1、Designation:D744418aStandard Practice forHeat and Humidity Aging of Oxidatively DegradablePlastics1This standard is issued under the fixed designation D7444;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A
2、number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice indicates how to test the oxidative degra-dation characteristics of plastics that degrade in the environ-ment under atmosphe
3、ric pressure and thermal and humiditysimulations,only,in the absence of any selected disposalenvironment such as soil,landfill,or compost.This practicedoes not by any extension or extrapolation of data or resultsgenerated indicate that such plastics are suitable for or willdegrade on disposal in the
4、se said environments.It is particu-larly noted that in real world environments such as soil,compost and landfill oxidations,if they occur,will predomi-nantly be under conditions where other interfering ingredientsare present and,in the case of landfill,at sub-atmosphericoxygen concentrations.This pr
5、actice,therefore,can only resultin a relative ordering of the potential for oxidation of plasticmaterials under the conditions tested,which are not alwaysreflective of their behavior in a particular real world disposalsystems.Prediction of the oxidation of a plastic under realworld disposal conditio
6、ns is an essential further testing inappropriate methodologies,such as Test Method D5338 forcomposting.No claims can be made for real world behaviorbased on this practice.1.2 This practice is only intended to define the exposureconditions of plastics at various temperatures in air at atmo-spheric pr
7、essure under controlled humidity levels for extendedperiods of time.The humidity levels and temperature rangesare selected to be within the variable recorded seasonal ranges(upper and lower levels)generally observed in disposal siteswhere such plastics are discarded.For example:soil(15 to 40percent
8、moisture);landfill(35 to 60 percent moisture),andcompost(45 to 70 percent moisture).It is optional to exposethe plastic at zero humidity,if comparison with specifiedhumidity ranges is of interest.Only the procedures for heat andhumidity exposures are specified,not the test method orspecimen,necessar
9、y for the evaluation of the heat and humid-ity exposure effects.The effect of heat and humidity on anyparticular property is determined by selection of the appropri-ate test method and specimen;however,it is recommended thatPractice D3826 be used to determine the embrittlementendpoint,which is defin
10、ed as that point in the history of amaterial when 75%of the specimens tested have a tensileelongation at break of 5%or less at an initial strain rate of 0.1mm/mm min.1.3 This practice is used to compare the effects of heat andhumidity at any selected temperature,such as those found inthe mentioned d
11、isposal environments,on the degradation of aparticular plastic by selection of an appropriate test method andspecimen.1.4 This practice is to be used in order to apply selectedexposure conditions when comparing the thermal-aging char-acteristics at controlled humidity levels of plastic materials asm
12、easured by the change in some property of interest(that is,embrittlement by means of loss of elongation,molecularweight,disintegration,etc.).It is very similar to PracticeD3045 but is intended for use in evaluating plastics designed tobe oxidized easily after use.The exposure times used for thisprac
13、tice will be significantly shorter than those used forPractice D30451.5 The type of oven used can affect the results obtainedfrom this practice.The user can use one of two methods foroven exposure.Do not mix the results based on one methodwith those based on the other one.1.6 ProcedureA:Gravity-Conv
14、ectionOvenRecommended for film specimens having a nominal thicknessnot greater than 0.25 mm(0.010 in.).1.7 Procedure B:Forced-Ventilation OvenRecommendedfor specimens having a nominal thickness greater than 0.25mm(0.010 in.).1.8 This practice recommends procedures for comparing thethermal and humidi
15、ty aging characteristics of materials at asingle temperature under dry or selected humidity conditions.Recommended procedures for determining the thermal agingcharacteristics of a material at a series of temperatures andhumidity conditions for the purpose of estimating time to adefined property chan
16、ge at some lower temperature are also1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.96 on Environmentally DegradablePlastics and Biobased Products.Current edition approved Sept.15,2018.Published October 2018.Originallyapproved in 2011.Last previous edition approved in 2018 as D744418.DOI:10.1520/D7444-18A.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Driv