《通用高分子材料》课程教学课件（PPT讲稿）Chapter 2 General Plastics 2-2 Thermoplastis

2-2General Thermoplastics

2-2 General Thermoplastics

Types of plasticsThere are 2 main types of plastics -Thermosets - Made from long chain moleculeswhich bond together stronglywhenthe plastics aremade.This means that they cannot be re-melted.Thermosets are rigid and non-flexible even at hightemperatures.Thermoplastics - Also made from long chainmolecules which are entangled but not bondedtogether.Thismeansthat they canbemelted andre-formed.("Thermo"=heat,"plastic"=abletobeformed)3

Properties & applicationsMaterialPropertiesApplicationsLDPE-LoWdensitySqueezybottles,Polythenetough,flexible,goodtoys,carrier bags,(Polyethylene)TV cablechemicalresistanceMilkcrates,HDPE-Highdensitybottles,pipes,stiffer, harder, can beThermoplasticssterilised,waxyfeelbuckets,bowlsContainerswithPolypropyleneExcellentgeneralpurpose material.Lightintegral hinges,(PP)hard,impactresistant,rope,packagingresistsbending(hinges)kettles,chaireasilyjoined&weldedshells,cratesAcrylicStiff,hard,clear,impactIlluminated signs,resistant,verydurablewindows,rearcar(PMMA)polisheswell,verygoodlights, lightingopticalproperties.units,displays5

Properties & applicationsMaterialPropertiesApplications(a) Conventional-light,-CD cases,Polystyrenehard, stiff, brittle,disposable cups,(PS)clearmodel kits(b) Toughened -better-Refrigeratorlinings, toysimpactresistance,Thermoplasticsstronger,pigmented(c)Expanded (foam)-Packaging,buoyant, light,sound and heatheat/soundinsulatorinsulation,ABSCasesforelectronicHighimpactstrength&(acrylonitriletoughness,verygoodgoods, toys,butadienestyrene)surfacefinish,durablephones,carcomponents6

Properties & applicationsMaterialPropertiesApplications-Hard, tough, gooduPVC-Pipes,gutteringweatherresistance,widebottles,window(polyvinylrange ofcolours,Uvframeschloride)stabilising neededHosepipes,sealPlasticisedPVC-Soft,flexible,goodThermoplasticselectricalinsulatorwallcoveringsPETDrinksbottlesClear,tough,flexiblegood chemical(polyethyleneresistanceterephthalate)NylonBearings,gearHard,tough, wearresistant,low friction,wheels,clothing,(polyamide)brushfilaments,self-lubricating,machines well, goodpowertool caseschemicalresistance7

ImportantPropertiesofPolymersStructure and ChemicalMakeup:The structure and Chemical make-up of a polymerprovides a backbone for the properties which acertain polymer will exhibit. The differentelements present in a polymer as well as the waythey interact dictate all of the properties in thematerial

Important Properties of Polymers Structure and Chemical Makeup: The structure and Chemical make-up of a polymer provides a backbone for the properties which a certain polymer will exhibit. The different elements present in a polymer as well as the way they interact dictate all of the properties in the material

TensileStrength:Tensile strength refers to how much stress a samplecan withstand before failing while being "stretched."Tensile strength is measured by stretching a polymerpiece of uniform dimensions under constant force andmeasuring how much it stretches before it fails. TensileModulus,whichisameasure of tensilestress,can thenbe calculated by the ratio of stress to strain. Wherestress is the ration of Force to cross sectional area ofthe polymer and strain is the ratio of change in lengthbefore failing to the original length of the polymer.Tensile strength is important to many applications ofpolymers, it allows a material to flex and 'bend withoutthethusmaterialreliable.makingbreaking

Tensile Strength: Tensile strength refers to how much stress a sample can withstand before failing while being "stretched. " Tensile strength is measured by stretching a polymer piece of uniform dimensions under constant force and measuring how much it stretches before it fails. Tensile Modulus, which is a measure of tensile stress, can then be calculated by the ratio of stress to strain. Where stress is the ration of Force to cross sectional area of the polymer and strain is the ratio of change in length before failing to the original length of the polymer. Tensile strength is important to many applications of polymers, it allows a material to flex and bend without breaking thus making the material reliable

Melting Point:The melting point of a material is the temperature,at a certain pressure where the solid phase of thematerial turns to the liguid phase of the material.This is important in polymers because a polymerwith a low melting point cannot be used in anapplication where temperature will exceed thattemperature

Melting Point: The melting point of a material is the temperature, at a certain pressure where the solid phase of the material turns to the liquid phase of the material. This is important in polymers because a polymer with a low melting point cannot be used in an application where temperature will exceed that temperature

Glass Transition Temperature:The glass transition temperature is the pointbetween solid and liquid where a decided changein properties of the material occur. This is thepoint where a material looses its glass-likeproperties and becomes more comparable torubber. The Tg is a second order phase transition,that is, there is no latent heat present in thechange

Glass Transition Temperature: The glass transition temperature is the point between solid and liquid where a decided change in properties of the material occur. This is the point where a material looses its glass-like properties and becomes more comparable to rubber. The Tg is a second order phase transition, that is, there is no latent heat present in the change

ImpactResistance:Impact resistance is the ability of a material towithstand sudden shocks or blows; it is a measure oftoughness. This property is extremely important inpolymers because so many polymers in everyday lifeneed to be impact resistant. Anything that has atendency to be dropped must be impact resistant, thisis what makes a polymer useful in such circumstances,it does not fail when dropped or slammed into

Impact Resistance: Impact resistance is the ability of a material to withstand sudden shocks or blows; it is a measure of toughness. This property is extremely important in polymers because so many polymers in everyday life need to be impact resistant. Anything that has a tendency to be dropped must be impact resistant, this is what makes a polymer useful in such circumstances, it does not fail when dropped or slammed into