Transcript NanoRelease TG 2

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
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 :
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release of MWCNTs from the products/articles
release measurement methods
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Main Questions
• Which polymers are relevant to current and nearterm 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
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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
9.0
0.5
2.8
2.8
4.3
12.2
8.7
8.0
0.8
13.9
10.2
26.8
Aerospace
Automotive
Construction
Defence
Electronics& DataStorage
Energy
Environment
Healthcare& Life Sciences
PersonalCare
Printing& Packaging
SportingGoods
Textiles
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.
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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
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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
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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%
3-15
5-15
Number walls
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.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
CNT in Epoxy:
CNT-NH2
B. Simard, NRC internal data
CNT-OH
CNT physical dispersion
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Polymer-specific Conclusions:
CNT Release potential
Green – low susceptibility for release
Yellow – moderately susceptible for release
Red – high susceptibility for release
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
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Phase 2.5 Findings
TG2 Whitepaper
Phase 2.5 Report
Lifecycle Focus
Consumer Use
+ some End of Life
Manufacture & Occupational
use
Polymers
Focus: Epoxy, PA, PU, PE, PC Epoxy, PA, PU, PE, PC, ABS,
Considered: PP, PVC, PET,
EV6, POM, PP, PS, PVC, PU,
PEEK, PMMA, elastomer
PET, PMMA, rubber
Degradation Pathways
Weathering, UV, Mechanical
Stress, Chemical, Thermal,
End of Live
Abrasion, Sanding,
Weathering
Release media
Air, Dust
Water
Air
Water, 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
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