Study On Preparation Of Conductive Polymer Blend Composites Through Regulating The Localization Of Carbon Nanotubes

Adding conductive particles into an insulated polymer matrix to prepare conductive polymer composites has attracted considerable attention due to that the composites exhibit wide application in areas, such as electronic devices, electromagnetic shielding materials, chemical sensors, and antistatic materials, etc. The commonly applied conductive fillers include carbon black (CB), carbon nanotubes (CNTs), graphite and metal powder, etc. Among these fillers, CNTs have received more attention due to their excellent conductivity in performance and large aspect ratio in microstructure. Adding CNTs into single polymer can not only improve the conductivity of the material, but also lower the percolation threshold. If CNTs are introduced into an immiscible polymer blend which shows cocontinuous structure, the percolation threshold could be further decreased through the so called’double percolation’mechanism. However, with the consideration of the cost, processing and practical application, the percolation threshold should be as small as possible. Thus, preparing the conductive polymer composites with lower percolation threshold is more important.In order to explore the preparation of the CNTs filled conductive polymer blend composites with lower percolation threshold, CNTs/CB hybrid fillers were first introduced into the immiscible polymer blends in this work. The effects of CNTs/CB on morphology and electrical conductivity were investigated systematically. At the same time, the influence of adding CNTs (or CB) on the electrical conductivity of composites containing CB (or CNTs) was comparatively investigated. Besides, by considering the factors which affected the selective location of CNTs, the other components including compatibilizer, organic montmorillonite (OMMT) and graphene oxide (GO) were respectively applied to regulate the location of CNTs at the interface of the blends. The effects of such special location state on morphology and electrical conductivity were also investigated. The main results obtained in this work are listed as follows:(1) CNTs/CB hybrid fillers were ntroduced nto polyamide6/acrylonitrile-butadiene-styrene (PA6/ABS) blend to prepare conductive composites. Both CNTs and CB were selectively located in the PA6phase because of its stronger polarity and lower viscosity compared with the ABS phase. It was proved that CNTs and CB exhibited the synergestic effect in improving the electrical conductivity of the composites, which was benefit for preparing the conductive polymer composites with lower CNTs content. Further results showed that adding CNTs into the composites with fixed CB content was favorable for fabricating conductive polymer composites.(2) The compatibilizers, maleic anhydride grafted SEBS (SEBS-g-MA) and maleic anhydride grafted ABS (ABS-g-MA), were introduced into polyprolene/polystyrene/carbon nanotubes (PP/PS/CNTs) composites and polycarbonate/acrylonitrile-butadiene-styrene/carbon nanotubes (PC/ABS/CNTs) composites, respectively. With the aid of compatilizer, CNTs were successfully located at the interface of the immiscible polymer blend through the suitable processing sequence. Also, the compatibilizer and CNTs showed the combined effect on decreasing the phase domain of the composites.For the PP/PS/SEBS-g-MA/CNTs system, when the (PS+SEBS-g-MA)/CNTs master batch was used, large agglomerates of CNTs were located in PS phase and the percolation threshold was suggested to be1.22wt%. If the master batch of (PP+SEBS-g-MA)/CNTs was used, most of CNTs were located at the interface, leading the percolation threshold of0.66wt%.For the PC/ABS/ABS-g-MA/CNTs system, most of CNTs were selectivity located in PC phase when the PP/CNTs master batch was used, the percolation threshold of the composites was suggested to be0.22wt%. If the master batch of ABS-g-MA/CNTs was used, a lot of CNTs could be observed at the interface of the blends clearly. The composite showed a much lower percolation threshold of0.05wt%, which was the smallest value reported so far in the CNTs filled conductive polymer blend composites.(3) Differnent contents of OMMT (0.05wt%-0.25wt%) were introduced into the polycarbonate/poly(vinylidene fluoride)/carbon nanotubes (PC/PVDF/CNTs) composites through two-step method. Morphological characterizations showed that the presence of the OMMT promoted the morphological change from the seaisland structure to the cocontinuous structure. Electrical resistivity measurements showed that the volume resistivity of the composites decreased first and then increased with increasing the content of OMMT, attributing to the differnernt location states of CNTs. At OMMT content of0.1wt%, CNTs were selectively located at the interface of the blends due to the barrier effect of OMMT, resulting the great decrease of electrical resistivity. Further increasing the content of the organoclay promoted the full migration of the CNTs from PVDF component to PC component. Moreover, a very low percolation threshold of the0.06wt%CNTs was obtained with the aid of the0.1wt%OMMT.(4) GO was introduced into polylactide/ethylene-co-vinyl acetate/carbon nanotubes (PLLA/EVA/CNTs) composites through two-step method. Morphological characterizations showed that more CNTs were found to be located at the interface due to the strong ’π-π’ stacking interactions and the different migration rates between CNTs and GO, resulting in the great decrease of electrical resistivity. Besides, the composites containing GO and CNTs exhibited much smaller percolation threshold (0.06wt%) compared with the composites containing only CNTs (0.24wt%).