Assessing Potential Nanoparticle Release During Nanocomposite Shredding Using Direct-Reading Instruments

Abstract

This study was conducted to determine if engineered nanoparticles are released into the air when nanocomposite parts are shredded for recycling. Test plaques made from polypropylene resin reinforced with either montmorillonite nanoclay or talc and from the same resin with no reinforcing material were shredded by a granulator inside a test apparatus. As the plaques were shredded, an ultrafine condensation particle counter; a diffusion charger; a photometer; an electrical mobility analyzer; and an optical particle counter measured number, lung-deposited surface area, and mass concentrations and size distributions by number in real-time. Overall, the particle levels produced were both stable and lower than found in some occupational environments. Although the lowest particle concentrations were observed when the talc-filled plaques were shredded, fewer nanoparticles were generated from the nanocomposite plaques than when the plain resin plaques were shredded. For example, the average particle number concentrations measured using the ultrafine condensation particle counter were 1300 particles/cm³ for the talc-reinforced resin, 4280 particles/cm³ for the nanoclay-reinforced resin, and 12,600 particles/cm³ for the plain resin. Similarly, the average alveolar-deposited particle surface area concentrations measured using the diffusion charger were 4.0 μm²/cm³ for the talc-reinforced resin, 8.5 μm²/cm³ for the nanoclay-reinforced resin, and 26 μm²/cm³ for the plain resin. For all three materials, count median diameters were near 10 nm during tests, which is smaller than should be found from the reinforcing materials. These findings suggest that recycling of nanoclay-reinforced plastics does not have a strong potential to generate more airborne nanoparticles than recycling of conventional plastics.

Keywords:

• nanoparticle
• nanocomposite
• recycling
• shredding

ACKNOWLEDGMENTS

The authors would like to thank the United States Council for Automotive Research (USCAR) for its financial support of this research. We appreciate the assistance of Noble Polymers in providing polymer test plaques for this project at minimal cost. We thank TSI Inc. and especially Greg Olson and Tim Johnson from TSI for providing training on the direct-reading aerosol instruments and for allowing the research team to borrow the Fast Mobility Particle Sizer used in the study. We also thank Will Rodgers and Candace Wheeler of General Motors for helpful discussions.