Influence of Surface Modified MWCNTs on the Mechanical, Electrical and Thermal Properties of Polyimide Nanocomposites

Polyamic acid, the precursor of polyimide, was used for the preparation of polyimide/multiwalled carbon nanotubes (MWCNTs) nanocomposite films by solvent casting technique. In order to enhance the chemical compatibility between polyimide matrix and MWCNTs, the latter was surface modified by incorporating acidic and amide groups by chemical treatment with nitric acid and octadecylamine (C18H39N), respectively. While the amide-MWCNT/polyimide composite shows higher mechanical properties at low loadings (< 3 wt%), the acid-MWCNT/polyimide composites perform better at higher loadings (5 wt%). The tensile strength (TS) and the Young's modulus (YM) values of the acid-MWCNT/polyimide composites at 5 wt% MWCNT loadings was 151 and 3360 MPa, respectively, an improvement of 54% in TS and 35% in YM over the neat polyimide film (TS = 98 MPa; YM = 2492 MPa). These MWCNT-reinforced composites show remarkable improvement in terms of thermal stability as compared to that for pure polyimide film. The electrical conductivity of 5 wt% acid modified MWCNTs/polyimide nanocomposites improved to 0.94 S cm(-1) (6.67 x 10 S-18 cm(-1) for pure polyimide) the maximum achieved so far for MWCNT-polyimide composites.