In this paper, we report on novel polyimide (PI) nanocomposites filled with binary mixtures of metal oxide (either TiO₂ or ZrO₂) nanoparticles and nanocarbon (either carbon nanofibers (CNFs) or functionalized carbon nanotubes (CNT_fs)). The structure and morphology of the materials obtained were comprehensively studied. An exhaustive investigation of their thermal and mechanical properties was performed. We revealed a synergistic effect of the nanoconstituents with regard to a number of functional characteristics of the PIs compared with single-filler nanocomposites, including thermal stability, stiffness (below and above glass transition temperature), yield point, and temperature of flowing. Moreover, the possibility of manipulating the properties of the materials by choosing a proper combination of the nanofillers was demonstrated. The results obtained can become a platform in the design of PI-based engineering materials with tailored characteristics capable of operating in extreme conditions.

The influence of nanosized cerium oxide as an active filler on the mechanical properties and thermal stability indices and heat resistance of films of thermally stable aromatic polyimides of various chemical structures is studied. It is shown that, depending on the polyimide structure the introduction of cerium oxide nanoparticles into the film can lead to a noticeable increase or a significant decrease in the thermal stability of the material during thermo-oxidative degradation. It is found that the thermal stability of the films increases significantly when polyimides containing sulfonic groups in elementary units serve as matrix polymers. The introduction of cerium oxide nanoparticles into such polyimides leads to an increase in the thermal stability of the films in air by 20–40°C. Moreover, in an inert medium the thermal stability indices for the films of matrix polymers and nanocomposites differ slightly. For all the studied polyimides, the introduction of cerium oxide does not cause a noticeable change in the glass transition temperature but in some cases leads to limitation of the compliance of the films in the temperature range above the glass transition.

A comparative assessment of the influence of 2D graphene structures derived from lignin, starch and cellulose through the self-propagating high-temperature synthesis method on the mechanical, thermal and electrical properties of poly(4,4’-oxydiphenylene pyromellitimide) films was conducted. It was found that the incorporation of synthesized nanoparticles allows for the modification of the mechanical properties of the polyimide material without a significant decrease in volume and surface resistivity. Dependencies of the changes in properties of nanocomposite film materials on the following factors have also been established and analyzed: the type of biopolymer from which the nanofiller was obtained; the morphometric parameters of the prepared nanosized material; the concentration of the nanofiller.