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
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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
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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?
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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
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Commercially Relevant Polymer-CNT
• Annual Global production of CNT –1000’s of tons– Numerous manufactures– $45-70 /kg
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.
12.28.7
0.8
13.9
26.8
10.2
2.8
2.80.5
8.0
9.0 4.3
Aerospace Automotive Construction Defence Electronics & Data StorageEnergy Environment Healthcare & Life SciencesPersonal CarePrinting & Packaging Sporting GoodsTextiles
Nanoposts.com. The Global Market for Carbon Nanotubes to 2015: A Realistic Assessment – 2nd 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
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Polymers Selected
Polymer Main Contributing Members
Epoxy Betsy Shelton, Douglas Hawkins, Tony Andrady
Polyamide Douglas Hawkins, Betsy Shelton, Eva Wong
Polyurethane Wendel Wohlleben, Yasir Sultan
Polyethylene Richard Zepp, Viktor Vejins, Darrel Boverhoff
Polycarbonate Justin 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
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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
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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.
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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
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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.
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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
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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
Baytubes C150P
Graphistrength Nanocyl NC7000
Showa Denko VGCF-X
Diameter 5-20 nm 10-15 nm 9.5 nm 10-15 nm
Length 1-10+ mm 0.1-10 mm 1.5 mm 3 mm
C purity > 95% >90% 90%
Number walls 3-15 5-15
Bulk density 140-160 kg/m3 80 kg/m3
http://www.graphistrength.com/sites/group/en/products/detailed_sheets/multi_wall_carbon_nanotubes_graphistrength/general_characteristics.pagehttp://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
CNT-NH2CNT-OH CNT physical dispersion
CNT in Epoxy:
B. Simard, NRC internal data
Polymer-specific Conclusions: CNT Release potential
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Epoxy Polyamide Polyurethane Polyethylene Polycarbonate
Mechanical Characteristics
Hard, brittle Soft, ductile Soft, ductile, elastomer
Soft, ductile Hard but ductile**
Photodegradation Rapid, CNT can stabilize
Susceptible Susceptible Low Susceptible
Oxidation Susceptible Susceptible Susceptible Susceptible Susceptible
Hydrolysis Susceptible Susceptible Susceptible Low Susceptible (esp. when exposed to
base)
Thermolysis Low Low Low Low Low
Mechanical Degradation
Low Low Low Low Low
Lifecycle* End of life processing
End of life processing
End of life processing
End of life processing
End of life processing
Summary Low Low Low Low 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 releaseYellow – moderately susceptible for releaseRed – high susceptibility for release
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Phase 2.5 FindingsTG2 Whitepaper Phase 2.5 Report
Lifecycle Focus Consumer Use+ some End of Life
Manufacture & Occupational use
Polymers Focus: Epoxy, PA, PU, PE, PCConsidered: PP, PVC, PET, PEEK, PMMA, elastomer
Epoxy, PA, PU, PE, PC, ABS, EV6, POM, PP, PS, PVC, PU, PET, PMMA, rubber
Degradation Pathways Weathering, UV, Mechanical Stress, Chemical, Thermal, End of Live
Abrasion, Sanding, Weathering
Release media Air, DustWater
AirWater, Dust
Polymer Additives Important to release Not studied; should be considered
CNT Functionalization Important to release Not 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
