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Charge for TG2

TG2 Materials Characteristics Relevant to the Analysis of Release Measurement Methods for Multi-walled Carbon Nanotubes in Polymer Systems .

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Charge for TG2

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  1. TG2Materials Characteristics Relevant to the Analysis of Release Measurement Methods for Multi-walled Carbon Nanotubes in Polymer Systems Contributing MembersChristopher 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

  2. 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

  3. 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?

  4. 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

  5. Commercially Relevant Polymer-CNT • Annual Global production of CNT –1000’s of tons • Numerous manufactures • $45-70 /kg Nanoposts.com. The Global Market for Carbon Nanotubes to 2015: A Realistic Assessment – 2nd Edition. August 2010. 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.

  6. 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

  7. Polymers Selected

  8. 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

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

  10. 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 potentialfor 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.

  11. 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

  12. 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.

  13. 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

  14. 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 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

  15. 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 CNT in Epoxy: CNT-OH CNT physical dispersion CNT-NH2 B. Simard, NRC internal data

  16. Polymer-specific Conclusions: CNT Release potential Green– low susceptibility for release Yellow– moderately susceptible for release Red– high susceptibility for release Potential for release of CNT under typical intended consumer use is expected to be low. * Degradation can increase release potential

  17. Phase 2.5 Findings

  18. 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

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