Presentation on theme: "POLYMERS Group Members Hacettepe University Seda KOCA"— Presentation transcript:
1POLYMERS Group Members 11.11.2009 Hacettepe University Seda KOCA Bengi AYDİLEKDidem Büşra KABAKÇIGözde ERGİNHacettepe University
2The Outline Reactions of polymers Addition Polymerization Step Growth PolymerizationKinetic Of PolymerizationPolymerization ProcessesBulk PolymerizationSolvent PolymerizationSuspention PolymerizationEmulsion PolymerizationSpecial Processes
3The Outline Chemical and Physical Structures of Polymers Polymer’s molecular structuresConfriguration and conformation of polymersChain structures of polymersPhysical Structures of PolymersPolymer crystallinityCrystallinity and amorphousness of polymers
4Outline Types of Polymers and Polymer Processing Members of Polymers Definition of Thermosets & ThermoplasticsCommon products and their propertiesForming Techniques of PolymersExtrusion of polymersInjection MoldingBlow MoldingThermoformingCompression MoldingCasting
5The Outline Recycling of Polymers Definiton of Recycling Why is recycling important?BenefitsRecycling of polymers
8Step-growth polymerization Chain-growth polymerization Differences between step-growth polymerization and chain-growth polymerizationStep-growth polymerizationChain-growth polymerizationGrowth throughout matrixGrowth by addition of monomer only at one end of chainRapid loss of monomer early in the reactionSome monomer remains even at long reaction timesSame mechanism throughoutDifferent 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 lengthMolar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerizationEnds remain active (no termination)Chains not active after terminationNo initiator necessaryInitiator required
9Step of Radical Chain Polymerization InitiationPropagationTermination
12TERMINATIONDead Polymer i.) Coupling or Combination; ii.) Disproportionation
13CHAIN TRANSFER REACTIONS Transfer to monomer reaction Transfer to initiator reaction Transfer to solvent reaction
14IONIC CHAIN POLYMERIZATION Using catalyst, not initiatorHighest reaction rateTermination step is just disproportionationEnvironment must be pureReaction occurs in the cold
15Anionic 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.
16CONDENSATION POLYMERIZATION Using catalystMinumum two functional groups requiredUsually linearMolecular weight increases slowly at low conversionHigh extents of reaction are required to obtain high chain length
17KINETICS OF POLYMERIZATION Reaction rate of ionic polimerization more than radicalic polimerizationSo kinetics of ionic polimerization are not calculatedBut kinetics of radicalic polimerization can be analysed
18Kinetic of Radicalic Polymerization Initiation; Propagation; Termination;
19Kinetic of Radicalic Polymerization Ro = overall rate of polimerizationRp = rate of chain propagationRi = rate of initiation stepRt = rate of termination step
20Kinetic of Condensation Polymerization Equivalent reactivity of functional groups.It may be first, second or third order by depending upon.
21Kinetic of Condensation Polymerization Assumption = a stoichiometry balance of monomer concentration
23Bulk Polymerization The simplest technique It gives the highest-purity polymerIngredients : monomer,monomer-soluble initiator,perhaps a chain transfer agentAdvantagesDisadvantagesHigh yield per reactor volumeDifficult of removing the lost traces of monomerEasy polymer recoveryDissipating heat produced during the polimerizationFinal product form
24Solution Polymerization Heat can be removed by conducting the polymerization in an organic solvent or waterInitiator or monomer must be soluble in solventSolvents have acceptable chain-transfer characteristicsSolvents have suitable melting or boiling points for the conditions of polymerizationIngredients : monomerinitiatorsolventAdvantagesDisadvantagesTemperature control is easySmall yield per reactor volumeEasy removedSolvent recovery
25Suspention Polymerization Coalescense of sticky droplets is prevented by PVANear the end of polymerization, the particles harder and they can be removed by filtration, then washingIngredients : water-insoluble monomer,water-insoluble initiator,sometimes chain transfer agentsuspention medium (water-usually)Advantages (according to bulk polymerization)DisadvantagesForming process not usingPolymer purity is lowStirring is easyReactor capital costs are higher than for solution polymerizationSeparation process is easy
26Emulsion Polymerization Particles are formed monosize with emulsion polymerizationPolymerization 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
27Molecular structure of polymers Typical structures are :linear (end-to-end, flexible, like PVC, nylon) branchedcross-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)
28Chemical Structure of Polymers Molecular configuration of polymersSide 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 groupsAtactic the radical groups are positioned at randomFigure 2: Isotactic Syndiotactic and Atactic combinations of a stereoisomers of polymer chain(http://www.microscopy-uk.org.uk/mag/imgsep07/atactic.png)
29Molecular 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)
30Table 1. Properties of Polypropylene Stereoisomers (Plastic Technology Handbook)
31Molecular 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( )
32Conformations 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 moleculeSome conformations: Anti (Trans), Eclipsed (Cis), and Gauche (+ or -)
33Other 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 typeGraft 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
34Physical 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 polymerThe 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.
35Polymer Crystallinity Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous contentX-ray scattering and electron microscopy have shown that the crystallites are made up of lamellae which,in turn, are built-up of folded polymer chainsFigure.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)
36Polymer 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 bondingFigure 7: Crystalline chain
37Polymer 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 chainsCrystallinity makes a polymers strong, but also lowers their impact resistanceCrystalline polymers are denser than amorphous polymers, so the degree of crystallinity can be obtained from the measurement of density Wc=Φcρc/ ρρ density of entire sampleρc density of the crystalline fraction.Φc volume fractionWc mass fraction
38Determinants 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)
39Polymer 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
40Cristillanity 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 regionsPolyethylene 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 )
41Examples... Highly crystalline polymers: Polypropylene, Nylon, Syndiotactic polystyrene..Highly amorphous polymers:Polycarbonate, polyisoprene, polybutadienePolymer structure and intermolecular forces has a major role of a polymer’s crystallinity.
42Classification of Polymers …with regard to their thermal processing behavior ;Thermoplastic Polymers (Thermoplastics)soften when heated and harden when cooledThermosetting Polymers (Thermosets)once having formed won’t soften upon heating
43Thermoplastics have linear or branched structure chains are flexible and can slide past each other
44have strong covalent bonds and weak intermolecular van der Waals bonds elastic and flexible above glass transition temperaturecan be heat softened, remolded into different formsreversible physical changes without a change in the chemical structure
45Thermosets chains chemically linked by covalent bonds hardening involves a chemical reaction which connects the linear molecules together to form a single macromolecule.
46Thermosetsonce polymerization is complete, cannot be softened, melted or molded non-destructively.have higher thermal, chemical and creep resistance than thermoplasticsThermosets suitable materials forCompositesCoatingsAdhesive applications
47Common thermoplastics Commodity PolymersPOLYETHYLENESPOLYPROPYLENEPOLYSTYRENEPOLYVINYLCHLORIDE-PVCPOLYMETHYLMETHACRYLATE-PMMAEngineering Polymers(have a thermal resistance °C)POLYCARBONATENYLON(POLYAMIDE)POLYETHYLEN TEREPHATALATE-PETHigh Performance Polymers (have a thermal resistance >150°C)POLYTETRAFLUOROETHYLENE-teflonPOLYARYLETHERKETONES-PEEK
48POLYETHYLENEprepared directly from the polymerization of ethylene (C2H4).two main types are; low-density (LDPE) and high-density polyethylene (HDPE)Advantagescheapgood chemical resistancehigh impact strength
49Limitationslow heat resistance (upper temperature limit is 60°)degrade under UV irradiation. high gas permeability, particularly CO2Applicationsextensively for piping and packagingchemically resistant fittings, garbage bagscontainers, cable covering
50POLYPROPLYLENEimproved mechanical properties compared to polyethylene; has a low density (900–915 kg/m3), harder, and has a higher strengthGood chemical and fatigue resistanceDisadvantagesOxidative degradation, high thermal expansion, high creep poor UV resistanceApplicationsmedical components, films for packaging (e.g. cigarette packets)reusable containers, laboratory equipment
51POLYSTYRENE a light amorphous thermoplastic Advantages low cost, easy to mould, rigid, transparentno taste, odor, or toxicity, good electrical insulationDisadvantagessensitive to UV irradiation (e.g. sunlight exposure)chemical resistance is poor, brittleApplicationsCD-DVD cases, electronic housings, food packaging, foam drink cups and egg boxes
52POLYVINYLCHLORIDE-PVC was the first thermoplastic used in industrial applicationsvery resistant to strong mineral acid and bases, good electrical insulators, flame-retardantTwo grades of the PVC material are available:rigid PVC is used in the construction industry for pipingcold water and chemicalsflexible PVC is used in wire and cable coating, paints, signs
54EPOXIES Advantage mechanically strong, highly adhesive good chemical and heat resistanceelectrical insulatorsDisadvantageexpensiveApplicationsas industrial adhesives, coatings or as matrices in advancedreinforced plastics and also as encapsulation media
55UNSATURATED POLYSTERS Advantagehard, high strengthcheap compared to Epoxy good electrical insulatorhigh heat resistanceDisadvantagepoor solvent resistance compared to other thermosetsApplicationsmolding or casting materials for a variety of electricalapplications, matrix for composites such as fiberglassboats, fences, helmets, auto body components
56PHENOLICS most commonly used thermosets high hardness, excellent thermal stability; low tendency to creepApplicationswiring devices, bottle caps, automotive parts, plugsand switches, as adhesives coatings and moldedcomponents for electrical applications
57POLYURETHANESdepending on the degree of cross-linking they behave as thermosets or thermoplasticslow cost, high impact strength, high adhesion propertiesbe processed into coatings, adhesives, binders, fibers and foams
58Methods of polymer fabrication Extrusion of polymersInjection MoldingBlow MoldingThermoformingCompression MoldingCasting
59Extrusion of polymers method used mainly for thermoplastics is a continuous process as long as raw pellets are suppliedis a process of manufacturing mostly long products of constant cross-section;i.e.. rods, sheets, pipes, films, wire insulation coating
60… extrusionpelletized material is successively compacted, melted and formed into a continuous charge of viscous fluidtemperature of the material is controlled by thermocouplesforcing soften polymer through a die with an openingthe product going out of the die is cooled by blown air or in water bath
62Injection Molding most widely used technique for thermoplastics highly productive method, profitable in mass production of large number of identical partspolymer 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 cavitypressure is maintained until solidification and then the mold opens and the part is removed
64Blow Moldingis a process in which a heated hollow thermoplastic tube (parison) is inflated into a closed molddisposable containers, recyclable bottles, automotive fuel tanks, tubs are producedinvolves manufacture of parison by extrusion, injection or stretching
65parison 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 cavityparison is then cut on the top, mold cools down, its halves open, and the final part is removed
67Thermoforming is a process of shaping flat thermoplastic sheet softening the sheet by heat, followed by forming it in the mold cavityThermosets can not be formed by the thermoforming because of their cross linked structure
68Thermoforming methods three thermoforming methods, differing in the forming stage:Vacuum Thermoforming; shaping a preheated thermoplastic sheet by means of vacuum produced in the mold cavityPressure Thermoforming;... by means of air pressure.Mechanical Thermoforming;... by direct mechanical force
70Compression Molding used mostly for molding thermoset resins pre-weighed amount of a polymer mixed with additives is placed into the lower half of the moldpolymer 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 cavitysuitable for molding large flat or moderately curved parts; side panels for automotive, electric housings etc.
72Casting both thermosets and thermoplastics may be cast. molten polymer is poured into a mold and allowed to solidifyfor thermoplastics solidification occurs upon coolingwhile thermoset’s hardening is a consequence of polymerization reaction
73REFERENCESFrançois Carderelli, Materials Handbook: A Concise Desktop Reference,2nded.,SpringerDonald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis GroupJ. A.Brydson, Plastics Materials, 7thed., HeinemannWilliam D. Callister ,Materials Science and Engineering,7th ed., Wiley
75What 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.
76Why Recycling is Important? Recycling Saves EnergyRecycling Saves Environmental Conditions and Reduces PollutionRecycling Saves Natural ResourcesEconomic BenefitsRecycling Saves Space for Waste Disposal
77Benefits• 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
78Recycling of polymers Recycling of Polymers Chemical recycling Mechanical recyclingEnergy recyclingChemolysisGlycolysisMethanolysisHydrolysisThermolysisPyrolysisHydrogenation
79Why 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.
80Conclusive Facts 1 t = 20,000 plastic bottles 25,000 t of bottles recycled in the UK in 2003 saved approximately25 million kWh of energy25 recycled PET bottles can be used to make an adult’s fleece jacketRecycling a single plastic bottle can conserve enough energy to light a 60 W lightbulb for up to 6 h
82We have done it!!!Ref: assets/ppt/1PlasticDebrisConference9.ppt
83Look at the changes you could make with recycling...
84REFERENCESassets/ppt/1PlasticDebrisConference9.pptFrançois Carderelli, Materials Handbook: A Concise Desktop Reference,2nded.,SpringerDonald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis Group
85REFERENCES J. A.Brydson, Plastics Materials, 7thed., Heinemann William D. Callister ,Materials Science and Engineering,7th ed., Wiley
86REFERANCESPlastic Technology Handbook, 4th Edition, Authors: Manas Chanda,Salil K. Roy