ASTM_D_7475_-_11.pdf

Designation:D747511Standard Test Method forDetermining the Aerobic Degradation and AnaerobicBiodegradation of Plastic Materials under AcceleratedBioreactor Landfill Conditions1This standard is issued under the fixed designation D7475;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This modification of Test Method D5526,which onlyconsidered anaerobic degradation,is used to determine thedegree and rate of aerobic degradation(as indicated by loss oftensile strength,molecular weight,possibly resulting in disin-tegration and fragmentation)and anaerobic biodegradation ofplastic materials in an accelerated bioreactor landfill testenvironment.It simulates the change from aerobic to anaerobicenvironments over time as landfill depth increases.Plasticmaterials found in landfills include discarded plastic productssuch as bags and wrappers and also deliberately applied plasticcovers as inter-layer sealers between daily refuse fills toprevent windblown scatter of garbage overnight or at otherdown times.This modification is a two-tiered test method inwhich the two tiers,which address aerobic degradation andanaerobic biodegradation,are most preferably run sequentiallyto more closely resemble the real world condition of abiologically active landfill,or a bioreactor landfill,but arefunctional independently and separately depending on theplastic under evaluation and the information sought:eitheraerobic degradation or anaerobic biodegradation or both.Thetiered system approach is shown schematically in Fig.1.InTier 1,the test plastic material is mixed with household waste,then pretreated and stabilized aerobically in the presence of air,in a sealed vessel in a temperature range that is consistent withthe average temperature range of those recorded for landfillsfor a time period of four weeks.The tier is an acceleratedsimulation of degradation with concomitant oxygen consump-tion and depletion with time as if oxidative degradationproceeds.In Tier 2 samples of the plastic materials pretreatedaerobically as described in Tier 1,are exposed to a methano-genic inoculum derived from anaerobic digesters operatingonly on pretreated household waste.The anaerobic decompo-sition and biodegradation occur under dry(more than 30%total solids)and static non-mixed conditions.If it is desired toonly assess anaerobic biodegradation of a plastic material,Tier2 is run using preconditioned household waste,as described inTier 1 but without the added plastic.The mixtures obtainedfrom Tier 1 and Tier 2 in this test method are sampled and usedto assess the environmental and health risks of plastic materialsthat are degraded in a landfill under aerobic and anaerobicconditions.1.2 This test method generates comparative data for severalmaterials and must not be used to make claims regardingbenefits of placing degradable or biodegradable plastics inlandfills.Claims must be limited to and dependent on theresults obtained from each tier.1.2.1 If only Tier 1 is run,then the claims must state:Willmodify the performance/physical properties(for example,mechanical properties will degrade),up to a measured percent,X%,in a given time period,Y days using Test Methods D3593(Molecular weight change)and Test Method D3826(tensilestrength change)in a biologically active“bioreactor”landfill.Report measured percent property changes and standards usedto measure the test results which are,for example,changes intensile strength,mass and molecular weight,as well as residualparticle size ranges in Section 14 to support the extent of suchclaims.1.2.2 If both Tier 1 and Tier 2 are run,then claims shallstate:Will biodegrade in a biologically active“bioreactor”landfill to a degree,X%,in Y days established by the testresults based on the extent to which the plastic sample isconverted to gaseous carbon in the form of carbon dioxide andmethane and this shall be made available according to Section14 to support the extent of such claims.It should be noted thatbiodegradation testing is very dependent on conditions chosenin this laboratory test and may well vary widely when the testis run with different inoculum,The results reported pertain onlyto the test conditions run and do not rule out potentialbiodegradation under other conditions and real world environ-ments.1.3 Tier 1 of this test method is designed to estimate theaerobic degradation of plastics,that is disintegration andfragmentation,only,by measuring the loss of physical andchemical properties of said plastics.The test environment isthen changed to that of Tier 2,an anaerobic condition,and1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.96 on EnvironmentallyDegradable Plastics and Biobased Products.