Enhanced electrical conductivity, mechanical modulus, and thermal stability of immiscible polylactide/polypropylene blends by the selective localization of multi-walled carbon nanotubes

Immiscible polylactide (PLA)/maleic anhydride-grafted polypropylene (PP) blend (50/50 by wt.%) composite films filled with different pristine multi-walled carbon nanotube (MWCNT) contents of 0.0-10.0 wt.% were manufactured by an efficient and facile melt-mixing/compression technique. The electrical, mechanical and thermal properties of the PLA/PP/MWCNT composite films were investigated by considering the morphological feature as well as the MWCNT content. SEM images of the composite films confirmed that the PLA domains were well dispersed in the PP matrix of the immiscible PLA/PP blends and that the MWCNTs were localized selectively and uniformly in the PP matrix of the composite films. Accordingly, the electrical resistivity of the composite films decreased considerably from ∼1010 Ω cm to ∼101 Ω cm with the increment of the MWCNT content. The DSC cooling thermograms supported the fact that the MWCNTs served as effective accelerating agents for the melt-crystallization of the composite films as well as the development of the α-form crystals in the PP matrix. The dynamic storage modulus and the thermal degradation stability of the composite films were also increased significantly with the increment of the MWCNT content. Overall, high performance in the electrical conductivity, melt-crystallization rate, mechanical modulus, and thermal degradation stability of the PLA/PP/MWCNT composite films was found to stem from the selective and uniform localization of the MWCNTs in the continuous PP matrix.