PET瓶_结晶介绍

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1、结晶简介CRYSTALLIZATION化学学名为”聚对苯二甲酸乙烯酯(聚酯)”，是由对苯二甲酸(TPA)及乙二醇(EG)聚合而成的热塑性聚合物，其反应化学式如下：(TPA=PTA)化学名称及其聚合反应PolyEthyleneTerephthalatePET结晶-热变化1.放热反应(EXO-THERMICREACTION)射出成型融熔态(MELTSTATE)固态瓶胚2.吸热反应(ENDO-THERMICREACTION)瓶口牙区结晶固态无定型瓶口结晶态瓶口QUENCHED△冷却加热BCPREFORMBEFORECRYSTALLIZATION未结晶瓶胚(注塑瓶胚)ACPREF

2、ORMAFTERCRYSTALLIZATION结晶瓶胚UnderstandingShrinkage&DistortionGlassTransitionTemperature(Tg)-isthepointatwhichaglasslikepolymerbecomessoftandpliable.AttheTgorslighlyabove,thepolymerchainsbecomefreetomove.InastandardstretchblownPETbottlethathasbeenheatedorfilledatTg,theresidualstressesimpart

3、edontheamorphousregionsduringorientationbecomefreetorelaxandthebottleshrinksanddeforms.ThetypicalglasstransitionTemperatureofastandardstretchblownPETbottleis~80°C.Asdiscussedearlierthisdoesnotmeetthetemperaturerequirementsforvarioushotfillproducts.结晶RateofCrystallization结晶速率PROCESSWINDOW结

4、晶速率温度加工窗结晶机制MechanismsforAchievingCrystallinityinPET拉伸诱导结晶—瓶身Orientation(“Strain-inducedcrystallinity”)-Improvesmechanicalandbarrierproperties增强抗力及阻隔效果-CanAchieve20-28%crystallinityinstandardPETbottlesidewall.PET瓶瓶壁之结晶度可达20-28%-Crystalsdonotinterferewithcontainerclarity可维持容器之透明度热诱导结晶---瓶口

5、Heating(“thermallyinducedcrystallinity”)-Improvesthermalstabilityofcontainer增强容器对热之稳定度-Canachieve30-35%crystallinity结晶度可达30–35%(NeckFinish瓶口)-Spheruliticcrystalsinterferewithclarityandcauseopacity所诱导之结晶大而致不透明LATTICE晶格,点阵结晶核未定型部位Crystallinty直线型分子结构结晶度高分枝型分子结构结晶度低瓶口于结晶时发生之变化体积收缩密度升高会散热释放内应力

6、会变形会变硬但耐热性增强耐化学性增强影响PET结晶之因素加热时间:时间长结晶度高加热温度:温度高结晶度高IV:IV低易结晶颜色:颜色深易结晶含水量:瓶胚含水份高易结晶OneofthemostimportantcharacteristicsofPETisreferredtoasI.V.(intrinsicviscosity).TheI.V.ofthematerial,measuredindl/g(deciliters/gram)isdependentuponthelengthofitspolymerchains.Thelongerthechains,thestifferth

7、ematerial,andthereforethehighertheI.V.Theaveragechainlengthofaparticularbatchofresincanbecontrolledduringpolymerization.IV是PET重要特征之一,原料之IV单位以dl/g表示(deciliters/gram);PETIV与聚合物之分子结构有关,聚合物之化学炼愈长,,黏稠愈大,也就是IV高.于聚合反应中可以控制所需要之平均化学炼长度(IV).I.V.ofabout:0.60-Wouldbeappropriate