Improving Volume Resistivity of Epoxy Nanocomposites Using Electrospun Polyacrylonitrile-Based Carbon Nanofibers and Their Silver Modification

The electrospinning technique was utilized to prepare non-woven fabric carbon nanofibers (CNFs) via polyacrylonitrile (PAN) precursor nanofibers. The volume resistivity (ρv) of non-woven mat CNFs containing the small size of beads and fiber diameters was lower than the ones possessing large beads and fiber diameters owing to the high specific surface area of the former. The ρv values of CNF mats prepared from 6.5 (fiber dia. ~120–250 nm) and 8.0 (fiber dia. ~250–600) wt% PAN solutions and carbonized at 950 °C were 0.32 and 1.33 Ω.cm, respectively. Additionally, the ρv value of CNF fabrics was improved by silver (Ag) modifications. The CNF mats containing Ag nanoparticles by in-situ preparing Ag nanoparticles in PAN solution prior to electrospinning and carbonization and Ag coating of CNF mats exhibited ρv values more or less 0.15 and 0.24 Ω.cm, respectively, even though the nanofiber diameter obtained from the former method was slightly larger than that of the latter. Effects of the fiber aspect ratio (L/D ratio) and the interconnecting network due to non-woven mat like fibers on the ρv were demonstrated by comparing the ρv of epoxy nanocomposites containing different forms of CNFs, non-woven fabric and short nanofibers. It was found that the ρv value of non-woven mat CNF/epoxy nanocomposite was much lower than that of short CNF/epoxy nanocomposite at 10 phr filler loading. Interestingly, the ρv values of non-woven mat CNF/epoxy nanocomposites dropped rapidly from 1010.5 Ω.cm at 0 phr filler content to 1.05 Ω.cm at about 10 phr filler content. Furthermore, the ρv values of non-woven mat CNF/epoxy nanocomposites leveled off to that of the filler itself or even lower at the filler dosage about 15 phr or higher, because the thickness of CNF mats impregnated in the epoxy composite was increased at high filler loading, thus yielding highly connected network inside the composite.