Methods to assess the impact of UV irradiation on the surface chemistry and structure of multiwall carbon nanotube epoxy nanocomposites

One of the most promising applications of nanomaterials is as nanofillers to enhance the properties of polymeric materials. However, the effect of nanofillers on polymers subjected to typical environmental stresses, such as ultraviolet (UV) radiation, high humidity, or elevated temperatures, is not well understood. This stems partly from a lack of a single analytical method to assess these impacts. In this study, multiwall carbon nanotube (MWCNT) epoxy nanocomposite materials were exposed to carefully controlled UV doses (equivalent of up to ≈4 years in Florida). A suite of microscopic, spectroscopic and gravimetric techniques were optimized and used to assess changes occurring in the sample mass, surface chemistry, and surface and sub-surface morphology after UV irradiation. Overall, photodegradation of the epoxy matrix was retarded by the presence of the 3.5% MWCNT filler, suggesting that MWCNTs may enhance the lifetime of nanocomposite materials. Multiple microscopic and spectroscopic techniques clearly showed accumulation of MWCNTs on the nanocomposite surface that grew with increasing UV dose, a finding that may be significant with regard to the potential risk of MWCNT release during the nanocomposite lifetime. These analytical methods will help enable a robust and informative assessment of transformations in polymer nanocomposites subject to environmental stresses.