Task Group Co-Chairs Debra Kaiser, NIST Aleks Stefaniak, NIOSH

Task Group Co-ChairsDebra Kaiser, NIST

Aleks Stefaniak, NIOSH

Contributing Task Group Members (to date)Keana Scott, Tinh Nguyen, and Rick Davis, NIST

Jurg Schutz, CSIRO, AustraliaFrank von der Kammer, University of Vienna, Austria

Dermont Bouchard, EPA

Technical Experts Consulted (to date)Robert Cook, Frank DelRio, Jeffrey Fagan, Justin Gorham, Angela Hight-Walker, Elijah Petersen, Keana Scott (NIST); Jeff Simpson

(Towson University)

Task Group 1 : Methods

NanoRelease Consumer Products: Multi-Wall Carbon Nanotube (MWCNT) in Polymers

Steering Committee Workshop

May 16-17, 2013

Work Flow

2

Methods:• Generation of released material• Representative sampling

• Sample preparation for measurement

• Measurement of released materialTG 1: Methods May16-17, 2013NanoRelease Steering Committee

Forms of released material

Release

Release scenarios

Driving forces

Sampling methods

Release ProcessesMWCNTs + polymer

MWCNT-polymercomposites

Products

Materials + Products

Methods and evaluation

Detection

Characterization

Quantification

Sample preparation

Measurement of Released Material

New and improved measurement methods

Interlaboratory studies

Standardized methods

Gaps and Needs

http://acswebcontent.acs.org/gcande/index.html


Materials and Consumer Products

3

Considerations:• Polymers identified by TG2: epoxy, polyamide (PA),

polyurethane (PU), polyethylene (PE), and polycarbonate (PC)

• MWCNTs only form of carbon nano-objects• Products too complex• Release from MWCNT-polymer composites: two

scenarios

500 nm

+ polymer

2 µm

forming

Raw MWCNTs MWCNT−polymer

composites

Sporting goods

SEM images: A. Vladar, NIST

TG 1: Methods May16-17, 2013NanoRelease Steering Committee



Measurement Concepts

4

• Detection: presence (yes or no) of MWCNTs; detection limit• Quantification: number or mass concentration of MWCNTs

in released material per unit volume or area of composite• Characterization: determination of characteristics and

properties of MWCNTs and fragments

Measurement “Hierarchy”*

* Adapted from von der Kammer et al., Trends Anal. Chem. 2011, 30, 425-436 (note: identification combined with detection)

Measurement methods include instrument specification , procedures or well-defined protocols, data analysis and representation, and data compilation in a common format




Measurement Concepts

5* Adapted from von der Kammer et al., Trends Anal. Chem. 2011, 30, 425-436 (note: identification combined with detection)

Qualitative vs. Quantitative Measurements• Qualitative

• ranges from, e.g., “the sample does or does not contain MWCNTs” to “the sample contains about 50% MWCNTs” per unit area or volume examined

• relative uncertainty in the estimate is large• Semi-Quantitative

• measurement of, e.g., number of MWCNTs as “counted” in a sample• not all MWCNTs present may be measured (e.g., encased MWCNTs)• difficult to perform measurements that are statistically significant

(e.g., tedious, representative sample)• Quantitative

• measurement produces a numerical result, e.g., the diameter ranges from 100 nm to 200 nm

• most MWCNTs present are measured• sufficient number of measurements to be statistically significant (can

report uncertainty) What degree of quantitation is required?




Release Scenario 1

6

• Polymer is not degraded (i.e., remains cross-linked)• Mechanical “driving force”: high energy process• Abrading, sanding, drilling…

MWCNT-polymer composite

fragments: may or may not contain MWCNTs

fragments and unbound MWCNTs

all studies report the presence of

fragments only in released material

some studies report the presence of

MWCNTs in released material

MWCNTs may protrude from fragment surface, be encased in fragment, or both

fragment sizes: 100 nm to 1 mm

TG 1: Methods June 21-22, 2013NanoRelease Steering Committee

TEM image of MWCNTs protruding from fragmentCena et al. J. Occup. Env. Hygiene. 2011, 8, 86-92.



Release Scenario 1: Sampling Methods: Fragments

7

Real-time instruments• Instantaneous measures of number, mass, size, or

surface area concentration• Not chemical-specific

Time-integrated samplers• Collection particles onto substrate for off-line analysis• Size-selective samplers

• Separate particles by aerodynamic or other size• Can be dichotomous or multi-stage samplers: 10’s of

nm to 10’s of μm• Collect particles with sizes well above the nanoscale;

agglomerates • ‘Total’ (non-size-specific) samplers

• Plastic cassette and conductive cowl samplers that hold filters

• Precipitators (some instruments can be size-selective)TG 1: Methods May16-17, 2013NanoRelease Steering Committee



Release Scenario 1: Sampling Methods, MWCNTs

8

Real-time instruments are problematic• Estimate ‘equivalent’ diameter assuming spherical shape• Problems with fibers (multiple charging effects, etc.)

Time-integrated samplers as described above•Conductive cowl sampler designed for fibers•Precipitators have good efficiency in

nanoscale




Release Scenario 1: What to Measure?

9

Presence of MWCNTs in fragments (detection)

Number or mass concentration of MWCNTs in fragments (quantification)

Physico-chemical characteristics or properties of MWCNTs in fragments, e.g., average size (diameter and length), size distribution, and surface composition

Relative amounts of fragments that contain MWCNTs vs. fragments that do not contain MWCNTs (by number or mass)

Average size and size distribution of the fragments

Shape of fragments

All of the same to the left Presence of unbound MWCNTs in sample

(detection) Relative amounts of fragments vs.

unbound MWCNTs in sample Number or mass concentration of

unbound MWCNTs in sample Physico-chemical characteristics or

properties of unbound MWCNTs in sample, e.g., average size (diameter and length), size distribution, and surface composition

fragments only fragments and unbound MWCNTs


Prioritization and selection of what to measure is the essential first step More than one measurement method is required for quantification and

characterization Sample large enough to yield a statistically relevant result (quantitative

measurements)



Release Scenario 1: Measurement Methods

10

12 published studies• fragments only (7); fragments and unbound MWCNTs (5) studies• Polymer: epoxy (7); PA (2), PC (2), PU (2), POM* (2), PMMA* (1)

* Polymers not considered by TG2: POM = polyoxymethlene, PMMA: Poly(methyl methacrylate)

SEM and TEM most widely used measurement methodsMethods for sizing fragments were not considered, except

for AUCTG 1: Methods May16-17, 2013NanoRelease Steering Committee

Measurement method Frequency of method

SEM (scanning electron microscopy) 10

TEM (transmission electron microscopy) 7

TEM-EDX (TEM-energy dispersive X-ray spectroscopy) 4

XPS (X-ray photoelectron spectroscopy) 2

AUC (analytical ultra-centrifugation) 2

LD (laser diffraction) 2

TOF-SIMS (time-of-flight secondary ion mass spectroscopy) 1

ICP-MS (inductively-coupled mass spectrometry) 1

AFM (atomic force microscopy) —

RS (Raman spectroscopy) —

UV-VIS (ultra-violet visible spectroscopy) —



Release Scenario 1: Method Specifications

11

Measurement method

Media

Spatial resoluti

onInformatio

n depthMaximum sample or scan area

Detection limit

Type of Information

SEM V 1 nm to 10 nm

near-surface to

few μm1 mm x 1 mm

one MWCNT per sample

areasemi-

quantitative

TEM UHV sub-nm 100 nm maximum 10 μm x 10 μm

one MWCNT per sample

areasemi-

quantitative

AUC LS 10 nm NA unlimited volume unknown quantitative

AFM A 10 nm 0.1 nm 50 μm x 50 μm one MWCNT per scan area

semi-quantitative

XPS UHV 10 nm 3 nm to 10 nm 700 μm x 2 mm

10 wt % MWCNTs in compositeb

semi-quantitative

Raman spectroscop

yA 1 μm 1 μm to 5

μm 1 μm5 wt %

MWCNTs in compositeb

qualitative to semi-

quantitative

UV-VIS A 100 nm to 1 μm

1 μm to 5 μm 1 μm unknown qualitative

Measurement media: A = ambient; LS = liquid suspension; V = vacuum (10-6 torr); UHV = ultra-high vacuum (10-9 torr)

Table completed with input from NIST experts; additional input is welcome




Release Scenario 1: Measured Characteristics

12

QL , qualitative: yes/no or rough estimateSQ, semi-quantitative: can get a numerical result that is a good estimate, uncertainty is medium to high, dependent on numerous factorsQN, quantitative: get a numerical result with low uncertainty

Measurement

method

Concentration of MWCNTs

Average size and size distribution

Surface compositi

on

Relative concentrati

ons of fragments

and unbound MWCNTs

in fragme

ntsUnbound

MWCNTs in

fragments

Unbound

MWCNTs

Fragments

SEM SQ SQ SQ SQ SQ NA SQ

TEM QL QL QL QL QL NA (EELS) QL

AUC NA NA NA QN QN NA QN

AFM SQ SQ SQ SQ SQ NA SQ

XPS SQ – total MWCNTs NA NA NA QN NA

RS QL – total MWCNTs NA QL NA NA NA

UV-VIS QL – total MWCNTs NA QL NA NA NA




Release Scenario 1: Method Evaluation

13

High: statistically relevant sample size; minimal sample preparation; broadly available commercial instrument; measurement requires minimal expertise and timeMedium: unlikely that sample size is statistically relevant; moderate sample preparation; moderate availability of instruments, may contract measurements; skilled expertise and significant measurement timeLow: sample size not statistically relevant; difficult sample preparation; few instruments available at e.g., user facilities; exceptional expertise and measurement timeFor detection (D), quantification (Q), and characterization (C)High: easy to detect, quantitative result for Q and CMedium: difficult to detect; semi-quantitative result for Q and CLow: not used for detection; qualitative result for Q and CTG 1: Methods May16-17, 2013NanoRelease Steering Committee

Measurement

method

Representative sample

amount

Ease of sample

preparation

Availability of

instruments

Practicality of

Measurements

D Q C

SEM M H H M H L M

TEM L H M M H L M

AUC H H M M M H H

AFM M M H H H L M

XPS H H M M M L M

Raman H H H M M L L

UV-VIS H H H M M L L



Conclusions for Scenario 1

14

• Must first prioritize and select key characteristics and properties of MWCNTs, in fragments and unbound, and fragments

• More than one method is required to determine a characteristic or property

• Numerous methods for detection of MWCNTs, unbound and in fragments

• Most methods for quantification (concentration of MWCNTs) are semi-quantitative at best, i.e., may get a numerical result that is a reasonable estimate, uncertainty is medium to high

• Most methods for characterization are semi-quantitative at best:• Tedious to measure a large enough amount of material for

statistically relevant results• For many methods, cannot measure MWCNTs encased in a

fragment• Validated protocols and reference materials essential for

accurate measurements• Validation of methods and data are difficult and time-

consuming

Measurement methods for released material


Release Scenario 2

15

• Polymer is chemically degraded in a binding or cross-linking sense• “Weathering”: optical (UV) and hydrolytic (humidity) “driving

forces”: low energy process• Accelerated weathering by long-term exposure or by accelerated

processes (e.g., the NIST “SPHERE”)

MWCNT-polymer composite

oligomers tangled network of MWCNTs on the surface of the

composite

potential subsequent release of unbound or tangled MWCNTs by

agitation, wear, chemical reaction, or fluid flow

200 nmPeteren et al.,

submitted to ACS Nano




Release Scenario 2: What to Measure?

16

Presence of MWCNTs (detection) Number or mass concentration of

MWCNTs on surface (quantification) Physico-chemical characteristics or

properties of MWCNTs , e.g., average size (diameter and length), size distribution, spatial distribution (degree of dispersion), and surface composition

Presence of MWCNTs in release media (detection)

Number or mass concentration of unbound MWCNTs per volume of media

Physico-chemical characteristics or properties of unbound MWCNTs in media, e.g., average size (diameter and length), size distribution, and surface composition

Tangled network of MWCNTs

Potential release of unbound MWCNTs

Prioritization and selection of what to measure is the essential first step More than one measurement method is required for quantification and

characterization Sample large enough to yield a statistically relevant result (quantitative

measurements)

Release media (dependent on lifecycle stage and mode of consumer use):

• Environmental media: air, water, sludge, soil…• Biological media: saliva, blood, tissue




Release Scenario 2: Measurement Methods

17

8 published studies• Polymer: epoxy (2); PA (3), PU (2), POM* (1)• Methods identified below considered only tangled network resulting

from polymer degradation (not subsequent release of MWCNTs or fragments by further action)

* Polymers not considered by TG2: POM = polyoxymethlene

SEM most widely used measurement method


Measurement method Frequency of method

SEM (scanning electron microscopy) 5

TEM (transmission electron microscopy) 2

SEM-EDX (SEM-energy dispersive X-ray spectroscopy) 1

XPS (X-ray photoelectron spectroscopy) 2

TOF-SIMS (time-of-flight secondary ion mass spectroscopy) 1

AFM (atomic force microscopy) —



Release Scenario 2: Measured Characteristics

18

QL , qualitative: yes/no or rough estimateSQ, semi-quantitative: can get a numerical result that is a good estimate, uncertainty is medium to high, dependent on numerous factorsQN, quantitative: get a numerical result with low uncertainty



Measurement

method

Concentration of

MWCNTs

Average size and size

distributionDegree of dispersion

Surface compositio

n

SEM SQ SQ SQ NA

TEM QL QL QL NA

AFM SQ SQ SQ NA

XPS QL NA NA QN



Release Scenario 2: Method Evaluation

19

High: statistically relevant sample size; minimal sample preparation; broadly available commercial instrument; measurement requires minimal expertise and timeMedium: unlikely that sample size is statistically relevant; moderate sample preparation; moderate availability of instruments, may contract measurements; skilled expertise and significant measurement timeLow: sample size not statistically relevant; difficult sample preparation; few instruments available at e.g., user facilities; exceptional expertise and measurement timeFor detection (D), quantification (Q), and characterization (C)High: easy to detect, quantitative result for Q and CMedium: difficult to detect; semi-quantitative result for Q and CLow: not used for detection; qualitative result for Q and C



Measurement

method

Representative sample

amount

Ease of sample

preparation

Availability of

instruments

Practicality of

Measurements

D Q C

SEM M M H M H M M

TEM L L M L H L L

AFM H M H M H M M

XPS H H M M M L M



Conclusions for Scenario 2

20

• Must first prioritize and select key characteristics and properties of MWCNT networks

• More than one method is required to determine a characteristic or property

• Numerous methods for detection of MWCNTs• Most methods for quantification (concentration of MWCNTs)

are semi-quantitative at best, i.e., may get a numerical result that is a reasonable estimate, uncertainty is medium to high

• Most methods for characterization are semi-quantitative at best:• Tedious to measure a large enough amount of material for

statistically relevant results• Difficult to separate tangled MWCNTs• Validated protocols and reference materials essential for

accurate measurements• Validation of methods and data are difficult and time-consuming

Measurement methods for tangled networks of MWCNTs


Recommendations

21

Pilot Testing and Interlaboratory Studies (ILS’s)• Start with a pilot study involving a few labs with great

expertise in the topic• Possible to design a pilot test and eventually an ILS for:

• Generation of released material in a controlled manner• Representative sampling of released material

• Very difficult to design a pilot test for measuring MWCNTs in polymer composites that would yield reproducible results

• Start with protocol development• Generation of released material by one or more specific

methods• Sampling or sample preparation protocols• Protocols for qualitative or semi-quantitative measurements

Standardization of Methods • Too early!• Requires well-defined, validated protocols for any methodTG 1: Methods May16-17, 2013NanoRelease Steering Committee



Documents

Task Group Co-Chairs Debra Kaiser, NIST Aleks Stefaniak, NIOSH