The Effect of Processing on the Electrical Properties of Exfoliated Graphite Nanoplatelet/Polylactic Acid Nanocomposite Films

Abstract

The potential for engineering/tailoring properties, specifically electrical properties, of polylactic acid (PLA) nanocomposite films is examined by comprehensively studying process-structure-property relationships. This work focuses on investigating the effect of composite processing methods and conditions on the electrical response of exfoliated graphite nanoplatelet (GNP) / PLA films. GNP are incorporated into the PLA matrix either via polymer dissolution / solution casting or via melt compounding and fiber melt spinning / compression molding to produce films of ~160 μm thickness. In order to investigate the effect of polymer crystallinity on the electrical response of the films, the melt compounded / compression molded films are either cooled rapidly (~16°C/min and denoted fast cooled or FC) or cooled slowly (~0.4°C/min and denoted slow cooled or SC) to alter the matrix crystallinity. Crystallinity and crystal structure of the composite films are investigated using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Mechanical properties are examined in tensile mode using a standard tension setup. Electrical properties of the films are examined using impedance spectroscopy (IS). The SC films percolated between 1 and 5wt% of GNP, followed by the solution cast films which percolated between 5 and 8wt% of GNP, and finally the FC films had the highest percolation between 12 and 15wt% of GNP. Furthermore, the percolation of the solution cast films can be lowered to below 5wt% of GNP by minimizing voids present in the films which can be done via compression. The differences in percolation can be attributed to differences in compounding technique and the polymer matrix crystallinity.