AnAssessmentofMassBalanceAccountingMethodsforWorkshopCertaincommercialentities,equipment,ormaterialsmaybeidentifiedinthisdocumentinordertodescribeanexperimentalprocedureorconceptadequately.SuchidentificationisnotintendedtoimplyrecommendationorendorsementbytheNationalInstituteofStandardsandTechnology,norisitintendedtoimplythattheentities,materials,orequipmentarenecessarilythebestavailableforthepurpose.PublicationsintheSP1500subseriesareintendedtocaptureexternalperspectivesrelatedtoNISTstandards,measurement,andtesting-relatedefforts.Theseexternalperspectivescancomefromindustry,academia,government,andothers.ThesereportsareintendedtodocumentexternalperspectivesanddonotrepresentofficialNISTpositions.Theopinions,recommendations,findings,andconclusionsinthispublicationdonotnecessarilyreflecttheviewsorpoliciesofNISTortheUnited

ExecutiveWhileplasticpackagingandotherplasticproductshavegreatbenefitstocivilization,thecurrentandhistoricalapproachestoend-of-lifemanagementhaveresultedinsignificantchallenges,particularlyinrecoveringandretainingtheeconomicandtechnicalvalueofthematerialsandpreventingplasticpollution.Mostplasticsputonthemarketendupinlandfillsorthenaturalenvironment,representingasignificantenvironmentalandsocietalimpactaswellasalossofeconomicvalue[1].ThecurrentplasticsrecyclingrateintheUnitedStates(U.S.)hoversaround9%,whileapproximately70%ofrecyclablepolyethyleneterephthalate(PET)andhigh-densitypolyethylene(HDPE)packagesarelosttolandfillsandtheenvironment[2,3].Astheenvironmentalandhumanhealthimpactsofplasticwastebecomebetterunderstood,manybrandshavecommittedtoambitiousrecycledcontenttargets,aimingtosupportacirculareconomyandreduceplasticwaste.SeveralU.S.stateshavealsoproposedorimplementedrecycledcontentmandates(e.g.,[4],[5],[6],and[7]).Thedominantrouteforrecyclingrecoveredplastichasbeenmechanicalrecycling.Indeed,thereisincreasingdemandforqualityfeedstocksformechanicalrecyclingandopportunitiestoexpandthisroute,whichislessresourceintensivethanmanyalternatives.However,existingmechanicalrecyclinginfrastructureislimitedinitsabilitytorecoveralltypesofplasticwaste,aswellastosupplythequalityandquantityofrecycledmaterialneededtomeetsomebrandgoals,functionalrequirements,andmandatesintherangeofsectorswheremandatesareexpected,suchasfoodpackaging,medical-gradeapplications,andtransparentmaterials(e.g.,automotiveheadlamplenses).Asaresult,chemicalrecycling―thereductionofpolymerstotheiroriginalmonomerformorothersmallmoleculeprecursorsforreintroductiontothesupplychain―hasgreatappeal,especiallyforthepolymericproductswhichstillposeachallengeformechanicalrecyclingmethods.Duetothenatureofchemicalrecycling,specificallythatchemicallyrecycledcarbonatomsandorganicmoleculesbecomeidenticaltovirginfeedstocksandthusnottraceableormeasurableintheprocess,MassBalance(MB)accountingisatoolthathasbeenproposed,andisalreadybeingappliedinsomecases,totrack,trace,andcertifycircularpolymers.WhileMBcertificationstandardshaveanextensivehistoryinothercommoditysectors,theyhaveonlyrecentlybeenconsideredinthepolymerssectorinpartduetorecenttechnologyadvancesandincentivestoexpandthescaleofchemicalrecycling.Ifproperlysupportedandexpanded,by2050,nearly60%ofplasticsproductioncouldbesourcedfromcomplementarymechanicalandchemicalrecyclingroutesglobally[8]andthenewmaterialscouldgenerate$2billionto$4billionofearningsannually.[9]Theonlywaytotransformthesystemandreachthesegoalsisthroughrapidanddiversifiedexpansionofarangeoftechnologies.Useofsuchtechnologiesraisesseveralquestionsandconcerns,however,including:theabilityofcollectionandsortationinfrastructuretosupplythenecessaryfeedstockquantitiesandquality,thetrade-offsinenergyconsumptionandoverallenvironmentalimpactsbetweenthevarioustheattributesoftherangeofresultingproducts,suchasfuels,andtheenergydemandsofsomechemicalprocesses,andsupply)–thesinglebiggestlimitingfactorinBOTHpathwaystomorecircularpolymers.

最終進(jìn)入垃圾填埋場或自然環(huán)境，這代表著重大的環(huán)境和社會影響以及經(jīng)濟(jì)價(jià)值的損失[1]。美國（U.S）9%，70的可回收聚對苯二甲酸乙二醇酯（PET）和高密度聚乙烯（HDPE）包裝被丟棄到垃圾填埋場和環(huán)境中[2,3]。[4],[5],[6],和[7）?；厥账芰系闹饕厥章肪€是機(jī)械回收。實(shí)際上，對機(jī)械回收的高質(zhì)無法在過程中追蹤或測量，質(zhì)量平衡（MB）核算是一種已被提出并在某些情況下應(yīng)用的工具，MB認(rèn)證標(biāo)準(zhǔn)在其他大宗商品行業(yè)有悠久的歷史，但由205060回收路線[8]2040[9]。要轉(zhuǎn)變系統(tǒng)并實(shí)現(xiàn)這些目 TheSaveOurSeas2.0Act(SOS2.0)(PublicLaw116-224),whichpassedinDecember2020,taskedtheNationalInstituteofStandardsandTechnology(NIST)withperformingastudyonMBmethodologiestocertifycircularpolymers.Inthiseffort,NISTheldathree-dayworkshopentitled“AssessmentofMassBalanceAccountingMethodsforPolymers”inMay2021.ThepurposeoftheworkshopwastoconvenestakeholderswithinterestinMBmethodologiesforcircularpolymers,includingexistingstandardizationandcertificationprogramsfocusedonpolymerproductsaswellasrelevantexpertisefromother,comparableindustries.Theworkshopincludedthreeplenarypresentationsandsixtopic-specificsessionswithknowledgeablespeakersandbreakoutroundtablediscussions.Keyfindingsfromtheworkshopinclude:MBaccountingisnotanewconcept,butitisonlynewlybeingappliedtothemanufactureofpolymersfromrecoveredpolymerfeedstocks.Therearemanyunsettledissues,ill-definedterms,andconflictingobjectiveswithregardstotheapplicationofMBcertificationtopolymers.Cleargoalsandobjectivesarenecessarytoalignsupplychainpartnersandcertificationcomponentsaccordinglyandensureareliablestructure,support,andbuy-infromUsingcommon,well-definedapproachestosetboundaryconditions(geographicalandtemporal)iscriticaltodeterminetheapplicabilityoftheMBsystemandestablishitsscope.Interoperabilityoftoolsanddataframeworksacrossstandardsandcertificationsystemsisimportantforintegrityandtransparencyandrequiresaligningcertaindefinitions,terminology,andmethods.Thevariabilityofregulationsatstateandlocallevels,whichoftenmandaterecycledcontent,butmayexcludeorprohibitchemicalrecycling,andmaysetconflictingstandardsforMBcertification.resultinconflictingrequirements,andsuboptimalsystem-leveldecisionmaking.Therearesignificantandcomplexneedsrelatedtoeducation,research,andClearandconsistentmessaging(business-to-businessandtotheconsumer)isneeded,becauseunderstandingMBisimportantandchallenging.Educationneedsofthefutureworkforce(dataandcurriculumintegration)needtobeidentifiedanddeveloped.Currenttoolsandmethodswerenotdesignedtocomprehensivelyaddressimpact,tradeoffs,andtechnologygapsinthecircularityofpolymers,especiallybeyondtheboundariesofindividualbusinesseswithinthesupplychain.Tofullyassessthemultipledimensionsofperformance,valueandimpactofcircularpolymers,economics,anddatasciencearecriticallyneeded.

2.0（SOS2.0）（116?224），202012授權(quán)美國國家標(biāo)準(zhǔn)與技術(shù)研究院（NIST）對質(zhì)量平衡（MB）方法進(jìn)行一項(xiàng)研究，以認(rèn)證循環(huán)聚合物。在此工作中，NIST20215在將質(zhì)量平衡認(rèn)證應(yīng)用于聚合物方面，存在許多未解決的問題、定義不明確的術(shù)語和pháp（地理和時(shí)間的）MB MBa.需要清晰一致的信息傳遞（企業(yè)間和企業(yè)對消費(fèi)者），因?yàn)槔斫庋h(huán)經(jīng)濟(jì)模式（MB）b（數(shù)據(jù)和課程整合）方面c.當(dāng)前的工具和方法并未設(shè)計(jì)為全面解決聚合物循環(huán)中的影響、權(quán)衡

Basedonthesefindings,NISThassevenrecommendationsfortheapplicationofMBtocertifycircularpolymers:transitioningtowardsacirculareconomyforpolymers.circularpolymers,alignedwithachievingtheprioritizedgoalsinrecommendation1.Establishprocessesandframeworksthatpromotesuccessfulexpansionofcollection,capacity,andmarketsforbothmechanicallyandchemicallyrecycledpolymers.Developopen,consensus-basedstandardsforcertificationmethodsandtoolsthataretransparent,requireinteroperabilityorreciprocity,andareavailabletotheentiresupplyEstablishtransparent,auditabledata,datastandards,andaframeworksuitedtotheneedsandintegrityoftheentiresupplyeroperability,andbroadadoption.Investinamultidisciplinaryresearchanddevelopmentprogramattheinterfaceofpolymerscienceandengineering,manufacturing,economics,anddata(privacy,sharing,andaccess)toenablemanufacturinginnovation,strongerdecisionmaking,andimprovededucationandcommunicationtools,andtoimprovesupplychainintegrityandaccountabilityforcircularSOS2.0alsotaskedNISTwith"anassessmentoftheenvironmentalimpactsofthefulllifecycleofcircularpolymers,includingimpactsonclimatechange."Throughthecourseofourresearchinpreparationforthisreport,weconcludedthatthereisnotsufficientinformationtomakeandstagesofthesupplychain,fromresourceextraction/feedstockstomoleculardesign,formulation,productdesign,consumptionpatterns,collectioninfrastructure,reprocessingstrategiesetc.,aswellastheenvironmentalimpactsofpolymerslosttotheenvironment,andthe(socio)economiccost-benefitanalysesofpolymers.Noneofthesecommunitieshasacomprehensive,translatable,ortransferableviewofthefulllifecycle.Thedatausedinthesestudiesareoftennotpubliclyavailable.Manystudiesarenotreproduced,oroutcomesarerootedinsubjectivecriteriawhichhavenotbeenbroadlyadoptedbylargecommunities.Thus,thereisaprofoundneedformeasurementandterminologyconsensus,broaderanddeeperdatasetswhicharefindable,accessible,interoperable,andreusable,aswellasconveningbodiestoengagethewiderangeofsocialandtechnicaldisciplinesandstakeholderstoidentifycommonunderstandingofthetradeoffsandprioritiesinthissortofanalysis.WebelievethatanagencylikeNIST,withitscoreresearchprograms,deepexpertiseinallthesedisciplinaryinterfacesandamissionalignedonbotheconomicsecurityandqualityoflife,isuniquelypositionedtoprovidetechnicalleadershipinthisendeavorincoordinationandcollaborationwithotherswithinfederal,state,andlocalgovernments,butitwillrequiresignificantinvestmentoftimeandresources.

基于這些發(fā)現(xiàn)，NISTMBMB1SOS2.0NISTNIST ListofBookBookandConsumerGoodsChainofEndofFederalTradeGreenhouseMassBookandConsumerGoodsChainofTableof Listof TheResponse:RecyclingandMassBalance MassBalance BrandandConsumer .. .. ....ThissectionThecurrentstateoftheglobaluseofplastics,theirroleintheeconomy,andtheproblemsintroducedthroughtheiruse;accountingforrecycledplasticcontentinendproducts;andTheapproachNISTusedtoidentifychallengesindeployingMBaccounting.StandardizedapproachestoMBaccountingwouldenablemorecrediblemarketingofrecycledcontentinendproductsfosteringmoreadoptionoftheapproach.TheProblem:CurrentStateofPlasticsTheword‘plastic’technicallyreferstoamaterialthatcanbesoftenedandreshapedbyapplyingheatwithoutlosingotherproperties,butoverthelastcenturythewordhasbecomethecommontermforacategoryofsyntheticorganicpolymersthathavebecomeessentialtomodernlife[10].Duetotheirmanyuseful,tailorablepropertiesandapplications,plasticsareusedinavarietyofindustrialsectorsincludingpackaging,construction,automotive,electronics,textiles,householditems,healthcare,andtoys[11].Thereisnoquestionthathumanhealth,comfort,andconveniencehavebeenvastlyimprovedbyplasticsandthatthelowfunctionality,andenvironmentalimpactofplasticsexceedsthatofmanyalternativematerials.In2019,globalplasticsproductionreached368milliontonnes,a2.5%increasefromtheyearprior[12].Thevastmajorityofplasticsproducedtodayarederivedfromfossilfuels,andglobalproduction–feedstockandprocessingenergycombined–representsaround8%ofannualoilandgasconsumption[13].Thishasbeenprojectedtoincrease,however,asplasticsareestimatedtobecomethebiggestsourceofnewdemandforoiloverthecomingdecades,andinsomeprojections,theonlysource[14,15].TheUnitedStatesinparticularisamajorproducerandconsumerofplastics,representing19%and21%ofglobalplasticsproductionandconsumption,respectively[16,17].Further,theNorthAmericanregionhasthehighestpercapitaplasticconsumptionintheworldat306poundspercapitaperyear[16].Figure1displaysaplasticsflowdiagramoftheaccumulatedvolumeofplasticsproducedbetween1950-2015[18,1].Plasticpackagingconstitutesthelargestmarketforplastics,representingnearly40%ofdemand,morethandoublethatofbuildingandconstruction,thenextleadingsector.Asaresult,themajorityofplasticsmanufacturedtodayarecommoditythermoplastics(90%),whichincludehigh,low,andlinearlow-densitypolyethylene(HDPE,LDPE,andLLDPE)(34.4%combined),polypropylene(PP)(24.2%),polyvinylchloride(PVC)(16.5%),andsmallerpercentagesofpolystyrene(PS),polyethyleneterephthalate(PET),engineeredplastics,andhigh-performancepolymers[19].Whiletheseplasticssharecommonfossilderivatives,theirproductionandprocessingalsoincludesavarietyofaddedchemicalsubstances,includingadditivestohelpmaintain,enhance,andimpartspecificproperties(e.g.,antioxidants,plasticizers,flameretardants),processingaidestoenableoreasetheproductionorprocessingofplastics(e.g.,polymerizationcatalysts,solvents,moldreleaseagents),andnon-intentionallyaddedsubstancesincludingbyproducts,breakdownproducts,andcontaminants[11,20,21,22,23,24,25].Infact,arecentinvestigationrevealedtheuseofmorethan10,000chemicalsubstancesinplasticproductformulation,onlyafractionofwhichhavebeenwidelystudiedandmanyofwhichareknownassubstancesofpotentialconcern[11].Manyofthesesubstancesarenotchemicallyboundtothepolymermatrixand,therefore,havethepotentialtobereleasedthroughoutthelifecycleoftheplastic.Theextensiveplasticseconomyhasresultedinsignificantchallengesatend-of-life(EoL),particularlyinrecoveringandretainingtheeconomicandtechnicalvalueofthematerials.AsshowninFigure1,

NIST通用術(shù)語[10]。由于塑料具有許多有用、可定制性能和應(yīng)用，它們被用于包裝、建筑、汽車、電子、紡織品、家用物品、醫(yī)療保健和玩具等各種工業(yè)部門[11]。毫無疑問，塑料極大地改善來自化石燃料，全球產(chǎn)量（原料和加工能源合計(jì)）8[13]。然而，1921%[16,17]。此外，北美洲是全球人均塑料消費(fèi)量最高的地區(qū)，每年人306[16]。11950?2015181年間生產(chǎn)的塑料累積體積的塑料流動圖。塑料包裝是塑料的最大市40%，是建筑和建筑行業(yè)的兩倍多，后者是下一個主要部門。因此，今天生產(chǎn)的絕大多數(shù)塑料都是通用熱塑性塑料（90），其中包括高密度聚乙烯（HDPE）、低密度聚乙烯（LDPE）和線性低密度聚乙烯（LLDPE）（34.4）、聚丙烯（PP）（24.2）、聚氯乙烯（PVC）（16.5），以及較小百分比的聚苯乙烯（PS）、聚對苯二甲酸乙二醇酯（PET）、工程塑料和高性能聚合物[19]。雖然這些塑料具有共同的化石衍生物，但它們的生產(chǎn)以及非有意添加的物質(zhì)，包括副產(chǎn)物、分解產(chǎn)物和污染物[11,20,21,22,23,24,25]。事實(shí)上，10,000 Figure1:Production,useandfateofallplasticsevermade,1950-2015(usedwithpermissionfromRRS(ResourceRecyclingSystems,Inc.)[18,1])anestimated79%ofallplasticwastegeneratedbetween1950-2015(4900ofthe6300millionmetrictons,Mtgenerated)hasbeendiscardedinlandfillsorthenaturalenvironment,12%wasincinerated,andamere9%hasbeenrecycledthroughmechanicalrecyclingprocesses[1,18].TheannualplasticsrecyclingrateintheUnitedStatesalsohoversaround9%,althoughtherateishigherforspecificplasticcontainertypes(e.g.,in2018therecyclingrateofPETbottlesandjarswas%andthatofHDPEnaturalbottleswas29.3%)[2,3].Ineffect,≈70%ofrecyclablePETandHDPEpackagesarelosttolandfillsortheenvironment,representingasignificantenvironmentalandsocialimpactaswellaslossofeconomicvalue.Interestinplasticwastehasgrowninrecentyearsasanincreasingbodyofresearchprovidesevidenceofthedistributionandconcentrationofunmanagedplasticdebrisinthenaturalenvironment(e.g.,marinepollution,airborneparticles,plantuptake)aswellasingestedbyhumans,animals,andorganisms(e.g.,[26,27,28,29,30,31,32,33]).Furthermore,globaltradedisruptionshaveexacerbatedtheissue,causingafundamentalreevaluationoftheexistinginfrastructureandmarkets,bothdomesticandglobal,forplasticwasterecovery,andmethodstoimproveretentionofmaterialsintheeconomy.Gapsremainintheresearch,particularlyfocusingonsourcesandscalablesolutionstoplasticwastegeneration[34,35].Assuch,aneedisemergingforbetterunderstandingofhowplastics,andparticularlypackaging,canbebetterrecoveredandrecycledatEoL.1：所有塑料的生產(chǎn)、使用和命運(yùn)，1950?2015（經(jīng)RRS（資源回收系統(tǒng)公司）[181垃圾填埋場或自然環(huán)境中，12%被焚燒，而只有9%通過機(jī)械回收過程進(jìn)行了回收[1,18]。美9（例如，2018PET罐的回收率為29.1%，HDPE天然瓶的回收率為29.3%）回收率更高[2,3]。實(shí)際上，≈70%的可回收PETHDPE近年來，對塑料廢物的關(guān)注度不斷提高，越來越多的研究提供了證據(jù)，表明未管理的塑料碎片在自然環(huán)境中（例如，海洋污染、空氣中的顆粒物、植物吸收）的分布和濃度，以及被人類、動物和生物體攝入（例如，,,,2,,,3,]）。此外，全球貿(mào)易中斷加劇了這一問題，導(dǎo)致對現(xiàn)有的塑料廢物回收基礎(chǔ)設(shè)施和市場的根本性重新評估，以及提高經(jīng)濟(jì)中材料保留率的方法。研究仍存在差距，特別是在塑料廢物產(chǎn)生的來源和可擴(kuò)展解決方案方面3,。因此，人們開始需要更好地理解如何更好地回收和回收塑料，尤其是包裝，在生命終結(jié)時(shí)（EoL）。TheResponse:RecyclingandMassBalanceWhilereducingandreusingplasticproductsandpackagingwillhaveapositiveimpact,acirculareconomyforplasticsmustincorporaterecyclingasamajorleverforaddressingplasticwaste.Plasticmaterialscanberecycledinavarietyofways;however,theeaseandeconomicsofrecyclingvariesamongpolymertypes(i.e.,resincodes),packagedesigns,producttypes,andproductdesigns[13].MechanicalrecyclingisthepredominantapproachtoplasticsrecyclingintheUnitedStates.andelsewhere.Theprocesstypicallyincludesseparationandsortingbasedonshape,density,size,color,orchemicalcomposition,followedbywashing,grinding(i.e.,sizereduction),compounding,andpelletizingpriortoconversiontonewplasticproductsorpackaging[36].Mechanicalrecyclinghasseverallimitations;amongthemaresupplychallengesresultingfromconsumerbehavior(e.g.,participationinrecycling)andaccesstorecyclingservices–akeychallengesharedwithchemicalrecycling.However,severalregulatory,technical,andeconomicchallengesalsoconstrainmechanicalrecycling,including:formechanicallyrecycledpolymerstomeet[9,37,36,13,38].Someofthetechnicalchallengesmaybelessenedwithmoreinvestmentinresearchandtechnology;however,moreneedstobedonetorapidlyexpandthevolumeofcircularpolymerflows.Asaresult,interestinchemicalrecyclinghasgrownsteadilyasameanstoovercomethetechnicallimitsofmechanicalrecyclingandincreaseplasticsrecyclingforpolymers,specificallytargetingdifficulttorecycleplastics.Ingeneral,chemicalrecyclinginvolvesadditionalchemicalprocesses,someofwhichbreakmolecularbondswhichcanreducepolymerstotheiroriginalmonomer(amongotherthings)unittoallowforre-polymerizationanduseinnewplasticmaterials.Indeed,chemicalrecyclingfacesthesamesocialchallengesasmechanicalrecycling,namelyconsumer/municipalparticipationinrecycling.However,chemicalrecyclingallowsfortheprocessingofmorediverseandmixedsourcesandshouldenableindistinguishableperformanceforprimematerialsathighlevelsofrecycledcontent.Theprocesscanalsogenerateothervaluablepetrochemicalfeedstocksincludingmonomerprecursors(e.g.,fuels,naphtha).Multiplechemicalrecyclingprocessesexistforplasticsandgenerallyfallintothreecategories:Purification,whereplasticisswollenordissolvedinasolvent,separated,andpurifiedtoextractdyesandadditivestoobtaina‘purified’plastic.Thisprocessdoesnotchangethepolymeratthemolecularlevel.TypicallyusedforPVC,PS,andpolyolefins.Decomposition(alsocalleddepolymerization),wherethemolecularbondswithincertaintypesofpolymerchainsarebrokenbybiological,chemical,orthermalmeanstoreverttothemonomerblocksformingthepolymer.Monomerscanbeeithersinglemolecularrepeatunitsormultiplerepeatunitsboundtogethercalled“oligomers”bothofwhichcanbereconstructedintoplastics.ThisprocessisusedforPET,PUR,PA,PS,PLA,PC,PHA,andPEF.Conversion,wheretheplasticisheatedinthepresenceofoxygen(gasification)orwithoutoxygen(pyrolysis)andtheplasticwasteisturnedbackintothedifferentmoleculesforminghydrocarbonchains(canbeusedonmixedplasticstreamsandissimilartocrackingprocessesinpetroleumrefining)[39,40].

物類型（即樹脂代碼）[13]。機(jī)械回收是美國及其他地區(qū)然后進(jìn)行清洗、研磨（即尺寸減小）[36]。機(jī)械的塑料。該過程不會改變聚合物在分子水平上的結(jié)構(gòu)。通常用于PVCPS分解（也稱為解聚），其中通過生物、化學(xué)或熱手段斷裂某些類型聚合物鏈內(nèi)的分子鍵，以還原為形成聚合物的單體塊。單體可以是單個分子重復(fù)單元或多個重復(fù)單元結(jié)合在一起稱為“低聚物”，兩者都可以重新構(gòu)建成塑料。該過程用于PET、PUR、PA、PS、PLA、PC、PHA和PEF。[39,40]。 Figure2presentsthehierarchyofrecyclingtechnologiesinacirculareconomyforplasticswithrespecttowheretheatomsand/ormoleculeswouldreenterthesupplychain.Manyconsumerbrandshavecommittedtoambitiousrecycledcontenttargets,aimingtosupportacirculareconomyandreduceplasticwaste(e.g.,[41][42][43]).Existingmechanicalrecyclinginfrastructurealoneisnotcurrentlycapableofsupplyingthequalityandquantityofrecycledmaterialneededtomeetgoalsbeingsetbysomebrandownersandnon-U.S.nationalpolicies.Still,bysomeestimatesthecapacityofthemechanicalrecyclingmarketcouldmorethandouble.Withadditionalresearchtosolvesomematerialandprocessingchallenges,itcouldexpandfurther.Thereisunmetdemandformechanicallyrecyclablefeedstocks,andithassomeattractivebenefitsrelativetootherroutes,includinglowerenergyintensityprocessing,higherconservationofmaterialmasseswithinthepolymerloop,andlong-termuseofrecoveredmaterialindurablegoodsapplications.Manystakeholdersbelievethat,evenwithinnovationandexpansionofcapacityandcollectioninfrastructure,mechanicalrecyclingalonewillnotbeablehandlethefullrangeofplasticswaste.Toaddresstheproblemmorefully,societywillneedcomplementarymethodsthataremoreintensive,andabletorecovervaluefrommorediversepolymertypesandproductformats,hencetheinterestinchemicalpathwaystoreturnmoleculesinvariousformstothesupplychain.Therehavebeenalargenumberof‘greenfield’constructionprojectsannouncedintheUnitedStatesthatareadvertisedasrelyingsolelyonrecycledpolymerstreamstoproducenewfeedstocks,thoughitisunclearifthecollectioninfrastructurewillbeabletosupplylargeenoughvolumestosupporttheiroperationinthenearterm.Somecompaniesareinterestedinincorporatingrecycledpolymerswithvirginfeedstocksusingexistingassets,thuseliminatingtheneedfornew,capitalintensiveinfrastructurededicatedtorecycledpolymerprocessing.However,whilesomechemicalrecyclingprocessesmayuseexistinginfrastructure,thisinfrastructureisnotdesignedforthesefeedstockstreams,thereforeextensivecapitalinvestmentsmaystillberequiredtoretrofitorbuildnewfacilities.Furthermore,relativetothescaleofchemicalproductionatthesefacilities,theinitialfractionsofrecoveredpolymersfedintothemisexpectedtobesmall.Therefore,tomaximizetheincentivetouserecoveredpolymersandtoincreasetheiruse,chainofcustodyapproachessuchasMBaccountingareusedtoenablestakeholderstousetheseassetsandtoovercomeefficiencyandcostbarriers.Oncerecoveredpolymersaremixedwiththeirvirgincounterpartsandchemicallyreprocessed,theyare,inprinciple,indistinguishablefromoneanother.Thismixingofrecycledandvirgininputsposesachallengeintheaccountingforrecycledcontentintheoutputofplasticproductsandpackaging,particularlyinthecaseofchemicalprocesses.Duringchemicalprocessing,complex,competing

[4142]43）?，F(xiàn)有的機(jī)械回收基礎(chǔ)設(shè)施目前尚無法提供滿足某些品牌所有者和非美國國家政

(e.g.,finechemicals,personalcare,orfuelsinadditiontopolymermanufacturing).Asaresult,MBaccountinghasbeenproposedandemployedasatooltotrace,track,andcertifycircularcontentinIneffect,MBisatoolusedtoincentivizeshiftsinthesupplychaintosupportmoresustainableandenvironmentallybeneficialtechnologiesorcapabilitiesthatareinitiallyeconomicallydisadvantageous.MBiswidelyusedinothercommoditysectors,includingtimber,agriculture(foodandcotton),andbiofuels.Itisnowbeingconsideredinthepolymerssectordueto1)itssuccessinothermarketsand2)theopportunitytoacceleratetheadvancementofchemicalrecyclingspecificallywheredifferentiationofoutputproductsbytheinputmaterialstreamsisbothdifficultandinefficient.TheapplicationofMBforplasticsoriginatedinEuropeandisseeingincreasingadoptionintheU.S.Further,emergingattentionandpolicyproposalsatthestateandfederallevel(e.g.,[44][45][46][47]),combinedwithincreasedbrandcommitmentshavespurredinterestinMBasameanstofacilitatepolymerrecyclingintheUnitedStates,eventhoughconcernsremainregardingquantificationofthenetenvironmentalimpactsoftheapproach.OnesuchfederalinitiativeistheSaveOurSeas2.0Act,signedintolawonDecember18,2020.TheActiscomposedofthreebroadcomponents:(1)strengthentheU.S.domesticmarinedebrisresponsecapability,(2)enhanceglobalengagementtocombatmarinedebris,and(3)improvedomesticinfrastructuretopreventmarinedebris.Section134oftheActtaskstheNationalInstituteofStandardsandTechnology(NIST)withperformingastudyonMBmethodologiestocertifycircularpolymers.Specifically,thestudyshallinclude“anidentificationandassessmentofexistingMBmethodologies,standards,andcertificationsystemsthatareormaybeapplicabletosupplychainsustainabilityofpolymers,consideringthefulllifecycleofthepolymer,andincludinganexaminationof(A)theInternationalSustainabilityandCarbonCertification[ISCC];and(B)theRoundtableonprogramsthatuseMBaccountingtocertifycircularpolymers.TheChallenges:StakeholderTorespondtotheMBassessment,NISThostedavirtualworkshopentitled“AssessmentofMassBalanceAccountingMethodsforPolymers”onMay3-5,2021.ThepurposeoftheworkshopwastoconvenestakeholdersassociatedwithMBmethodologies,includingexistingstandardizationandcertificationprogramsfocusedoncircularpolymersaswellasother,comparableindustries.Participantsincludedrepresentativesassociatedwithbrandowners,chemical/polymermanufacturers(e.g.resinproducers),converters,themechanicalrecyclingindustries,thirdpartycertificationbodies,andconsumerinterestgroups.Throughpresentationsanddiscussions,participantshelpedtoidentifyandassessexistingMBmethodologies,standards,andcertificationsystemsthatareormaybeapplicabletoassigningrecycledcontentinthesupplychainofpolymers.Further,theworkshopaimedtoassesschallenges,includinganylegalorregulatorybarriers,todevelopingastandardandcertificationsystemforcircularpolymers.ThisreportsummarizedtheworkshopoutcomesandprovidesrecommendationsforadvancingMBforcircularpolymers.Workshopplanningandorganizationinvolvedoutreachtostakeholderstoidentifycoreareasofinterest.Theresultingagendaincludedthreeplenarypresentationsandsixtopic-specificsessions:

化學(xué)品生產(chǎn)多種產(chǎn)品，這些產(chǎn)品最終可能進(jìn)入多個供應(yīng)鏈（例如，精細(xì)化學(xué)品、個人護(hù)理或燃料，除了聚合物制造）。因此，MB物中的循環(huán)內(nèi)容。實(shí)際上，MB些技術(shù)或能力最初在經(jīng)濟(jì)上具有劣勢。MB（食品和棉花）1）2）加速化學(xué)回收的機(jī)會（特別是輸入材料流區(qū)分輸出產(chǎn)品既困難又低效），MBMB[44454647），MB作為促進(jìn)美國聚合物回收手段的2.0202012183134（NIST）對海洋垃圾（MB）方法進(jìn)行一項(xiàng)研究，以認(rèn)證循環(huán)聚合物。具體而言，該研究應(yīng)包括MB方法、標(biāo)準(zhǔn)和認(rèn)證系統(tǒng)的識別和評估，這些方法或可能適用于聚合物供應(yīng)鏈可持續(xù)MBA[ISCC；以及(B[RSB][45MB會計(jì)來認(rèn)為響應(yīng)材料平衡評估，NIST2021535 Eachsessionincludedapresentationbyanexpertonthetopic,followedbyabreakoutdiscussioninwhichparticipantswererandomlyassignedtovirtualroundtables.NISTfacilitatorsleddiscussionsbasedonpreparedquestions.TheplenarypresentersincludedanindustryexpertonMBaccountingforpolymers,anEPArepresentative,andapanelofexistingMBcertificationorganizations.Intotal,agendaandparticipationlistareprovidedinAppendicesAandB,respectively.2MassBalanceMBisoneoffivecommonchainofcustody(CoC)modelsdesignedtocreatetransparencyandtrustthroughoutthevaluechainregardingpropertiesofgoodsandmaterialsthatareotherwisedifficulttodistinguish[48].Suchpropertiesincludeorigin,rawmaterialcomposition,andproductionpractices.TheCoCmodelsarecommonlyappliedtotracesustainablyand/orethicallyproduced/processedmaterialsthatarenotidentifiablecomparedtotheircounterparts.ThefiveCoCmodelsshowninFigure3sharethecommonobjectiveofguaranteeingsolidbookkeepingandcorroboratingalinkbetweentheinputwithspecificcharacteristics(e.g.,sustainable,recycled,organic)enteringtheproductionsystemandthatoftheout-goingproduct[49].Themodelsdifferinhowtheymanageandrecordthatlink,andthesetofrulesformixing,balancing,andtracking.Figure3:Fivecommonchainofcustodymodels.*RepresentswherecreditsorallocationcanbeadjustedforlossesintheMBapproach.NIST（MB）核EPAMB10012