Understanding the effect of polymer crystallinity on the electrical conductivity of exfoliated graphite nanoplatelet/polylactic acid composite films

Electrically conductive exfoliated graphite nanoplatelet (GNP) / polylactic acid (PLA) nanocomposite films were fabricated using a two-step, scalable melt compounding process. The effect of the polymer’s physical properties, such as crystallinity, on the mechanical and electrical properties of the composites were determined. The crystallization characteristics of PLA were altered significantly by altering the cooling rate during compression molding of the films. The crystallinity and crystal structure were investigated using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The mechanical and electrical properties were also examined as a function of PLA’s crystallinity dictated by the cooling rate during compression molding. The electrical conductivity was examined using impedance spectroscopy. For the same GNP content, the crystallinity increases by ~40 % and electrical conductivity increases by ~3 orders of magnitude with decreased cooling rate indicating a strong correlation between polymer physical properties and electrical conductivity of the polymer composites. This mechanism can be utilized to tailor the electrical conductivity of a given filler/polymer system by tuning the physical properties of the polymer, without altering the fillers’ characteristics or the processing method, which is the common approach used.