The structural transformationss of oriented poly(vinyl alcohol) (PVA) fibers impregnated with potassium bisulfate (PBS) were studied in detail on the way from PVA precursor fibers till carbonized at a temperature of 1000 °C fibers. It has been shown that the impregnation of PVA fibers with a sulfur-containing compound (PBS) is an efficient technique to decrease the thermoplasticity of PVA fibers during heat treatment at high temperatures in air and argon and contributes to a high yield of coke residue after heat treatment up to 1000 °C. TMA, TGA, DSC, mass spectrometry, FTIR, Raman spectroscopy, SEM, WAXS and SAXS were used to study the structural transformations of oriented PVA fibers impregnated with PBS at the stages of their preliminary thermal stabilization (215 °C), thermal stabilization (215–400 °C) and carbonization (400–1000 °C). A reaction scheme has been proposed that fully describes carbonization chemistry in the entire studied temperature range. The processing temperature of 215 °C was found to be optimal for preliminary thermal stabilization of PVA fibers impregnated with PBS. The heat treatment in an inert medium can be recommended as the optimal for thermal stabilization of fibers impregnated with PBS. The characteristics of the carbonized PVA fibers, such as strength, modulus and electrical conductivity, were close to the characteristics of commercial cellulose-based carbon fibers yarns.

On the basis on polyvinyl alcohol (PVA), carbonized fibers were produced in the form of a complex technical thread with tensile strength above 200 MPa and specific electrical conductivity of at least 0.5 S/cm. Using thermogravimetric and differential thermal analysis, Raman scattering, and wide-angle X-ray diffraction, structures of these fibers were characterized. The structural parameters of carbonized PVA fibers are close to the parameters of carbonized coal tar pitch obtained by heat treatment at 1000°C. The structure and properties of carbonized fibers modified with potassium bisulfate were also studied.

На основе поливинилового спирта получили карбонизованные волокна в виде комплексной технической нити с разрывной прочностью выше 200 МПа и удельной электропроводностью не менее 0,5 См/см. С помощью термогравиметрического и дифференциально-термического анализа, методов Рамановского рассеяния и рентгеновской дифракции в больших углах рассеяния охарактеризовали структуры этих волокон. Структурные параметры карбонизованных ПВС-волокон близки к параметрам карбонизованного каменноугольного пека, полученного термообработкой при 1000 °C. Также исследовали структуру и свойства карбонизованных волокон, модифицированных бисульфатом калия.

The structural transformations of oriented PVA fibers impregnated with potassium bisulfate during their heat treatment in air to a temperature of 600°C were studied. The preliminary thermal stabilization of the impregnated fibers was conducted in air at 215°C for 1 h with maintenance of a high degree of orientation of the fibers. The melting peak of the preliminarily thermally stabilized impregnated PVA fibers is completely suppressed during their subsequent heat treatment in air, and the yields of coke residue are 48 and 43% of the thermally stabilized fiber mass at 500 and 600°C, respectively.

The low-temperature chemical crosslinking of a copolymer of vinylidene fluoride and tetrafluoroethylene was studied through various physicochemical methods. The reaction was conducted in solution in the presence of diethylenetriamine as a crosslinking agent. The penetration of the mixture molecules and the crosslinking agent only in the amorphous phase of the copolymer was provided via selection of the ratio between a good solvent (dimethylformamide) and a poor solvent (ethanol). Owing to this, the crosslinking reaction occurred in the amorphous phase and hardly involved the crystals. This outcome was confirmed by wide-angle X-ray diffraction data. The structural and chemical changes in the amorphous phase during crosslinking were recorded with the use of IR spectroscopy and differential scanning calorimetry. It is shown that crosslinking is accompanied by the formation of C=C bonds in the copolymer chains. The study of high-voltage polarization and conductivity during exposure to bipolar rectangular pulses suggested that crosslinking leads to an increase in the carrier concentration. It was found that the surface potentials in the films increase with an increase in the number of high-voltage pulses applied to the sample. This circumstance is attributed to the fact that the double bonds formed in the copolymer chains can effectively trap negatively charged carriers.