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This study investigates the evolution of morphology and electrical properties of polypropylene (PP)/polystyrene (PS) blend nanocomposites under controlled steady shear flow. These nanocomposites contain either few-layer graphene (FLG) or a mixture of FLG and multi-walled carbon nanotubes (MWCNT), prepared via a conventional melt-mixing. Composites were created by premixing FLG or FLG/MWCNT with either PP [PP/PS/FLG or PP/PS/(FLG+MWCNT)] or PS [PS/PP/FLG or PS/PP/(FLG+MWCNT)] at a PP/PS ratio inducing co-continuous morphology. Results showed a significant reduction in the percolation threshold (PT) for PS/PP/FLG composites, with an 81% decrease compared to PS/FLG. When FLG was premixed with PS, PT required only 2 wt. % FLG, compared to 5.9 wt. % in PP/PS/FLG. Steady shear deformation disrupted the electrical network in both PP/PS/FLG and PS/PP/FLG composites. However, the PS/PP/FLG composites exhibited greater stability in electrical conductivity at lower FLG concentrations (above 3 wt. %) compared to the PP/PS/FLG composites (above 6 wt. %). The applied shear did not affect the co-continuous morphology of the blend-based composites containing 1 wt. % or more of FLG. Additionally, the synergistic effects of the hybrid FLG/MWCNT mixture on the electrical conductivity and rheological properties of both PP/PS/(FLG+MWCNT) and PS/PP/(FLG+MWCNT) composites were evaluated. The incorporation of MWCNT into both PP/PS/FLG and PS/PP/FLG composites significantly enhanced the formation of a hybrid electrical network structure, leading to a further reduction in the percolation threshold concentration of FLG. Specifically, in PP/PS/FLG composites, PT decreased from 5.9 to 1–3 wt. % of FLG, while in PS/PP/FLG composites, PT dropped from 2 to 1 wt. % of FLG. [ABSTRACT FROM AUTHOR]

Conductive polymeric materials are commonly obtained by adding conductive nanoparticles to blends of immiscible polymers that form a cocontinuous morphology. However, during processing, morphology changes, affecting material properties. This study investigates the impact of steady shear deformation on the morphological and electrical properties of a model system consisting of polypropylene/polystyrene/multiwall carbon nanotubes (MWCNTs). The findings reveal that the deformation results in the coarsening of the blend morphology and disruption of the electrical network, increasing both the rheological and electrical percolation threshold concentrations. The evolution of both electrical and morphological properties depends on MWCNT concentration, strain amplitude, and shear rate. The MWCNT concentration, below a certain level, leads to a disruption in electrical conductivity at high shear rates. However, if the MWCNT concentration is above 1 wt. %, the balance between filler network breakup and nanoparticle diffusion is maintained, resulting in stable electrical conductivity and morphology. [ABSTRACT FROM AUTHOR]

In this work, a study of the linear viscoelastic properties of co-continuous polypropylene/polystyrene blends filled with multiwall carbon nanotubes (MWCNTs) is presented. The YZZ rheological model [W. Yu et al., Polymer 51, 2091–2098 (2010)] is employed to correlate the rheological behavior of the blends with their microstructure and electrical properties. A test design involving a sequence of small amplitude oscillatory shear and a time sweep (simulating thermal annealing) is used to evaluate the morphology and evolution of electrical properties. It was shown that the YZZ rheological model could be successfully modified to be able to quantify a co-continuous morphology of filled composites. The calculated characteristic domain size was found to be in good agreement with the experimental data obtained via scanning electron microscopy. Furthermore, it is shown that the characteristic domain size slightly decreased after 30 min of thermal annealing. It was shown, as well, that thermal annealing promoted a reduction in the electrical percolation threshold (wt. % MWCNT) from 0.28 to 0.06. [ABSTRACT FROM AUTHOR]

The effect of the crystallization of polypropylene (PP) forming an immiscible polymer blend with polystyrene (PS) containing conductive multi-wall carbon nanotubes (MWCNTs) on its electrical conductivity and electrical percolation threshold (PT) was investigated in this work. PP/PS/MWCNTs composites with a co-continuous morphology and a concentration of MWCNTs ranging from 0 to 2 wt.% were obtained. The PT was greatly reduced by a two-step approach. First, a 50% reduction in the PT was achieved by using the effect of double percolation in the blend system compared to PP/MWCNTs. Second, with the additional thermal treatments, referred to as slow-cooling treatment (with the cooling rate 0.5 °C/min), and isothermal treatment (at 135 °C for 15 min), ultra-low PT values were achieved for the PP/PS/MWCNTs system. A 0.06 wt.% of MWCNTs was attained upon the use of the slow-cooling treatment and 0.08 wt.% of MWCNTs upon the isothermal treatment. This reduction is attributed to PP crystals' volume exclusion, with no alteration in the blend morphology. [ABSTRACT FROM AUTHOR]