Influence of processing conditions on sensitivity of conductive polymer composites to organic solvent vapours

Abstract Electrical properties of two conductive polymer composites (CPC) not yet studied in the literature, poly(amide12-b-tetramethylene oxide)-carbon black (PEBAX-CB) and poly(ethylene-co-ethyl acrylate)-carbon black (EEA-CB) in the presence of two organic solvent vapours, chloroform and toluene, have been studied as a function of processing conditions (in the melt by extrusion and from solution by casting). The experiments show that the electrical response of the CPC to solvent vapours can be modulated not only by changing the chemical nature of the polymer but also by tailoring the CPC morphology, i.e. the area accessible to solvent molecules both at a micro and nanometric scale and the conductive paths structure. For this purpose, the use of either block or statistical copolymers is interesting in achieving microphase separation or good CB dispersion, respectively. The results show on the one hand that important responses to solvent vapours Δ R / R max can be achieved with high conductivity samples but at the detriment of response time. On the other hand, the use of the curve shape, i.e. the diffusion mode characterised by Δ R / R max versus t curves slope and onset, would allow us to decrease the number of CPC necessary for vapour detection. Moreover, sorption kinetic measurements show that toluene diffusivity is about two times lower in EEA-CB than in EEA. This phenomenon can be explained by a hindrance effect of the carbon black particles and a decrease of plasticization of EEA chains by toluene molecules due to interactions between EEA and CB. Therefore, the sensitivity of the CPC to solvent vapours results from conductive particles disconnection due to volume expansion during the matrix swelling.