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Abstract: The relation between shear-mixing time in the melt, polymer crystal size, and electrical conductivity is studied for high density polyethylene carbon nanotubes nanocomposites with the help of in-situ rheo-dielectric and rheo-small angle synchrotron X-ray scattering (SAXS) techniques. Results show that the memory of crystal structure obtained after melt-mixing is not easily removed by re-melting and annealing. The conductivity of composites shear-mixed for 20 min cannot reach that of 10 min samples, even after additional quiescent annealing for 6000 s at 190 °C. The rheo-SAXS data further indicate that the temperature needed to melt all the crystals is higher for the longer time shear-mixed composites. These results all suggest that with long processing time, larger crystals are nucleated and grow on the nanotubes, which reduce electrical conductivity, presumably because they prevent electrical contact between the nanotubes. [Copyright &y& Elsevier]

We show how styrene-ethylene-propylene-styrene (SEPS) triblock copolymer uniquely reduces the electrical percolation threshold after matrix crystallization of conductive nanocomposites based on high viscosity HDPE with low amounts of pristine multiwall carbon nanotubes (CNT). Rheo-dielectric and Flash DSC techniques are used to demonstrate that SEPS interferes with the nucleation ability of CNT on HDPE crystallization in a way that favors contacts between the nanotubes after crystallization as well as it improves CNT dispersion. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the influence of nanoparticle–polymer interactions on the apparent migration behavior of multiwall carbon nanotubes (CNTs) in an immiscible polymer blend of ethylene-acrylate copolymer (EA) and polyamide 12 (PA). The polymer-CNTs interaction is tuned by using different surface modification strategies, comprising grafting and coating. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) are chosen as surface modifiers. The nanocomposite materials are prepared by melt-blending polymer-modified-CNTs in EA and PA. Polymer-grafted-CNTs tend to concentrate at the PA/EA interface, even if predispersed in PA, as opposed to pristine CNTs, which stay inside PA under the same circumstances. This new behavior is consistent with the morphology of PA/EA/(PMMA or PS) ternary blends and suggest a dominance of interfacial thermodynamics on CNTs localization. If we use polymer-coated-CNTs instead, the behavior depends on molar mass of the coating polymer. For low molar mass, it is similar to that of pristine CNTs and indicates desorption of the coating, owing to the weak interaction with the CNTs surface. Interestingly, we observe that long PS chains do not desorb and can drive the CNTs to the interface of the PA/EA blend. Moreover, the influence of kinetics is clearly observed through the dependence of CNTs interfacial confinement on dispersed droplet size. [Copyright &y& Elsevier]

Abstract: The present study demonstrates the effect of unfunctionalized MultiWalled Carbon Nanotubes (MWNTs) interfacial confinement on coalescence suppression in an immiscible polymer blend exhibiting a sea-island morphology. The effect of carbon nanotubes on morphological stabilization in polyamide (PA)/ethylene–methyl acrylate random copolymer (EA) blends is studied using electronic microscopy techniques. Owing to their interfacial localization, MWNTs are shown to enhance both phase dispersion and stability of the dispersed phase for long mixing time (at least 60 min) and very low filler content (0.5 wt.-% MWNTs) compared to what was previously observed in literature. MWNTs also produce a more uniform distribution of droplets size. The main stabilization mechanism proposed is the formation of a deformable barrier network providing a mechanical barrier against coalescence. Blends stabilized by solid anisotropic nanoparticles, like MWNTs, could therefore offer an interesting alternative to blends compatibilized by block-copolymers. [Copyright &y& Elsevier]