Overview: This research proposal describes plans to study the release of nano-TiO2 and CNTs from polymer nanocomposites using highly sensitive quantitative analytical techniques. Most nanoparticles (NPs) will enter the environment initially as components of solid phase materials (i.e., nanoproducts). One of the most important types of nanoproducts are polymer nanocomposites that incorporate NPs such as carbon nanotubes (CNTs), nano-silver, or nano-scale metal oxides due to their ability to enhance polymer properties such as conductivity and load bearing capabilities. Indeed, polymer nanocomposites are already present in consumer products such as bicycles, anti-static parts for fuel lines, and packaging materials used in the electronic and food industries. Motivation for studying NP release from polymer nanocomposites is derived from two overriding considerations: (i) the paucity of information on the release of NPs from nanoproducts, despite the crucial role that NP release will play in determining the risk posed by NPs in the environment; and (ii) our initial results which indicate that NPs can indeed be released from polymer nanocomposites, and that NP release can be detected with single particle inductively coupled plasma mass spectrometry (spICPMS).
Intellectual Merit: The proposed research will transform our understanding of NP release from nanoproducts by identifying the factors that control the extent, nature, and rate of NP release. This will be accomplished by preparing and characterizing polymer nanocomposites containing nano-TiO2 or CNTs, where the identity of the matrix as well as the surface chemistry and NP loading will be varied. These well-defined composites will then be subjected to potential NP release scenarios and "accelerated aging" conditions that include photolysis, mechanical stress, thermal cycling and exposure to harsh oxidants. The concentration and nature of NPs released from the nanocomposites will then be evaluated. A major obstacle in conducting NP release studies is the need to measure extremely low (e.g. ng/L) concentrations of NPs. To overcome this obstacle, we will use spICPMS and field-flow fractionation (FFF-ICPMS) to determine particle size distributions and ng/L concentrations of nano-TiO2. Although detecting CNTs in spICPMS by measuring the carbon signal is ambiguous, the PIs have shown that embedded metal NPs can serve as proxies for CNTs. This approach allowed us to use spICPMS to detect CNT released from polymer nanocomposites. A key component of the work is to further improve spICPMS methodology for quantitative analysis of CNTs and to combine spICPMS and FFF-ICPMS to identify the physical form of released NPs.
Broader Impacts: By integrating state-of-the-art detection capabilities into an experimental plan where well-defined polymer composites are exposed to potential release scenarios, we will be able to evaluate the effects of both nanocomposite composition and variable environmental conditions on the extent and rate of NP release. These data will enable us to identify release mechanisms as well as the polymer nanocomposite characteristics and the exposure conditions where NP release is most (and least) likely to occur. This new information will improve not only the accuracy of risk assessment and life cycle analysis models, but also inform the design of future nanoproducts that retain commercial value without contributing to adverse environmental health and safety effects. Analytical methods and experimental protocols developed will also provide a platform for researchers to examine NP release from other nanoproducts. Students who participate in this inherently interdisciplinary research project will acquire a unique skill set that incorporates elements of environmental science and engineering, materials chemistry, and analytical science, providing them with many career opportunities. Project results will be disseminated through presentations at national scientific meetings and local colleges as well as publications in peer-reviewed journals. The scientific impact of this project will be further enhanced by continuing to teach short courses on spICPMS applications at international meetings. The educational outreach will build on and expand our previous activities of involving undergraduates from 4-year colleges in research and in bringing in high school teachers for summer research programs. This project will also be used as a vehicle to incorporate concepts of nanoproduct use and impact into existing K-12 educational modules that we have developed and which have been used successfully in several Colorado high schools.
