Microstructure-rheological percolation-mechanical properties correlation of melt-processed polypropylene-multiwall carbon nanotube nanocomposites: Influence of matrix tacticity combination

• Four-fold enhancement in relative fracture strain due to tacticity modification of PP matrix.
• Rheological percolation shifts to higher loading of MWNT in stereoregularity modified PP.
• van-Gurp Palmen plot reiterates composition dependence of rheological percolation transition.
• Constitutive modeling confirms the role of strain-component in non-Newtonian flow dynamics.

Isotactic and blend of iso-tactic: syndio-tactic (70:30) polypropylene (PP) matrices based melt-mixed PP/MWNT nanocomposites are comparatively evaluated with regard to morphological, rheological and mechanical properties. Relatively increased mean free space lengths (lf) between nanotubes in syndiotactic blended PP/MWNT nanocomposites with its manifestations on the rheological percolation up to a higher extent of MWNT loading (øc ∼ 1.4 × 10−3 in isotactic to øc ∼ 6.1 × 10−3 in iso–syndio blend) vis-à-vis enhanced normalized (∼four-times) tensile failure strain has been observed. The rheological percolation confirming the formation of a mechanically responsive network structure was ascertained following the power-law relationship between storage modulus and critical volume fraction. Construction of van-Gurp Palmen plot indicated a transition in the rheological response attributed to the network morphology getting shifted to higher concentration of MWNT in the syndio-modified than the iso-unmodified nanocomposites. Constitutive modeling of complex viscosity response of the nanocomposites functionally demonstrated the percolation and relaxation dynamics of polymer chains. The Tg remained affected more by the polymer–nanotube entanglements in iso–syndio than in iso-only system. The increase in strain at break has been attributed to an overall reduction in crystallinity in the syndio-modified PP/MWNT nanocomposites.

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