Characterization of Nanosilica Release from a Weathered Nanosilica/Polyurethane Coating

H-C Hsueh, C-Y Lu, S-R Huang, Y-L Cheng, D. Jacobs, S.A. Rabb, L.L. Yu, T. Nguyen, L. Sung
National Institute of Standards and Technology,
United States

Keywords: nanoparticle release, nanocoating, degradation, UV radiation, ICP-OES, LSCM


Polymer nanocoatings are widely used outdoor environment because the excellent properties. The addition of nanoparticles can improve performance properties including mechanical, electrical, chemical and ultraviolet resistance. However, because polymer in coating are susceptible to degradation by weathering elements, nanoparticles in nanocoatings may be release to the surface into the environment during the life cycle, which potentially poses an environmental health and safety issue. This study investigated the protocols and mechanism to quantify the release of nanosilica form polyurethane (PU) nanocoating after UV exposure. Specimens of a commercial PU coating having 5 % mass nanosilica were exposed in a well-controlled high-intensity UV environment at National Institute of Standards and Technology (NIST). To characterize the nanosilica on the nanocoating surface at different exposure times, an Atomic Force Microscopy (AFM) and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDXS) were used. To induce particle release from coatings, two release methods/protocols were conducted on the UV exposed specimens. (1) Simulated rain test method: Particles from the surface of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using inductively coupled plasma-optical emission spectroscopy (ICP-OES) to determine the amount of silicon released from the nanocoatings. (2) Mechanical abrasion via a rotary abrader test method: a novel, rapid, and non-destructive laser scanning confocal microscopy (LSCM) method was used for quantifying the number and size distribution of surface-bound particles on the abraded surface. And ICP-OES was used to analyze the release silicon from collected from abraded surface and abrasion wheels. Results from two released methods will be compared. Preliminary results show the amount of nanosilica release increased with UV dose. These quantitative data will be used to develop a model to predict the long-term release of nanosilica from polyurethane nanocoatings that are used outdoors. References: 1. Wohlleben W, Vilar G, Fernandez-Rosas E, Gonzalez-Galvez D, Gabriel C, Hirth S, Frechen T, Stanley D, Gorham J, Sung L, Hsueh H-C, Chuang Y-F, Nguyen T, and Vazquez-Campos S, “A pilot interlaboratory comparison of protocols that simulate aging of nanocomposites and detect released fragments,” Environ. Chem. 11 (4) 402-418, (2014) 2. Jacobs, D, Huang, SR, Cheng, YL, Rabb, S, Gorham, JM, Krommenhoek, PJ, Yu, LL, Nguyen, T, Sung, L, “Investigating the Process of Surface Degradation and Nanoparticle Release of a Commercial Nanosilica / Polyurethane Coating Under UV Exposure,” J. Coat. Technol. Res.,13(5) 735-751 (2016) 3. Wohlleben, W, Neubauer, N, ‘‘Quantitative Rates of Release from Weathered Nanocomposites are Determined Across 5Orders of Magnitude by the Matrix, Modulated by the Embedded Nanomaterial.’’ NanoImpact, 1 39–45 (2016) 4. H-C Hsueh, D. S. Jacobs, J M. Gorham, S A. Rabb, L L. Yu, C-C Tien, T. Nguyen and L. Sung, “Kinetics of Photodegradation and Nanoparticle Surface Accumulation of a Nanosilica/Epoxy Coating Exposed to UV Light,” J. Coat. Technol. Res., DOI 10.1007/s11998-016-9911-4 (2017)