TG2 Materials Characteristics Relevant to the Analysis of Release Measurement Methods for...
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TG2 Materials Characteristics Relevant to the Analysis of Release Measurement Methods for Multi-walled Carbon Nanotubes in Polymer Systems Contributing
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
Slide 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
2
Slide 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? 3
Slide 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
4
Slide 5
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.
Slide 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
6
Slide 7
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
Slide 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 8
Slide 9
Purpose of MWCNT Use in Polymer Improved electrical
conductivity Improved thermal conductivity Improved mechanical
properties Weight reduction Flame retardancy Extended wear Reduced
friction 9
Slide 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 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
Slide 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
11
Slide 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. 12
Slide 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 13
Slide 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 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
Slide 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 15 CNT-NH 2 CNT-OHCNT
physical dispersion CNT in Epoxy: B. Simard, NRC internal data
Slide 16
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
Slide 17
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
Slide 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 18