Surface analysis of EVOH and its nanocomposite photoageing: Particles effect
Résumé
The comprehensive study of photoinduced morphological and chemical changes of the surface of ethylene vinyl alcohol copolymer (EVOH) and new EVOH/zeolite nanocomposite as a potential candidate for packaging of flexible electronics was carried out. The films ageing was performed upon accelerated photoageing conditions with low-pressure mercury lamps as a light source. The impact of particles addition was evaluated in terms of surface photochemical behaviour and durability. The morphology data obtained by atomic force microscopy (AFM) and scanning electron microscopy (SEM) were complemented by information collected by time-of-flight secondary ion mass spectrometry (ToF-SIMS), providing high sensitivity and selectivity for database analysis. The combined results showed the complexity of photoageing processes and highlighted significant difference in surface behaviour for plain polymer and nanocomposite. It reflects different evolution of surface morphology with roughness increase for nanocomposite and smoothing in case of plain polymer upon photoageing. This phenomenon was interpreted by the theory of particles accumulation at the surface of the films due to polymer photooxidation and was supported by information on chemical composition at the surface obtained by ToF-SIMS. Evolution of ion peak areas displayed an increase of the particle-related ions at the surface of the films with irradiation time. At the same time, monitoring of different CxHy− and CxHyOz− ions indicated chemical modifications of polymer structure.