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TG2 Materials Characteristics Relevant to the Analysis of Release Measurement Methods for Multi-walled Carbon Nanotubes in Polymer Systems Contributing Members Christopher Kingston (Co-Chair), Richard Zepp (Co-Chair), Phil Sayre, Anthony Andrady, Betsy Shelton, Douglas Hawkins, Eva Wong, Yasir Sultan, Wendel Wohlleben, Darrell Boverhof, Viktor Vejins, Richard Fehir, Justin Roberts

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Charge for TG2 Identify the factors that influence the selection and use of MWCNTs - polymer combinations in commercial use with respect to how those factors may affect : release of MWCNTs from the products/articles release measurement methods 2

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Main Questions Which polymers are relevant to current and near- term production of consumer goods containing MWCNT? How do the properties of those polymers impact the potential for MWCNT release from the finished products/articles? What implications do the materials properties have on measurement methods? 3

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Criteria for Polymer Selection Representation of a range of releases Brittle vs. soft, chemically resilient vs. chemically labile, environmentally stable (UV, moisture) vs. environmentally susceptible Likelihood of direct exposure to consumers Potential degree of consumer exposure Commercial/industrial production volume Availability of data on the CNT/polymer system Likelihood of modifications to polymer during production or manufacture (coatings, additives, stabilizers, painting, etc.) Expert opinion 4

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Commercially Relevant Polymer-CNT Annual Global production of CNT 1000s of tons Numerous manufactures $45-70 /kg 5 Production of CNT (conservative estimate) through 2016 (Future Markets, Inc.) Future Markets, Inc. The World Market for Carbon Nanotubes, Nanofibers, Fullerenes and POSS: Applications, Products, End User Markets, Companies and Revenues. September 2011. Future Markets, Inc. Nanomaterials in plastics and advanced polymers. April2012. Nanoposts.com. The Global Market for Carbon Nanotubes to 2015: A Realistic Assessment 2 nd Edition. August 2010.

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Which Polymers? Limited direct feedback from industry Limited market report data specifying polymers Future Markets, Inc. 2012: Epoxy, PI, phenolic, PP, PMMA, PS, PEO, PCL, PA, PET No quantitative production volume information Some information on commercial internet sites Anecdotal information Expert opinion by TG and SC members Polymers Considered: Epoxy, PA, PU, PE, PC, PP, PVC, PET, PEEK, PMMA, Phenolic, PP, PEO, POM, PCL, PI, Elastomer 6

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Polymers Selected 7 PolymerMain Contributing Members EpoxyBetsy Shelton, Douglas Hawkins, Tony Andrady PolyamideDouglas Hawkins, Betsy Shelton, Eva Wong PolyurethaneWendel Wohlleben, Yasir Sultan PolyethyleneRichard Zepp, Viktor Vejins, Darrel Boverhoff PolycarbonateJustin Roberts, Richard Fehir

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Topics Covered in TG2 White Paper Basic description of the polymer: Uses in conjunction with CNT industries/markets; production volume; etc. General potential for release of CNT &/or breakdown of polymer (based on CNT+polymer, or just polymer studies) MWCNT traits that may affect release from polymer Use of stabilizers & plasticizers in polymer composites - affects degradation Implications for release based on commercial use Any other life cycle information easily gathered that would inform potential for CNT release 8

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Purpose of MWCNT Use in Polymer Improved electrical conductivity Improved thermal conductivity Improved mechanical properties Weight reduction Flame retardancy Extended wear Reduced friction 9

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Processes of Potential Importance in Degradation and Release Photodegradation Hydrolysis Oxidation (esp. autooxidation) Thermolysis likely to have minimal impact Mechanical degradation and wear pose minor potential for direct release during typical consumer use (but can have important indirect effects) Related points: Degradation processes depend on polymer structure e.g. PA and PU are susceptible to hydrolysis but PE is not. 10

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Release Variability is Linked Primarily to Environmental Factors That Drive Degradation The variability of release from one scenario to another is linked to variability in physical, chemical, and biological agents that drive the degradation. E.g. if the MWCNT composites are located in dark, cool environments release is much slower because light intensity is much lower and photodegradation is slower. Composite degradation and release is likely to be generally slow under conditions of usual consumer use; inadvertent exposure of composites to incompatible chemical environments that accelerate degradation could lead to more significant release 11

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Role of CNTs in Inducing Release from Composites CNTs appear to be resistant to degradation compared to polymer matrices but are capable of influencing the degradation rates of the polymer matrix. Currently-available data indicate that CNTs can retard degradation of the polymers. The greater stability of CNTs compared to polymer matrix during degradation can lead to enhancement of CNT concentrations in degraded material especially near surface of weathered material; but availability of CNT may be reduced by entangling with matrix residue. Inefficient dispersion of CNT can cause "pockets" of CNT agglomerates that result in weak spots within the composite and sites of breakage; could lead to release of unbound CNT. 12

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Degradation and Release Can be Modulated by Polymer Additives Added UV stabilizers and free radical scavengers slow degradation Added pro-oxidants accelerate matrix degradation by increasing levels of reactive oxygen species in matrix 13

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Variability of CNT and implications on release CNT are not a single molecule Multiple manufacturing technologies Polydispersed batches Physical, chemical properties and interface with polymers depends on source of CNT 14 Baytubes C150P GraphistrengthNanocyl NC7000 Showa Denko VGCF-X Diameter5-20 nm10-15 nm9.5 nm10-15 nm Length 1-10+ m0.1-10 m1.5 m3 m C purity> 95%>90%90% Number walls3-155-15 Bulk density140-160 kg/m 3 80 kg/m 3 http://www.graphistrength.com/sites/group/en/products/detailed_sheets/multi_wall_carbon_nanotubes_graphistrength/general_characteristics.page http://www.baytubes.com/product_production/baytubes_data.html http://www.nanocyl.com/en/Products-Solutions/Products http://www.sdk.co.jp/english/products/137/139/2042.html

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CNT Functionalization & Dispersion As-produced CNT have strong bundling tendencies Low interfacial interaction with polymers Improving dispersion enhances composite properties such as conductivity and mechanical strength; possibly linked to release of CNTs Processing conditions Functionalization 15 CNT-NH 2 CNT-OHCNT physical dispersion CNT in Epoxy: B. Simard, NRC internal data

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Polymer-specific Conclusions: CNT Release potential 16 EpoxyPolyamidePolyurethanePolyethylenePolycarbonate Mechanical Characteristics Hard, brittleSoft, ductile Soft, ductile, elastomer Soft, ductileHard but ductile** Photodegradation Rapid, CNT can stabilize Susceptible LowSusceptible Oxidation Susceptible Hydrolysis Susceptible Low Susceptible (esp. when exposed to base) Thermolysis Low Mechanical Degradation Low Lifecycle* End of life processing Summary Low Potential for release of CNT under typical intended consumer use is expected to be low. * Degradation can increase release potential Green low susceptibility for release Yellow moderately susceptible for release Red high susceptibility for release

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Phase 2.5 Findings 17 TG2 WhitepaperPhase 2.5 Report Lifecycle FocusConsumer Use + some End of Life Manufacture & Occupational use PolymersFocus: Epoxy, PA, PU, PE, PC Considered: PP, PVC, PET, PEEK, PMMA, elastomer Epoxy, PA, PU, PE, PC, ABS, EV6, POM, PP, PS, PVC, PU, PET, PMMA, rubber Degradation PathwaysWeathering, UV, Mechanical Stress, Chemical, Thermal, End of Live Abrasion, Sanding, Weathering Release mediaAir, Dust Water Air Water, Dust Polymer AdditivesImportant to releaseNot studied; should be considered CNT FunctionalizationImportant to releaseNot studied; should be considered

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General Conclusions Despite the numerous differences a number of common tendencies have been deduced Polymer degradation represents the greatest potential for CNT release Photodegradation polymer dependent; CNT can improve photostability Hydrolysis polymer dependent; significant potential for release Oxidation polymer dependent; significant potential for release Thermolysis CNT generally improve thermal stability low potential for release Overall LOW potential for release from consumer goods under normal/recommended use 18