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1、Chapter 2 Thermoplastics,Introduction,Thermoplastics vs ThermosetsThermal propertiesStrengthUsesProcessingTypes of ThermoplasticsAmorphous plasticsSemi-crystalline plastics,Amorphous vs.Crystalline Thermoplastics,Amorphous(a-morphous=without shape)-The polymer chains are in random arrangement.Molecu
2、lar structure is incapable of forming regular order(crystallizing)with molecules or portions of molecules regularly stacked in crystal-like fashion.Molecular arrangement is randomly twisted,kinked and coiled.Crystalline-The polymer chains form a regular pattern.Molecular structure forms regular orde
3、r(crystals)with molecules or portions of molecules regularly stacked in crystal-like fashion.Molecular arrangement is arranged in an ordered fashion.,Amorphous Commodity ThermoplasticsMaterials,Acrylic(PMMA)Polystyrene(PS)Acrylonitrile-Butadiene-Styrene(ABS)Polyvinyl Chloride(PVC)Polyethylene Terept
4、halate Glycol(PETG)Cellulose Acetate Butyrate(CAB),Amorphous Commodity ThermoplasticsKey Characteristics,Low cost,temperature resistance and strengthGood dimensional stabilityBonds wellTypically,but not always,transparent,Semi-Crystalline Commodity Thermoplastics Materials,Polyethylene(PE)High Densi
5、ty Polyethylene(HDPE)Low Density Polyethylene(LDPE)Polypropylene(PP)Polymethylpentene(PMP),Semi-Crystalline Commodity Thermoplastics Key Characteristics,Low cost,temperature resistance and strengthExcellent chemical resistanceLow COF Near zero moisture absorptionVery good electrical propertiesGood t
6、oughness,Commodity Resins,Big FourPolyethylene(PE)Polypropylene(PP)Polyvinyl Chloride(PVC or Vinyl)Polystyrene(GPPS General Purpose Polystyrene also includes Styrofoam or expanded polystyrene eps),Of the seven symbols used for domestic recycling,5 of them are for commodity plastics.,Polyolefins,PP a
7、nd PE are often given a special name,polyolefinsPolyolefins means oil like&refer to oily and waxy feel these materials haveConsists of only carbon and hydrogen,they are all aliphatic groups,Polyethylene(PE),Mer unitPolymer chain,Polyethylene,LDPEHigh Pressure/High Temperature processingHigh“H”activa
8、tionbranchingHDPELow Pressure/Ziegler-Natta catalystLittle branchingHighly crystallineLLDPE“Copolymer”side chains prevent crystalizationImprove toughness,strength,ESCRCrosslinked PE,Forms of PE,PolyethyleneHistory Polyethylene(PE)was developed in 1898 by a German chemist named Hans von Pechmann.He p
9、repared it by accident while heating diazomethane.Structure The structure of PE is probably the simplest in the polymer world.It is made up of the monomer Ethylene and contains only C-C and C-H bonds which makes it very stable.,The most common application for polyethylene that everyone can identify
10、with is the polyethylene milk jug.,Polyethylene FormsPE comes in a wide variety of forms made by changing the density,branching,and crystalline structure of the basic polyethylene chain.HDPE is probably the most common form people are familiar with so the properties provided will be for HDPELDPE Low
11、 Density Polyethylene,Polyethylene FormsLLDPE Linear Low Density Polyethylene UHMWPE Ultra High Molecular WeightPolyethylene Usually around 8-10,000monomers need to be linked up in order to make the polyethylene useable as apolymer.For UHMWPE the number of monomers is around 70,000.PEX Cross-Linked
12、Polyethylene HDPE is probably the most common form people are familiar with so the properties provided will be for HDPE,Polyethylene-Considerations Density HDPE has a specific gravity of 0.95 which means that it will float in water.Crystallinity HDPE is semi-crystalline(around 65%)Hygroscopy HDPE is
13、 not hygroscopic and does not require drying when processedTg HDPE has a glass transition temperature of-180FTm HDPEs crystals melt at around 280 F,but it is commonly processed in a melt range of 375 525 F.,Polyethylene-Considerations Price HDPE is one of the cheapest polymers in terms of cost.The c
14、ommodity polymers are generally cheaper than the engineering grade polymers depending on the quantity purchased.Mechanical Properties HDPE is generally considered to have poor mechanical properties with the exception of impact strength.Its tensile strength averages around 4,000 psi and its tensile m
15、odulus around 150,000 psi.Chemical Resistance HDPE has excellent chemical resistance.It is one of the most chemically resistant thermoplastic resins.This is the reason it is commonly used in bottles for detergents and other household chemicals.,Polyethylene-ConsiderationsOptical Properties-HDPE has
16、a high degree of crystallinity making its optical properties quite poor.Flammability-Unmodified HDPE is classified in the“quite flammable”category which is the lowest rating a plastic can achieve.This rating is determined by a flammability test.HDPE not only burns and continues to burn,but usually a
17、lso drips flaming melt which continues to burn.This is not a good property for a plastic material to have.Electrical Properties-The electrical properties ofHDPE are moderate but it is used for sometypes of wire coatings.,Polyethylene-Considerations Weatherability-HDPE is very susceptible to weatheri
18、ng making its uses in outdoor applications somewhat limited unless it is modified to withstand the ultraviolet rays of the sun.Processability HDPE is easily processed in virtually all standard plastic forming processes.Thermal Sensitivity HDPE is not very thermally sensitive.It can remain at high te
19、mperatures for long periods of time without suffering thermal degradation.It is commonly used to purge other materials out of the processing machinery because of its thermal resistance.,Cl,Chlorosulfonated polyethylene,Properties,Good resistance to ozone,heat,flame,chemicals and solvents Low tempera
20、ture flexibility Heat-ageing resistance,Uses&Applications,Hose products,roll covers,tank linings,wire and cable covers,footwear,and building products,Random chlorination of PE(25-45%Cl)Incorporation of infrequent chlorosulfonic groups(SO2Cl)as preferred cross-linking sites,Caused by,Cross-linking un
21、it,Highly polar unit,Ethylene copolymer series,Ethylene vinyl acetate(EVA),Low crystallinity gives it a low melting point and excellent low temperature toughness.,EVA based hot-melts are able to fulfill various requirements in applications such as packaging,bookbinding or label sticking,Polar functi
22、onality promotes adhesion to polar substrates(paper,polyester,wood,and leather),Polar functional moiety,:packaging,adhesives,wire,cable and health care.,Applications,Ethylene copolymer series,Acrylic ester decreases the crystallinity of the polymer,Key benefits of ethylene acrylic ester copolymers,E
23、xcellent thermal stability Excellent adherence to many substrates(polyethylene,polystyrene,polypropylene,OPP,etc.)Good chemical resistance Good elastic propertiesExcellent mechanical behavior at low temperature,Ethylene-Acrylic Ester copolymers,Ethylene copolymer series,They can be divided into seve
24、ral product families depending on the acrylic ester type(methyl,ethyl or butyl acrylate),Third monomer-MAH:maleic anhydride-GMA:glycidyl methacrylate.,-Increase final adhesion properties-Heat resistance or long term ageing properties.,The roles of third monomer,Ethylene acrylic ester terpolymers,Ion
25、omers,:An ionomer is an ion containing polymer.It is more than just a polymer with ionic groups.We call any old polymer with ionic groups a polyelectrolyte,special kind of polyelectrolyte.,containing both nonionic repeat units and small amounts of ion containing repeat units less than 15%of polymer,
26、Characteristics:,The polar groups tend to cluster together,away from the nonpolar polymer backbone chains,not closslinked polymer,a type of thermoplastic called a reversible crosslinker,This phenomenon allows for a polymer with the properties of an elastomer and the processability of a thermoplastic
27、.These ionomers are sometimes known as thermoplastic elastomers,Reversible crosslinking behavior of ionomers,Ionomers,Example:,Polymerization between ethylene and methacrylic acid,ionomer,Acidic property,ethylene,methacrylic acid,Poly(ethylene-co-methacrylic acid),Semipermeable membrane,Ion filter,F
28、uel cells,Electrodialysis,Applications,Dupon:Surlyn TM,Dupon:Nafion TM,Functional moiety,Ethylene propylene rubber,EP rubber(EPR),poly(ethylene-co-propylene),Glass transition temperature:-50 deg.C,:A random copolymer of ethylene and propylene.A rubbery noncrystalline material,Properties,Non-polar el
29、astomers,Good electrical resistivity,Resistance to polar solvents(i.e.,water,acids,alkalies,ketones,alcohols),radiator,appliance hose,tubing,belts,electrical insulation,roofing membrane,rubber mechanical goods,High-voltage tape,Rubber mechanical goods,Polyethylene-ConsiderationsDecoration and Assemb
30、ly HDPE can be difficult to decorate and assemble with some methods because of its low surface energy.Inks tend to bead-up on it and adhesives can have a hard time sticking to it.It has a waxy feel to it due to its low Tg and many assembly methods that use friction to generate heat for bonding have
31、difficulty processing HDPE.Creep HDPE creeps badly due to its low glass transition temperature.This leads to low dimensional stability and is reason it is not used in some applications.Recyclability HDPE and all other PEs are highly recyclable.Recycled products madefrom PEs include trash cans,deterg
32、ent bottles,flower pots,grocery bags,and composite decking.,Polyethylene-ApplicationsConsumer goods-Toys,food storage containers,buckets,PolypropyleneHistory Polypropylene(PP)was developed in Spain in 1954 by professor Giulio Natta.He was able to produce the resin by using catalysts from the Polyeth
33、ylene industry and applying them to propylene gas.Structure The PP monomer is a single bond between two carbon atoms and can be seen below.It is similar to Polyethylene in many ways,but the methyl group that takes the place of the hydrogen reduces the chain flexibility,making polypropylene a stiffer
34、 material.,Methyl group,Polypropylene FormsPP comes in a few varieties:Homopolymer-General purpose grade,very versatileBlock Copolymer-5-15%ethylene,improved impact strength to below 20 C Random Copolymer-Co-monomers arranged randomly on the molecular chain,more flexibility and better clarity,Polypr
35、opylene-ConsiderationsDensity PP has a specific gravity of 0.93 which means that it will float in water.Crystallinity PP is semi-crystalline(around 75%)Hygroscopy PP is not hygroscopic and does not require drying when processedTg PP has a glass transition temperature of-9 CTm PPs crystals melt at ar
36、ound 176C,but it is commonly processed in a melt range of 215 280 C.,Polypropylene-ConsiderationsPrice PP is a very cheap and extremely common polymer.The commodity polymers are generally cheaper than the engineering grade polymers depending on the quantity purchased.Mechanical Properties PP has a t
37、ensile strength that averages around 31 MPa and its tensile modulus around 1200 MPa.Chemical Resistance PP has excellent chemical resistance.It is one of the most chemically resistant thermoplastic resins.It is not quite as good as HDPE,but it is still one of the best in terms of chemical resistance
38、.,Polypropylene-Considerations Optical Properties-PP has a high degree of crystallinity making its optical properties quite poor.Flammability-PP is classified in the“quite flammable”category which is the lowest rating a plastic can achieve.PP not only burns and continues to burn,but usually also dri
39、ps flaming melt which continues to burn.This is not a good property for a plastic material to have in certain applications.Electrical Properties-PP has excellent electrical properties making it very useful as an insulating material on high voltage capacitors.,Polypropylene-Considerations Weatherabil
40、ity-PP has a poor weathering resistance and is especially susceptible to extreme cold and high degrees of UV raysProcessability PP is easily processed in virtually all standard plastic forming processesThermal Sensitivity PP is not very thermally sensitive.It can remain at high temperatures for long
41、 periods of while suffering little if any thermal degradation,Polypropylene-Considerations Decoration and Assembly PP is difficult to decorate but when it is decorated the most common method is using a hot stamp.Hot stamping is a fairly simple process which has an endless variety of colors,metals,de
42、signs,etc.Creep PP creeps badly due to its low glass transition temperature This is another reason it is not used in some applications.Recyclability PP is recyclable but not in any meaningful quantities.Recycled products made from PP include plastic lumber,and car battery cases.Many times it is mixe
43、d in with the PE regrind and processed together due to their similar processing qualities.,Advantages of PolypropyleneLow CostExcellent flexural strengthGood impact strengthProcessable by all thermoplastic equipmentLow coefficient of frictionExcellent electrical insulationGood fatigue resistanceExce
44、llent moisture resistanceService Temperature to 126 CVery good chemical resistance,Disadvantages of PolypropyleneHigh thermal expansionUV degradationPoor weathering resistanceSubject to attack by chlorinated solvents and aromaticsDifficulty to bond or paintOxidizes readilyflammable,Polypropylene-App
45、licationsConsumer goods-Food storage containers,weather resistant clothing,indooroutdoor carpeting,Polypropylene is usually used for food storage containers so that they dont warp and lose their shape in the microwave or in the dishwasher.,Polypropylene ApplicationsMedial Applications-Syringes,stora
46、ge containers for needles,surgical disposable fabricAutomotive-Instrument panels,fender liners,and brake/coolant reservoirs,Polypropylene-ApplicationsPackaging-Notably anything with a living hinge is usually made from PP like tic-tac container lids and shampoo bottle lids,food storage containers,wat
47、er bottles,pill bottle lids,etc.Construction-Non-electric fuses,insulating material for power capacitors,Polypropylene,Polyvinylchloride(PVC),Mer unitPolymer chain,Polyvinyl ChlorideHistory Polyvinyl was discovered by accident on two separate occasions.The first discovery occurred in 1835 by Henri V
48、ictor Regnault(1810-1878),a French chemist and physicist.The second finding came 37 years later,in 1872 by Eugene Baumann.Structure PVC is made up of hydrogen,carbon,and Chlorine.The large Chlorine atom helps to protect the polymer chain from chemical attack,but makes the material more shear and hea
49、t sensitive.,Polyvinyl Chloride-Considerations Forms PVC comes in a wide variety of forms:Plasticized PVC(PPVC)Rigid PVC(RPVC)Semi-Rigid PVCThe mechanical properties and hardness of PVC are frequently modified with the use of plasticizers.The properties provided will mostly be for Rigid PVC(RPVC)unl
50、ess otherwise stated.,Polyvinyl Chloride-Considerations Density RPVC has a specific gravity of 1.4 which means that it will not float in water.It is one of the densest unfilled thermoplastics.Crystallinity RPVC is an amorphous material,it only achieves around 8%crystallinityHygroscopy RPVC is not hy
