Effect of single-walled carbon nanotubes and carbon nanofibers on the structure and mechanical properties of thermoplastic polyimide matrix films

The effects of additives of single-walled carbon nanotubes prepared via electric-arc synthesis and carbon nanofibers produced via gas-phase synthesis on the crystallization capacities and mechanical and electric properties of composite films of a thermoplastic polyimide (PI) matrix based on 1,3-bis-(3,3', 4,4'-dicarboxyphenoxy)benzene and 4,4'-bis-(4-aminophenoxy)biphenyl after their uniaxial drawing and additional annealing are studied. The use of these fillers induces the heterogeneous nucleation of a crystalline phase of PI on the nanoparticle surface. A higher specific interface area in the case of addition of carbon nanotubes relative to that of carbon nanofibers leads to the formation of the crystalline structure of PI with a small crystallite size and high imperfection. Uniaxial drawing leads to the formation of a supermolecular structure that is optimum for crystallization during additional annealing and removes the kinetic hindrances to crystal growth. The properties of these fillers have a significant effect on the orientation of the nanoparticles and the matrix macromolecules during the uniaxial drawing of the films, which is accompanied by an increase in the elastic modulus with an increase in the draw ratio and the ability of the composite films to undergo orientational crystallization during additional annealing.