Scenarios and methods that induce protruding or released CNTs after degradation of nanocomposite materials

All materials undergo life-cycle processes and ultimately lose their structural integrity, thus releasing solids that were originally embedded within that material. Nanocomposite materials consist of nanofillers embedded in a matrix of varying chemical composition, including for example cements and plastic polymers or polymer coatings. There are concerns that engineered nanomaterials, such as multi-wall carbon nanotubes (CNTs), may be released to humans or the environment from degradation of nanocomposite-enabled products, from degradation of waste from these products at the end of the life-cycle, and from waste materials generated during manufacturing. Matrices may be disrupted mechanically by machining and/or stress crack formation (Fig. 1 , horizontal axis), or chemically by dissolution or shortening of polymer chain length from various processes, such as chemical or UV light exposure (Fig. 1 , vertical axis). Nanocomposite materials with embedded nanofillers may hence release these nanofillers in certain scenarios of use and disposal (Nowack et al. 2012 ). If the nanofiller has been identified to represent a human health or environmental hazard the extent of polymer degradation and possible CNT release should be assessed before commercialization of a product that contains them to ensure that human and environmental exposures remain safe (Petersen et al. 2011 ; Som et al. 2010 ). Especially CNTs are a known hazard upon inhalation (Landsiedel et al. 2010 ; Ma-Hock et al. 2009 ), but only two dozen papers have reported experimental data on release from engineered nanofiller composites, even fewer on CNT composites (Kuhlbusch et al. 2011 ; Petersen et al. 2011 ).