Abstract
This work studied the impact of three types of styrene-butadiene (SB and SBS) block copolymers on the morphology, electrical, and rheological properties of immiscible blends of polypropylene:polystyrene (PP:PS)/multi-walled carbon nanotubes (MWCNT) with a fixed blend ratio of 70:30 vol.%. The addition of block copolymers to PP:PS/MWCNT blend nanocomposites produced a decrease in the droplet size. MWCNTs, known to induce co-continuity in PP:PS blends, did not interfere with the copolymer migration to the interface and, thus, there was morphology refinement upon addition of the copolymers. Interestingly, the addition of the block copolymers decreased the electrical resistivity of the PP:PS/1.0 vol.% MWCNT system by 5 orders of magnitude (i.e., increase in electrical conductivity). This improvement was attributed to PS Droplets-PP-Copolymer-Micelle assemblies, which accumulated MWCNTs, and formed an integrated network for electrical conduction. Molecular simulation and solubility parameters were used to predict the MWCNT localization in the immiscible blend. The simulation results showed that diblock copolymers favorably interact with the nanotubes in comparison to the triblock copolymer, PP, and PS. However, the interaction between the copolymers and PP or PS is stronger than the interaction of the copolymers and MWCNTs. Hence, the addition of copolymer also changed the localization of MWCNT from PS to PS–PP–Micelles–Interface, as observed by TEM images. In addition, in the last step of this work, we investigated the effect of the addition of copolymers on inter- and intra-cycle viscoelastic behavior of the MWCNT incorporated polymer blends. It was found that addition of the copolymers not only affects the linear viscoelasticity (e.g., increase in the value of the storage modulus) but also dramatically impacts the nonlinear viscoelastic behavior under large deformations (e.g., higher distortion of Lissajous–Bowditch plots).]
Highlights
Filled polymer blends are among the most attractive options to develop new materials for electrical conduction
The results presented in this manuscript illustrate how the addition of styrenebutadiene (SB) block copolymer can alter the localization of multi-walled carbon nanotubes (MWCNT) in polypropylene:polystyrene (PP:PS) immiscible blends
We investigated the effect of three different block copolymers with various styrene and butadiene contents and structures on the morphological, electrical, and rheological properties of PP:PS/70:30/MWCNT blend nanocomposites
Summary
Filled polymer blends are among the most attractive options to develop new materials for electrical conduction. For immiscible blends, depending on the number of species incorporated, two or more phases form and different morphological structures are generated [1,2,3,4,5]. Depending on the ratio of components in the blends and by controlling different mixing conditions [10,11], diverse structures can be generated (Figure 1): droplets dispersed in a matrix phase, employed to increase the toughness of pristine polymers [12]; fiber-like and lamellar structures, which offer barrier properties [10,13]; co-continuous morphology, suitable for electrical applications [14,15]; and several other structures
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