STRUCTURE-PROCESS-PROPERTY RELATIONSHIP OF EXFOLIATED GRAPHITE NANOPLATELET/POLY(LACTIC ACID) COMPOSITE FILMS

摘要

Conductive films have many applications including electromagnetic shielding, photovoltaics, gas sensors, and more [1]. Recently, a substantial amount of work has been done with carbon nanotubes (CNT) or CNT buckypaper (BP)/thermosetting resin [2] composite films replacing more traditional metallic fillers due to metal's high density, cost, and susceptibility to corrosion of metals [1]. Incorporation of CNT into polymer matrices is difficult due to the CNT's strong van der Waals interactions and high surface area [3] and the one dimensional structure limits the two dimensional in-plane conductivity of the composite films. However, BP is a dense network or mat of CNT [2, 4] and is extremely desirable in creating highly conductive films due to the abundance of nanotube pathways. BP is also a desirable alternative to CNT due to its ability to be handled like a more traditional carbon fiber mat [3]. However, the dense network of CNT that BP is comprised of makes it extremely difficult for polymers to penetrate and achieve good interfacial interactions. Natural graphite (NG), like CNT, offers superior conductivity since both materials share the same chemistry. NG is a planar structure composed of layers of fused benzene rings (hexagonally arranged covalently bonded carbon atoms) held together by relatively weak van der Waals interactions [5]. The planar structure of NG allows for superior conductivity in the plane of the benzene network [6]. In addition, due to this relatively weak interlayer force, NG can easily be intercalated and exfoliated to produce exfoliated graphite nanoplatelets (GNP) [5]. The further exfoliation of natural graphite enhances its potential use in polymer composites by creating a filler that can produce multiple conductive pathways allowing the GNP polymer composites to have a lower percolation threshold [1, 6].