We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops “seating” on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction.

Carbon-fiber-reinforced plastics are composite materials with record-high specific strength, which depends on the efficiency of stress redistribution between the reinforcing fibers by the polymer matrix. The problem is the accurate assessment of adhesion in the carbon fiber–polymer matrix system since it affects the overall strength of the composite. This paper provides a novel electrochemical method for determining adhesion by estimating the critical length of carbon fibers that protrude above the fracture surface of the fiber-reinforced composite using their electrical conductivity and insulating properties of the polymer matrix. The method has been successfully applied to evaluate adhesion in carbon plastics having an epoxy matrix filled with nanoparticles of different anisometry: carbon nanotubes, organomodified montmorillonite, or detonation nanodiamonds. In addition to adhesion measurements, the effect of nanoparticles on the viscosity of epoxy binder, its impregnation efficiency of carbon fibers, curing, glass transition, and tensile strength of fiber-reinforced composites was estimated. Nanodiamonds at a mass fraction of 0.1% proved to be the most effective for improving the quality of epoxy carbon plastics, increasing fiber–matrix adhesion by 2.5 times, tensile strength by 17%, and not decreasing the glass transition temperature.

The effect of 3D printing conditions (sample position relative to the plane of the build plate, as well as temperature, extruder nozzle diameter, and infill density) on the mechanical properties of polyethylene terephthalate glycol samples has been studied. The main factor determining the elastic and strength properties of parts obtained by 3D printing is the porosity of the samples associated with the infill density and the orientation of the sample relative to the plane of the build plate during printing. Decreasing the nozzle diameter helps to reduce porosity and improve the mechanical properties of the product, but increases the duration of printing.

Concentrated metal-in-polymer suspensions (55 vol.% and 60 vol.%) of aluminum powder dispersed in low molecular weight polyethylene glycol) demonstrate elastoplastic properties under compression and shear. The rheological behavior of concentrated suspensions was studied in a rotational rheometer with uniaxial compression (squeezing), as well as shearing superimposed on compression. At a high metal concentration, the elasticity of the material strongly increases under strain, compared with the plasticity. The elastic compression modulus increases with the growth of normal stress. Changes in the shear modulus depend on both normal and shear stresses. At a low compression force, the shear modulus is only slightly dependent on the shear stress. However, high compression stress leads to a decrease in the shear modulus by several orders with the growth of the shear stress. The decrease in the modulus seems to be rather unusual for compacted matter. This phenomenon could be explained by the rearrangement of the specific organization of the suspension under compression, leading to the creation of inhomogeneous structures and their displacement at flow, accompanied by wall slip. The obtained set of rheological characteristics of highly loaded metal-in-polymer suspensions is the basis for understanding the behavior of such systems in the powder injection molding process.