Impact of UV irradiation on multiwall carbon

16 Multiwall carbon nanotubes (MWCNTs) are nanofillers used in consumer and structural 17 polymeric products to enhance a variety of properties. Under weathering, the polymer matrix will 18 degrade and the nanofillers may be released from the products potentially impacting ecological or 19 human health. In this study, we investigated the degradation of a 0.72 % (by mass) 20 MWCNT/amine-cured epoxy nanocomposite irradiated with high intensity ultraviolet (UV) light 21 at various doses, the effects of UV exposure on the surface accumulation and potential release of 22 MWCNTs, and possible mechanisms for the release resistance of the MWCNT surface layer 23 formed on nanocomposites by UV irradiation. Irradiated samples were characterized for chemical 24 degradation, mass loss, surface morphological changes, and MWCNT release using a variety of 25 analytical techniques. Under 295 nm to 400 nm UV radiation up to a dose of 4865 MJ/m, the 26 nanocomposite matrix underwent photodegradation, resulting in formation of a dense, entangled 27 MWCNT network structure on the surface. However, no MWCNT release was detected, even at 28 very high UV doses, suggesting that the MWCNT surface layer formed from UV irradiation of 29 polymer nanocomposites resist release. Four possible release resistance mechanisms of the UV30 induced MWCNT surface layer are presented and discussed. 31