包装用聚乙烯(PE)的性能介绍

DetailedintroductiononPolyethyleneWilliamR&D,APPropackHowtoproducePEfromoil?100×104tonbaseoil4kindsbasicmaterialinpetrolproduction:►Alkynes(acetylene)►Olefins(ethene,propylene,butylene,butadiene)

►Arene(benzene、toluene、dimethylbenzene)►Themixedgasofabovematerialethene

15×104t，Propylene9.0×104t，Butadiene2.5×104t，Arene8.0×104t，Petrol9.0×104t，Eldingoil

47.5×104tcrackingBaseoilFirstproductionSecondproductionCommodityoilThirdproductionManufacturebasicorganisechemicalproductionmaterialOilwithseveralboilingpointrangePE,PP,PSandsoonDistillcatalyse、hydrocracking、delayedcoking

、catalyticreforming、dehydrochlorination

、hydrorefining

PolymerizationTankreactorTypicalparticlesizedistributionofPEgranulesPelletcreatingLDPEisahighlybranchedhomopolymerwhichcontainsbothshort-chainandlong-chainbranches.HDPE,MDPEandLLDPEconsistofpredominantlylinearmoleculeswithshort-chainbranches,dependingonthetypeandamountofcomonomers.

PE:m=0EVOH:R=-OH

EVA:R=-COOCH3

PVA:n→0,R=-OH

EAA:R=-COOH,

EMAA,PB-1andsoon.TheclassificationofPENote:ClassificationofpolyethylenegradesbydensityinaccordancewithASTM1248.ClassificationofPEbydensityThebranch-freesequencesofthechainsarefoldedatroomtemperaturetoformcrystallamellae(crystallites).Thelamellaearesheet-likestructuresofuniformthickness;theactualthicknessofthelamellaedependsonthedegreeofbranchingofthemoleculesandontheirthermalhistory.Moleculeloops,chainends,relativelylongbranchesandcomonomer-containingsegmentsofthechainsprotrudefromthecrystallamellae.Thesedefectsformamorphousregionsbetweenthelamellae.ThecrystalstructureofPEresinPolyethylenehasadensityof1.0g/cm3inthecrystallineregionsandadensityof0.86g/cm3intheamorphousregions.ThedensitydescriptionofPEDPE=

xDCrystal+(1-x)DamorphousXiscrystallinityHowtocalculatethedensityofmixedPE?两种结晶性聚合物形成共混物的密度d为

1/d=w1/d1+w2/d2

（1）

其中,d1、d2分别为两种结晶性聚合物共混后的密度

w1、w2分别为两种结晶性聚合物的重量分数

第一种结晶性聚合物共混后的密度d1为

1/d1=X1/d1c+(1-X1)/d1a

（2）

第二种结晶性聚合物共混后的密度d2为

1/d2=X2/d2c+(1-X2)/d2a

（3）

其中,d1c、d2c，d1a、d2a分别为两种结晶性聚合物的晶相及非晶相密度.X1、X2分别为两种结晶性聚合物共混后的结晶度

将式（2）、式（3）代入式（1）得

1/d=w1*[X1/d1c+(1-X1)/d1a]+w2*[X2/d2c+(1-X2)/d2a]

Inpractice,theaveragemolarmasscanbedeterminedmosteasilybyindirectmethods,asthemeltflowrateinaccordancewithASTM1248orasthesolutionviscosityinaccordancewithISO1628,measuredas0.15%solutionindecahydronaphthalene,measuredastheviscositynumberV.N.(J)orStaudingerindex.TheMFRIandViscosityofPEηRV=ηSP/C=Km.MwηRV:reducedviscosityC:concentrationKm:aexperiencedconstantMw:MolecularmassMolarmassdistribution(MMD)ofPEProductsinwhichthecomonomersarepreferentiallyincorporatedintothehighmolar-massregionsoftheMMD(“inverse"comonomerdistribution)combineuniquepropertyfeaturesinoneproductlikehighstiffnessandhighenvironmentalstresscrackingresistance(ESCR).InfluencefactorsinmachineMolarmassregulatorResidencetimePelletsFlakesComonomerCatalyst/initiatorstabilizersadditivesPolymerizationofethylene•Automobileindustry•Electricalindustry•Chemicalindustry/packagingofhazardousmaterials•Leisureandsportsarticles•Medical,pharmaceuticalandcosmeticsindustries•Foodindustries•Agricultureandhorticulture•HousewaresApplicationofPEThemostimportantPropertiesofthePEWithincreasingpressurethethroughputincreasesoverproportionately:theresistancetoshear,theshearviscosity,decreaseswithincreasingshearrate(“shear-thinning"behaviour).Theviscosityasafunctionofshearrateisshownforvariouspolyethylene.“Shear-thinning”behaviour

Newtonianfluidnon-NewtonianfluidTheshearviscosityisessentiallyonlyafunctionoftheinstantaneousshearrateandisvirtuallyindependentoftheoverallshearofthemelt.Incontrasttheextensionalviscositydependsonthecurrentrateofextensionaswellasonthetotalextensionofthemelt.ExtensionalviscosityLDPEexhibitsapronouncedincreaseinextensionalviscosityevenathighextension(extensionalsolidification)anddoesnotachieveasteady-statevalue.LinearHDPEwithanarrowMMD,bycontrast,givesaconstantandcomparativelylowextensionalviscosityvalue.Inthecaseofslowflowthroughalongdie,themacromoleculeshavethebestopportunitytorelaxtheorientation,whichisnotverypronouncedanywayundertheseconditions.DieRheologyofPEinproductionarough,wavysurfacestructureoftheextrudateasaconsequenceofelasticturbulenceinthedieinlet。“slip-stick“effectsduetothetransitionfromwalladhesiontowallslipofthemeltinthedieoutlet,whichcanalsooccuralongthedieperiphery.Stiffnessismeasuredintermsofthetensilemodulusortheshearmodulus.Anoverviewoftheelasticbehaviourofaselectionofproductsasafunctionoftemperatureisgivenbythecurvesfortheshearmodulusandthelogarithmicdecrementofthemechanicaldamping.PhysicalpropertiesofPEThehardnessofethylenehomopolymersandcopolymersincreasesonlyslightlywithincreasingmolarmassatconstantdensity.Yieldstress,tensilestrengthandtensilestrainatbreakaredeterminedinaccordancewithISO527.Creepexperimentsatconstantstress,knownasretardationexperiments,showtheincreaseinelongationduetothestressovertime.Averyvividsummaryofthestress–strainbehaviourasafunctionoftimeisgivenbytheso-calledisochronicstress–straincurves.CreepphenomenonEffectingonCOFandwearrateofmeanpressureDSCcurveofdifferentPELighttransmissionofPEasafunctionofwave-lengthSurfaceresistivityasafunctionofrelativehumidityLightandelectronicperformanceofPEBehaviouroncontactwithmediaChemicalresistanceWaterabsorptionEthylenehomopolymersandethylenecopolymerswith-olefinsarewaterrepellentowingtotheirnonpolarstructure.Thewaterabsorption(DIN53495Method1)isless