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外文资料翻译资料来源：书籍文章名：Chapter 2 The Properties of Plastics书刊名：English for Die & Mould Design and Manufacturing作 者：刘建雄王家惠廖丕博主编出版社：北京大学出版社，2002章 节：2.2 The Properties of Plastics页 码：P24P31文 章 译 名： 塑料的性能 ThePropertiesofPlasticsPlastics are organic materials made from large molecules that are constructed by a chain-like attachment of certain building-block molecules. The properties of the plastic depend heavily on the size of the molecule and on the arrangement of the atoms within the molecule. For example, polyethylene is made from the ethylene building block that is initially a gas.Througha processcalledpolymerization,achainofethylenemoleculesisformedbyvalencebondingofthecarbonatomswithintheethylenemolecule.Thehighmolecularweightproductwhichresultsiscalledapolymer.Hence,thedesignationpolyethyleneisusedtodistinguishthehigh-molecular-weightplasticfromitsgaseouscounterpart,ethylene,whichisthemonomerthatbecomespolymerized.The“poly”referstothe“many”ethylenebuildingblockmoleculesormonomers,whichjointoformthepolyethyleneplasticmolecule.Frequently,theterm“resin”isused,interchangeablywith“polymer”todescribethebackbonemoleculeofaplasticmaterial.However,“resin”issometimesusedtodescribeasyrupyliquidofbothnaturalandsyntheticresin.Plastics,inthefinishedproductform,areseldomcomprisedexclusivelyofpolymerbutalsoincludeotheringredientssuchasfillers,pigments,stabilizers,andprocessingaids.However,designationoftheplasticmaterialormoldingcompoundisalwaystakenfromthepolymerdesignation.Broadlyspeakingplasticsmaybedividedintotwocategories:thermoplasticsandthermosetplastics.Theclassesofmaterialsaresonamedbecauseoftheeffectoftemperatureontheirproperties. 2.2.1Thermosets Thermosetplasticsarepolymerswhicharerelativelyuselessintheirrawstates.Uponheatingtoacertaintemperatureaachemicalreactiontakesplacewhichcausesthemoleculestobondtogetherorcross-link.Aftervulcanizationandpolymerization,orcuring,thethermosetmaterialremainsstableandcannotreturntoitsoriginalstate.Thus,”thermo-set”identifiesthosematerialsthatbecomesetintheiruseablestateresultingfromtheadditionofheat.Normally,athermosetpolymerismixedwithfillersandreinforcingagentstoobtainthepropertiesofamoldingcompound.Thermosetsarethehardestandstiffestofallplastics,arechemicallyinsolubleaftercuring,andtheirpropertiesarelessaffectedbychangesintemperaturethanaretheheat-sensitivethermoplastics.Theclosestnon-plasticcounterpartstothermosetsinpropertiesareceramics.Commonexamplesofthermosetplasticsare:phenolics,melamine,urea,alkyds,andepoxies.Moldingcompoundsmadefromthesepolymericresinsalwayscontainadditionalfillersandreinforcingagentstoobtainoptimumproperties.2.2.2Thermoplastics Thermoplasticpolymersareheat-sensitivematerialswhicharesolidsatroomtemperature,likemostmetals.Uponheating,thethermoplasticsbegintosoftenandeventuallyreachameltingpointandbecomeliquid.Allowingathermoplastictocoolbelowitsmeltingpointcausesresolidificationorfreezingoftheplastic.Successiveheatingandcoolingcyclescauserepetitionofthemelting-freezingcyclejustasitdoesformetals.Thefactthatthermoplasticsmeltisthebasisfortheirprocessingintofinishedparts.Thermoplasticsmaybeprocessedbyanymethodwhichcausessofteningormeltingofthematerial.Examplesofthermoplasticfabricationtechniquesusingmeltingare:injectionmolding,extrusion,rotationalcasting,andcalendering.Fabricationmethodswhichtakeadvantageofsofteningbelowthemeltingpointare:thermoforming(vacuumorpressure),blowmolding,andforging.Ofcourse,normalmetal-cuttingtechniquescanalsobeappliedtothermoplasticsinthesolidstate.Commonexamplesofthermoplasticsare:polyethylene,polystyrene,polyvinylchloride(PVC),andnylon(polyamide).2.2.3Fillers Plasticsoftencontainotheraddedmaterialscalledfillers.Fillersareemployedtoincreasebulkandtohelpimpartdesiredproperties.Plasticscontainingfillerswillcurefasterandholdclosertoestablishedfinisheddimensions,sincetheplasticshrinkagewillbereduced.Woodflouristhegeneral-purposeandmostcommonlyusedfiller.Cottonfrock,producedfromcottonlinters,increasesmechanicalstrength.Forhigherstrengthandresistancetoimpact,cottonclothchoppedintosectionsabout1/2-inchsquarecanbeprocessedwiththeplastic.Asbestosfibermaybeusedasafillerforincreasedheatandfireresistance,andmicaisusedformoldingplasticpartswithsuperiordielectriccharacteristics.Glassfibers,silicon,cellulose,clay,ornutshellflourmayalsobeused.Nutshellflourisusedinsteadofwoodflourwhereabetterfinishisdesired.Plasticpartsusingshortfiberfillerswillresultinlowercosts,whilethosewithlongfiberfillershavinggreaterimpactstrengthsaremoreexpensive.Othermaterials,notdefinedasfillers,suchasdyes,pigments,lubricants,accelerators,andplasticizersmayalsobeadded.Plasticizersareaddedtosoftenandimprovethemoldabilityofplastics.Fillerandmodifyingagentsareaddedandmixedwiththerawplasticbeforeitismoldedorformed.2.2.4PropertiesofPlastics 1.GeneralProperties Theproblemofselectingplasticmaterialsisthatoffinding thematerialwithsuitablepropertiesfromthestandpointofintendedservice,methodsofformingandfabricating,andcost.Newandimprovedplasticmaterialspossessingalmostanydesiredcharacteristicarebeingintroducedcontinually.Thereareplasticsthatdonotrequireplasticizersthathavegreaterflexibilityunderlowertemperatures,andarestableunderhighertemperatures.Someresistwater,acids,oils,andotherdestructivematter.Thewideuseofplasticstestifiestotheirvalue;however,fundamentallimitationsshouldbeconsideredwhenapplyinganewmaterialoradaptinganoldmaterialtonewapplications.2. EffectsofTemperature Plasticsareinclinedtowardrigidityandbrittlenessatlowtemperatures,andsoftnessandflexibilityathightemperatures.Theyarefundamentallyunstabledimensionallywithrespecttotemperature,andaresusceptibletodistortionandflowwhensubjectedtoelevatedtemperatures.Thethermoplasticsareparticularlysusceptible,whilethethermosettingplasticsaremuchmoreresistant,differing,however,onlyindegree.Thedistinctionbetweenthethermalstabilityofthethermosettingandthermoplasticresinsisnotwelldefined.Atruedistinctioncanbedrawnonlybetweenindividualplastics,ratherthanbetweenclassesofplastics.Hightemperaturesnotonlyseriouslyreducethemechanicalpropertiesofplastics,butalsoacceleratethedestructiveactionofexternalagentstowhichtheyaresensitive.Continuousheatingalsomayinducebrittlenessandshrinkageinheavilyplasticizedmaterialsbyvolatilizationofplasticizers.Theuseofoneplasticincontactwithadissimilarplasticinaproposedapplicationshouldbecheckedfirstinthelightofpossible”migrationofplasticizer”,sometimesresultingindiscolorationorhardeningofoneoftheplastics.Ingeneral,moderatetemperaturesarerequiredforstorageofplasticsoverlongperiods;lowtemperaturesaretobeavoidedbecauseofthelow-temperaturebrittlenessofmostoftheplastics,andhightemperaturesshouldbeavoidedbecauseoftherapidlossofmechanicalproperties,volatilizationofplasticizers,andthesusceptibilityofalargenumbertodistortion.Plastics,withonlyafewexceptions,areextremelysensitivetotheeffectsofwater.High-humidityatmospheresinducewaterabsorptionandvariedresultingeffects,dependinguponthecompositionandformulationoftheplastics.Increasedwatercontentplasticizessomematerials,andthereisageneralloweringofthemechanicalproperties.Waterabsorptionisresponsibleforswellingincertainplasticsandtheultimatedecompositionofafew.Moistorwetatmospheresmayextractplasticizersfromheavilyplasticizedmaterialsandalsoprovideconditionsfavorabletofungalgrowth.Inrecentyears,however,newplasticshavecomeintousethathavefirst-classmoistureresistanceandmaycontainwaterindefinitelywhileresistingotherinfluencesatthesametime.Extremelydryenvironmentsmaycausebrittlenessincertainplasticsasaresultoflossofwaterthatnormallycontributesto theirplasticity.Cyclicwetanddryatmospheresaremoredestructivetoplasticsthancontinuousexposureatconstanthumiditybecauseofthemechanicalstressesinducedintheplasticsbyswellingandshrinkingwithmoistureabsorptionandmoistureemission.Relativelyconstant,moderatetolowhumiditiesarepreferredforplasticstoragebecauseoftheadverseeffectsofwateronthestructureandpropertiesofthesematerials,andthepossibilityofplasticizerlossbyextractionandfungalattackinmoistatmospheres 3.EffectsofLight Prolongedexposuretosunlightwillaffectadverselyallplasticswithexceptionoftetrafluoroethylene(Teflon).Thechangeinducedbytheultravioletcomponentsmayvaryinkindandseverityfromslightyellowingtocompletedisintegrationasaresultofthechemicaldegradationofthepolymericcompoundorplasticizers.Lossofstrength,reducedductility,andincreasedfragilityusuallyaccompanysuchaction.Manyplasticsareofferedinspecialformulationscontaining“ultravioletinhibitors”whichshouldbeutilizedwhenthisinfluenceispresent.Exposureofplasticstosunlightduringstorageshouldbeavoided,especiallywhenthetransparencyofclearmaterialsistobepreserved.4.Weight Asafamily,plasticsarelightwhencomparedtometals.Mostplasticshaveaspecificgravitybetween1.35and1.45,whichislessthanthatofmagnesium.5.ElectricalResistivity Plasticshaveexcellentelectricalresistivitymakingthemhave wideapplicationasaninsulatingmaterial.Inthehigh-frequencyapplications,plasticsareparticularlyadvantageousand,consequently,arebeingusedtoalargeextentinthefieldsofradarandtelevision.6.HeatInsulation Plasticshavelowheatconductionand,consequently,haveapplicationasaninsulatingmaterial.Inparticular,theyareusedashandlesforappliancesandtoolssubjectedtoheat. Fabrication Theprincipalcharacteristicofplasticsfromfabricationstandpointiscaseofmolding.Boththermosettingandthermoplasticmaterialslendthemselvestomoldingirregularandcomplexshapeswithrelativelyshortcuringcycles.Plasticsmaybejoinedbyusingvariouscements,chemicalsolvents,andmechanicalfasteners.Heat-sealing,whichparallelssomewhattheweldingprocessofmetals,isusedextensivelyinjoining lightthermoplasticfilms.Insuchcases,dielectricheatingisthetechniqueusuallyused.Frictionadhesionhashadmoderateapplicationalsointhejoiningofsmallthermoplasticparts.Plasticscanbemachinedwithconventionalmachinetools.However,certaincautionsshouldbeexercised.Inordertomaintaina goodfinish,aheavyflowofcoolantshouldbeusedsoastoavoidtemperaturesthatwilldistortthework.Insomethermosettinglaminates(glass,forexample),thecustomaryhigh-speedsteeltoolwillnotstandupinviewoftheabrasiveactionofthelaminatingmaterial.Here,eithertungstencarbideorceramiccuttingtoolsmustbeused.7.EffectsofOxygen Organicplasticsarenearlyallsubjecttooxidationwhenexposedtotheatmosphere.Theprocessisacceleratedbyhightemperaturesandlight;but,overlongperiodsoftime,oxidativedeteriorationmaytakeplaceatroomtemperature.Oxidationsusceptibilitydependslargelyuponthechemicalnatureoftheplasticandits compounding.Materialswiththegreatestnumberofdoublebonds intheirmolecularstructurewillgenerallybethemostsensitive tooxidation.Yellowingandagraduallossofstrengthandductilityaretheprincipalresultsofoxidativeprocesses.Oxidationisnotaproblemofgreatmagnitudeinstorage,sincetherigidplasticsareratherresistanttooxidativedeterioration undermoderateconditions. 8.EffectsofLoading Undermoderateconditionsthecommonthermoplasticmaterialsaresubjecttodistortionandflowwhensignificantlyloaded.Suchplasticscannotbeexpectedtomaintainahighdegreeofmechanical stabilityoverextendedperiodswhensubjectedtostress;especiallyisthistruewhentheyarealsoexposedtorelativelyhightemperatures.Thethermoplasticsshould,however,ma-intainthemselvesfairlywellwhennotsubjecttoloadorwhensubjectedtoonlymoderateload.Recently,fillers,suchasglasswool,havebeenaddedtothermoplasticstofurtherimprovethisproperty.Thethermosettingplasticsaremuchmoreload-stablethanthethermoplasticsbecauseoftheirstructureandtheinclusionoffillersintheirformulation.Inthelaminatedformtheyprovidearatherhighorderofdistortionandcreepresistance.Whennotsubjectedtomechanicalstresstheymaybeconsideredtobehighlystable.Thesematerials,however,maysuffercreepoverlongperiods,especiallywhenmaintainedatelevatedtemperatures.Thethermoplastictypesshouldnotbesubjectedtoloadwhenstored;and,wheneverpossible,theloadingofstress-bearingthermosettingmoldingsorlaminatesshouldberemovedorreduced.10. ChemicalStability Plastics,ingeneral,possessahighdegreeofinherentstabilitywithrespecttochemicaldeterioration.Inmanyinstances,thisstabilitymaybefortifiedbytheadditionoftheproperstabilizersduringcompounding.Whilethereisvastdifferencefromoneplastictoanother,thegeneralstatementmaybemadethatthere isaplasticavailabletoresistvirtuallyanycommercialchemical.塑料的性能热塑性塑料熔体是热塑性塑料加工成品的基础。热塑性塑料可以用任何方法加工，导致材料软化或熔化。t的例子采用熔融的气塑制造技术有：注射成型、挤压、旋转铸造和压延。利用熔点以下软化的制造方法有：热成型(真空或压力)，吹塑，锻造。当然，普通的金属切削技术也可以应用于固态热塑性塑料.热塑性塑料的常见例子CS为：聚乙烯、聚苯乙烯、聚氯乙烯(PVC)和尼龙(聚酰胺)。2.2.3填料 塑料是由大分子制成的有机材料，由某些积木分子组成的链状附着体构成。塑料的性能在很大程度上取决于o的大小。f分子和原子在分子内的排列。例如，聚乙烯是由最初是气体的乙烯构件制成的。通过聚合法乙烯分子中的碳原子价键形成了一条乙烯分子链。高分子量的产物被称为聚合物。因此，聚乙烯是用来区分高分子量塑料与其气态对应物乙烯，乙烯是聚合的单体。“poly”指的是“多”et。聚烯类物质的组成分子或单体，它们连接在一起形成聚乙烯塑料分子。经常使用“树脂”一词，并与“聚合物”互换来形容背板。塑料的分子。然而，“树脂”有时被用来描述天然和合成树脂的糖浆液体。塑料，以成品的形式，很少被包括在内。广泛的聚合物，但也包括其他成分，如填料，颜料，稳定剂，和加工助剂。然而，塑料材料或模塑化合物的名称总是从聚合物称广义地说，塑料可分为两类：热塑性塑料和热固性塑料。由于温度的影响，2.2.1热固性材料热固性塑料是一种聚合物，在其原始状态下是相对无用的。在加热到一定温度时，会发生化学反应，使分子结合在一起，或交叉链接。经过硫化、聚合或固化后，热固性材料保持稳定，不能恢复到原来的状态。因此，“热集”识别了那些成为由于加温而处于可用状态。通常，热固性聚合物与填料和增强剂混合，以获得模塑化合物的性能。热固性塑料是所有塑料中最坚硬、最坚硬的，固化后不溶于化学，其性能受温度变化的影响小于热敏热塑性塑料。抽搐。与热固性材料最接近的非塑性材料是陶瓷。热固性塑料的常见例子有：酚醛、三聚氰胺、尿素、醇酸和环氧。成型化合物f这些树脂总是含有额外的填料和增强剂，以获得最佳的性能。2.2.2 热塑性塑料热塑性聚合物是一种热敏材料，在室温下是固体，就像大多数金属一样。加热后，热塑性塑料开始软化，最终达到熔点，变成液体。允许热塑性塑料冷却到其熔点以下会导致溶解。塑料的冻结或冻结。连续的加热和冷却循环会导致熔化-冻结循环的重复，塑料通常含有其它被称为填料的附加材料。使用填料来增加体积并帮助赋予所需的性能。含有填料的塑料将更快地固化并保持更紧密以确定成品尺寸，由于塑料收缩将减少。木粉是一种通用的，也是最常用的填充剂.棉质长袍，由棉短绒制成，增加。机械强度。为了更高的强度和抗冲击能力，将棉布切成约1/2英寸的方形，可以用塑料加工。石棉纤维可用作填充剂提高了耐热性和耐火性，云母用于成型具有优良介电特性的塑料零件。玻璃纤维、硅、纤维素、粘土或壳面也可以使用。n在需要更好的光洁度的地方，用utshell面粉代替木粉。使用短纤维填料的塑料零件会降低成本，而长纤维填料的成本会更高。行动能力更昂贵。其他未定义为填料的材料，如染料、颜料、润滑剂、促进剂和增塑剂也可加入。增塑剂被添加到软化和IM中。证明塑料的可模塑性。填充剂和改性剂在成型或成型之前，先加入原塑料，然后与其混合。2.2.4塑料性能1. 一般特性塑料材料的选择问题是从服务目的、成型方法、制造方法、成本等方面寻找性能合适的材料。新的和改进的塑料材料具有几乎任何所需的特性正在不断引入。有些塑料不需要具有更大柔韧性的增塑剂。呃温度低，在高温下是稳定的。有些能抵抗水、酸、油和其他破坏性物质。塑料的广泛使用证明了它们的价值；然而，基本的l在应用新材料或使旧材料适应新应用时，应考虑模仿。2. 温度效应塑料在低温下倾向于刚性和脆性，在高温下倾向于柔软和灵活。就温度而言，它们在尺寸上基本上是不稳定的。，并且在高温下易受变形和流动的影响。热塑性塑料特别敏感，而热固性塑料则更耐高温，差别很大。然而，吴只在学位方面。热固性树脂和热塑性树脂的热稳定性之间的区别还没有很好地界定。只有在单个pl之间才能进行真正的区分。不是在塑料类之间。高温不仅严重降低了塑料的力学性能，而且加速了外界因素对Wi的破坏作用。它们很敏感。连续加热也可通过增塑剂的挥发而在严重增塑材料中引起脆性和收缩。一种塑料与迪西米的接触在提议的应用中，LAR塑料应首先根据可能的“增塑剂迁移”进行检查，有时会导致其中一种塑料变色或硬化。一般来说，塑料的长期储存需要适度的温度；由于大部分塑料的低温脆性，所以必须避免低温。由于力学性能的迅速丧失、增塑剂的挥发和大量变形的敏感性，应避免Gh温度的升高。塑料，除了少数例外，对水的影响极为敏感。高湿度的大气会引起不同的吸水率，并会产生不同的影响，这取决于成分。塑料的配方。水分含量的增加使一些材料的力学性能普遍下降。吸水是导致宫颈肿胀的原因。在塑料和最终分解的几个。潮湿或潮湿的大气可以从高度塑化的材料中提取增塑剂，也可以为真菌的生长提供有利条件。参考文献然而，在过去的几年里，新塑料已经投入使用，它们具有一流的防潮性能，并且在抵抗其他影响的同时，也可能无限期地含有水。极度干燥的环境可能会导致某些塑料材料的脆性，这是由于水分的流失，而水的流失通常会导致塑料的可塑性。循环潮湿和干燥的大气对塑料比连续暴露在恒定湿度下，由于机械应力在塑料中引起的溶胀和收缩与吸湿和水分排放有关。相对由于水对这些材料的结构和性能的不利影响，以及增塑剂lo的可能性，所以在塑料储存中首选恒定、中、低湿度。潮湿大气中的SS提取与真菌攻击3. 光的影响长时间暴露在阳光下会对所有塑料产生不利影响，但四氟乙烯除外（特氟隆）。紫外线成分引起的变化可能与S的种类和严重程度不同由于聚合物或增塑剂的化学降解而完全崩解。失去强度，降低延性，增加脆性通常是accom。有这样的行动。许多塑料是以含有“紫外线抑制剂”的特殊配方提供的，当这种影响存在时，应加以利用。期间塑料暴露于阳光下应避免储存，特别是在要保持透明材料的透明度时。4. 韦特作为一个家庭，塑料与金属相比是轻的。大多数塑料的比重在1.35到1.45之间，比镁的比重小。5. 电阻率塑料具有优异的电阻率，因而作为一种绝缘材料有着广泛的应用。在高频应用中，塑料特别有利，因此Y，在很大程度上被用于雷达和电视领域。6. 绝热塑料具有低导热性，因此作为绝缘材料有着广泛的应用。特别是，它们被用作受热的电器和工具的把手。7. 制造从制造角度看，塑料的主要特点是成型。热固性材料和热塑性材料都适合于用Re成型不规则和复杂的形状。固化周期短。塑料可以使用各种水泥、化学溶剂和机械紧固件连接。热密封与金属的焊接过程平行，在连接热密封中得到了广泛的应用。热塑性薄膜。在这种情况下，电介质加热是通常使用的技术。摩擦粘着在小型热塑性零件的连接中也有一定的应用。塑料可以用传统的机床加工。但是，应采取某些警告措施。为了保持良好的光洁度，应使用大量的冷却剂，以避免温度升高。会扭曲作品的模型。在一些热固性层压板(例如玻璃)中，由于层压材料的磨料作用，传统的高速钢工具将不会起立。艾尔。在这里，必须使用碳化钨或陶瓷刀具。8. 氧效应有机塑料在暴露于大气中时几乎都会受到氧化。这一过程是由高温和光加速的，但在很长一段时间内，氧化恶化。可能在室温下发生。氧化敏感性在很大程度上取决于塑料的化学性质及其复配。m中双键数最大的材料分子结构通常对氧化最敏感。变黄和逐渐失去强度和延展性是氧化过程的主要结果。氧化不是一个很大的储存问题，因为硬质塑料在中等条件下是相当抵抗氧化劣化的。9. 加载效应在适当的条件下，普通热塑性材料在显著加载时会发生变形和流动。这种塑料不可能维持高度的机械稳定。当他们承受压力时，会长时间处于状态；尤其是当他们也暴露在相对较高的温度下时。然而，热塑性塑料应该是属于自己的。当不受负荷或只承受中等负荷时，良好。最近，在热塑性塑料中加入了玻璃棉等填料，以进一步改善这一性能。热固性塑料由于其结构和填料的存在，比热塑性塑料具有更高的负载稳定性。在层叠形式中，它们提供了一个相当不错的高次变形和抗蠕变性能。当没有受到机械应力时，它们可以被认为是高度稳定的。然而，这些材料可能会长期蠕变，特别是在高温下保持。热塑性材料储存时不应承受载荷；凡有可能，应移除或减少承受应力的热固性模塑或层压板的负荷。10. 化学稳定性一般来说，塑料在化学退化方面具有高度的内在稳定性。在许多情况下，加入适当的稳定剂可以加强这种稳定性。在复合过程中。虽然一种塑料和另一种塑料有很大的不同，但一般的说法是，有一种塑料可以抵抗几乎任何商业化学品。12
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