Twin-screw extrusion is the preferred process to commercially produce nanocomposites by compounding the nanoparticles and polymer melts. Polymer nanocomposites, which contain nanoparticles dispersed in a polymer matrix, provide improved properties at low filler loadings. Nano alumina particles recently have been used as fillers to polymer matrix that contributed to enhanced physical properties of nanocomposites. Recently, concerns had been expressed that airborne nanoparticles particularly of nano alumina released during compounding might present serious contamination of the air in the workplace. Researchers with experience in environmental health and polymer manufacturing monitored the compounding process for a model nano alumina-containing nanocomposite using a TSI Fast Mobility Particle Spectrometer (FMPS). FMPS measurements were taken at background locations, source locations, and operators’ breathing zones; in parallel to the FMPS real-time measurement, airborne nanoparticles were collected using polycarbonate filters fitted with filmed grids driven by a personal air sampling pump. Filter samples were analyzed for particle morphology and elemental composition. It was found that the nanoparticle number concentration was elevated during processing. The released nanoparticles are a complex mixture of the individual nano alumina particles, agglomerates of those particles, polymer fume particles, and perhaps others.
Airborne nanoparticles; Nanoalumina, Nanocomposite compounding, Nanoparticle mobility size, Twin screw extruder (TSE).
second inorganic or organic phase; traditionally, micrometer-sized particles have been used as the filler. In polymer nanocomposites, these fillers have at least one dimension less than 100 nm (Kojima et al., 1993). These fillers include alumina, carbon black, silica, talc, calcium carbonate, layered Polymers are often reinforced using silicates (nano clays), and recently, silver and engineered nanoparticles such as carbon nanotubes. Although the nanometer-sized particles allow low filler loadings (< 10%w) in nanocomposites with retention of flexibility and impact properties, the resulting nano compound’s properties are highly dependent on dispersion of the primary filler particles through the polymer matrix. With good dispersion, each particle is wetted completely by the melted polymer, creating a very high interfacial surface area that can improve the properties of the polymer (McCarrie and Winter, 2003).
Since commercial compounding (mixing) of nanocomposites is typically achieved by feeding the nanoparticles and polymer into a twin-screw extruder, the airborne particles associated with nanoparticle reinforcing agents are of particular concern, as they can readily enter the body through inhalation. Recent research has suggested that nanometer-sized particles of many materials, including nano alumina, display greater toxicity than for larger particles, and aggregated nanoparticles can be disaggregated in the lung after inhalation (Ferin et al., 1991; Wolff et al., 1988; Zhang et al., 2000; Renwick et al., 2004; Warheit, 2004). In addition, Maynard et al. (2005) concluded that aerosol control methods have not been well-characterized for nanometer-sized particles, although theory and limited experimental data indicate that conventional ventilation, filtration, and other engineering control approaches should be applicable in many situations.
Consequently, researchers with experience in occupational and environmental health and melt compounding of polymer nanocomposites investigated the magnitude of exposures to airborne nanoparticles associated with the commercial compounding of nanocomposites. A series of twin-screw extrusion trials presented in this study were monitored during fall 2006 and spring 2007. Three sets of data monitored under similar conditions were selected for presentation here. The filler used for this compounding process was nano alumina particles; other fillers were not used for this study. We studied the characteristics of nanoparticle release, agglomeration, and transport in the compounding workplace.
CONCLUSIONS AND RECOMMENDATIONS
This study demonstrates conclusively that the compounding of polymers and nano alumina in a TSE can release large quantities of nanoparticles into the air. Large quantities of nanoparticles were released during the extruder heating phase while feeding polymer pellets only, and feeding the nano alumina/polymer mixture. Nanoparticles released in the heating and polymer feed phases are likely to be polymer fume. When the nano alumina particles were used instead of micrometer-size particles as fillers, the nanoparticles released during nano compounding are a complex mixture of the individual nano alumina particles, agglomerates of those particles, polymer fume particles, and perhaps others. Elevated nanoparticle levels were measured at the source, the room background, and the operators’ breathing zone.
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FULL Paper PDF file:Airborne Nanoparticle Release Associated with the Compounding of Nanocomposites using Nanoalumina as Fillers
Su-Jung (Candace) Tsai*
Joey L. Mead
Carol F. Barry
Michael J. Ellenbecker
Airborne Nanoparticle Release Associated with the Compounding of Nanocomposites using Nanoalumina as Fillers
Chemistry Aerosol and Air Quality Research Corpus ID: 67756963
PDF reference and original file: Click here
Professor Siavosh Kaviani was born in 1961 in Tehran. He had a professorship. He holds a Ph.D. in Software Engineering from the QL University of Software Development Methodology and an honorary Ph.D. from the University of Chelsea.