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POLYMERS Group Members Hacettepe University Seda KOCA

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1 POLYMERS Group Members 11.11.2009 Hacettepe University Seda KOCA
Bengi AYDİLEK Didem Büşra KABAKÇI Gözde ERGİN Hacettepe University

2 The Outline Reactions of polymers Addition Polymerization
Step Growth Polymerization Kinetic Of Polymerization Polymerization Processes Bulk Polymerization Solvent Polymerization Suspention Polymerization Emulsion Polymerization Special Processes

3 The Outline Chemical and Physical Structures of Polymers
Polymer’s molecular structures Confriguration and conformation of polymers Chain structures of polymers Physical Structures of Polymers Polymer crystallinity Crystallinity and amorphousness of polymers

4 Outline Types of Polymers and Polymer Processing Members of Polymers
Definition of Thermosets & Thermoplastics Common products and their properties Forming Techniques of Polymers Extrusion of polymers Injection Molding Blow Molding Thermoforming Compression Molding Casting

5 The Outline Recycling of Polymers Definiton of Recycling
Why is recycling important? Benefits Recycling of polymers

6 Reactions of Polymers Addition Polymerization (Chain Growth)
Step Growth Polymerization (Condensation)

7

8 Step-growth polymerization Chain-growth polymerization
Differences between step-growth polymerization and chain-growth polymerization Step-growth polymerization Chain-growth polymerization Growth throughout matrix Growth by addition of monomer only at one end of chain Rapid loss of monomer early in the reaction Some monomer remains even at long reaction times Same mechanism throughout Different mechanisms operate at different stages of reaction (i.e. Initiation, propagation and termination) Average molecular weight increases slowly at low conversion and high extents of reaction are required to obtain high chain length Molar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerization Ends remain active (no termination) Chains not active after termination No initiator necessary Initiator required

9 Step of Radical Chain Polymerization
Initiation Propagation Termination

10 INITIATION

11 PROPAGATION

12 TERMINATION Dead Polymer i.) Coupling or Combination; ii.) Disproportionation

13 CHAIN TRANSFER REACTIONS
Transfer to monomer reaction Transfer to initiator reaction Transfer to solvent reaction

14 IONIC CHAIN POLYMERIZATION
Using catalyst, not initiator Highest reaction rate Termination step is just disproportionation Environment must be pure Reaction occurs in the cold

15 Anionic Polymerization=Living Polymerization
If the starting reagents are pure and the polimerization reactor is purged of all oxygen and traces of water, polimerization can proceed until all monomer is consumed.

16 CONDENSATION POLYMERIZATION
Using catalyst Minumum two functional groups required Usually linear Molecular weight increases slowly at low conversion High extents of reaction are required to obtain high chain length

17 KINETICS OF POLYMERIZATION
Reaction rate of ionic polimerization more than radicalic polimerization So kinetics of ionic polimerization are not calculated But kinetics of radicalic polimerization can be analysed

18 Kinetic of Radicalic Polymerization
Initiation; Propagation; Termination;

19 Kinetic of Radicalic Polymerization
Ro = overall rate of polimerization Rp = rate of chain propagation Ri = rate of initiation step Rt = rate of termination step

20 Kinetic of Condensation Polymerization
Equivalent reactivity of functional groups. It may be first, second or third order by depending upon.

21 Kinetic of Condensation Polymerization
Assumption = a stoichiometry balance of monomer concentration

22 POLYMERIZATION PROCESSES
Bulk Polymerization Solvent Polymerization Suspention Polymerization Emulsion Polymerization Special Processes Electrochemical Polymerization Radiation Polymerization Grow-discharge (Plasma)

23 Bulk Polymerization The simplest technique
It gives the highest-purity polymer Ingredients : monomer, monomer-soluble initiator, perhaps a chain transfer agent Advantages Disadvantages High yield per reactor volume Difficult of removing the lost traces of monomer Easy polymer recovery Dissipating heat produced during the polimerization Final product form

24 Solution Polymerization
Heat can be removed by conducting the polymerization in an organic solvent or water Initiator or monomer must be soluble in solvent Solvents have acceptable chain-transfer characteristics Solvents have suitable melting or boiling points for the conditions of polymerization Ingredients : monomer initiator solvent Advantages Disadvantages Temperature control is easy Small yield per reactor volume Easy removed Solvent recovery

25 Suspention Polymerization
Coalescense of sticky droplets is prevented by PVA Near the end of polymerization, the particles harder and they can be removed by filtration, then washing Ingredients : water-insoluble monomer, water-insoluble initiator, sometimes chain transfer agent suspention medium (water-usually) Advantages (according to bulk polymerization) Disadvantages Forming process not using Polymer purity is low Stirring is easy Reactor capital costs are higher than for solution polymerization Separation process is easy

26 Emulsion Polymerization
Particles are formed monosize with emulsion polymerization Polymerization is initiated when the water-soluble radical enters a monomer-containing micelles. Ingredients : water-insoluble monomer, water-soluble initiator, chain transfer agent, dispersing medium (water), fatty acid, surfactant such as sodium salt of a long chain

27 Molecular structure of polymers
Typical structures are : linear (end-to-end, flexible, like PVC, nylon)  branched cross-linked (due to radiation, vulcanization) network (similar to highly cross-linked structures,termosetting polymers) Figure1. Schematic representation of (a) linear, (b and c) branched, and (d and e) cross-linked polymers. The branch points and junction points are indicated by heavy dots (Plastic Technology Handbook-Manas Chanda Salil K. Roy)

28 Chemical Structure of Polymers
Molecular configuration of polymers Side groups atoms or molecules with free bonds, called free-radicals, like H, O, methyl affects polymer properties. Stereoregularity describes the configuration of polymer chains : Isotactic is an arrangement where all substituents are on the same side of the polymer chain. Syndiotactic polymer chain is composed of alternating groups Atactic the radical groups are positioned at random Figure 2: Isotactic Syndiotactic and Atactic combinations of a stereoisomers of polymer chain (http://www.microscopy-uk.org.uk/mag/imgsep07/atactic.png)

29 Molecular configuration of polymers
FIGURE.3. Diagrams of (a) isotactic, (b) syndiotactic, and (c) atactic configuration in a vinyl polymer. The corresponding Fischer projections are shown on the right. (Plastic Technolgoy Handbook)

30 Table 1. Properties of Polypropylene Stereoisomers (Plastic Technology Handbook)

31 Molecular configuration of polymers
Geometrical isomerism: The two types of polymer configurations are cis and trans. These structures can not be changed by physical means (e.g. rotation). The cis configuration  substituent groups are on the same side of a carbon-carbon double bond. Trans  the substituents on opposite sides of the double bond. Figure4.cis trans configurations of polyisoprene ( )

32 Conformations of a Polymer Molecule
Conformation The two atoms have other atoms or groups attached to them configurations which vary in torsional angle are known as conformations (torsional angle:The rotation about a single bond which joins two atoms ) Polymer molecule can take on many conformations. Different conformation different potential energies of the moleculeSome conformations: Anti (Trans), Eclipsed (Cis), and Gauche (+ or -)

33 Other Chain Structures
Copolymers polymers that incorporate more than one kind of monomer into their chain (nylon) Three important types of copolymers: Random copolymer contains a random arrangement of the multiple monomers. Block copolymer contains blocks of monomers of the same type Graft copolymer contains a main chain polymer consisting of one type of monomer with branches made up of other monomers. Figure 5 :Block Copolymer Graft Copolymer Random Copolymer

34 Physical Characteristics of Polymers
The melting or softening temperature ↑ molecular weight ↑ The molecular shape of the polymer has influence on the elastic properties. ↑ coils the ↑ elasticity of the polymer The structure of the molecular chains has an effect on the strength and thermal stability. ↑ crosslink and network structure within the molecule ↑ the strength and thermal stability.

35 Polymer Crystallinity
Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content X-ray scattering and electron microscopy have shown that the crystallites are made up of lamellae which,in turn, are built-up of folded polymer chains Figure.6 Schematic representation of (a) fold plane showing regular chain folding, (b) ideal stacking oflamellar crystals, (c) interlamellar amorphous model, and (d) fringed micelle model of randomly distributed crystallites (Plastic Technology Handbook)

36 Polymer crystallinity
Crystallinity occurs when linear polymer chains are structurally oriented in a uniform three dimensional matrix. Three factors that influence the degree of crystallinity are: i) Chain length  ii) Chain branching  iii) Interchain bonding Figure 7: Crystalline chain

37 Polymer cristallinity
Crystallinity influences: Hardness,modulus tensile, stiffness, crease, melting point of polymers. Most crystalline polymers are not entirely crystalline. The chains, or parts of chains, that aren't in the crystals have no order to the arrangement of their chains Crystallinity makes a polymers strong, but also lowers their impact resistance Crystalline polymers are denser than amorphous polymers, so the degree of crystallinity can be obtained from the measurement of density  Wc=Φcρc/ ρ ρ  density of entire sample ρc  density of the crystalline fraction. Φc volume fraction Wc mass fraction

38 Determinants of Polymer Crystallinity
The degree of crystallinity of a polymer depends on the rate of cooling during solidification as well as on the chain configuration. In most polymers, the combination of crystalline and amorphous structures forms a material with advantageous properties of strength and stiffness. Figure 8: Mixed amorphous crystalline macromolecular polymer structure (http://web.utk.edu/~mse/Textiles/Polymer%20Crystallinity.htm)

39 Polymer cristallinity
Polymer molecules are very large so it might seem that they could not pack together regularly and form a crystal. Regular polymers may form lamellar crystals with parallel chains that are perpendicular to the face of the crystals. A crystalline polymer consists of the crystalline portion and the amorphous portion. The crystalline portion is in the lamellae, and the amorphous portion is outside the lamellae . Figure 9. Arrangement of crystalline and amorphous portions

40 Cristillanity and amorphousness
An amorphous solid is formed when the chains have little orientation throughout the bulk polymer. The glass transition temperature is the point at which the polymer hardens into an amorphous solid. In between the crystalline lamellae,regions with no order to the arrangement of the polymer chains  amorphous regions Polyethylene can be crystalline or amorphous. Linear polyethylene is nearly 100% crystalline. But the branched polyethylene is highly amorphous. Figure 10.Linear and Branched Polyethylene (http://pslc.ws/macrog/kidsmac/images/pe03.gif )

41 Examples... Highly crystalline polymers:
Polypropylene, Nylon, Syndiotactic polystyrene.. Highly amorphous polymers: Polycarbonate, polyisoprene, polybutadiene Polymer structure and intermolecular forces has a major role of a polymer’s crystallinity.

42 Classification of Polymers
…with regard to their thermal processing behavior ; Thermoplastic Polymers (Thermoplastics) soften when heated and harden when cooled Thermosetting Polymers (Thermosets) once having formed won’t soften upon heating

43 Thermoplastics have linear or branched structure
chains are flexible and can slide past each other

44 have strong covalent bonds and weak intermolecular van der Waals bonds
elastic and flexible above glass transition temperature can be heat softened, remolded into different forms reversible physical changes without a change in the chemical structure

45 Thermosets chains chemically linked by covalent bonds
hardening involves a chemical reaction which connects the linear molecules together to form a single macromolecule.

46 Thermosets once polymerization is complete, cannot be softened, melted or molded non-destructively. have higher thermal, chemical and creep resistance than thermoplastics Thermosets suitable materials for Composites Coatings Adhesive applications

47 Common thermoplastics
Commodity Polymers POLYETHYLENES POLYPROPYLENE POLYSTYRENE POLYVINYLCHLORIDE-PVC POLYMETHYLMETHACRYLATE-PMMA Engineering Polymers(have a thermal resistance °C) POLYCARBONATE NYLON(POLYAMIDE) POLYETHYLEN TEREPHATALATE-PET High Performance Polymers (have a thermal resistance >150°C) POLYTETRAFLUOROETHYLENE-teflon POLYARYLETHERKETONES-PEEK

48 POLYETHYLENE prepared directly from the polymerization of ethylene (C2H4). two main types are; low-density (LDPE) and high-density polyethylene (HDPE) Advantages cheap good chemical resistance high impact strength

49 Limitations low heat resistance (upper temperature limit is 60°) degrade under UV irradiation.  high gas permeability, particularly CO2 Applications extensively for piping and packaging chemically resistant fittings, garbage bags containers, cable covering

50 POLYPROPLYLENE improved mechanical properties compared to polyethylene; has a low density (900–915 kg/m3), harder, and has a higher strength Good chemical and fatigue resistance Disadvantages Oxidative degradation, high thermal expansion, high creep poor UV resistance Applications medical components, films for packaging (e.g. cigarette packets)reusable containers, laboratory equipment

51 POLYSTYRENE a light amorphous thermoplastic Advantages
low cost, easy to mould, rigid, transparent no taste, odor, or toxicity, good electrical insulation Disadvantages sensitive to UV irradiation (e.g. sunlight exposure) chemical resistance is poor, brittle Applications CD-DVD cases, electronic housings, food packaging, foam drink cups and egg boxes

52 POLYVINYLCHLORIDE-PVC
was the first thermoplastic used in industrial applications very resistant to strong mineral acid and bases, good electrical insulators, flame-retardant Two grades of the PVC material are available: rigid PVC is used in the construction industry for piping cold water and chemicals flexible PVC is used in wire and cable coating, paints, signs

53 Common thermosets EPOXIES UNSATURATED POLYESTERS PHENOL FORMALDEHYDE (PHENOLIC) POLYURETHANES

54 EPOXIES Advantage mechanically strong, highly adhesive
good chemical and heat resistance electrical insulators Disadvantage expensive Applications as industrial adhesives, coatings or as matrices in advanced reinforced plastics and also as encapsulation media

55 UNSATURATED POLYSTERS
Advantage hard, high strength cheap compared to Epoxy  good electrical insulator high heat resistance Disadvantage poor solvent resistance compared to other thermosets Applications molding or casting materials for a variety of electrical applications, matrix for composites such as fiberglass boats, fences, helmets, auto body components

56 PHENOLICS most commonly used thermosets
high hardness, excellent thermal stability; low tendency to creep Applications wiring devices, bottle caps, automotive parts, plugs and switches, as adhesives coatings and molded components for electrical applications

57 POLYURETHANES depending on the degree of cross-linking they behave as thermosets or thermoplastics low cost, high impact strength, high adhesion properties be processed into coatings, adhesives, binders, fibers and foams

58 Methods of polymer fabrication
Extrusion of polymers Injection Molding Blow Molding Thermoforming Compression Molding Casting

59 Extrusion of polymers method used mainly for thermoplastics
is a continuous process as long as raw pellets are supplied is a process of manufacturing mostly long products of constant cross-section; i.e.. rods, sheets, pipes, films, wire insulation coating

60 … extrusion pelletized material is successively compacted, melted and formed into a continuous charge of viscous fluid temperature of the material is controlled by thermocouples forcing soften polymer through a die with an opening the product going out of the die is cooled by blown air or in water bath

61 extruder

62 Injection Molding most widely used technique for thermoplastics
highly productive method, profitable in mass production of large number of identical parts polymer in form of pellets is fed into machine and is pushed forward into a heating chamber then the molten plastic is forced through a nozzle into the enclosed mold cavity pressure is maintained until solidification and then the mold opens and the part is removed

63

64 Blow Molding is a process in which a heated hollow thermoplastic tube (parison) is inflated into a closed mold disposable containers, recyclable bottles, automotive fuel tanks, tubs are produced involves manufacture of parison by extrusion, injection or stretching

65 parison in a semi molten state is placed in a two piece mold having the desired shape
parison is inflated by air blown, taking a shape conforming that of the mold cavity parison is then cut on the top, mold cools down, its halves open, and the final part is removed

66

67 Thermoforming is a process of shaping flat thermoplastic sheet
softening the sheet by heat, followed by forming it in the mold cavity Thermosets can not be formed by the thermoforming because of their cross linked structure

68 Thermoforming methods
three thermoforming methods, differing in the forming stage: Vacuum Thermoforming; shaping a preheated thermoplastic sheet by means of vacuum produced in the mold cavity Pressure Thermoforming;... by means of air pressure. Mechanical Thermoforming;... by direct mechanical force

69 Thermoforming by vacuum and mechanical force

70 Compression Molding used mostly for molding thermoset resins
pre-weighed amount of a polymer mixed with additives is placed into the lower half of the mold polymer is preheated prior to placement into heated mold cavity ,half of the mold moves down, pressing on the polymer charge and forcing it to fill the mold cavity suitable for molding large flat or moderately curved parts; side panels for automotive, electric housings etc.

71

72 Casting both thermosets and thermoplastics may be cast.
molten polymer is poured into a mold and allowed to solidify for thermoplastics solidification occurs upon cooling while thermoset’s hardening is a consequence of polymerization reaction

73 REFERENCES François Carderelli, Materials Handbook: A Concise Desktop Reference,2nded.,Springer Donald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis Group J. A.Brydson, Plastics Materials, 7thed., Heinemann William D. Callister ,Materials Science and Engineering,7th ed., Wiley

74 Recycling: A Sector of Solid Waste Management

75 What is Recycling? Recycling refers to the process of collecting used materials which is usually considered as ‘waste’ and reprocessing them. Recycling varies from ‘re-use’ in the sense that while re-use just means using old products repeatedly, recycling means using the core elements of an old product as raw material to manufacture new goods.

76 Why Recycling is Important?
Recycling Saves Energy Recycling Saves Environmental Conditions and Reduces Pollution Recycling Saves Natural Resources Economic Benefits Recycling Saves Space for Waste Disposal

77 Benefits • Conserves Resources • Prevents emissions of greenhouse gasses & water pollutants • Supplies valuable raw materials to industry • Saves tax-payer dollars • Creates jobs • Stimulates development of greener technologies • Reduces the need for new landfills and incinerators

78 Recycling of polymers Recycling of Polymers Chemical recycling
Mechanical recycling Energy recycling Chemolysis Glycolysis Methanolysis Hydrolysis Thermolysis Pyrolysis Hydrogenation

79 Why do we use mechanical, chemical and energy recycling?
Hence mechanical recycling is realy best suited to clean plastic waste,such as packaging material. Chemical recycling of waste plastics is important issue. We have applied reaction in water or organic solvent in sub- or supercritical condition to convert polymers into its monomers. Condensed polymers such as polyethylene terephthalate or nylon 6 were depolymerized to its monomers by hydrolysis of alcoholysis in supercritical water or alcohol.

80 Conclusive Facts 1 t = 20,000 plastic bottles
25,000 t of bottles recycled in the UK in 2003 saved approximately 25 million kWh of energy 25 recycled PET bottles can be used to make an adult’s fleece jacket Recycling a single plastic bottle can conserve enough energy to light a 60 W lightbulb for up to 6 h

81 SOME PHOTOS

82 We have done it!!! Ref: assets/ppt/1PlasticDebrisConference9.ppt

83 Look at the changes you could make with recycling...

84 REFERENCES assets/ppt/1PlasticDebrisConference9.ppt François Carderelli, Materials Handbook: A Concise Desktop Reference,2nded.,Springer Donald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis Group

85 REFERENCES J. A.Brydson, Plastics Materials, 7thed., Heinemann
William D. Callister ,Materials Science and Engineering,7th ed., Wiley

86 REFERANCES Plastic Technology Handbook, 4th Edition, Authors: Manas Chanda,Salil K. Roy


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