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Task Group Co-Chairs Debra Kaiser, NIST Aleks Stefaniak, NIOSH Contributing Task Group Members (to date) Keana Scott, Tinh Nguyen, and Rick Davis, NIST.

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Presentation on theme: "Task Group Co-Chairs Debra Kaiser, NIST Aleks Stefaniak, NIOSH Contributing Task Group Members (to date) Keana Scott, Tinh Nguyen, and Rick Davis, NIST."— Presentation transcript:

1 Task Group Co-Chairs Debra Kaiser, NIST Aleks Stefaniak, NIOSH Contributing Task Group Members (to date) Keana Scott, Tinh Nguyen, and Rick Davis, NIST Jurg Schutz, CSIRO, Australia Frank 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

2 Work Flow 2 Methods: Generation of released material Representative sampling Sample preparation for measurement Measurement of released material TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Forms of released material Release Release scenarios Driving forces Sampling methods Release Processes MWCNTs + polymer MWCNT-polymer composites 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

3 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, 2013 NanoRelease Steering Committee

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

5 Measurement Concepts 5 * Adapted from von der Kammer et al., Trends Anal. Chem. 2011, 30, (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? TG 1: Methods May16-17, 2013 NanoRelease Steering Committee

6 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, 2013 NanoRelease Steering Committee TEM image of MWCNTs protruding from fragment Cena et al. J. Occup. Env. Hygiene. 2011, 8,

7 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, 2013 NanoRelease Steering Committee

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

9 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 onlyfragments and unbound MWCNTs TG 1: Methods May16-17, 2013 NanoRelease Steering Committee  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)

10 Release Scenario 1: Measurement Methods 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 methods Methods for sizing fragments were not considered, except for AUC TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Measurement methodFrequency 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)—

11 Release Scenario 1: Method Specifications 11 Measurement method Media Spatial resolution Information depth Maximum sample or scan area Detection limit Type of Information SEMV 1 nm to 10 nm near-surface to few μm 1 mm x 1 mm one MWCNT per sample area semi-quantitative TEMUHVsub-nm 100 nm maximum 10 μm x 10 μm one MWCNT per sample area semi-quantitative AUCLS10 nm NA unlimited volumeunknown quantitative AFMA10 nm0.1 nm50 μm x 50 μm one MWCNT per scan area semi-quantitative XPSUHV10 nm3 nm to 10 nm700 μm x 2 mm 10 wt % MWCNTs in composite b semi-quantitative Raman spectroscopy A1 μm1 μm to 5 μm1 μm 5 wt % MWCNTs in composite b qualitative to semi-quantitative UV-VISA 100 nm to 1 μm 1 μm to 5 μm1 μmunknownqualitative 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 TG 1: Methods May16-17, 2013 NanoRelease Steering Committee

12 Release Scenario 1: Measured Characteristics 12 QL, qualitative: yes/no or rough estimate SQ, semi-quantitative: can get a numerical result that is a good estimate, uncertainty is medium to high, dependent on numerous factors QN, quantitative: get a numerical result with low uncertainty Measurement method Concentration of MWCNTs Average size and size distribution Surface composition Relative concentrations of fragments and unbound MWCNTs in fragments Unbound MWCNTs in fragments Unbound MWCNTs Fragments SEMSQ NASQ TEMQL NA (EELS)QL AUCNA QN NAQN AFMSQ NASQ XPSSQ – total MWCNTsNA QNNA RSQL – total MWCNTsNAQLNA UV-VISQL – total MWCNTsNAQLNA TG 1: Methods May16-17, 2013 NanoRelease Steering Committee

13 Release Scenario 1: Method Evaluation 13 High: statistically relevant sample size; minimal sample preparation; broadly available commercial instrument; measurement requires minimal expertise and time Medium: unlikely that sample size is statistically relevant; moderate sample preparation; moderate availability of instruments, may contract measurements; skilled expertise and significant measurement time Low: sample size not statistically relevant; difficult sample preparation; few instruments available at e.g., user facilities; exceptional expertise and measurement time For detection (D), quantification (Q), and characterization (C) High: easy to detect, quantitative result for Q and C Medium: difficult to detect; semi-quantitative result for Q and C Low: not used for detection; qualitative result for Q and C TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Measurement method Representative sample amount Ease of sample preparation Availability of instruments Practicality of Measurements DQC SEMMHHMHLM TEMLHMMHLM AUCHHMMMHH AFMMMHHHLM XPSHHMMMLM RamanHHHMMLL UV-VISHHHMMLL

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

15 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 nm Peteren et al., submitted to ACS Nano TG 1: Methods May16-17, 2013 NanoRelease Steering Committee

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

17 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 TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Measurement methodFrequency 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)—

18 Release Scenario 2: Measured Characteristics 18 QL, qualitative: yes/no or rough estimate SQ, semi-quantitative: can get a numerical result that is a good estimate, uncertainty is medium to high, dependent on numerous factors QN, quantitative: get a numerical result with low uncertainty Table completed with input from NIST experts; additional input is welcome TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Measurement method Concentration of MWCNTs Average size and size distribution Degree of dispersion Surface composition SEMSQ NA TEMQL NA AFMSQ NA XPSQLNA QN

19 Release Scenario 2: Method Evaluation 19 High: statistically relevant sample size; minimal sample preparation; broadly available commercial instrument; measurement requires minimal expertise and time Medium: unlikely that sample size is statistically relevant; moderate sample preparation; moderate availability of instruments, may contract measurements; skilled expertise and significant measurement time Low: sample size not statistically relevant; difficult sample preparation; few instruments available at e.g., user facilities; exceptional expertise and measurement time For detection (D), quantification (Q), and characterization (C) High: easy to detect, quantitative result for Q and C Medium: difficult to detect; semi-quantitative result for Q and C Low: not used for detection; qualitative result for Q and C Table completed with input from NIST experts; additional input is welcome TG 1: Methods May16-17, 2013 NanoRelease Steering Committee Measurement method Representative sample amount Ease of sample preparation Availability of instruments Practicality of Measurements DQC SEMMMHMHMM TEMLLMLHLL AFMHMHMHMM XPSHHMMMLM

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

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


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