Structure, processing, and properties of polyacrylpnitrile/carbon nanotube composite films
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Vapor grown carbon nanofibers (VGCNFs) developed in 1980s are being widely used for reinforcing composites. Carbon nanotubes (CNTs) discovered in early 1990 can be classified as single wall carbon nanotubes (SWNTs), double wall carbon nanotube (DWNTs) and multi wall carbon nanotubes (MWNTs) depending on the number of grapheme layer forming the carbon nanotube. Polyacrylonitrile (PAN), a commercially important polymer is a predominant precursor for carbon fiber. Carbonized and activated PAN/SWNT films can find application as electrochemical supercapacitor electrodes. This study is focused on the structure, processing and properties of polyacrylonitrile/carbon nanotube (CNT) composite films. PAN/SWNT (60/40) composite film have been processed with unique combination of tensile strength, modulus, electrical conductivity, dimensional stability, low density, solvent resistance, and thermal stability. PAN molecular motion above the glass transition temperature (Tg) in the composite film is significantly suppressed, resulting in high PAN/SWNT storage modulus above Tg. The specific modulus of PAN/VGCNF composite films is consistent with the predictions of the Halpin-Tsai equation up to 20% VGCNF loading. The magnitude of modulus and other property enhancement is reduced as the nanofiber loading is increased (up to 40%). Further increase in nanofiber loading (> 40%) in composite results in modulus and tensile strength lower than those of control PAN. Electrical percolation was observed at 3.1 vol% VGCNF loading. PAN/CNT composite films were processed using SWNTs, DWNTs, MWNTs and VGCNFs to study the effect of various nanotubes on the composite properties. PAN/CNT films have been characterized by wide angle X-ray diffraction (WAXD), Raman spectroscopy, and scanning as well as transmission electron microscopy. Films have also been characterized for electrical conductivity, tensile and dynamic mechanical properties. Mechanical property results have been analyzed in terms of the nanotube surface area determined by nitrogen gas adsorption. PAN/CNT composite films and fibers are characterized using solid state 1HNMR spin lattice relaxation time (T1). With the addition of nanotubes, the T1 values for the PAN matrix generally decreased, and the reduction mechanism is discussed. The optical anisotropy of SWNT in PAN/SWNT composites was observed in their polarized infrared spectra and analyzed using the effective medium theory.