Controlling MWCNT partitioning and electrical conductivity in melt compounded polypropylene/poly(ethylene-co-octene) blends

- Polypropylene-graft- aminomethylpyridine is added in TPO/MWCNT blends.
- The compatibilizer affects partitioning of MWCNTs in the blend phases.
- TPO blends with a percolation threshold of 0.5 wt% MWCNTs are prepared.
- Electrical conductivities of the order of 10−2 S/m are achieved.
- The blend conductivity is optimized by controlling the compounding time.

Composites containing multi-walled carbon nanotubes (MWCNTs) within polypropylene (PP)/poly (ethylene-co-octene) (EOC) blends are prepared using different melt compounding strategies, in the presence of polypropylene-graft-maleic anhydride (PP-g-MA) and polypropylene-graft- aminomethylpyridine (PP-g-Py) compatibilizers. Experimental evidence that MWCNTs are thermodynamically driven to localize preferentially in the EOC phase agrees with estimates of the partition coefficient using measured surface energy values. Addition of PP-g-Py alters the interfacial tension between the PP matrix and the MWCNTs; as a result some nanotubes remain in the PP phase. All blend compositions display lower electrical percolation thresholds compared to the neat matrix, with a minimum at 0.5 wt% MWCNTs for blends having a co-continuous blend morphology. A kinetic approach, involving pre-mixing the MWCNTs with PP and adding the EOC phase, is employed to monitor the evolution of morphology, MWCNT migration and the ensuing electrical conductivity, as a function of residence time. The morphology is fully developed and MWCNT migration is complete within 2 min of melt mixing with the EOC. The electrical conductivity is reduced considerably after 2 min of compounding, due to the migration of the MWCNTs within the dispersed EOC phase.

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