Release of Nanomaterials During Weathering of Polymer Nanocomposites

D.H. Fairbrother, R. Lakone, J.J. Wang, A. Barber, R.B. Reed, J.F. Ranville
Johns Hopkins University,
United States

Keywords: polymer nanocomposites, nanomaterials, EHS

Summary:

Most engineered nanomaterials will enter the environment within manufactured nanoproducts, such as polymer nanocomposites. Release is the necessary precursor to exposure and therefore the quantification of nanoparticle release rates from nanocomposites is important not only from a life cycle perspective, but also for risk assessment. However, information on nanoparticle release is only just starting to emerge; in my presentation I will discuss two separate approaches to measuring nanoparticle release. The first part of my presentation will focus on the results from model studies in which nancomposites, produced in the lab, composed of carbon nanotubes (CNTs) embedded in polymers (e.g. chitosan, polystyrene) were subjected to accelerated weathering by exposure to UV irradiation in aqueous environments. The supernatants generated during these studies were sampled for single particle-inductively coupled plasma mass spectrometry (spICPMS) analysis and the concentration of CNTs released was measured by the detection of their embedded residual metal catalysts. The presence of CNTs was found to significantly retard the rate of polymer photodegradation and lead to the steady accumulation of a dense CNT mesh at the surface. During the initial stages of photodegradation, as this protective mesh is forming at the surface, sp-ICPMS data suggests that CNTs are being released from the nanocomposite, but at much lower concentrations than would have been predicted on the basis of the polymer mass loss. To complement these studies, additional control experiments were also performed to ensure that the metals remain attached to the CNT during the release process. These results highlight both the progress and significant experimental challenges that still remain in quantifying exposure to engineered nanomaterials from manufactured products. The second part of my presentation will center on the design and preliminary results obtained from outdoor weathering studies currently running in multiple geographically and climatically distinct locations across the United States. While the primary goal is to measure nanoparticle release from nanocomposites, the overall experimental design emphasizes flexibility: with the ability to measure nanoparticle release rates, characterize changes in nanocomposite composition and morphology, as well as provide a means to assess any resulting toxicity and changes in efficacy due to weathering. At each location, site specific weather data is continuously collected, allowing for correlation of nanocomposite weathering with climatic variations.