Development and characterization of expanded graphite filled-PET/PVDF blend: thermodynamic and kinetic effects

Expanded graphite (EG) filled polyethylene terephthalate (PET)/polyvinylidene fluoride (PVDF) blend composites were prepared via melt blending by applying different mixing protocols: either premixing EG in the PET phase, premixing EG in the PVDF phase, or simultaneous mixing of the components. The blends were characterized for their thermal, rheological, mechanical, and electrical properties as well as microstructure analysis. The mixing protocol had a substantial effect on the electrical resistivity of the composites. When EG was premixed within PET phase, the blend exhibited a well-defined co-continuous structure which was characterized by a three orders of magnitude decreased electrical resistivity relative to the simultaneous mixing procedure. The improvement in the electrical properties of the blend can be attributed to the double percolation effect. Morphology analysis showed that EG was selectively confined and dispersed in the PET continuous phase of the blend. Melt rheological behavior of the composites made evidence of preferable interactions between EG and PET molecules as well as effective filler dispersion, whereas EG practically did not interact with PVDF molecules. Morphology analysis showed good correlation with the electrical and rheological properties of the blend and revealed that EG was selectively confined and dispersed in the PET continuous phase of the blend. It can be deduced that both thermodynamic and kinetic drives encourage the selective localization of EG filler in PET phase. Copyright (C) 2016 John Wiley & Sons, Ltd.