Testing of Nanoparticle Release from a Composite Containing Nanomaterial Using a Chamber System

Summary

Nanoparticle release is tested using a chamber system that includes a condensation particle counter, an optical particle counter and sampling ports to collect filter samples for microscopy analysis. The proposed chamber system can be effectively used for nanomaterial release testing with a repeatable and consistent data range.

Abstract

With the rapid development of nanotechnology as one of the most important technologies in the 21^st century, interest in the safety of consumer products containing nanomaterials is also increasing. Evaluating the nanomaterial release from products containing nanomaterials is a crucial step in assessing the safety of these products, and has resulted in several international efforts to develop consistent and reliable technologies for standardizing the evaluation of nanomaterial release. In this study, the release of nanomaterials from products containing nanomaterials is evaluated using a chamber system that includes a condensation particle counter, optical particle counter, and sampling ports to collect filter samples for electron microscopy analysis. The proposed chamber system is tested using an abrasor and disc-type nanocomposite material specimens to determine whether the nanomaterial release is repeatable and consistent within an acceptable range. The test results indicate that the total number of particles in each test is within 20% from the average after several trials. The release trends are similar and they show very good repeatability. Therefore, the proposed chamber system can be effectively used for nanomaterial release testing of products containing nanomaterials.

Introduction

Nanomaterial exposure has mostly been studied in relation to workers in workplaces manufacturing, handling, fabricating, and packaging nanomaterials, while consumer exposure has not been studied extensively. A recent analysis of the environmental and health literature database created by the International Council of Nanotechnology (ICON) also indicated that most nanomaterial safety research has focused on hazards (83%) and potential exposure (16%), with the release from nanocomposites, representing consumer exposure, only representing 0.8% ¹. Thus, very little is known about consumer exposure to nanomaterials.

Nanoparticle release has been used to estimate consumer exposure in simulation studies, including the abrasion and weathering of nanocomposites, washing textiles, or dustiness testing methods, such as the rotating drum method, vortex shaking method, and other shaker methods ^2-3. Plus, several international attempts, such as the ILSI (International Life Science Institute) nanorelease and EU NanoReg, have been made to develop technology to understand the release of nanomaterials used in consumer products. The ILSI nanorelease consumer product launched in 2011 represents a life-cycle approach to nanomaterial release from consumer products, where phase 1 involves nanomaterial selection, phase 2 covers evaluation methods, and phase 3 implements interlaboratory studies. Several monographs and publications on the safety of nanomaterials in consumer products have also been published ^4-6.

Meanwhile, NanoReg represents a common European approach to the regulatory testing of manufactured nanomaterials and provides a program of methods for use in simulation approaches to nanorelease from consumer products 2. ISO TC 229 is also trying to develop standards relevant to consumer safety and submit a new working item proposal for consumer safety. The OECD WPMN (working party on nanomaterials), especially SG8 (steering group on exposure assessment and exposure mitigation), recently conducted a survey on the direction of future work, especially consumer and environmental exposure assessment. Therefore, in light of these international activities, the Korean Ministries of Trade, Industry and Energy launched a tiered project in 2013 focused on the "Development of technologies for the safety evaluation and standardization of nanomaterials and nanoproducts". Plus, several consumer safety-relevant studies to standardize nanomaterial release from consumer products have also been published ^7-8.

An abrasion test is one of the simulation approaches included in the ILSI nanorelease and NanoReg ^2-3 for determining the potential emission level of nanoparticles from different commercial composite products. The mass weight loss is deduced based on the difference in the specimen weight before and after abrasion using an abrasor. The nanocomposite sample is abraded at a constant speed, a sampler sucks up the aerosol, and the particles are then analyzed using particle counting devices, such as a Condensation Particle Counter (CPC) or optical particle counter (OPC), and collected on a TEM (transmission electron microscopy) grid or membrane for further visual analysis. However, conducting an abrasion test for nanocomposite materials requires a consistent nanoparticle release, which is difficult due to particle charging as a result of abrasion and when the particle sampling is conducted near the emission point ^{2-3, 9-11}.

Accordingly, this paper presents a chamber system as a new method for evaluating nanomaterial release in the case of abrasion of nanocomposite materials. When compared with other abrasion and simulation tests, the proposed chamber system provides consistent nanoparticle release data in the case of abrasion. Moreover, this new test method has been used widely in the field of indoor air quality and semi-conduct industry as total particle number counting method ^{12, 13}. Therefore, it is anticipated that the proposed method can be developed into a standardized method for testing nanoparticle release from consumer products containing nanomaterials.

Protocol

1. Preparation of Instruments and Specimens

1. Abrasor
   1. Based on an abrasion tester, use an abrasor with one specimen rotation stage (140 mm diameter), two abrasion wheel holders, and a rotation speed of 30 - 80 rpm.
   2. Use a weight to secure the abrasion wheel to the abrasion wheel holder, which also applies load to the test specimen.
   3. Install an additional air inlet to provide better suspension for the abrased particles, as shown in Figure 3. Use a 1/8"-diameter tube located 15 mm above and 40 mm away from the center of the test specimen.
2. Abrasion wheel
   1. Wrap the abrasion wheel (55 mm diameter, 13 mm thick) with sand paper (100 grit and brand new).
3. Specimen
   1. Specimen is a composite containing nanomaterial for abrasion test. To installed at abrasor, the specimen should be prepared with 140 mm diameter.
4. Chamber
   1. Use stainless steel for the chamber walls to avoid particle deposition due to electrostatic force. Place the abrasor inside the chamber (volume 1 m³) (Table 1), and locate the air inlet and outlet in the upper and lower part of the chamber, respectively. Use a mixer, consisting of three perforated plates, at the air outlet to achieve a uniformly mixed particle flow.
5. Neutralizer
   1. As electro-statically charged particles enhance particle deposition on the chamber walls, use a neutralizer (soft X-ray ionizer) to minimize the charged state of the particles.
6. Online measuring instruments ^{12, 13}
   1. Use a CPC and OPC to measure the particle number concentration and particle size distribution as per manufacturer's instructions.
   2. Install the CPC and OPC at the outlet of the chamber to measure the particle number concentration and particle size distribution.
7. Particle sampling instruments
   1. Sample the released particles using a particle sampler containing filter media or a TEM grid to analyze the particle morphology and components.
   2. Install the particle sampler containing filter media or a TEM grid at the outlet of the chamber to analyze the morphology of the release particles.

2. Abrasion Test for Nanoparticle Release Using Chamber System

NOTE: The abrasion test conditions are described in Table 2.

1. Locate the abrasor in the center of the chamber.
2. Install the test specimen on the specimen rotation stage of the abrasor.
3. Secure the abrasion wheels in the abrasion wheel holders with a 1,000 g weight to apply load to the test specimen.
4. Locate the neutralizer (soft X-ray ionizer) 28 cm away from the center of the test specimen at a 45° angle, as seen in Figure 2, to reduce the electro-static particle deposition on the chamber walls.
   NOTE: The neutralizer removes the electrostatic force by beam exposure. However, since the air inlet and abrasion wheels are located above the specimen rotation stage, this restricts the access of the neutralizer beam to the surface of the test specimen. Therefore, the neutralizer is located diagonally to allow the beam to reach as much of the specimen surface as possible.
5. Operate the blower installed at the outlet of the chamber at a 50 L/min flow rate.
6. Supply 25 L/min additional particle-free suspension air using an air compressor through the additional air inlet.
   NOTE: The particles, which are generated by abrasion, were deposited on surface of the specimen and abrasion wheels, strongly. Therefore, it is hard to measure the abrased particles. The additional air inlet can help to solve this problem to particle suspension.
7. Check the background particle number concentration inside the chamber to reach an average particle number concentration for 1 h of below 1 #/cc using CPC, as described in Figure 4.
8. Operate the specimen rotation stage of the abrasor using a step motor that rotates the specimen rotation stage at 72 rpm with 1,000 rotations.
9. Measure and record the released particle number concentration and particle size distribution using the CPC and OPC.
   NOTE: The particles released from the nanocomposites are suspended and carried by the air that is being pumped. These suspended particles are eventually transported to the outlet following the airstream. The released particles are then detected by the CPC and OPC at the outlet of the chamber. A CPC and OPC are most frequently used for measuring the particle number concentration, while an OPC can also measure the particle size distribution.
10. Sample the released particles using a particle sampler containing filter media or a TEM grid.
    NOTE: The particles released from nanocomposites by abrasion move to the outlet of the chamber following the airstream. At the outlet of the chamber, the released particles can be sampled using a particle sampler. The released particles collected on filter media or a TEM grid can then be analyzed using TEM or SEM (scanning electron microscopy).
11. Stop the measurement and sampling when the particle number concentration reaches below 0.1% of the peak particle number concentration.
12. Save the all data (CPC, OPC) and remove all the samples (test specimens).
13. Use a new specimen and new abrasion wheels for each test, and wash the chamber and abrasor with kimwipes and IPA (iso-propyl alcohol) after each abrasion test to confirm repeatability.

Results

Abrasion Test Repeatability Using Chamber System

The total particle numbers were consistent for 8 abrasion tests, as shown in Table 3. The CPC measured an average of 3.67 x10⁹ particles, while the OPC counted an average of 1.98 x 10⁹ particles (> 0.3 µm). The deviations were within 20%, which represented a consistent release of particles during abrasion.

Discussion

The most critical steps when conducting the nanorelease test from nanocomposite materials using an abrasion test were: 1) using a chamber system made of stainless steel with a neutralizer to remove the electrostatic charge generated by abrasion and reduce the deposition of particles on the chamber walls; 2) supplying additional air to provide better particle suspension; and 3) sampling the released particles and online monitoring using a CPC and OPC from the outlet that contained a mixer consisting of three perforated pl...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Foamex	Taeyoung, R. of Korea
MWCNT (multiwalled carbon nanotube) composite	Hanwha, Incheon, R. of Korea		2% MWCNTs in low density polyethylene
Abrasion Paper	Derfos, R. of Korea	#100	100 grit sand paper
Condensation Particle Counter (CPC)	TSI Inc, Shoreview, MN	UCPC 3775
Optical Paritcle Counter (OPC)	Grimm, Ainring, Germany	1.109
Mini Particle Sampler	Ecomesure, Saclay, France
Quantifoil Holey Carbon Film	TED PELLA Inc. USA	1.2/1.3
Filter Holder			custom made
Polycarbonate Filter	Millipore, USA	CAT No. GTTP02500
Soft X-ray Ionizer (Neutralizer)	SUNJE, R. of Korea	SXN-05U
Field Emission-Scanning Electron Microscope (FE-SEM)	Hitachi	S-4300