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Understanding Particle Generation and the Risk of Occupational Exposure and Environmental Release of Nanoparticles During Processing of Nanocomposite Materials


EMSL Project ID
21798

Abstract

Understanding the potential impacts of nanotechnology on human health and the environment requires an understanding of the potential for release and exposure of potentially toxic nanomaterials during manufacturing operations. Typical manufacturing steps for nanocomposite materials (materials consisting of a nanoparticle or nanotube in a bulk, typically polymer, matrix) include cutting, sanding, drilling and related activities. Normal performance of each of these activities generates particles, and may liberate components of a composite material. However, when these activities are performed on nanocomposite materials, there is a chance the nanomaterial will be liberated as described below, thereby creating the potential for occupational exposure or environmental release of waste containing free nanoparticles or nanotubes. No studies have been performed to date on nanocomposite materials; this study is the first to focus on the potential to generate free nanoparticles during sanding of a surface of a structural nanocomposite material.

The function of multi-walled nanotubes (MWNTs) in a nanocomposite material is to provide additional toughness and resistance to crack propagation. When incorporated into a polymer matrix, there is evidence that carbon nanotubes enhance materials strength by, e.g., bridging cracks. The failure mode for both MWNT and SWNT is a combination of pullout and nanotube fracture. In some cases, the strength of adhesion between the polymer and the NT surface determines the relative amount of fracture and pullout. The implication of this work is that, for some MWNT composite materials with very good adhesion, there is the possibility that the outer graphene sheets of a MWNT may delaminate during the pullout phase, leading to free nanotubes. Furthermore, subsequent fracture of the MWNT may lead to creation of unbound MWNT fragments that may then be aerosolized by the grinding process, generating the potential for worker exposure and environmental release.

This initial study will be undertaken to determine the number, concentration, size distribution, morphology and chemistry of particles generated by a typical process on a polymer nanocomposite. In particular, a sanding operation is to be performed upon MWNT-epoxy resin composite panels consisting of a standard carbon-carbon composite with a top layer containing 1% by weight MWNT's (50-70 nm diameter) dispersed into the resin phase of the binder. The MWNTs are surface modified to ensure good adhesion within the binder, and the MWNT have been treated to ensure good dispersal.

The grinding experiments will be carried out in a glove box customized to support simultaneous real-time monitoring of particle size distribution, number and concentration (using both an optical particle counter and a condensation particle counter) and collection of filter samples for ex situ characterization. Particle size, morphology and degree of aggregation will be evaluated using both scanning and transmission electron microscopy. Raman spectroscopy and near Infrared (NIR) fluoresence will be used to determine particle chemistry. The experimental design provided for 2-3 replicates of panels with and without MWNT, as well as background samples collected in the absence of processing, using two sanding grit sizes.

Project Details

Project type
Exploratory Research
Start Date
2006-09-08
End Date
2007-09-10
Status
Closed

Team

Principal Investigator

Daniel Gaspar
Institution
Pacific Northwest National Laboratory

Team Members

Amit Gupta
Institution
Battelle Columbus

Timothy Johnson
Institution
Pacific Northwest National Laboratory

Zheming Wang
Institution
Pacific Northwest National Laboratory