid-state crystallization.

Like most materials, PET tends to produce many small crystallites when crystallized from an amorphous solid, rather than forming one large single crystal. Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them. This scattering means that crystalline PET is opaque and white in most cases. Fiber drawing is among the few industrial processes that produce a nearly single-crystal product. Literature Review Chapter 2

2.3.7. Degradation

PET is subject to various types of degradations during processing. The main degradations that can occur are hydrolytic, thermal and probably most important thermal oxidation. When PET degrades, several things happen: discoloration, chain scissions resulting in reduced molecular weight, formation of acetaldehyde and cross links ("gel" or "fish-eye" formation). Discoloration is due to the formation of various chromophoric systems following prolonged thermal treatment at elevated temperatures. This becomes a problem when the optical requirements of the polymer are very high, such as in packaging applications. Acetaldehyde is normally a colorless, volatile substance with a fruity smell. It forms naturally in fruit, but it can cause an off-taste in bottled water. Acetaldehyde forms in PET through the "abuse" of the material. High temperatures (PET decomposes above 300 °C or 570 °F), high pressures, extruder speeds (excessive shear flow raises temperature) and long barrel residence times all contribute to the production of acetaldehyde. When acetaldehyde is produced, some of it remains dissolved in the walls of a container and then diffuses into the product stored inside, altering the taste and aroma. This is not such a problem for non-consumables (such as shampoo), for fruit juices (which already contain acetaldehyde), or for strong-tasting drinks like soft drinks. For bottled water, however, low acetaldehyde content is quite important, because if nothing masks the aroma, even extremely low concentrations (10-20 parts per billion in the water) of acetaldehyde can produce an off-taste. The thermal and thermooxidative degradation results in poor processability characteristics and performance of the material.

One way to alleviate this is to use a copolymer. Comonomers such as CHDM or isophthalic acid lower the melting temperature and reduce the degree of crystallinity of PET (especially important when the material is used for bottle manufacturing). Thus the resin can be plastically formed at lower temperatures and/or with lower force. This helps to prevent degradation, reducing the acetaldehyde content of the finished product to an acceptable (that is, unnoticeable) level. See copolymers, above. Other ways to improve the stability of the polymer is by using stabilizers, mainly antioxidants such as phosphites. Recently,

28 Literature Review Chapter

2 molecular level stabilization of the material using nanostructured chemicals has also been considered.

2.3.8. Antimony

Antimony (Sb) is a catalyst that is often used as antimony trioxide (Sb2 C>3 ) or antimony triacetate in the production of PET. After manufacturing a detectable amount of antimony can be found on the surface of the product- this residue can be removed with washing. Antimony also remains in the material itself and can thus migrate out into food and drinks- exposing PET to boiling or microwaving can increase the levels of antimony significantly, possibly above USEPA maximum contamination levels . The drinking water limit in the USA for antimony is 6 parts per billion . Although antimony trioxide is of low toxicity when taken in orally, its presence is still of concern. The Swiss Federal Office of Public Health investigated the amount of antimony migration, comparing waters bottled in PET and glass: the t antimony concentrations of the water in PET bottles was higher, but still well below the allowed maximal concentrations. The Swiss Federal Office of Public Health concluded that small amounts of antimony migrate from the PET into bottled water, but that the health risk of the resulting low concentrations is negligible (1% o f the "tolerable daily intake" determined by the WHO). A later (2006) but more widely publicized study found similar amounts of antimony in water in PET bottles. The WHO has published a risk assessment for antimony in drinking water.

Commentary published in Environmental Health Perspectives in April 2010 suggested that PET might yield endocrine disruptors under conditions of common use and recommended research on this topic. Proposed mechanisms include leaching of phthalates as well as leaching of antimony. Other authors have published evidence indicating that it is quite unlikely that PET yields endocrine disruptors .

2.3.9. Bottle processing equipment

There are two basic molding methods for PET bottles, one-step and two-step. In two-step molding, two separate machines are used. The first machine injection molds the preform, which resembles a test tube with the bottle-cap threads already

29 molded into place. The body of the tube is significantly thicker, as it will be inflated into its final shape in the second step using stretch blow molding.

In the second process, the preforms are heated rapidly and then inflated against a two-part mold to form them into the final shape of the bottle. Preforms (uninflated bottles) are now also used as containers for candy.

In one-step machines, the entire process from raw material to finished container is conducted within one machine, making it especially suitable for molding non-standard shapes (custom molding), including jars, flat oval, flask shapes etc. Its greatest merit is the reduction in space, product handling and energy, and far higher visual quality than can be achieved by the two-step system [13].

t 2.4. THERMOPLASTIC PRODUCTS MANUFACTURE

2.4.1. GENERAL

Thermoplastic resins are available to the processing industry as pellets of resin. Converting the raw material into useful products can involve separate segments of the plastics industry. As Figure 2.7 suggests, the resin might be compounded by a custom compounder and formed into the final product by a processor or a fabricator. The compounding can also be carried out by the processor in an in-house facility.

30 Literature Review Chapter 2

Figure 2.7.Flow diagram illustrating components of plastics industry. The resin raw material needs to be mixed intimately with a variety of chemical additives to impart specific properties to the end product. Additives are used widely in the plastics industry, in nearly all types of plastic products. The use of common plastics in consumer products would not be possible without the use of additives. For instance, vinyl plastics (particularly PVC) undergo easy thermal and photodegradation; no useful products can be made with it if stabilizer additives designed to protect the resin during thermal processing and use were not available. Selecting the appropriate set of additives called for by a given product and mixing these in correct proportion with the resin is referred to as compounding. . To ensure adequate mixing or dispersion of the additive, the mixing is accomplished by passing the resin and additive mixture at a temperature high enough to melt the thermoplastic, through a mixing screw in an extruder (a compounding extruder). Care is taken not to overheat or overshear the mix to an extent to cause chemical breakdown of the plastic itself or the additive materials. The now “compounded” resin with the additives evenly distributed within its bulk is repelletized, cooled, dried (where the pelletization is carried out undercooling water), and stored for subsequent processing. Processing is the final step that converts the compounded material into a useful plastic product. Basically, the compounded resin needs to be melted into a liquid and heated to a temperature that allows easy handling of the fluidized plastic or the “melt.” This melt is fed into molds or dies to force the material into required

31 Literature Review Chapter 2

shapes and quickly cooled to obtain the product. Usually, some minor finishing is needed before the product is made available to the consumer. The basic principals involved in common processing methods associated with high- volume products will be discussed briefly below.

2.4.2. Extrusion Processing

The most important processing technique for common thermoplastics is extrusion, where the plastic material is melted in a tubular metal chamber and the melt forced through a die. The design of an extruder is not unlike a toothpaste tube (heated, of course, to melt the resin), and tubular products such as plastic rods, plastic tubes, * plastic drinking straws, coatings on electrical wire, and fibers for textile applications can be manufactured using an appropriately engineered die. To exert enough pressure to force the viscous melt through the small die orifice, an Archimedean screw is used. Most of the heat needed to melt the resin is derived from the mechanical shearing action of the screw, although external heating is also provided. The screw transports the resin from the inlet (at the hopper) through a long passage with several heating regions into a heated die.

The resin passes through a region of the screw (with decreased depth in screw channels) that ensures further mixing and consolidates the melt removing any empty spaces or bubbles in melt prior to reaching the mold. The passage of melt is controlled by a layer of mesh on its way to the entrance of the die; this breaker plate assembly (with screen pack) serves to filter out any particulate debris and to control the melt flow into the die. The design of the die determines the geometric features of the product extruded. Figure 2.8 shows the main features of a simple single-screw extruder, along with three types of common extrusion dies. The simplest die is a precisely drilled hole or a slit yielding a rod or a ribbon product. A slightly more complicated design (a circular orifice with a central solid region) produces pipes and

32 Literature Review Chapter

2 tubing. The first two dies shown in the diagram are for tube (or pipe) products and laminates. The third is a specialized die for coating thermoplastic resins on electrical conductors. As the conductor is drawn through the cylindrical die, it contacts the molten polymer introduced from the top of the die. Extremely complicated dies are used in the extrusion of complicated profiles, for instance, in plastic window and door frames. The product emerging from the die is handled by “down stream” equipment that would essentially cool (in case of pipe cut to size) and collect the product for storage. The actual pieces of equipment used for the purpose depend on the type of product manufactured.

(a) . Melt from J extruder

Coated wire

Annular die Stit die Crosshead die

(b)

Figure 2.8 Main features of a simple single-screw extruder, along with three types of common extrusion dies

2.4.3. Injection Molding

Injection molding is one of the most popular processing operations in the plastics industry. In recent years, more than half the processing machinery manufactured were injection-molding machines. The equipment is basically designed

33 Literature Review Chapter

2 to achieve the melting of the resin, injecting the melt into a cavity mold, packing the material into the mold under high pressure, cooling to obtain solid product, and ejecting the product for subsequent finishing. It is different from extruders in that a mold is used instead of a die, requiring a large force to pack the melt into the mold. A machine is typically classified by the clamping force (which can vary from 1 to 10,000 tons!) and the shot size determined by the size of the article to be manufactured. Other parameters include injection rate, injection pressure, screW design, and the distance between tie bars. The machine is generally made of (a) a hydraulic system, (b) plasticating and injection system, (c) mold system, and (d) a clamping system. The hydraulic system delivers the power for the operation of the equipment, particularly to open and clamp down the heavy mold halves. The injection system consists of a reciprocating screw in a heated barrel assembly and an injection nozzle.

The system is designed to get resin from the hopper, melt and heat to correct • temperature, and deliver it into the mold through the nozzle. Electrical heater bands placed at various points about the barrel of the equipment allow close control of the melt temperature. The mold system consists of platens and molding (cavity) plates typically made of tool-grade steel. The mold shapes the plastic melt injected into the cavity (or several cavities). Of the platens, the one attached to the barrel side of the machine is connected to the other platen by the tie bars. A hydraulic knock-out system using ejector pins is built into one of the platens to conveniently remove the molded piece.

The machine operates in an injection-molding cycle. The typical cycle sequence is, first, the empty mold closes, and then the screw movement delivers an amount of melt through the nozzle into it. Once the mold is full, the pressure is held to “pack” the melt well into the mold. The mold is then cooled rapidly by a cooling medium (typically water, steam, or oil) flowing through its walls, and finally the mold opens to eject the product. It is common for this cycle to be closely monitored and to be mostly automated by the use of sophisticated control systems. Figure 2.9 shows a diagram of a simple injection molding machine indicating the hydraulic, injection,

34 Literature Review Chapter

and mold systems. The mold filling (a), compaction (b), cooling (c), and ejection (d) steps are also illustrated in Figure 2.9. shows a modern injection-molding machine.

Hopper Nozzie Heaters _r I Cl OIZ1QIZ3 □ cm Clamping .. system

Reciprocating screw Hydraulic system Injection system Mold system

Nozzle \ t? Q T Moving Stationary platen platen (a) (b) (c) id)

Figure 2.9 .Diagram of a simple injection-molding machine indicating the hydraulic, injection, and mold systems .When a multicavity mold designed for several “parts” is used, the ejected product is complex, consisting of runners, a spruce, and flashing that needs to be removed (and recycled) to obtain the plastic product. Figure 2.10 shows a molding with one of the product “parts” removed from it.

Figure 2.10 Injection-molded piece.

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2.4.4. Blow Molding

This is the primary processing technique used to fabricate hollow plastic objects, particularly bottles, which do not need a very uniform distribution of wall thickness. It is a secondary shaping technique that inflates the preprocessed plastic (usually extruded) against the inside walls of the mold with a blow pin. In addition to extrusion blow molding, injection blow molding and stretch blow molding are commonly employed. With most polymers, especially when the product size is large, extrusion blow molding is used; while injection blow molding is typically used with smaller products with no handleware. Semicrystalline materials that are difficult to blow are molded by stretch blow molding. Common resins such as PVC, PS, PP, LDPE, HDPE, and PET are blow molded routinely. Figure 2.11 illustrates the steps involved in extrusion blow molding.

r mm [. !

< 3 C> Empty Plastic tube Mold Cold air Mow mord ext aided closes injected opens

Figure 2.11 Blow molding of plastic bottle. In extrusion blow molding, the most common blow-molding process, an extruder is used to produce a thick-walled plastic tube called the parison. The parison is extruded directly into a water-cooled cavity mold, which is then closed, and air injected through the top or the neck of the container. The softened polymer in the parison inflates against the wall o f the mold, which cools the m elt and solidifies it into the mold shape. The mold opens and the part is removed and deflashed to remove any excess plastic. While the wall thickness of the parison itself is uniform, that of the product formed (a bottle) will not be uniform because of its different geometry. This variation in wall thickness needs to be taken into account when designing products intended for blow molding. In this processing cycle most of the time is spent on cooling the mold. Therefore, it is usual to have several molds set up on a rotating table that takes up sections of parison from a single continuous extruder to optimize the process.

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In injection blow molding, an injection-molding machine replaces the extruder. In the first stage a parison with the threads of the finished bottle molded in is injection molded onto a core element. The injected parison core is then carried to the next station on the machine, where it is blown up into the finished container as in the extrusion blow-molding process above. In some instances the parison might be stretched inside the mold to obtain a biaxially oriented plastic product.

As the parison is injection molded, there is good control of the weight of the final product in this type of blow molding.

In stretch blow molding (for resins such as PET used in soda bottles) an injection-molded preform (usually obtained from a separate specialized vendor) is used. The preform is loaded into a simple machine that heats it to soften the plastic and stretches it inside the mold to shape the plastic into a bottle.

2.4.5. Extrusion Blowing of Film

Extrusion blowing of common plastics such as polyethylenes into film is one of the oldest processing techniques (dating back to the 1930s in the United States). The basic process is simple and is based on a special annular die that is connected to one or more extruders. In the simple case with a single extruder, the molten plastic material is extruded vertically upwards through the die into a thin-walled plastic tube. Blowing air into the tube expands the soft molten polymer, deforming it circumferentially into a tube with a wider diameter, while the pickup and winding up of the collapsed tube elongates the tube in the machine direction. The ratio of the pickup or haul-off rate to that of extrusion is called the draw-down ratio. The tubular film can be blown up by air only while it is soft and soon forms a “freeze line” at a maximum diameter (the ratio of the diameter at the freeze line to that of the annular die is the blow-up ratio for the film). To obtain a uniform film, it is crucial to maintain constant extrusion rates and a symmetric stable “bubble” or the inflated cylinder of polymer at all times during processing. Typically the bubble can be 15-30 Literature Review Chapter

2 ft tall and up to several feet in diameter. The processing variables as well as the grade of resin used for film blowing determines the quality and uniformity of the film product Figure 2.12 shows a diagram of film blowing equipment.

The same process can also be used to produce a multilayered film using several extruders, one for each type of resin used, and a feed block to direct the resin into different layers. The layers need to be selected carefully for their processing characteristics as well as their performance in the final product. For instance, in coextrusion of a barrier film for packaging applications, different layers of the film might be selected for different functionality needed in the prod.

Figure 2.12 Schematic representation of extrusion blowing of plastic film.

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2.5 Polyester and PET R ecycling Industry

2.5.1 General

When recycling polyethylene terephthalate or PET or polyester, two ways generally have to be differentiated: 1-The chemical recycling back to the initial raw materials purified terephthalic acid (PTA) or dimethyl terephthalate (DMT) and ethylene glycol (EG) where the polymer structure is destroyed completely, or in process intermediates like bis-G- hydroxyterephthalate. 2-The mechanical recycling where the original polymer properties are being maintained or reconstituted.

Chemical recycling of PET will become cost-efficient only applying high capacity recycling lines of more than 50,000 tons/year. Such lines could only be seen, * if at all, within the production sites of very large polyester producers. Several attempts of industrial magnitude to establish such chemical recycling plants have been made in the past but without resounding success. Even the promising chemical recycling in Japan has not become an industrial break through so far. The two reasons for this are at first the difficulty of consistent and continuous waste bottles sourcing in such a huge amount at one single site and at second the steadily increased prices and price volatility of collected bottles. The prices of baled bottles increased for instance between the years 2000 and 2008 from about 50 Euro/ton to over 500 Euro/ton in 2008.

Mechanical recycling or direct circulation of PET in the polymeric state is operated in most diverse variants today. These kinds of processes are typical of small and medium-sized industry. Cost-efficiency can already be achieved with plant capacities within a range of 5 000 - 20 000 tons/year. In this case, nearly all kinds of recycled-material feedback into the material circulation are possible today. These diverse recycling processes are being discussed hereafter in detail. Literature Review Chapter

Besides chemical contaminants and degradation products generated during first processing and usage, mechanical impurities are representing the main part of quality depreciating impurities in the recycling stream. Recycled materials are increasingly introduced into manufacturing processes, which were originally designed for new materials only. Therefore, efficient sorting, separation and cleaning processes become most important for high quality recycled polyester.

When talking about polyester recycling industry we are concentrating mainly on recycling of PET bottles which are meanwhile used for all kinds of liquid packaging like water, carbonated soft drinks, juices, beer, sauces, detergents, household chemicals and so on. Bottles are easily to distinguish because of shape and consistency and separate from waste plastic streams either by automatic or hand sorting processes. The established polyester recycling industry exists of three major sections: PET bottle collection and waste separation— waste logistics Production of clean bottle flakes— flake production Conversion of PET flakes to final products— flake processing

Intermediate product from the first section is baled bottle waste with a PET content greater than 90%. Most common trading form is the bale but also bricked or even loose, pre-cut bottles are common in the market. In the second section the collected bottles are converted to clean PET bottle flakes. This step can be more or less complex and complicated depending on required final flake quality. During third step PET bottle flakes are processed to any kind of products like film, bottles, fiber, filament, strapping or intermediates like pellets for further processing and engineering plastics.

Aside this external polyester bottle recycling numbers of internal recycling processes exist, where the wasted polymer material does not exit the production site to the free market and where the waste is reused at one and the same production circuit. In this way for instance fiber waste is directly reused to produce fiber, preform waste is directly reused to produce performs and film waste is directly reused to produce film

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2.5.2 PET bottle recycling

Purification and decontamination - the most important processing steps during polyester recycling.Thf success of any recycling concept is hidden in the efficiency of purification and decontamination at the right place during processing and to the necessary or desired extent.Generally, the following applies: the sooner foreign substances are removed, in the process, and the more thoroughly this is done, the more efficient the process is.

The high plasticization temperature of PET in the range of 280°C is the reason why almost all common organic impurities such as PVC, PLA, polyolefin, chemical wood-pulp and paper fibers, polyvinyl acetate, m elt adhesive, coloring agents, sugar , and proteins residues are transformed into colored degradation products which, in their turn, might release reactive degradation products additionally. Then, the number of defects in the polymer chain increases considerably. Naturally, the particle size distribution of impurities is very wide, the big particles of 60-1000 /am— which are visible by naked eye and easy to filter— representing the lesser evil since their total surface is relatively small and the degradation speed is therefore lower. The influence of the microscopic particles, which— because they are many— increase the frequency of defects in the polymer, is comparable bigger. The motto "What the eye does not see the heart cannot grieve over" is considered to be very important in many recycling processes. Therefore besides efficient sorting the removal of visible impurity particles by melt filtration processes is playing a particular part in this case. In general one can say that the processes to make PET bottle flakes from collected bottles are as versatile as the different waste streams are different in their composition and quality. In view of technology there isn’t just one way to do it. There are meanwhile many engineering companies which are offering flake production plants and components, and it is difficult to decide for one or other plant design. Nevertheless there are principles which are sharing most of these processes. Depending on composition and impurity level of input material the general following process steps are applied. 1. Bale opening, briquette opening Literature Review Chapter

2. Sorting and selection for different colors, foreign polymers especially PVC, foreign matter, removal of film, paper, glass, sand, soil, stones and metals 3. Pre-washing without cutting 4. Coarse cutting d r^or combined to pre-washing 5. Removal of stones, glass and metal- 6. Air sifting to remove film, paper and labels 7. Grinding, dry and / or wet 8. Removal of low-density polymers (cups) by density differences 9. Hot wash 10. Caustic wash 11. Caustic surface etching, maintaining intrinsic viscosity and decontamination . 12. Rinsing 13. Clean water rinsing 14. Drying 15. Air sifting o f flakes 16. Automatic flake sorting 17. Water circuit and water treatment technology 18. Flake quality control 2.5.3 Impurities and material defects The number of possible impurities and material defects which accumulate in the polymeric material is increasing permanently— when processing as well as when using polymers— taking, into account a %to\\«v% sets'\ce Ivfe \vn\e, fma\ applications and 'repealed \ec^c\\Y\g. Ns far as iecyc\ed PKY botVies are concerned, the defects mentioned can be sorted in the following groups:

Reactive. p o U jestex OR- at COCft\- e w i - a t XvafcsfejreweA trtfc S w a reactive end groups, e.g. formation of vinyl ester end groups through dehydration or decarboxylation of terephthalate acid, reaction of the OH- or COOH- end groups with mono-functional degradation products like mono-carbonic acids or alcohols. Results are decreased reactivity during re-polycondensation or re-SSP and broadening the

molecular weight distribution.

b) The end group proportion shifts toward the direction of the COOH end groups built up through a thermal and oxidative degradation. Results are decrease in reactivity, Literature Review Chapter

2 increase in the acid autocatalytic decomposition during thermal treatment in presence of humidity. c) Number of poly-functional macromolecules increases. Accumulation of gels and long-chain branching defects. d) Number, concentration and variety of non polymer-identical organic and inorganic foreign substances are increasing. With every new thermal stress, the organic foreign substances will react by decomposition. This is causing the liberation of further degradation-supporting substances and coloring substances. e) Hydroxide and peroxide groups build up at the surface of the products made of polyester in presence of air (oxygen) and humidity. This process is accelerated by ultraviolet light. During an ulterior treatment process, hydro peroxides are a source of oxygen-radicals which are source of oxidative degradation. Destruction of hydro peroxides is to happen before the first thermal treatment or during plasticization and can be supported by suitable additives like antioxidants. Taking in consideration the above mentioned chemical defects and impurities, * there is ongoing a modification of the following polymer characteristics during each recycling cycle, which are detectable by chemical and physical laboratory analysis. In particular: Increase of COOH end groups Increase of color number b Increase of haze (transparent products ) Increase of oligomer content Reduction in filterability Increase of by-products content such as acetaldehyde, formaldehyde Increase of extractable foreign contaminants Decrease in color L Decrease of intrinsic viscosity or dynamic viscosity - Decrease of crystallization temperature and increase of crystallization speed Decrease of the mechanical properties like tensile strength, elongation at break or elasticity modulus Broadening of molecular weight distribution

43 Literature Review C h ap ter 2

The recycling of PET-bottles is meanwhile an industrial standard process which is offered by a wide variety of engineering companies

2.5.4 Processing examples for recycled polyester Recycling processe^with polyester are almost as varied as the manufacturing processes based on primary pellets or melt. Depending on purity of the recycled materials polyester can be used today in most of the polyester manufacturing processes as blend with virgin polymer or increasingly as 100% recycled polymer. Some exceptions like BOPET-film of low thickness, special applications like optical film or yarns through FDY-spinning at > 6000 m/min or microfilaments and micro fibers are produced from virgin polyester only.

2.5.4.1 Simple re-pelletizing of bottle flakes This process consists in transforming bottle waste into flakes, by drying and crystallizing the flakes, by plasticizing and filtering, as well as by pelletizing. Product is an amorphous re-granulate of an intrinsic viscosity in the range of 0.55-0.7 dC/g, depending on how complete pre-drying of PET flakes has been done. Special feature are: acetaldehyde and oligomers are contained in the pellets at lower level; the viscosity is reduced somehow, the pellets are amorphous and have to be crystallized and dried before further processing. Processing to: Non-woven, Staple fiber, Filaments, Carpet yarn, A-PET film for thermoforming, Packaging stripes, BOPET packaging film, Bottle resin by SSP, Engineering plastics, Addition to PET virgin production.

Choosing the re-pelletizing way means having an additional conversion process

\\iVi\Or\ v=> aV owe eweTg} vrv\eTVS\\e, cos\ conswrn'vng, causes XhetvtvaX destruction. At the other side the pelletizing step is providing the following advantages: o Quality uniformization o Processing flexibility increased o Product selection and separation by quality

o Intermediate quality control o Intensive melt filtration

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o Modification by additives

2.5.4.3 Manufacture of PET-pellets for bottles (B-2-B) and A-PET

/ This process is, in principle, similar to the one described above; however, the pellets produced are directly (continuously or discontinuously) crystallized and then subjected to a solid-state polycondensation (SSP) in a tumbling drier or a vertical tube reactor. During this processing step, the corresponding intrinsic viscosity of 0.80 - 0.085 d£/g is rebuild again and, at the same time, the acetaldehyde content is reduced to < 1 ppm.

The fact that some machine manufacturers and line builders in Europe and USA make efforts to offer independent recycling processes, e.g. the so called bottle- to-bottle (B-2-B) process, such as URRC or BUHLER, aims at generally furnishing proof of the "existence" of the required extraction residues and of the removal of model contaminants according to FDA applying the so called challenge test, which is necessary for the application of the treated polyester in the food sector. Besides this process approval it is nevertheless necessary that any user of such processes has to constantly check the FDA-limits for the raw materials manufactured by himself for his process.

2.5.4.4 Direct conversion of bottle flakes

In order to save costs, one is working on the direct use of the PET-flakes, from the treatment of used bottles, with a view to manufacturing an increasing number of polyester intermediates. For the adjustment of the necessary viscosity, besides an efficient drying of the flakes, it is possibly necessary to also reconstitute the viscosity through polycondensation in the melt phase or solid-state polycondensation of the flakes. The latest PET flake conversion processes are applying twin screw extruders, multi screw extruders or multi rotation systems and coincidental vacuum degassing to remove moisture and avoid flake pre-drying. These processes allow the conversion of un-dried PET flakes without substantial viscosity decrease caused by hydrolysis.

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Looking at the consumption of PET bottle flakes the main portion of about 70% is converted to fibers and filaments. When using directly secondary materials such as bottle flakes in spinning processes, there are a few processing principles to obtain. ?

High speed spinning processes for the manufacture of POY normally need a viscosity of 0.62-0.64 d£/g. Starting from bottle flakes, the viscosity can be set via the degree of drying. The additional use of Ti02 is necessary for full dull or semi dull yarn. In order to protect the spinnerets, an efficient filtration of the melt is, in any case is necessary. For the time being the amount of POY made of 100% recycling polyester is rather low because this process requires high purity of spinning melt. Most of the time a blend of virgin and recycled pellets is used.

Staple fibers are spun in an intrinsic viscosity range which rather lies somewhat lower and which should be between 0.58 and 0.62 df/g. In this case, too, the required viscosity can be adjusted via drying or vacuum adjustment in case of vacuum extrusion. For adjusting the viscosity, however, an addition of chain length

Spinning non-woven— in the fine titer field for textile applications as well as heavy spinning non-woven as basic materials, e.g. for roof covers or in road building— can be manufactured by spinning bottle flakes. The spinning viscosity is again within a range of 0.58-0.65 d£/g. One field of increasing interest where recycled materials are used is the manufacture of high tenacity packaging stripes— and monofilaments. In both cases, the initial raw material is a mainly recycled material of higher intrinsic viscosity. High tenacity packaging stripes as well as monofilament are then manufactured in the melt spinning process

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2.5.5 Recycling back to the initial raw materials

2.5.5.lGlycolysis anc|rpartial glycolysis

The polyester which has to be recycled is transformed into an oligomer by adding ethylene glycol or other glycols during thermal treatment. The aim and advantage of this way of processing is the possibility of separating the mechanical deposits directly and efficient through a progressive and stepwise filtration. The filtration fineness of the last filtration step has a decisive effect on the quality of the end product. Taking partial recycling with partial glycolysis as an example, it is to be demonstrated how bottle waste can successfully be recycled in a continuously operating polyester line which is manufacturing pellets for bottle applications.

The task consists in feeding 10-25% bottle flakes and maintaining at the same time the quality of the bottle pellets which are manufactured on the line. This aim is solved by degrading the PET bottle flakes— already during their first plasticization which can be carried out in a single- or multi-screw extruder— to an intrinsic viscosity of about 0.30 d£/g by adding small quantities of ethylene glycol and by subjecting the low viscosity melt stream to an efficient filtration directly after plasticization. Furthermore, temperature is brought to the lowest possible limit. In addition, with this way of processing, the possibility of a chemical decomposition of the hydro peroxides is possible by adding a corresponding P-stabilizer directly when plasticizing. The destruction of the hydro peroxide groups is, with other processes, already carried out during the last step of flake treatment for instance by adding H 3P03. The partially glycolyzed and finely filtered recycled material is continuously fed to the esterification or prepolycondensation reactor, the dosing quantities of the raw materials are being adjusted accordingly. The treatment of polyester waste through total glycolysis to convert the polyester to bis-beta hydroxy-terephthalate, which is vacuum distilled and can be used, instead of DMT or PTA, as a raw material for polyester manufacture, has been executed on an industrial scale in Japan as experimental production.

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2.5.5.4 Hydrolysis

Recycling processes, through hydrolysis of the PET to PTA and MEG, are operating under high pressures under supercritical conditions. In this case, PET-waste will be directly hydrolyzed applying for instance supercritical water steam. Purification of crude terephthalic acid will be carried out by re-crystallization in acetic acid / water mixtures similar to PTA purification. Industrial-scale lines based on this chemistry have not been known to date.

2.5.5.3 Methanolysis

Methanolysis is the recycling process which has been practiced and tested on a large scale for many years in the past. In this case, polyester waste is transformed with methanol into DMT, under pressure and in presence of catalysts. After this an efficient filtration of the methanolysis product is applied. Finally the crude DMT is purified by vacuum distillation. The methanolysis is only rarely carried out in industry today because polyester production based on DMT shrunk tremendously and with this DMT producers disappeared step by step during the last decade [14],

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2.5.6 Practices in Collection and Recycling of PET Bottles

2.5.6.1 Collection There are four basic ways in which communities worldwide offer recycling collection services for PET plastic bottles and containers to their residents. The first method known as Returnable Container Legislation, or "Bottle Bills" These containers, when returned by the consumer for the redemption value, facilitate recycling by aggregating large quantities of recyclable materials at beverage retailers and wholesalers to be collected by recyclers, while simultaneously providing the consumer with an economic incentive to return soft drink containers for recycling. The second and most widely accessible, collection method is curbside collection of recyclables. Curbside recycling programs are generally the most convenient for community residents to participate in and yield high recovery rates as a result .Residents are requested to sepa/ate designed recyclables from their household garbage and to place them into special receptacles or bags. The third collection method is known as drop-off recycling . In this method, containers for designed recyclables materials are placed at central collection locations throughout the community, such as parking lots, schools, or other civic associations. Residents are requested to deliver their recyclables to the drop-off location, where recyclables are separated by material type into their respective collection containers. Drop-off centers require much less investment to establish than curbside programs, yet do not offer the convenience of curbside collection. The last collection method employs the use of buy-back centers. As most buy-back centers are operated by private companies, they often provide incentives, through legislation or grants and loan programs, that can assist in the establishment of buy-off centers for their residents. Most buy-off centers have purchasing specifications that require consumers to source separate recyclable materials brought for sale, e.g. removal of caps from bottles. PET plastic wastes are also collected by the following ways: ■ Private Collection -This type of collection is done in restaurants, hotels, business establishments, supermarkets and fast food chains.

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■ Household Consumer - The household consumers segregate and sell their plastif waste to eco-aids. However , some of them dispose their commingled solid waste to garbage bins or containers for pickup by dump trucks or garbage collectors. ■ Junk Shops- There are many junk shops collecting recyclable items and separate them. They buy from scavengers and household consumers and sell their scrap to the recyclers/ processors. PET bottles are sold after sorting and cleaning (removal of cover and label) from the commingled waste. ■ Middleman - The middleman or consolidators operates in the following ways: a) collects and grinds PET industrial waste "on- site", b) collects and grinds PET industrial and post consumer waste in their own plant, and c) collects PET industrial/ consumer waste and sell them to PET recyclers

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2.5.6.2 Recycling PET bogles

Recycling of PET bottles

Design for Separation, the Serendipitous Result

Collected PET containers are delivered to materials recovery facility (MRF) or a plastic intermediate processing facility (IPC) to begin recycling process. Literature Review Chapter

Segregation & Grinding/Flaking (MRFs) separate collected recyclables into their different categories. PET bottles are separated based on type/number, color and processing method then baled for sale to (IPCs), (PRFs) or reclaimers. (PRFs) further sorted PET bottles by color sorting, granulating and shipment to reclaimers as "dirty" regrind for processing into a form that can be used by converters. Cleaning & Drying At reclaiming facility, the dirty flake passes through series of sorting and cleaning stages to separate PET from other contaminants (labels, glue, fines and very small PET particles). The flakes then washed with detergent in a "scrubber", then passed through "float/sink" classifier to remove float base cups(HDPE) and caps ring(PP). Some reclaimers use "hydrocyclone" for this step. Then the flakes thoroughly dried in a "centrifugal dryer" and passed through "electrostatic separator" for aluminum separation. X-Ray separation may also be used for removal of PVC. Cleaned PET flake or pellet is then processed by reclaimers or converters into commodity-grade raw material such as fiber, sheet or engineered compounded pellet which finally sold to end-users manufacturing new products. There are five major generic end-use categories recycled PET: 1) Packaging applications e.g. bottles. 2) Sheet &film applications e.g. laundry scoops. 3) Strapping. 4) Engineered resins applications e.g. reinforced compounds for automobiles 5) Fiber applications e.g. carpets, fiberfill

2.5.6.3 Designing Community s PET Recycling Collection Program Properly designed PET recycling collection programs greatly increase the quantity and quality of PET collected and can reduce overall recycling system costs. In order to maximize the recovery and value of PET plastic containers our community recycling collection program, two best practices should be followed when designing program. The first is to establish an effective and ongoing consumer education program. The second best practice is to designate all PET bottles with screw-neck tops as acceptable for recycling.

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There are seven basic messages that should be included in any consumer education or promotional program aimed at the collection of PET bottles. 1) with screw-neck tops to be placed for collection or brought to a collection location. PET can be identified by looking for the "#1 code. Any non-bottle PET should be excluded. 2) Only PET bottles that are clear or transparent green should be included for recycling . Other colors to be excluded. 3) Consumers should remove lips, caps and other closures from PET bottles placed for recycling. 4) All PET bottles that are setout for recycling should be completely free of contents and rinsed clean. 5) Consumers should flatten PET bottles prior to setting out for collection. 6) Consumers should never place any material other than the original content into PET bottles for recycling. 7) Hypodermic needles are increasipg safety concern at recycling facilities [15].

53 Chapter Three

Materials &* Methods Materials & Methods Chapter

! 3 Materials & Methods

3.1 The Study Area

Khartoum state is one of the 26 states of Sudan , located in the middle of Sudan. It contains three provinces, Khartoum, Omdurman and Khartoum North with eight localities. It has area of 22,122 Km2 and estimated population of approximately 7,152,102 (2008). Khartoum, the national capital of Sudan, is the capital of Khartoum state. Khartoum state is linked with other states through traffic networks highways roads, railways and airways.

In Khartoum state there are (7) seven soft drinks factories and more than (50) fifty water bottling factories. All of these factories are using PET plastic bottles for their packaging. Four of the seven soft drinks factories are in Khartoum North industrial area, two in Omdurman and one in Khartoum new industrial area. Most of these factories are distributing their products to all states of Sudan. There are also (4) four formal small-scale grinding plastic recycling units and many informal recycling units in Khartoum state. Only one of the formal units is grinding collected PET bottles for export. There are also (2) two PET preform (bottles) factories newly established in Geury industerial area.

54 Materials & Methods Chapter 3

3.1.1 Khartoum State Map (Google).

3.2 Sources & Methods of Data Collection

PET bottles have been a focus of interest of this study due to the littering problem. Therefore, information was reviewed to gain an understanding of the following aspects: the plastic chain with emphasis on existing plastic waste management practices of PET bottles, also the relevant stakeholders and the parteners that exist between them. In addition, emphasis was placed on studying soft drinks & water factories and plastic recycling units and their constrains in handling PET. Materials & Methods Chapter 3

Information and data for this study were gathered from diverse sources mainly, Bank of Sudani, Customs Authorities, Ministry of Industry, Sudanese Chamber of Industries Association, Khartoum State Cleaning Scheme, soft drinks & water factories and plastic recycling units. Two questionnaires were developed and designed so as to get the relevant data, views points of various stakeholders and feasible recommendations that help in mitigation of the problem. Interviews were also carried out with various representatives in the plastic chain. Face to face, on site interviews as possible were undertaken as this was the effective means of gathering information. -The study was conducted in July 2010. -Soft drinks and water bottling factories in Khartoum state are taken as sample for this study. -Data collected from Bank of Sudan and Customs Authorities covering the period 2005 - 2009. , -Survey and data results were managed and analyzed by Excel and e-view analytical methods.

3.3 Statistical Analysis Methods

The data collected were presented in charts and graphs applying Excel program which is the preferred program and much more useful for creating charts and graphs for data presentation as well as developing projections. E-view program was also applied for the future forecasting.

Microsoft Excel is a spreadsheet application written and distributed by Microsoft for Microsoft Windows and Mac OS X . It features calculation, graphing tools, pivot tables and a macro programming language called (VBA ) Visual Basic for Applications .(It has been a very widely applied spreadsheet for these platforms, especially since version 5 in 1993 .Excel forms part of Microsoft Office .The current versions are Microsoft Office Excel 2010 for Windows and 2008 for Mac. Microsoft Excel has the basic features of all spreadsheets using a grid of cells arranged in numbered rows and letter-named columns to organize data manipulations like Materials & Methods Chapter 3 arithmetic operations .It has a battery of supplied functions to answer statistical, engineering and financial needs .In addition, it can display data as line graphs, histograms and charts, and with a very limited three-dimensional graphical display.

EViews (econometric Views) statistical package for Windows, used mainly for time-series oriented econometric analysis . It is developed by Quantitative Micro Software (QMS), now apart of HIS .The current version of EView is 7.1, released in April 2010. EViews can be used for general statistical analysis and econometric analyses, such as cross-section and panel data analysis and time series estimation and forecasting .EViews combines spreadsheet and relational database technology with the traditional tasks found in statistical software, and uses a Windows GUI .This is combined with a programming language which displays limited object orientation. EViews relies heavily on a proprietary and undocumented file format for data storage.

57 Chapter Four Results & Discussion Results & Discussion Chapter 4

4 Results & Discussion

4.1 Results

In general, table (4.1) shows imported plastic materials in metric tons and their values in 1000 $ for virgin plastic resin, plastic products and PET preform (bottles) during the years 2005 - 2009. And table (4.2) shows annual increment of PET preform (bottles) during 2007 -July 2010. The figures (4.1a) -(4 .6b) respectively illustrate graphical relationship between particulars, by using excel program, during the same period. A forecast for imports of PET preform (bottles) was shown in table (4.3) by applying eviews package.

Sudan imports of plastic materials increased annually, in year 2005 reached 54540 tons virgin plastic resin of value 61,292,000 $,107,420 tons plastic products of value 73,341,000 $ and 9,611 tons PET preform (bottles) of value 18,137,000 $.

In 2006 imported of virgin resin was 64,403 tons of value 63,259,000 $ 55,511 tons plastic products of value 85,124,000 $ and 10,400 tons PET of value 18,235,000

In 2007 virgin resin was 65,146 tons of value 94,354,000 $, 53,790 tons plastic products of value 98,072,000 $ and 9,915 tons PET preform of value 17,384,000 $.

In 2008 virgin resin increased to 75,233 tons of value 129,106,000 $, 62,860 tons plastic products of value 117,616,000 $ and 15,81 I tons PET preform of value

29,780,000 $. In 2009 imported virgin resin reached 108,856 tons of value 139,234,000 $, 117,616 tons plastic products of value 80,945,000 $ and 22,444 tons PET preform of value 38,899,000 $.

In this year 2010, from January to July, imports of plastic materials show significant increase. Virgin resin reached 58,565 tons of value 71,795,000 $, 38,271 tons plastic products of value 85,662,000 $ and 17,336 tons PET preform of value

58 Results & Discussion Chapter 4

34,564,000 $. Therefore, PET preform imports estimated to reach by end of 2010 approximately 30000 tons.

f 4.1.1 Excel Presentation The results obtained as in table (4.1) are presented in graphical and charts forms by applying Excel Microsoft Program as shown in figures (4.1a,b) - (4.6a,b); Figures (4.1a) and (4.1b) represent quantities and values of the imported virgin plastic resin according to year. Figures (4.2a) and (4.2b) represent imported PET preform quantities and values according to year. Figures (4.3a) and (4.3b) represent yearly imported plastic products in quantities and values. Figures (4.4a), (4.4b) and (4.5a), (4.5b) illustrate the comparative relationship between virgin resin, PET preform and plastic products imports in quantity/value during the years 2005 -2009. Figures (4.6a) and (4.6b) show the ratio of PET preform imports to virgin plastic resin in quantities and values during the same period.

59 4

Table(4.1) Imported Plastic Resin I Products I PET Perform (bottle) Period 2005 - 2009

2005 2006 2007 2008 2009

ITEM Quantity Value Q V Q V Q V Q V MT X1000$ MT X I000$ MT X I000$ MT X I000$ MT X I000$

Virgin Plastic Resin 54,580 61,292 64,403 63,259 65,146 94,354 75,233 129,106 108,856 139,234

Plastic Products 107,420 73,341 55,571 85,124 53,790 98,072 62,860 117,616 80,945 175,047 j

PET Preform 9,611 18,137 10,400 (bottles) 18,235 9,915 17,384 15,811 29,780 22,444 38,899

% age PET/Virgin 17.6% Plastic Resin 16.0% 15.2% 21% 20.6%

60 Table (4.2) Estimate PET Preform (bottle) 2010 4

2 0 0 7 2 0 0 8 2 0 0 9 2 0 1 0 2 0 1 1 Year/MT 2 0 1 2 2 0 1 3 2 0 1 4 2 0 1 5

PET preform 9915 15811 22444 30000 35972 41892 47812 53732 59652

Increment 5896 6633 7556 5972 5920 5920 5920 5920

% annual increment 59.4% 41.9% 33.7% 20% * 16% 14% 12% 11%

Table (4.2) PET Preform (bottle) % Annual Increment

61 Results & Discussion Chapter 4

Virgin Plastic Resin

i 2005 i 2006 2007 2008 2009

Fig (4.1a)

Virgin Plastic Resin

i 2005 l 2006 2007

2008

2009

Fig (4.1b)

62 Results & Discussion Chapter 4

PET Preform(bottles) 1

Fig (4.2a)

PET Preform(bottles)

Fig (4.2b)

63 Chapter 4 I

Plastic Products

107420 12005 i 2006 2007 i 2008 2009

Fig (4.3a)

Plastic Products

I 2005 12006 i 2007 12008 I 2009 Results & Discussion Chapter 4

Ratio of PET preform imports to virgin plastic (Quantities)

100%

9 0 % y 80% f 70% - 60% - 12% c 4% 15% '9% 9% ■ Virgin Plastic Rosin 5 0 % y 40% ■ PET Preform(bottles)

3 0 % y 20% - 1% 10% - lj8% 1,6% L5% . 1% 0% 4^ 2005 2006 2007 2008 2009

Fig (4.6a)

in plsticRatio of preform imports to virg (Values)

■ Virgin Plastic Resin

■ PET Preform(bottles)

Fig (4.6b

65 Results & Discussion Chapter 4

i Virgin Plastic Resin

l Plastic Products

PET Preform(bottles)

2005 2006 2007 2008 2009

Fig (4.4a)

Comparative relation between virgin resin, PET &plastic products imports (Quantities)

66 Results & Discussion Chapter 4

m Virgin Plastic Resin ■ Plastic Products

■ PET Preform(bottles)

20000 0 2005 2006 2007 2008 2009

Fig (4.5a)

200000 180000 160000 140000 120000 — Series 1 100000 Series2 80000 Series3 60000 40000 20000 0 <1) 0 < D <1> 0 ) 3 3 3 3 LU £ 03 03 03 03 03 > > > > cl lij >

2005 2006 2007 2008 2009

Item

Fig (4.5b) een virgin resinComparative relation betw, PET &plastic products imports (Values) Results & Discussion Chapter 4

Eviews Package Application

Forecast for PET Preform (bottles) Imports

Forecast: XF3 Actual: X Forecast sample: 2005 2015 Adjusted sample: 2005 2010 Included observations: 6

Root M ean Squared Error 2882.624 M ean Abs. Percent Error 2363.590 M ean Absolute Percentage Error 18.51712 Theil Inequality Coefficient 0.080414 Bias Proportion 0 .0 00000 Variance Proportion 0.038883

XF3 ± 2 S.E.

Dependent Variable: X Method: Least Squares Date: 08/23/10 Time: 13:35 Sample(adjusted): 2006 2010 Included observations: 5 after adjustinc endpoints Variable Coefficient Std. Error t-Statistic Prob. T 5920.110 797.5212 7.423137 0.0177 C -621159.7 85990.06 -7.223622 0.0186 RESID01(-1) 0.742890 0.418197 1.776413 0.2176 R-squared 0.968474 Mean dependent var 17714.00 Adjusted R-squared 0.936948 S.D.dependent var 8533.157 S.E. of regression 2142.689 Akaike info criterion 18.46122 Sum squared resid 9182236. Schwarz criterion 18.22688 Log likelihood -43.15305 F-statistic 30.71985 Durbin-Watson stat 2.986481 Prob(F-statistic) 0.031526

Y = C + BT Y = -62110 + 5920.11 T + .74289 e Since Y : PET Preform T : Y ear C : intercept B : Slope ofT e : error

68 Results & Discussion Chapter 4

Years PET Preform "bottles" Growth Rate 2005 9611 2006 10400 2007 9915 -5% 2008 15811 59% 2009 22444 42% 2010 30000 34% 2011 35972.51 20% 2012 41892.62 16% 2013 47812.73 14% 2014 53732.84 12% 2015 59652.95 11%

Table (4.3)

4.1.3 Soft Water bottling Factories Survey drink &

The result of the survey, visits, meetings and interviews conducted with key personnel in some selected soft drink and water bottling factories indicated that PET industrial waste generated as rejects during the processing of preforms to stretch blow molding into bottles was in the range 0.5 - 3%. The industrial waste depends mainly on the machine efficiency and the preforms quality. This PET waste is clean, easily identified/ defined and segregated.

69 ■

Results & Discussion Chapter 4

4.2 Discussion

< As shown in Figures (4.2a) and (4.2b) imported quantities and values of PET preform were increasing annually. In year 2005 the quantity imorted was 9600 tons of value 18,137,000$ increased teremendously to reash 22444 tons of value 38,899,000$ and expected to reash 30000 tons by the end of this year 2010. This high increase in PET consumption due to introduction of additional capacities and investments in soft drinks and water plants as well as partial replacement of glass bottles by PET. Table (4.3) illustrates forecasted quantities of PET Preform up to year 2015 by applying eview statistical package. PET Preform estimated to reash approximately 60000 tons in year 2015 which is twice the quantity estimated in year 2010. This expected high rising in PET consumption will require serious measures to be taken to pose environmental challenges for the whole country and Khartoum State in particular.

70 Chapter Five Conclusion &Recommendations Conclusion & Recommendation Chapter 5

5. Conclusion &Recommendations

^ 5.1. Conclusion Population growth and rapid pace of urbanization pose several environmental challenges for Khartoum State. One of the challenges is the waste management, and especially plastic waste management. The environmental issues regarding plastic waste and PET in particular, arise predominately due to the gradual changes in lifestyle, the throwaway culture that plastic propagate, and also the lack of an efficient waste management system contribute to the widespread problem. PET Preform (bottles) imported during the last five years (2005-2009) was increasing due to high demand of soft drinks and bottled water and estimated to reach 30000 tons by the end of this year 2010. Prediction of PET preform for the coming five years as shown in table (4.3) estimated to reach approximately 60000 tons in year 2015. This expected rise and increasing consumption of PET bottles will create environmental problems that must be addressed by identifying and introducing recycling as one of the best practical cleaner production tool to achieve sustainable development. Mechanical recycling of PET bottles is the most preferred recovery route for homogeneous and relatively clean plastic waste stream. It is well suited for developing countries since it is less cost-intensive and currently being employed in Khartoum plastic recycling units. Collection process is the key to successful recycling of PET bottles and plastic waste. It lies on consumers that must become educated and motivated through designed community educational program so that identification and collection of recyclables containers becomes a routine activity. With abundance of PET bottles, the current recycling units are very low capacities and the process is just grinding, cleaning and baling for export. PET industrial waste from factories rejects ranged from 0.5% to 3% which is clean and easily recyclable. Conclusion & Recommendation C h ap ter 5

5.2. Recommendations Based on the findings and results of this study, it is recommended that:

• Government support to Khartoum cleaning scheme and other private companies working in waste management to achieve better performance and exert more effort in collection and sorting plastic waste and in particular PET bottles.

• Necessity to cooperation and coordination among the various actors, government, private sector, informal sector, NGOs and the industry to create job opportunities for the limited income people to participate in PET / plastic collection .

• Promote recycling of PET bottles and other plastic waste through adoption of good practices in collection and selection of the appropriate methods, (refer to section 2.5.6)

• Designing community PET recycling collection program greatly increase the quantity and quality of collection and reduce the overall recycling cost. Two best practices should be followed : - To establish an effective and ongoing consumer education program. - To designate all PET bottles with screw-neck tops as accepted for recycling. ( Refer to section 2.5.6.3 )

• Initiate regional and international knowledge transfer from countries with successful practices in PET collection and recycling.

• Promote and encourage current and new investments in PET recycling by offering subsidies.

• Promote and encourage current and new investments in production of PET preform.

• Prohibit imports of second hand machinery or old technologies for soft drink and water bottling factories, however new machinery contributes to waste saving.

• Promote conducting feasibility studies to determine the viability of the

establishment of PET resin industry using Sudanese petroleum.

-72- Conclusion & Recommendation Chapter 5

Review of the existing laws and policies on plastic waste with particular to PET rising consumption to address the problem of littering by encouraging recycling. Promote conducting further researches and studies in future.

-73- -

References

^ References

[1] Anthony L. Andrady, Plastic and the Environment, John Wiley & Sons Publisher, New Jerrsy, 2003, p 77-120. [2] Hong Kong Plastic Technology Center, Techo. Economic and Market Research Study, Trade and industry Department Hong Kong 2001, p 3-1 [3]Chemistry in Britain, Good News for Polyolfin in Chemistry in Britain, 2001, p 31. [4] K. Ziegler, Angew, Chem. 67, 33, 1955. [5] W. H. Joyce, Energy and Environment in the 21st Century, Eds. Iw. Tester, Massachusetts Institute of Technology, Cambridge, MA, 1991. [6] T. J. Canvanaugh and E.B. Nauman, Trends Polym. Sci. 1995. [7] D. A. Howe, in J. E. Mark, ed. Polymer Data Handbook, Oxford University Press, New York, 1999, p 781.

[8] A. Sustic and B. Pellon, Adhesive Age Nov. 17, 1991. [9] M. J. Balow, in H. J. Karian, ed, Handbook o f Polypropylene Composites, Marcel Dekker, New York 1999 p 555. [10] D. F. Cadogan, Plst- Rubber Compos. 28, 476, 1999. [11] J. Habnfeld and B. D. Dalke, in H.F. Mark, C. G. Overbeger, G. Menges, eds., Encyclopedia o f Polymer Science and Engineering, 1989, p64. [12] Y. C. Yen and J- T. Haung, Styrene and Polymer, SRI International, Menlo Park, CA, 1984.

[13] http : //en. Wikipedia-org /Wiki/ Polyethylene terephthalate, 17.5.2010. [14] http : //en Wikipedia- org/W iki/ Plastic Recycling, 17.5.2010.

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