Management of PET Plastic Bottles Waste Through Recycling In ...

Sudan Academy o f Science

E ng ineering R esearch A nd Industrial T echnology C ouncil

Management of PET Plastic Bottles

Waste Through Recycling In

Khartoum State

t

A Thesis submitted in partial fulfillment o f the requirement for

the degree o f M aster o f Science in Cleaner Production

By:

Nabeel Bedawi Ismail Fadlalla

B.Sc(hon),chem.. Eng-U o f 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 o f 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 o f 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 o f 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 o f

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 o f plastic waste through recycling.

Based on the analysis and findings recommendations have been made that

ensure on recycling o f 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

ن ص خل ست م

ف سة هذه تهد را د ى ال ح إل را ن آلية اقت مك ها ي رة ب دا ت إ ة النفايا كي ستي ال ة الب الي و طوم ب خر ال

شكل ص وب ت أخ PE' عبوا T J ة كي ستي ال سة الب را ة ود مكاني دة إ عا ها إ ر وي د ة ت سيل ن كو وسائل م

ج تا إلن ف ا ظ ألن ة ا ي ا م ة ح ئ ي ب ل ا و ل ق ي ق ح ف ت دا ه ة ال مي ن ت ل ة ا م ا د ست م ل .ا

م ع ت م ت ج ا ن ا ي ب ل ت و ا ما و عل م ل ة ا ص خا ل ه ا ذ ه ة ب س را د ل ن ا ق ع ري ت ط ا ن ا ي ب ست إل و ا

ت ال ب ا ق م ل ة ا صي خ ش ل ت ا عا ا م جت إل ا ت و را ا زي ل ع وا ق وا م ل ة ل ف ل خت م ل ة ا ف ضا ال ا ى ب ت ال ما و عل م ل ق و ا ائ وئ ل ا

ة مي س ر ل ة ا ر د صا ل ن ا ة ع د ت ع ها ة ج ي ع ج ر ها م م ه ك أ ن ن ب دا و س ل ى ا ز ك ر م ل ة ا ر ا د إل ا ة و م عا ل ك ا ر ما ج ل ل

ى و رت زا ة و ع ا ن م ل ر و ا ما ث ست إل ة ا ك ر ش ة و ف ظا ة ن الي م و و ط ر خ ل ا ا ه ت ا ي حل م ع و ن صا م ت و وبا ر ش م ل ا

صانر الغازية ى المعدنية المياه و والع ت والت خذ ى أ وه ة عين ألكثر ك ما ا خدا ست ل لعبوات ا •PET ا

ت رصد تم ا البيانا ه ض ر ع ت جداول فى و آكسل وندوز برنامج باستخدام بيانية ورسوما

Excel ضا ج واي م رنا راء Eview ب ت إلستق وقعا ستقبلية الت م ي ال ت الت ر ا ث ى أ ت ال طربة زيادا ض م

ى ك ف ال ه ست د PETJ' إ ل ق م ى ن ن 60م0م إل ي ط ر ل مت ق م ا ع ل و ل ح ي 20ب ك ض أ ال ه ست ال ا

ع وق مت ل م ا ا ع ا . 2010 ل م ل م ك ش را ي ط ا خ ي ن ي م ب ز ل ست ر ي ف ضا د ت و ه ج ل ن ا ع م ي م ء ج كا ر ش ل ع ا ض و ل

ل و حل ل ة ا ي ل م ع ل ة ا سب ا ن م ل ظا ا ا ف ى ح ة عل ئ ي ب ل ك ا ذل ة و د ا ع إ ر ب وي د ذه ت ت ه ا ف خل م ل ة ا ي ك ي ست ال ب ل ص ا خل ت ل وا

علميت بطرق ن ١'

ى ء ط و ج ض ئ ا ت ن ل ت ا ال ي حل ت ل ا ك و ل ت ت ل ا ن ا ي ب ل م ا ع ت ض ت و حا ر ت ق م ل ت ا ا صي و ت ل ا ى و عل

عادة ر إ ت تدوي كية PET،J' عبوا ستي ال ة الب ريق ط ة بال كي كاني مي ي ال مد والت عت ي ت س ف سا ال آلية على ا

ع مي ج ت ل ز ا ر ف ل ن وا ح ط ل ا ة و ف ظا ن ل ا ع و ي صن ت ل ا ع و ة م س را ة د ي ن ا ك م ق ا ي طب ق ت ر ط ل ى ا ر خ ال ة ا ي ئ ا ي م ي ك ل ا

ء جرا ث وإ حو ضافية ب ى إ ل هذا ف مجا ت ال حا ر ة كمقت ستقبلي م

Table of Content

Table of ContentsAcknowledgment I

Abstract II

Arabic Abstract III

Content IV

List o f Tables VII

List o f 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(V inyl 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 o f 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 o f PET-pellets 45

for Bottles (B-2-B)

2.5.4.3 Direct Conversion o f Bottle Flakes 45

2.5.5 Recycling Back to the Initial Raw Materials 47

2.5.5.1 G lycolysis and Partial G lycolysis 47

2.5.5.2 Hydrolysis 48

2.5.5.3 Methanlysis 48

2.5.6 Practices in Collection& Rcycling o f 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 o f 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&RECOM M ENDATIONS

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 o f imported PET preform during period 2005-2010

Table (4.3) Forecast o f PET Preform (bottles) to Year 2015

VII

Figure (2.1) Common polymers derived from crude oil &natural gas

Figure (2.2) Stress strain graph o f thermoplastic material.

Figure (2.3) Schematic representation o f levels o f chain branching in different types

of polyethylenes

Figure (2.4) Simplified flow diagram o f Unipol process.

Figure (2.5) Flow diagram for suspension or polymerization o f vinyl chloride.

Figure (2.6) Simplified flow diagram for solution polymerization o f styrene.

Figure (2.7) Flow diagram illustrating components o f plastics industry

Figure (2.8) Main features o f a simple single-screw extruder

Figure (2.9) Diagram o f a simple injection-molding machine

Figure (2.10) Injection-molded piece.

Figure (2.11) Blow molding o f plastic bottles

Figure (2.12) Schematic representation o f extrusion blowing o f 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 o f PET preform imports against Virgin

Resin quantity/value

List of Figures

AbbreviationsTSW 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 Chapter1

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 o f 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 o f 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 o f problems.*

There are two major categories o f 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 o f 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--------------------------------------------------------------------------------------------

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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 o f PET resin .'consumer' bottles are used for other products such as

,salad dressing ,peanut butter and jullies ,H alf o f the polyester carpet made in united

states is made from recycled PET bottles .The rise o f use o f custom bottle and the

increased consumption o f 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 o f the approaches to solution o f the plastic waste problem is through

recycling for its numerous benefits justifying the aim o f this study that essentially

meant to contribute to sustainable consumption and production o f PET bottles in

particular. Recycling o f plastics should be carried in such a m anner to minimize the

pollution level during the process and as a result to enhance the efficiency o f 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 o f a waste/scrap into a product with

characteristics similar to those o f original product.

Secondary recycling involves processing o f waste/scrap plastics into materials that

have characteristics different from those o f original plastics product.

Tertiary recycling involves the production o f basic chemicals and fuels from plastics

waste/scrap as part o f the municipal waste stream or as a segregated waste.

Quaternary recycling retrieves the energy content o f waste/scrap plastics by

burning/incineration.

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1.2 Objectives o f 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 o f PET bottles waste.

■ To recommend on what to be done to support the growth o f PET bottle

recycling.

Chapter TwoLiterature 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 o f the old black dial telephones

and in early electrical fittings. Since that time, plastics have grown rapidly and have

now become an indispensable part o f everyday life. The exponential growth o f

plastics and rubber use, essentially over a short period o f half a century, is a testimony

to the versatility, high performance, and cost effectiveness o f polymers as a class o f

materials.

Polymers derive their exceptional properties from an unusual molecular

architecture that is unique to polymeric materials, consisting o f 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 o f their high visibility in

packaging and building applications Many o f the common thermoplastics used today,

however, were developed after the 1930s; and a few o f 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 o f 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 o f polyethylene

4


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based on novel metallocene catalysts has been developed. Polypropylene manufacture

started relatively late in the 1950s only after the stereospecific Z iegler-N atta catalysts

that yielded high-molecular-weight propylene polymers became available. While a

range o f copolymers o f ethylene is also commercially available, the homopolymer o f

propylene enjoys the highest volume o f 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 o f nylons (introduced in 1939 at the W orld’s Fair in

New York) yielded a material that particularly served the allied war effort.

The millions o f metric tons o f 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 o f 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 o f catalytically converting

the heavier components (or “residues” from this distillation) o f crude oil into lighter

more useful components. About 45% o f the crude oil reaching a refinery is converted

to gasoline.

Ethylene from cracking o f 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 o f the propylene fraction, which can be

converted into vinyl chloride and to ethyl benzene (used to make styrene)..

5

For the purpose o f 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 o f 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.

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2

*

Fig 2.2 Stress strain graph o f thermoplastic material.

Thermoplastics are elastic and flexible above a glass transition temperature

specific for each one— the midpoint o f a temperature range in contrast to the sharp

melting point o f a pure crystalline substance like water. Below a second, higher

melting temperature, Tm, also the midpoint o f 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 o f 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 o f the polymer chain.

Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If

the crystallites are larger than the wavelength o f 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

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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 o ff a bit from one another. Before the introduction o f

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 o f 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 o f 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 o f

thermoplastics that can be and are widely recycled. Animal horn, made o f 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 o f the common thermoplastic materials that are produced in

large volume and therefore o f particular environmental significance.. For the present

purpose “common” plastics include the high-volume commodity resins polyethylene,

polypropylene, poly(vinyl chloride), polystyrene, and thermoplastic polyester.


2

2.2.1. Polyethylenes

Polyethylenes, the most widely used class o f plastics in the world, include

several copolymers o f ethylene in addition to the homopolymer. The polyethylene

homopolymer has the simplest chemical structure o f 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 o f the

macromolecules to pack closely into a dense matrix and also control the extent of

crystallinity in the material. Because o f 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 o f 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 o f polymer (somewhat representative o f the

simple structure shown above). These chains are able to align and pack easily; HDPE

therefore has the highest degree o f crystallinity in a polyethylene. Its molecular

weight is high enough (and the chain branching minimal) to obtain a degree o f

crystallinity as high as 70-95% (and a correspondingly high density in the range o f

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 o f 0.910-0.930 g/cm3 and a

crystallinity o f only 40-60% . LDPE has a melting temperature range o f 110-115°C.

The amount o f crystallinity and the melt temperature o f the resin can even be further

9


2

reduced by incorporating a small amount o f a suitable co-monomer. When the

branches on polymer chain are mostly short chains, a linear low-density polyethylene

with a density range o f 0.915-0.940 g/cm3 and a higher degree o f crystallinity o f 40-

60% is obtained. Figure 2.3 shows a schematic o f the nature o f chain branching in

the three varieties o f 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 o f only about a third o f the thickness. Given the cost effectiveness of

LLDPE, it is likely to be used increasingly (mainly at the expense o f LDPE) in future

packaging applications. [3]

10

L iterature Review C h ap te r

2

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

Ethylene for the manufacture o f polyethylene is derived from cracking various

components o f petroleum oil such as the gasoline fraction, gas oil, or from

hydrocarbons such as ethane. While petroleum remains the predominant source o f 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 o f sugar cane industry,

via the dehydration o f ethanol.

11


2

The polymerization o f 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 o f 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 o f 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 o f 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 o f the new

metallocene catalysts with little engineering modification. A schematic diagram o f a

Unipol-type reactor is shown in Figure 2.4 [5]

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2

Blower

Figure 2.4 .Simplified flow diagram o f Unipol process.

2.2.2. POLYPROPYLENE

Polypropylene is typically manufactured by the direct polymerization o f

propylene in a low-pressure process employing Z iegler-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) o f 85-99. The isotactic form o f 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 o f about 0.92-0.94 g/cm3. The weight-average

molecular weight o f polypropylene from these processes is in the range o f 300,000-


2

600,000 with a polydispersity index o f about 2 -6 [7]. Some atactic polypropylene

results as a by-product9 o f the process and has found limited practical use [8]. The

atactic form is mostly amorphous and has a density o f only about 0.85-0.90 g/cm3.

Small amounts o f the syndiotactic form o f polypropylene (where the methyl groups

on repeat units are located on alternate sides o f 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 o f petroleum fractions

or the steam cracking o f hydrocarbons during the production o f 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 o f about 60-80°C and at 0.5-1.5 MPa, and the final product is obtained

as a solid suspension o f polypropylene in the liquid phase. Isolation o f 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 o f not using any diluents, but they generally suffer

from relatively poorer catalyst performance and some limitations on the

stereoregularity o f resins. In 1975 with the introduction o f improved third-generation

catalysts that facilitate the reaction at the same temperature but at the slightly higher

pressure o f 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 o f at least 99.8%)

14


2

is used in place o f the ethylene monomer feed. A suitable co-monomer (usually

ethylene) is also generally used. Most o f the advantages o f gas-phase processes cited

for polyethylene also apply to the production o f polypropylene [6].

Over a third o f the polypropylene produced in the United States is ultimatel

processed into useful products by injection molding. A wide range o f resins spanning

a melt flow index (MFI) range o f 2 to >70 g/10 min is available for this purpose. In

North American markets a majority o f the polypropylene is injection molded into

products or spun into fibers for use in various textile applications. The latter includes

sacks made o f 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 o f 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 o f

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 o f polypropylene is also common, and is used in the production o f

bottles and containers.

15


2

Dewatering and drying of product

Figure 2.5 Flow diagram for suspension or emulsion polymerization o f 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 o f vinyl chloride monomer (VCM). In

theory the chemical structure o f the polymer is simple, consisting o f 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 o f the presence o f only a single

chlorine atom, two types o f 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


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 o f 75-85°C and a

crystalline melting point o f 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 o f 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 o f 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 o f 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


2

temperature o f 50-75°C and at a pressure o f 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 o f

-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). F igure 2.6 shows

aschematic representation o f the manufacturing process [10].

Styrene

Solvent

v y

rStyrene and solvent

recovery

DevolatilizerV.J

\ ‘ / \ /

Reactors

Polystyrene to cutter

Extruder

Figure 2.6 .Simplified flow diagram for solution polymerization o f styrene.

2.2.4. POLYSTYRENE

General-purpose polystyrene (also called crystal polystyrene because o f the

clarity o f resin granules) is a clear, hard, glassy material with a bulk density o f 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 o f products in

which the resin could be used, was soon overcome when the highimpact toughened

grades o f polystyrene containing rubber became available. The resin is available as a

18


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. H igh-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 o f about 7.5 and 16

g/10 min, respectively. Impactgrade

resin accounts for about half o f the demand for polystyrene and is widely

used in injection molding o f consumer products. Some copolymers such as

(acrylonitrile- butadiene-styrene) copolymers (ABS), styrene-acrylonitrile

copolymers (SAN), and styrene-m aleic anhydride copolymers (SMA) are also

commercially available [11], Copolymer o f styrene with butadiene (SBR) is an

important elastomer widely used in passenger tire applications.

The first commercial production o f 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 o f 98%

are common in this process. The thermal cracking reaction that produces the

dehydrogenation is carried out at 630°C in the presence o f a catalyst, commonly a

mixture o f Fe203 , C r203 , and K 2C 03 . The reaction yields a mixture o f 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 o f a free-radical reaction inhibitor

(generally /-butyl catechol). A relatively small amount o f 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

2


While bulk or emulsion polymerization can also be used for the purpose, the

commercial manufacture o f polystyrene is mostly carried out in a solution process

using a free-radical initiator. The solvent, typically ethylbenzene, used at a level o f 2 -

30%, controls the viscosity o f the solution. H igh-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 o f 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 .


2

2.3. POLY (ETHYLENE TEREPHTHALATE)

2.3.1. GENERAL

Polyethylene terephthalate

n

Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)),

commonly abbreviated PET, PETE, or the obsolete PETP or PET-P), is a

thermoplastic polymer resin o f 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 o f the monomers (done immediately after

esterification/transesterification) with ethylene glycol as the byproduct (the ethylene

glycol is directly recycled in production).

The majority o f the world's PET production is for synthetic fibers (in excess

of 60%) with bottle production accounting for around 30% o f 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 o f the trade names o f PET products are Dacron, Diolen, Tergal,

Terylene, and Trevira fibers, Cleartuf, Eastman PET and Polyclear bottle resins,


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 o f polymerized units o f 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 o f its trade names, "Mylar"),

PET can be aluminized by evaporating a thin film o f 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 o f 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 o f 1. One o f the uses for a recycled PET bottle is for the

manufacture o f 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 C hap ter

2

Because o f the recyclability o f PET and the relative abundance o f post

consumer waste in the form o f 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 o f 25% post-consumer

recycled content.

PET, as with many plastics, is also an excellent candidate for thermal disposal

(incineration), as it is composed o f carbon, hydrogen, and oxygen, with only trace

amounts o f catalyst elements (but no sulfur). PET has the energy content o f soft coal.

PET was patented in 1941 by the Calico Printers' Association o f M anchester. The

PET bottle was patented in 1973 by Nathaniel W yeth.

2.3.3. Intrinsic viscosity

One o f the most important characteristics o f PET is referred to as intrinsic

viscosity (IV) The intrinsic viscosity o f the material, measured in deciliters per gram

(dC/g) is dependent upon the length o f its polymer chains. The longer the polymer

chains, the the more entanglements between chains and therefore the higher the

viscosity. The average chain length o f a particular batch o f resin can be controlled

during polycondensation.

The intrinsic viscosity range o f 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 d t/g Sheet grade for thermoforming

24


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 o f a desiccant or dryers before the PET is fed into the

processing equipment.

Inside the dryer, hot dry air is pumped into the bottom o f 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 o f 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 o f water per million parts o f 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


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 o f copolymer are more desirable for a

particular application. For example, cyclohexane dimethanol (CHDM) can be added

to the polymer backbone in place o f 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 o f 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


2

belts. For PET bottles, the use o f small amounts o f CHDM or other comonomers can

be useful: if only small amounts o f 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 o f polyester fibers.

tPET 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.


2

2.3.7. Degradation

PET is subject to various types o f 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 o f acetaldehyde and cross

links ("gel" or "fish-eye" formation). Discoloration is due to the formation o f various

chromophoric systems following prolonged thermal treatment at elevated

temperatures. This becomes a problem when the optical requirements o f 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 o f acetaldehyde. When acetaldehyde

is produced, some o f it remains dissolved in the walls o f 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 o f 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 o f

crystallinity o f 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 o f the finished product to an acceptable (that is, unnoticeable) level. See

copolymers, above. Other ways to improve the stability o f the

polymer is by using stabilizers, mainly antioxidants such as phosphites. Recently,

28


2

molecular level stabilization o f 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 o f PET. After manufacturing a detectable

amount o f antimony can be found on the surface o f 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 o f 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 o f low toxicity when taken in orally, its

presence is still o f concern. The Swiss Federal Office o f Public Health investigated

the amount o f antimony migration, comparing waters bottled in PET and glass: thet

antimony concentrations o f the water in PET bottles was higher, but still well below

the allowed maximal concentrations. The Swiss Federal Office o f Public Health

concluded that small amounts o f antimony migrate from the PET into bottled water,

but that the health risk o f the resulting low concentrations is negligible (1% o f the

"tolerable daily intake" determined by the W HO). A later (2006) but more widely

publicized study found similar amounts o f 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 o f common use

and recommended research on this topic. Proposed mechanisms include leaching o f

phthalates as well as leaching o f 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 o f 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 o f 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. THERM OPLASTIC PRODUCTS M ANUFACTURE

2.4.1. GENERAL

Thermoplastic resins are available to the processing industry as pellets o f

resin. Converting the raw material into useful products can involve separate segments

o f 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


2

Figure 2.7.Flow diagram illustrating components o f plastics industry.

The resin raw material needs to be mixed intimately with a variety o f chemical

additives to impart specific properties to the end product. Additives are used widely in

the plastics industry, in nearly all types o f plastic products. The use o f common

plastics in consumer products would not be possible without the use o f 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 o f 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 o f 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 o f 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 o f the fluidized plastic or

the “melt.” This melt is fed into molds or dies to force the material into required

31


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 o f 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 o f the heat needed to melt the resin is derived from the mechanical shearing

action o f 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 o f 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 o f melt is controlled

by a layer o f mesh on its way to the entrance o f 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 o f the die determines the geometric features o f the

product extruded. Figure 2.8 shows the main features o f a simple single-screw

extruder, along with three types o f 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


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 o f the die. Extremely complicated dies are

used in the extrusion o f 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 o f pipe cut to size) and collect the product for

storage. The actual pieces o f equipment used for the purpose depend on the type o f

product manufactured.

(a)

. Melt from J extruder

Coated wire

Annular die Stit die Crosshead die

(b)

Figure 2.8 Main features o f a simple single-screw extruder, along with three types o f

common extrusion dies

2.4.3. Injection M olding

Injection molding is one o f 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


2

to achieve the melting o f 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 o f 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 o f 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 o f (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 o f the equipment, particularly to open and clamp

down the heavy mold halves. The injection system consists o f 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 o f the equipment allow close control o f the

melt temperature. The mold system consists o f platens and molding (cavity) plates

typically made o f tool-grade steel. The mold shapes the plastic melt injected into the

cavity (or several cavities). O f the platens, the one attached to the barrel side o f the

machine is connected to the other platen by the tie bars. A hydraulic knock-out system

using ejector pins is built into one o f 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 o f 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 o f sophisticated control systems. Figure 2.9 shows a

diagram o f a simple injection molding machine indicating the hydraulic, injection,

34


2

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

_rHeaters

ICl OIZ1QIZ3 □ cm

..

Reciprocatingscrew

Clampingsystem

Hydraulic system Injection system Mold system

Nozzle\

Movingplaten

TStationary

platen

t?Q

id)(a) (b) (c)

Figure 2.9 .Diagram o f 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 o f 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 o f the product “parts” removed from it.

Figure 2.10 Injection-molded piece.

35

L iterature Review Chapter

2

2.4.4. Blow M olding

This is the primary processing technique used to fabricate hollow plastic

objects, particularly bottles, which do not need a very uniform distribution o f wall

thickness. It is a secondary shaping technique that inflates the preprocessed plastic

(usually extruded) against the inside walls o f 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.

Emptymord

rPlastic tube

ext aided

mm

Moldcloses

[. !

Cold air injected

< 3 C>

Mowopens

Figure 2.11 Blow molding o f 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 o f 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. W hile the wall thickness o f the parison itself is uniform, that o f the

product formed (a bottle) will not be uniform because

o f 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 o f 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 o f parison from a single

continuous extruder to optimize the process.

36


2

In injection blow molding, an injection-molding machine replaces the

extruder. In the first stage a parison with the threads o f 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 o f the weight o f the

final product in this type o f 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 o f common plastics such as polyethylenes into film is one

o f 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

o f the collapsed tube elongates the tube in the machine direction. The ratio o f the

pickup or haul-off rate to that o f 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 o f the diameter at the freeze line to that o f 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 o f polymer at all times during processing. Typically the bubble can be 15-30


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 o f the film

product Figure 2.12

shows a diagram o f film blowing equipment.

The same process can also be used to produce a multilayered film using

several extruders, one for each type o f 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 o f a barrier film for packaging applications, different layers o f the film

might be selected for different functionality needed in the prod.

Figure 2.12 Schematic representation o f extrusion blowing o f plastic film.

38


2

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 o f PET will become cost-efficient only applying high

capacity recycling lines o f more than 50,000 tons/year. Such lines could only be seen,*

if at all, within the production sites o f very large polyester producers. Several attempts

o f 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 o f 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 o f collected bottles. The prices o f baled bottles increased for instance

between the years 2000 and 2008 from about 50 Euro/ton to over 500 Euro/ton in

2008.

M echanical recycling or direct circulation o f PET in the polymeric state is

operated in most diverse variants today. These kinds o f processes are typical o f small

and medium-sized industry. Cost-efficiency can already be achieved with plant

capacities within a range o f 5 000 - 20 000 tons/year. In this case, nearly all kinds o f

recycled-material feedback into the material circulation are possible today. These

diverse recycling processes are being discussed hereafter in detail.


2

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 o f PET bottles which are meanwhile used for all kinds o f liquid

packaging like water, carbonated soft drinks, juices, beer, sauces, detergents,

household chemicals and so on. Bottles are easily to distinguish because o f shape and

consistency and separate from waste plastic streams either by automatic or hand

sorting processes. The established polyester recycling industry exists o f three

major sections:

PET bottle collection and waste separation— waste logistics

Production o f clean bottle flakes— flake production

Conversion o f 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 o f products like film, bottles, fiber,

filament, strapping or intermediates like pellets for further processing and engineering

plastics.

Aside this external polyester bottle recycling numbers o f 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

40


2

2.5.2 PET bottle recycling

Purification and decontamination - the most important processing steps during

polyester recycling.Thf success o f 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 o f PET in the range o f 280°C is the reason

why almost all common organic impurities such as PVC, PLA, polyolefin, chemical

wood-pulp and paper fibers, po lyvinyl 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

o f defects in the polymer chain increases considerably. Naturally, the particle size

distribution o f impurities is very wide, the big particles o f 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

o f the microscopic particles, which— because they are many— increase the frequency

o f 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 o f 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 o f 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 o f these processes.

Depending on composition and impurity level o f input material the general following

process steps are applied.

1. Bale opening, briquette opening


2

2. Sorting and selection for different colors, foreign polymers especially PVC,

foreign matter, removal o f film, paper, glass, sand, soil, stones and metals

3. Pre-washing without cutting

4. Coarse cutting d r^o r combined to pre-washing

5. Removal o f stones, glass and metal-

6. Air sifting to remove film, paper and labels

7. Grinding, dry and / or wet

8. Removal o f 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. W ater circuit and water treatment technology

18. Flake quality control

2.5.3 Impurities and material defects

The number o f 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. poU jestex O R - a t C O C ft\- ew i - a t XvafcsfejreweA trtfc S w a

reactive end groups, e.g. formation o f vinyl ester end groups through dehydration or

decarboxylation o f terephthalate acid, reaction o f 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 o f the COOH end groups built

up through a thermal and oxidative degradation. Results are decrease in reactivity,


2

increase in the acid autocatalytic decomposition during thermal treatment in presence

o f humidity.

c) Number o f poly-functional macromolecules increases. Accumulation o f gels and

long-chain branching defects.

d) Number, concentration and variety o f 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 o f further

degradation-supporting substances and coloring substances.

e) Hydroxide and peroxide groups build up at the surface o f the products made o f

polyester in presence o f air (oxygen) and humidity. This process is accelerated by

ultraviolet light. During an ulterior treatment process, hydro peroxides are a source o f

oxygen-radicals which are source o f oxidative degradation. Destruction o f 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 o f the following polymer characteristics during each

recycling cycle, which are detectable by chemical and physical laboratory analysis.

In particular:

Increase o f COOH end groups

Increase o f color number b

Increase o f haze (transparent products )

Increase o f oligomer content

Reduction in filterability

Increase o f by-products content such as acetaldehyde, formaldehyde

Increase o f extractable foreign contaminants

Decrease in color L

Decrease o f intrinsic viscosity or dynamic viscosity -

Decrease o f crystallization temperature and increase o f crystallization speed

Decrease o f the mechanical properties like tensile strength, elongation at break

or

elasticity modulus

Broadening o f molecular weight distribution

43

Literature Review C h ap te r

2

The recycling o f PET-bottles is meanwhile an industrial standard process

which is offered by a wide variety o f engineering companies

2.5.4 Processing examples for recycled polyester

Recycling processe^w ith polyester are almost as varied as the manufacturing

processes based on primary pellets or melt. Depending on purity o f the recycled

materials polyester can be used today in most o f the polyester manufacturing

processes as blend with virgin polymer or increasingly as 100% recycled polymer.

Some exceptions like BOPET-film o f 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 o f 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 o f an intrinsic viscosity in the range o f 0.55-0.7 dC/g,

depending on how complete pre-drying o f 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\O r\ v=> a V o w e e w e T g } v rv \ e T V S \ \ e , c o s \ c o n s w r n 'v n g , c a u s e s X h e tv tv a X

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

44


2

o M odification by additives

2.5.4.3 M anufacture o f 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 o f 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 o f the "existence" o f the required extraction residues and o f the removal o f

model contaminants according to FDA applying the so called challenge test, which is

necessary for the application o f the treated polyester in the food sector. Besides this

process approval it is nevertheless necessary that any user o f such processes has to

constantly check the FDA-limits for the raw materials manufactured by him self for

his process.

2.5.4.4 Direct conversion of bottle flakes

In order to save costs, one is working on the direct use o f the PET-flakes, from

the treatment o f used bottles, with a view to manufacturing an increasing number o f

polyester intermediates. For the adjustment o f the necessary viscosity, besides an

efficient drying o f the flakes, it is possibly necessary to also reconstitute the viscosity

through polycondensation in the melt phase or solid-state polycondensation o f 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 o f

un-dried PET flakes without substantial viscosity decrease caused by hydrolysis.

45


2

Looking at the consumption o f PET bottle flakes the main portion o f 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 o f POY normally need a

viscosity o f 0.62-0.64 d£/g. Starting from bottle flakes, the viscosity can be set via the

degree o f drying. The additional use o f T i02 is necessary for full dull or semi dull

yarn. In order to protect the spinnerets, an efficient filtration o f the melt is, in any case

is necessary. For the time being the amount o f POY made o f 100% recycling

polyester is rather low because this process requires high purity o f spinning melt.

Most o f the time a blend o f 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 o f

vacuum extrusion. For adjusting the viscosity, however, an addition o f 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 o f 0.58-0.65 d£/g.

One field o f increasing interest where recycled materials are used is the manufacture

o f high tenacity packaging stripes— and monofilaments. In both cases, the initial raw

material is a mainly recycled material o f higher intrinsic viscosity. High tenacity

packaging stripes as well as monofilament are then manufactured in the melt spinning

process

46


2

2.5.5 Recycling back to the initial raw materials

2.5.5.lG lycolysis 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 o f this way o f processing is the possibility o f separating the mechanical

deposits directly and efficient through a progressive and stepwise filtration. The

filtration fineness o f the last filtration step has a decisive effect on the quality o f 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 o f 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

o f about 0.30 d£/g by adding small quantities o f 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 o f processing, the possibility o f a chemical decomposition o f the hydro peroxides

is possible by adding a corresponding P-stabilizer directly when plasticizing. The

destruction o f the hydro peroxide groups is, with other processes, already carried out

during the last step o f 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 o f the raw

materials are being adjusted accordingly.

The treatment o f polyester waste through total glycolysis to convert the polyester to

bis-beta hydroxy-terephthalate, which is vacuum distilled and can be used, instead o f

DMT or PTA, as a raw material for polyester manufacture, has been executed on an

industrial scale in Japan as experimental production.

47


2

2.5.5.4 Hydrolysis

Recycling processes, through hydrolysis o f 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 o f 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 M ethanolysis

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 o f catalysts. After this an

efficient filtration o f 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],

48


2

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 o f 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 o f 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 o f curbside collection.

The last collection method employs the use o f 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 o f caps from bottles.

PET plastic wastes are also collected by the following ways:

■ Private Collection -T h is type o f collection is done in restaurants,

hotels, business establishments, supermarkets and fast food chains.

49


2

■ Household Consumer - The household consumers segregate and sell

their p lastif waste to eco-aids. However , some o f 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 o f 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 p lan t, and c) collects PET industrial/ consumer waste and sell

them to PET recyclers

50


2

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.


2

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 o f 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 o f 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 o f PET collected and can reduce overall recycling system costs.

In order to maximize the recovery and value o f 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.

52

Literature Review

2

Chapter

There are seven basic messages that should be included in any consumer

education or promotional program aimed at the collection o f PET bottles.

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

1) with screw-neck tops to be placed for collection or

[15].

53

Chapter ThreeMaterials & Methods

*

Materials & Methods Chapter

3

! 3 Materials & Methods

3.1 The Study Area

Khartoum state is one o f the 26 states o f Sudan , located in the middle o f

Sudan. It contains three provinces, Khartoum, Omdurman and Khartoum North with

eight localities. It has area o f 22,122 Km2 and estimated population o f approximately

7,152,102 (2008). Khartoum, the national capital o f Sudan, is the capital o f 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 o f these factories are using PET plastic bottles for

their packaging. Four o f 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 o f Sudan. There are also (4)

four formal small-scale grinding plastic recycling units and many informal recycling

units in Khartoum state. Only one o f 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


3

3.1.1 Khartoum State Map (Google).

3.2 Sources & M ethods o f Data Collection

PET bottles have been a focus o f interest o f this study due to the littering

problem. Therefore, information was reviewed to gain an understanding o f the

following aspects: the plastic chain with emphasis on existing plastic waste

management practices o f 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.


3

Information and data for this study were gathered from diverse sources mainly,

Bank o f Sudani, Customs Authorities, Ministry o f Industry, Sudanese Chamber o f

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 o f various stakeholders and feasible recommendations that help in

mitigation o f 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 o f 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 o f 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.

M icrosoft Excel is a spreadsheet application written and distributed by

Microsoft for M icrosoft 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 o f Microsoft Office .The current

versions are Microsoft Office Excel 2010 for Windows and 2008 for Mac. Microsoft

Excel has the basic features o f all spreadsheets using a grid o f cells arranged in

numbered rows and letter-named columns to organize data manipulations like


3

arithmetic operations .It has a battery o f supplied functions to answer statistical,

engineering and financial needs .In addition, it can display data as line graphs,

EV iews (econometric Views) statistical package for Windows, used mainly

for time-series oriented econometric analysis . It is developed by Quantitative Micro

Software (QMS), now apart o f HIS .The current version o f EView is 7.1, released in

April 2010. EV iews can be used for general statistical analysis and econometric

analyses, such as cross-section and panel data analysis and time series estimation and

forecasting .EV iews 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.

EV iews relies heavily on a proprietary and undocumented file format for data storage.

histograms and charts, and with a very limited three-dimensional graphical display.

57

Chapter FourResults & 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 o f PET

preform (bottles) during 2007 - J u ly 2010. The figures (4.1a) - (4 .6 b ) respectively

illustrate graphical relationship between particulars, by using excel program, during

the same period. A forecast for imports o f PET preform (bottles) was shown in table

(4.3) by applying eviews package.

Sudan imports o f plastic materials increased annually, in year 2005 reached

54540 tons virgin plastic resin o f value 61,292,000 $,107,420 tons plastic products of

value 73,341,000 $ and 9,611 tons PET preform (bottles) o f value 18,137,000 $.

In 2006 imported o f virgin resin was 64,403 tons o f value 63,259,000 $ 55,511

tons plastic products o f value 85,124,000 $ and 10,400 tons PET o f value 18,235,000

In 2007 virgin resin was 65,146 tons o f value 94,354,000 $, 53,790 tons plastic

products o f value 98,072,000 $ and 9,915 tons PET preform of value 17,384,000 $.

In 2008 virgin resin increased to 75,233 tons o f value 129,106,000 $, 62,860

tons plastic products o f value 117,616,000 $ and 15,81 I tons PET preform o f value

29,780,000 $.

In 2009 imported virgin resin reached 108,856 tons o f value 139,234,000 $,

117,616 tons plastic products o f value 80,945,000 $ and 22,444 tons PET preform of

value 38,899,000 $.

In this year 2010, from January to July, imports o f plastic materials show

significant increase. Virgin resin reached 58,565 tons o f value 71,795,000 $, 38,271

tons plastic products o f value 85,662,000 $ and 17,336 tons PET preform o f value

58


4

34,564,000 $. Therefore, PET preform imports estimated to reach by end o f 2010

approximately 30000 tons.

f4.1.1 Excel P resentation

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 o f 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 o f 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

ITEM

2005 2006 2007 2008 2009

QuantityMT

ValueX1000$

QMT

VX I000$

QMT

VX I000$

QMT

VX I000$

QMT

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

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

60

Tabl

e (4

.2) E

stim

ate

PET

Prefo

rm

(bot

tle)

2010

4

Year/MT 2 0 0 7 2 0 0 8 2 0 0 9 2 0 1 0 2 0 1 1 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


4

Virgin Plastic Resin

Fig (4.1a)

Virgin Plastic Resin

i 2005

i 2006

2007

2008

2009

Fig (4.1b)

i 2005

l 2006

2007

2008

2009

62


4

1PET Preform(bottles)

Fig (4.2a)

PET Preform(bottles)

Fig (4.2b)

63

Chapter

4I

Plastic Products

107420 12005

i 2006

2007

i 2008

2009

Fig (4.3a)

Plastic Products

I 2005

12006

i 2007

12008

I 2009


4

Ratio of PET preform imports to virgin plastic (Quantities)

100%

9 0 % y 80% f

70% - 60% - 12% 5 0 % y40%3 0 % y 20% - 10% - lj8%0% 4^

c 4%

1,6%

15%

L5%

'9%

1%

9%

. 1%

2005 2006 2007 2008 2009

■ Virgin Plastic Rosin

■ PET Preform(bottles)

Fig (4.6a)

in plsticRatio of preform imports to virg (Values)

Fig (4.6b

■ Virgin Plastic Resin


65


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


4

20000

0200 5 2 0 0 6 20 0 7 2 0 0 8 2009

m Virgin Plastic Resin

■ Plastic Products


Fig (4.5a)

20000018000016000014000012000010000080000600004000020000

0

LU £cl lij

<1) 0 <D <1> 0)3 3 3 3

03 03 03 03 03> > > > >

2005 2006 2007 2008 2009

Item

— Series 1 Series2

Series3

Fig (4.5b)

een virgin resinComparative relation betw, PET &plastic products imports(Values)


4

Eviews Package Application

Forecast for PET Preform (bottles) Imports

XF3 ± 2 S.E.

Forecast: XF3Actual: XForecast sample: 2005 2015Adjusted sample: 2005 2010Included observations: 6

Root Mean Squared Error 2882.624M ean Abs. Percent Error 2363.590M ean Absolute Percentage Error 18.51712Theil Inequality Coefficient 0.080414

Bias Proportion 0 .000000Variance Proportion 0.038883

Dependent Variable: XMethod: Least Squares

Date: 08/23/10 Time: 13:35Sample(adjusted): 2006 2010

Included observations: 5 after adjustinc endpointsVariable Coefficient Std. Error t-Statistic Prob.

T 5920.110 797.5212 7.423137 0.0177C -621159.7 85990.06 -7.223622 0.0186

RESID01(-1) 0.742890 0.418197 1.776413 0.2176R-squared 0.968474 Mean dependent var 17714.00

Adjusted R-squared 0.936948 S.D.dependent var 8533.157S.E. of regression 2142.689 Akaike info criterion 18.46122

Sum squared resid 9182236. Schwarz criterion 18.22688Log 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

SinceY : PET Preform

T : Y ear C : intercept

B : Slope o fT e : error

68


4

I

Years PET Preform "bottles" Growth Rate2005 96112 0 0 6 104002 0 0 7 9 915 -5%

2008 15811 59%

2009 2 2 4 4 4 42%

2010 3 0 0 0 0 34%

2011 35972.51 20%

2012 4 1 8 9 2 .6 2 16%

2013 4 7 8 1 2 .7 3 14%

2014 5 3 7 3 2 .8 4 12%

2015 5 9 6 5 2 .9 5 11%

Table (4.3)

4.1.3 Soft Water bottling Factories Survey drink &

The result o f 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 o f 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

■


4

4.2 Discussion

<As shown in Figures (4.2a) and (4.2b) imported quantities and values o f 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 o f value 38,899,000$

and expected to reash 30000 tons by the end o f this year 2010. This high increase in

PET consumption due to introduction o f additional capacities and investments in soft

drinks and water plants as well as partial replacement o f glass bottles by PET.

Table (4.3) illustrates forecasted quantities o f 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 FiveConclusion

&Recommendations

Conclusion & Recommendation Chapter5

5. Conclusion &Recommendations

5.1. Conclusion

Population growth and rapid pace o f urbanization pose several environmental

challenges for Khartoum State. One o f 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 o f 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 o f this year 2010.

Prediction o f 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 o f PET bottles will create environmental problems that must

be addressed by identifying and introducing recycling as one o f the best practical

cleaner production tool to achieve sustainable development.

Mechanical recycling o f 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 o f 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 o f 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 te r5

5.2. R ecom m endations

Based on the findings and results o f 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 o f PET bottles and other plastic waste through adoption of

good practices in collection and selection o f the appropriate methods, (refer to

section 2 .5 .6)

• Designing community PET recycling collection program greatly increase the

quantity and quality o f 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 o f PET

preform.

• Prohibit imports o f 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 o f the

establishment o f PET resin industry using Sudanese petroleum.

-72-

Conclusion & Recommendation Chapter5

Review o f the existing laws and policies on plastic waste with particular to

PET rising consumption to address the problem o f littering by encouraging

recycling.

Promote conducting further researches and studies in future.

-73-

-

References

References

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New Jerrsy, 2003, p 77-120.

[2] Hong Kong Plastic Technology Center, Techo. Economic and Market Research

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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 o f 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. W ikipedia-org /W iki/ Polyethylene terephthalate, 17.5.2010.

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

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