Photodegradation of polymer-CNT nanocomposites: effect of CNT loading and CNT release characteristics
Information is currently lacking on the effect that carbon nanotubes (CNTs) have on the mechanism and extent of polymer photodegradation as well as the quantity, kinetics, and form of CNTs released. To address this, we followed in detail the photodegradation of a photolabile CNT-polymer nanocomposite (CNT-PNC), composed of single walled CNTs and polycaprolactone. Analysis of released CNT-containing fragments was accomplished with single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The mechanism of polymer photodegradation remained unchanged upon CNT inclusion, although polymer mass loss decreases systematically as CNT loading increases. This inhibitory effect is due to the light absorption and scattering properties of CNTs, which reduces the depth of photolysis and consequently the extent of CNT-PNC mass loss. Preferential CNT retention in the polymer during photodegradation results in CNT release at lower quantities than predicted based on their mass loading. The form of the released CNTs depends on CNT loading and evolves as the CNT-PNC photodegradation process proceeds. For CNT-PNCs with higher CNT loadings, multiple CNTs are initially released embedded within polymer fragments; as CNT-PNC degradation slows, released fragments contain predominantly isolated CNTs. For sufficiently long irradiation times, a dense CNT-mat forms at the surface, stabilizing the CNT-PNC towards further polymer or CNT loss. Extrapolating our findings to other CNT-PNC systems suggests that the quantity and form of released CNTs, as well as the extent of CNT-PNC photodegradation, will be influenced by the CNT loading and will evolve over the course of the CNT/PNC photodegradation process.