Tangled Multi-Walled Carbon Nanotubes

Nanomaterial dustiness

Administrative data

Endpoint:

nanomaterial dustiness

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2017

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

EN 15051 (Workplace atmospheres - Measurement of the dustiness of bulk materials - Requirements and reference test methods)

GLP compliance:

not specified

Type of method:

vortex shaker

Details on methods and data evaluation:

The test procedure is based on the use of:
- a respirable cyclone for gravimetric sampling,
- a CPC as reference instrument for number concentration measurement,
- the MPS for collection of particles for EM observations/analysis,
- the ELPI for size-resolved aerosol measurement.

The central component of the experimental set-up consists of a specially designed stainless steel cylindrical tube (inner diameter of 31 mm, volume of 102 cm3) with a conical bottom that is continuously shaken in a circular orbital motion (displacement amplitude: 4 mm; angular frequency: 30 Hz), into which a small volume (0.5 cm3) of the test sample is placed.

HEPA-filtered air is passed through the cylindrical tube at a flow-rate ¿¿¿¿¿¿ of 8.4 l/min in order to transfer the emitted aerosol inside the tube to the sampling and measurement section. The aerosol emitted during the vibration is drawn from the outlet tube to the real-time instruments and sampling devices through an initial flow splitter, which divides the aerosol flow into two flows directed toward two identical respirable cyclones (GK2.69, SKC) operating at Qc = 4.2 l/min. One of these respirable cyclones is equipped with a cassette containing a pre-weighed filter for gravimetric analysis. The sampled particle mass is then used to determine the respirable mass dustiness index. The second respirable cyclone acts as a particle selector for the real-time instruments and the TEM grid sampler positioned downstream. Due to the short sampling time (~10 s), the TEM grid sampler requires a bypass system (equipped with a 25-mm filter cassette) in order to maintain a constant flow through the respirable selector. To prevent exposure of the operator during tests as well as during the disassembly and cleaning sequences between each test, the entire test bench is housed within an approved ventilated enclosure that has been specially designed for the safe handling of powders (LEV systems, Safetech).

Because (i) the entire range of particle sizes corresponding to the respirable size fraction should be assessed for the risk of exposure by inhalation [12], (ii) a single, rather than two, size-resolved instrument is preferred, and (iii) the size-resolved instrument should have a high time resolution (~1 s), the Electrical Low Pressure Impactor (ELPI™, Dekati Ltd) was selected for the size-resolved instrument. As a reference instrument for counting particles, a condensation particle counter (CPC Model 3007, TSI Inc.) was used.

To collect airborne particles for subsequent observation and analysis by electron microscopy, a specific TEM grid sampler (MPS, Ecomesure) equipped with Holey Carbon Film on 400 Mesh In compliance with the requirements of EN15051-1 [5], the air in the experimental set-up was controlled for humidity (RH = 50.9 ± 0.6 %) and monitored for temperature (22.1 ± 0.3 °C) for the duration of the experiments.
Copper Grids (S147-A, Agar Scientific) was used. The electron microscopy observations were conducted at the Laboratoire Amiante Fibres Particules (LAFP) with a transmission electron microscope (120 kV JEM-1400, Jeol) equipped with a CCD camera (ES500 Erlangshen ES500, Gatan Inc.). The JEM-1400 is also equipped with an EDS microanalysis system (Oxford Instruments). Prior to each observation, a size calibration at the magnification used for EM observation of the samples was performed with certified polystyrene latex spheres of 0.88 µm diameter. The collected particles was not counted and sized in this study as our intention was only to characterize the samples from a qualitative and global point of view.

Carbon impregnated conductive flexible tubing was used to connect the different parts of the set-up as well as the instruments.

In compliance with the requirements of EN15051-1, the air in the experimental set-up was controlled for humidity (RH = 50.9 ± 0.6 %) and monitored for temperature (22.1 ± 0.3°C) for the duration of the experiments.

The test samples were weighed with a XP205 analytical balance (10 µg readability, Mettler Toledo), and the 37-mm filters used for the respirable cyclone were weighed with a MX5
microbalance (1 µg readability, Mettler Toledo). The filters used in this study are PVC membrane filters with a pore size of 5 µm (GLA 5000, SKC Inc.). This type of filter was chosen because of its low tare weight and low moisture pickup for gravimetric stability.

The test samples were prepared by pouring 0.5 cm3 of powder into an Eppendorf microtube. After filling, the tubes were weighed to the nearest 10 µg. The samples were then conditioned for at least 24 h prior to the dustiness test in a laboratory-made humidity-controlled chamber at 50 ± 2 % RH.

After cleaning the entire test bench, and/or, if necessary, changing the tubing and connections, and having equipped the cyclone with a pre-weighed filter for gravimetric analysis, the airflows were checked using a flow calibrator. The cleanliness of the air through the test bench was then assessed from CPC measurements. The by-pass line was then opened and the main line closed in order to fill the pre-conditioned 0.5 cm3 test sample into the cylindrical tube. The mass of the test sample Mo was obtained from the difference between the mass of the filled microtube and mass of the microtube after emptying.

In parallel, the real-time instruments started recording the background level, over about 180 s. Finally, at the same time, the incoming air flow was switched on in the main line and the agitation was turned on. The test sequence comprised 60 s of agitation, with the measurement continuing for another 540 s, thus giving a total of 600 s for the sampling (respirable cyclone) and real-time measurement (CPC and ELPI). Sampling with the MPS was carried out for around 10 s after the peak in concentration.

After each test, the respirable sampling filter was gently removed from the cassette and gravimetric analysis was then performed according to the laboratory protocol in order to obtain the mass delta mf of the collected particles. This mass was used to determine the mass-based dustiness index.

Real-time instrument data files from the CPC and the ELPI¿ were saved and the data were subsequently analysed using specific calculation tools developed in the laboratory in order to determine the number-based dustiness index, emission rate and size distribution.
During cleaning of the test bench and measurement instruments, the operator wore a powered respirator, protective gloves with sleeves and a cotton laboratory coat.

Sampling:

Powder Sample Amount : 0.5 cm3

Test material

Test material information

Constituent 1

Reference substance name:

GRAPHISTRENGTH C100

IUPAC Name:

GRAPHISTRENGTH C100

Constituent 2

Reference substance name:

Tangled Multi-Walled Carbon Nanotubes

EC Number:

701-160-0

Cas Number:

7782-42-5

Molecular formula:

Hollow tubular carbon, 1-dimensional nano structures with hexagonal arrangement of carbon atoms

IUPAC Name:

Tangled Multi-Walled Carbon Nanotubes

Test material form:

solid: nanoform

Data gathering

Instruments:

Transmission electron microscope (120 kV JEM-1400, Jeol) equipped with a CCD camera (ES500 Erlangshen ES500, Gatan Inc.). The JEM-1400 is also equipped with an EDS microanalysis system (Oxford Instruments).

Results and discussion

Dustiness index

Dustiness index 1

Key result

Mean:

ca. 1 700 mg/kg

St. dev.:

160 mg/kg

Remarks on result:

other:

Remarks:

Respirable mass dustiness index

Dustiness index 2

Key result

Mean:

ca. 40 000 other: 1/mg

St. dev.:

1 304 other: 1/mg

Remarks on result:

other:

Remarks:

Respirable number dustiness index

Any other information on results incl. tables

The respirable fraction of TMWCNT is about 1700 mg/kg.

This value applies specifically to the tested sample and is diffrent from the one gererated by the NANOGENOTOX program in the same test item (also summarised by the JRC: "JRC - Multi-walled Carbon Nanotubes, NM-400, NM-401, NM-402, NM-403: Characterisation and physico-Chemical Properties, 2014") due to differences in protocols.

Applicant's summary and conclusion

Conclusions:

The respirable fraction of TMWCNT is about 1700 mg/kg.
This value applies specifically to the tested sample and is diffrent from the one gererated by the NANOGENOTOX program in the same test item (also summarised by the JRC: "JRC - Multi-walled Carbon Nanotubes, NM-400, NM-401, NM-402, NM-403: Characterisation and physico-Chemical Properties, 2014") due to differences in protocols.