Release and transformation of ZnO nanoparticles used in outdoor surface coatings for UV protection

Abstract

A major area of growth for "nano-enabled" products has been the addition of nanoparticles (NPs) to surface coatings including paints, stains and sealants. Zinc oxide (ZnO) NPs, long used in sunscreens and sunblocks, have found growing use in surface coating formulations to increase their UV resistance, especially on outdoor products. In this work, ZnO NPs, marketed as an additive to paints and stains, were dispersed in Milli-Q water and a commercial deck stain. Resulting solutions were applied to either Micronized-Copper Azole (MCA) pressure treated lumber or a commercially available composite decking. A portion of coated surfaces were placed outdoors to undergo environmental weathering, while the remaining samples were stored indoors to function as experimental controls. Weathered and control treatments were subsequently sampled periodically for 6 months using a simulated dermal contact method developed by the Consumer Product Safety Commission (CPSC). The release of ZnO NPs, and their associated degradation products, was determined through sequential filtration, atomic spectroscopy, X-Ray Absorption Fine Structure Spectroscopy, and electron microscopy. Across all treatments, the percentage of applied zinc released through simulated dermal contact did not exceed 4%, although transformation and release of zinc highly dependent up dispersion medium. For MCA samples weathered outdoors, water-based applications released significantly more zinc than stain-based, 180 +/− 28, and 65 +/− 9 mg/m 2 respectively. Moreover, results indicate that the number of contact events drives material release.

LONG-TERM field study of a Waterborne paint with a nano-additive for biodeterioration control

“…The UV-shielding ZnO NPs property results promising in coating technology. These NPs could spread their activity to the protective system, increasing the resin resistance to photo-chalking and fungal growth [23,24]. This would be consistent with the efforts to extend the service life of outdoor paints.…”

“…It is known that the UV-shielding effect of ZnO particles is attributed to the absorption in the UV spectrum but, at the same time, this allows that the electrons from the forbidden band can jump into the conduction band resulting in the generation of electron-hole pairs [24]. These positive holes and negative electrons can react with water, oxygen molecules or hydroxyl groups on the surface of the particles leading to the formation of free radicals that might degrade the binder polymer [39].…”

Single- and Multi-Element Quantification and Characterization of TiO2 Nanoparticles Released From Outdoor Stains and Paints

“…The near absence of measured environmental concentrations of TiO 2 (or any other) NPs greatly complicates their risk assessment. Indeed, most laboratory and in situ studies on NP release from coatings have been limited to a qualitative or semi-quantitative demonstration of release (e.g., with microscopy) or quantitative measurements based on the total metal content (Kägi et al, 2008;Olabarrieta et al, 2012;Al-Kattan et al, 2013;Zuin et al, 2014;Hincapié et al, 2015;Hischier et al, 2015;Kaegi et al, 2017;Zhang et al, 2017;Clar et al, 2018Clar et al, , 2019 -rather than a specific determination of the NP forms. Using a sensitive, magnetic-sector ICP-MS, we were recently (Azimzada et al, 2020) able to quantify mass and number release rates of TiO 2 NPs from painted surfaces during natural weathering cycles.…”

Transformation of zinc oxide nanoparticles in synthetic lung fluids

“…The product is sold as an additive for water-based surface coatings, such as stains, for UV protection. This product has been characterized in detail in our previous work [ 21 , 22 , 40 ]. Briefly, total metal concentration was determined via ICP-OES (Agilent 5110).…”

“…Previously, research regarding consumer health and ENMs has focused on physical release and dermal exposure [ 11 , 15 , 17 – 20 ]. A wiping method has been used to track the release of copper particles, ZnO, and CeO 2 NPs from micronized copper azole (MCA) pressure-treated lumber to assess dermal release concerns [ 17 , 19 , 21 , 22 ]. Additionally, Taber abrasion and sanding have also been used to model dermal release [ 23 , 24 ].…”