Mechanical Performance of Nanostructured Thermoplastic Polyimide Films

Abstract

The effects of multiwalled carbon nanotubes (MWCNTs) on the mechanical performance, namely, strength, fracture resistance, and creep recovery of polyimide (PI) films, were investigated by testing different formulations of PI/MWCNTs films. The loadings of MWCNTs used were 0.1 and 0.5 wt%. A novel method of dispersing MWCNTs in PI was developed and optimized. The processing conditions for fabricating PI films have also been developed and optimized. The mechanical performance of the optimized PI films was evaluated. It was found that the strength of the PI films dried at 60°C increased by 55% and 72% for the 0.1% MWCNT and 0.5% MWCNT loadings, respectively, while the fracture resistance increased by 23% for the 0.1% MWCNTs and then decreases at a loading of 0.5% MWCNTs. The strength of the neat and nanostructured films increased after annealing. However, there was a shift in the annealing temperature at which the maximum strength occurs as the MWCNT loadings increased. The fracture resistance of all the samples increased at an annealing temperature of 150°C and then decreased as the temperature continued to increase up to 250°C. Creep recovery studies showed that the compliance of the PI films decreased with increasing MWCNT loading at room temperature and increases for all the samples as the testing temperature increases to 200°C. Also, the viscosity and percentage strain recovery of the samples increased with increasing MWCNT loading and decreased with increasing temperature. Generally, the percentage strain recovery is between 85%, for samples tested at high temperatures (200°C), and 94%, for those tested at low temperatures (25°C).