At the beginning of the 20th century, the Belgian chemist Leo Bakeland, who worked in the United States, discovered a method for the synthesis of polymeric phenol-formaldehyde resin. By itself, this resin is a fragile substance with low strength. Bakeland found that adding fibers, particularly wood flour, to the resin prior to hardening, increased its strength. The material he created, called "Bakelite", has gained wide popularity: it does not soften when heated, does not conduct electricity, is resistant to corrosion and is easy to process. The first mass-produced product made from Bakelite in 1916 was a Rolls-Royce gear knob. Since then, filled polymers have been widely used in various industries.
To date, more than ten thousand grades of filled polymers of various compositions are known. The combination of polymers with nanoparticles gives materials with increased rigidity, impact strength and abrasion resistance. The transition to nanosized fillers significantly improved the characteristics of composites: permeability decreased, optical transparency increased, fire resistance increased, while the degree of filling decreased. Polymer nanocomposites have excellent barrier properties, electrical conductivity, thermal conductivity, increased strength, heat resistance and thermal stability, as well as reduced flammability.
Among the polymers with increased heat resistance and widely used in the manufacture of high-temperature plastics, adhesives, dielectrics, and other materials, polyimides stand out. Polyimide resins serve as the matrix of lightweight carbon fiber reinforced composites. Due to their outstanding thermal and mechanical resistance, as well as resistance to ionizing radiation, they are suitable for replacing metal parts of aircraft hulls. Polyimide resins are used to make electrical insulating varnishes and enamels with high heat resistance, elasticity and good dielectric properties. The use of polyimides is limited by the fact that they are generally non-thermoplastic and require high temperatures to form products. If you choose a polyimide matrix with a low molding temperature, the heat resistance decreases.
It is possible to obtain a composite material with high performance properties if carbon nanotubes, carbon fibers, and nanosized silicon carbide are used as fillers.
Research of such composite materials is carried out in the Laboratory of Special Organic Synthesis of the Center for the Transfer of Scientific Technologies and Developments of FSUE IREA. Films with various contents of nanotubes and silicon carbide, carbon-fiber reinforced plastics based on carbon fibers and polyimide have been manufactured. The samples obtained are characterized by increased radiation and heat resistance.
For example, a small, not more than 1%, content of nanosized silicon carbide makes the material non-combustible: when the composite enters a fire, it is covered with a protective layer of inorganic nature, which prevents further spread of fire. It can be assumed that such a composite will be in demand as a non-combustible heat-resistant insulation for electrical cables, especially since it is distinguished by ease of application, a small layer thickness and, therefore, low weight.
A polyimide matrix with the inclusion of fragments of polysiloxanes and crown ethers can serve as a basis for proton-conducting membranes, as well as new sorption materials suitable for the selective extraction of heavy metals, including radioactive isotopes, from aqueous solutions.
Polyimide-based nanocomposite materials are a good option for shielding against radiation. The radiation resistance of polyimides is associated with the high strength of bonds and the fact that competing processes occur during irradiation: breaking of macrochains and macromolecular crosslinking. A nanocomposite based on a heat-resistant and radiation-resistant polyimide matrix and nanostructured boron carbide not only absorbs thermal neutron radiation, but also increases the fire resistance of the material.