Polyimides (PIs) are materials that are resistant to high temperatures and crucial for the manufacturing of films, fibers, coatings, and 3D-printed items. PIs are widely used as electrically insulating materials in electronics and electrical engineering. This study investigated how the chemical structure (i.e., choice of initial monomers), the synthesis conditions of the prepolymer (i.e., choice of amide solvent), and the conditions for forming polyimide films (i.e., final curing temperature) affect the thermophysical properties and short-term electrical strength of obtained polyimide films of different chemical structures. In this work, we varied the compositions of the dianhydrides used for synthesizing polyamic acids—pyromellitic acid (PMDA), tetracarboxylic acid diphenyl oxide (ODPA) and 1,3-bis(3′,4-dicarboxyphenoxy)benzene acid (R)—with a constant diamine: 4,4′-oxydianiline (ODA). Additionally, we varied the amide solvents employed: N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). This study represents the first investigation into how the choice of solvent in the synthesis of thermoplastic polyimide prepolymers affects their short-term electrical strength. The molecular weights of the polyamic acids were determined using gel permeation chromatography (GPC). The deformation and strength characteristics of the investigated films were also assessed. The thermophysical properties of the polyimides were evaluated via dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). X-ray diffraction analysis and infrared spectroscopy (IR) were conducted on the examined film samples. The short-term electrical strength was also evaluated.

Results of own works of the authors and works of the Russian, Japanese, Korean and American experts in creation nanocomposites of refractory metals with increased strength characteristics for cathodes are analyzed in this report. It is shown, that though monocrystals have shown the better characteristics in comparison with traditional polycrystals as cathodes, more radical way of increase of operational characteristics of the X-ray tubes is application refractory nanostructural materials. Some results of investigations in which the work function electrons of nanocrystal tungsten is lower by 0.8 eV than that of traditional tungsten are given. This effect is able to increase the intensity of X-radiation considerably (by a factor of more than 5) at the same cathode temperatures or decrease the temperature of a cathode by 400 °C at the same intensity of X-radiation.

The electret properties and electrical conductivity of polypropylene-polyphenylene sulfide (PP-PPS) composites were studied. The results reveal that the effective surface charge density is higher in fibrous-porous materials (FPM) compared to film-based composites. In the electrical conductivity-temperature dependence, a characteristic up-turn is observed at a temperature of 110 °C, where the high-temperature segment of the curve corresponds to the intrinsic conductivity of the composite. The low-temperature segment can be attributed to structural defects. Additionally, two relaxation maxima are identified in the thermally stimulated depolarization (TSD) current spectra. The low-temperature peak is associated with the charge relaxation at the matrix-filler interface, a phenomenon driven by Maxwell — Wagner polarization. The high-temperature maxima are likely related to the relaxation of charges governed by the intrinsic conductivity of PP in its amorphous phase. Исследованы электретные свойства и электропроводность полимерных композитов полипропилен-полифениленсульфид (ПП-ПФС). Показано, что эффективная поверхностная плотность заряда значительно выше у волокнисто-пористых материалов (ВПМ) по сравнению с пленочными. Установлено, что на графиках зависимостей удельной электропроводности композитов от обратной температуры наблюдается излом при температуре примерно 110 °C. Высокотемпературный участок кривой характеризует собственную проводимость диэлектрика, низкотемпературный — «структурно чувствительную» или примесную. В спектрах токов термостимулированной деполяризации (ТСД) наблюдается два релаксационных максимума. Низкотемпературный максимум тока определяет процесс релаксации заряда, накопленного на границе раздела матрицы (ПП) и наполнителя (ПФС), что обусловлено поляризацией Максвелла — Вагнера. Высокотемпературный максимум тока предположительно связан с релаксационным процессом, обусловленным собственной проводимостью ПП в аморфной фазе.

This work focuses on new poly(lactic acid) electroactive packaging composite films with different mass percentages of a filler. Hydroxyapatite (HA), Poviargolum (PA) and vapor-grown carbon fibers (VGCF) were used as fillers. The films were produced by extrusion. Mechanical, electric and electretic properties were studied. Time dependences of the electretic potential differences were identified. The properties of the samples were compared and the most suitable films (0.5% HA, 5% PA, 0.5% VGCF) were chosen. В данной работе исследованы электрофизические свойства новых композиционных диэлек­триков на основе полилактида. С целью улучшения электретных свойств в полилактид были до­бавлены наполнители: гидроксиапатит, повиаргол, углеродные нановолокна. В ходе выполнения работы получены данные о скорости спада электретной разности потенциалов на образцах, об их проводимости, а также относительной диэлектрической проницаемости. Проведены испытания на механическую прочность. Проанализировано влияние наполнителей на электрофизические и механические свойства полилактида. На основе полученных данных были выбраны наибо­лее подходящие концентрации наполнителей для композитов, которые планируется применять в качестве упаковки.

АБСОРБЦИОННЫЕ И НИЗКОЧАСТОТНЫЕ ХАРАКТЕРИСТИКИ ПОЛИИМИДОВ С РАЗНОЙ ЖЕСТКОСТЬЮ МОЛЕКУЛ