塑件内应力检测ESCR.doc

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1、MATERIALSTESTINGEvaluatingEnvironmentalStressCrackingofMedicalPlasticsEricJ.MoskalaandMelanieJonesWhenaplasticisexposedtoachemicalenvironment,thematerialmayundergonumerouschanges.Thesecanincludeweightgainiftheplasticabsorbsthechemical,weightlossiftheplasticisdegradedbyth

2、echemicalorifthechemicalextractslow-molecular-weightcomponentsoftheplastic,dissolutionifthechemicalisagoodsolvent,orotherchangessuchasvariationsinopacityorcolor.Iftheplasticisunderstress,itmayalsoexperienceenvironmentalstresscracking,whichcanbedefinedasthecrazingandcrack

3、ingthatmayoccurwhenaplasticunderatensilestressisexposedtoaggressivechemicals.Thepotentialforenvironmentalstresscrackingisofparamountconcernwhenplasticsareusedinmedicaldevicecomponentssuchasluersandstopcocks.Intheseapplications,chemicalssuchasisopropanolandlipidsolutionsc

4、aninitiatecrazes—microcracksbridgedbypolymerfibrils—intheplasticandseriouslycompromiseitsmechanicalintegrity.Productslikemedicalluerscanbesusceptibletocrazingwhenunderstressandexposedtoaggressivechemicals.Photo:EastmanChemicalCo.Theproperselectionofamedicalplasticrequire

5、sathoroughanalysisandinterpretationofthephenomenonofenvironmentalstresscracking.Thegoalofthisarticleistoprovideaframeworkforevaluatingthesuitabilityofaplasticformedicalusesintermsofitsstress-crackbehavior.Ourstrategywillbetoexamine,insomedetail,therolesofthethreecritical

6、componentsofenvironmentalstresscracking:thechemicalenvironment,theplastic,andthetensilestress.THECHEMICALENVIRONMENTChemicalsthatcauseenvironmentalstresscrackingcanbedividedintothosethatswellorwetthepolymerandthosethatchemicallyreactwiththepolymer.Anexampleofthelatterwou

7、ldbethecausticoraqueoussodiumhydroxidethatcanhydrolyzepoly(ethyleneterephthalate)(PET).1Thereductioninpolymermolecularweightfromthehydrolysiscanleadtocrazingandeventualcatastrophicfailure—amechanismthathasbeenidentifiedastheprobablecauseforstress-crackfailuresinone-piece

8、carbonatedsoft-drinkcontainers.2Thisarticle,however,willemphasizechemicalsthatcausestresscrackingsimply