Objectives. To investigate the properties of intumescent fire-retardant materials based on plasticized polyvinyl chloride and oxidized graphite as functions of their content of nitrile butadiene rubber.Methods. Intumescent fire-retardant materials with different contents of nitrile butadiene rubber (from 0 to 20 wt %) were obtained. The materials were prepared in the form of a sheet 38–52 mm wide and 1.5–1.9 mm thick by means of flat-die extrusion using a twin-screw compounding extruder. The raw materials used were plasticized polyvinyl chloride with a K-value of 71, nitrile butadiene rubber with a bound acrylonitrile content of 31–35%, oxidized graphite, and ultrafine aluminium hydroxide. The properties of the raw materials and the resulting fire-retardant materials were investigated using infrared spectroscopy, thermal analysis, scanning electron microscopy, as well as mechanical tests, flammability tests, and thermal shock foaming tests.Results. The mechanical, thermal, and fire-retardant properties of the obtained materials were studied as functions of their contents of nitrile butadiene rubber. The dynamics of foaming in the temperature range from 300 to 800°C were also explored. The flammability rating was determined. The dependence of fire-retardant properties on the melt viscosity of fire-retardant materials was described. The thermal properties were found to be in the temperature range of 40 to 900°C.Conclusions. The study found that the introduction of nitrile butadiene rubber into fire-retardant materials leads to a change in a number of properties: a decrease in density and hardness; a decrease in tensile strength; an increase in relative elongation; an increase in melt viscosity by 16 times; and, accordingly, a decrease in foaming rate by a factor of 1.43–1.65. It was established that the foaming rate has a linear dependence on the viscosity of the melt of fire-retardant materials. The introduction of rubber leads to an increase in the strength of foamed char by a factor of 4.8. Thermal analysis showed that increasing the rubber content leads to an increase in heat resistance from 222 to 236°C, and resistance to oxidation of foamed graphite in the composition of foamed char from 601 to 659°C. The presence of rubber does not have a noticeable effect on flammability. The established flammability rating for all compositions is V-0.

The present paper describes the influence of various types of expandable graphite on the fire-retardant properties of intumescent coating based on PVC binder. The optimal content of the expandable graphite required to achieve maximum fire protection efficiency was determined by incorporation of different amount of expandable graphite (5

The impact of introducing a nonwoven polyamide PA 12-E material on the mechanical properties of polymer composite materials based on epoxy autoclave prepreg T107 has been investigated. This study demonstrates that the incorporation of nonwoven fabric does not lead to a decrease in the mechanical properties of the composites. A significant advantage of composites reinforced with nonwoven fabric is their enhanced impact resistance. During a free impact with an energy of 6.67 J per 1 mm of the sample, complete breakdown with fiber destruction occurs in samples without nonwoven material. In contrast, samples containing nonwoven material exhibit damage characterized by stratification without compromising the fibers. The compressive strength after impact increased from 260 to 320 MPa with the addition of nonwoven material. Consequently, the proposed modification of the commercial prepreg will expand the material’s range of applications and enhance safety, particularly in aircraft structures.

We have proposed and developed a method for measuring the thermal conductivity of highly efficient thermal conductors. The measurement method was tested on pure metals with high thermal conductivity coefficients: aluminum (99.999 wt.% Al) and copper (99.990 wt.% Cu). It was demonstrated that their thermal conductivities at a temperature of T = 22 ± 1 °C were <λAl> = 243 ± 3 W/m·K and <λCu> = 405 ± 4 W/m·K, which was in good agreement with values reported in the literature. Artificial graphite (ρG1 = 1.8 g/cm3) and natural graphite (ρG2 = 1.7 g/cm3) were used as reference carbon materials; the measured thermal conductivities were <λG1> = 87 ± 1 W/m·K and <λG2> = 145 ± 3 W/m·K, respectively. It is well established that measuring the thermal conductivity coefficient of thin flexible graphite foils is a complex metrological task. We have proposed to manufacture a solid rectangular sample formed by alternating layers of thin graphite foils connected by layers of ultra-thin polyethylene films. Computer modelling showed that, for equal thermal conductivities of solid products made of compacted thermally exfoliated graphite and products made of a composite material consisting of 100 layers of thin graphite foil and 99 layers of polyethylene, the differences in temperature fields did not exceed 1%. The obtained result substantiates our proposed approach to measuring thermal conductivity of flexible graphite foil by creating a multi-layer composite material. The thermal conductivity coefficient of such a composite at room temperature was <λGF> = 184 ± 6 W/m·K, which aligns well with measurements by the laser flash method.

Flexible graphite foils with varying thicknesses (S = 282 ± 5 μm, M = 494 ± 7 μm, L = 746 ± 8 μm) and an initial density of 0.70 g/cm3 were obtained using the nitrate method. The specific electrical and thermal conductivity of these foils were investigated. As the density increased from 0.70 g/cm3 to 1.75 g/cm3, the specific electrical conductivity increased from 69 to 192 kS/m and the thermal conductivity increased from 109 to 326 W/(m·K) due to the rolling of graphite foils. The study showed that conductivity and anisotropy depend on the shape, orientation, and contact area of thermally expanded graphite (TEG) mesoparticles (mesostructural factor), and the crystal structure of nanocrystallites (nanostructural factor). A proposed mesostructural model explained these increases, with denser foils showing elongated, narrowed TEG particles and larger contact areas, confirmed by electron microscopy results. For graphite foils 200 and 750 μm thick, increased density led to a larger coherent scattering region, likely due to the rotation of graphite mesoparticles under mechanical action, while thinner foils (<200 μm) with densities > 1.7 g/cm3 showed increased plastic deformation, indicated by a sharp reduction in the coherent scattering region size. This was also evident from the decrease in misorientation angles with increasing density. Rolling reduced nanocrystallite misorientation angles along the rolling direction compared to the transverse direction (TD) (for 1.75 g/cm3 density ΔMA = 1.2° (S), 2.6° (M), and 2.4° (L)), explaining the observed anisotropy in the electrical and mechanical properties of the rolled graphite foils. X-ray analysis confirmed the preferred nanocrystallite orientation and anisotropy coefficients (A) using Kearns parameters, which aligned well with experimental measurements (for L series foils calculated as: A0.70 = 1.05, A1.30 = 1.10, and A1.75 = 1.16). These calculated values corresponded well with the experimental measurements of specific electrical conductivity, where the anisotropy coefficient changed from 1.00 to 1.16 and mechanical properties varied from 0.98 to 1.13.

In this work, the possibilities of introducing nitric acid molecules with a solution concentration of 75–98% into graphite matrices in the form of synthetic quasi-monocrystal graphite and natural graphite of four different farcical compositions were determined in order to identify factors of the acid concentration and graphite size on the production process and properties of graphite foil. The actual stage of graphite intercalation in the resulting compound was determined by X-ray diffraction analysis (XRD). The differences in the temporal patterns of the intercalation process for different intercalation stages (from 2 to 5) are demonstrated. The obtained acid solutions were used in the manufacturing of flexible graphite foil from natural graphite of four different particle size distributions. The mass characteristics of the intermediate and final products were determined as the graphite was treated with these solutions. The actual difference in the characteristics of the raw materials and intermediate synthetic products was recorded by measuring the electrical conductivity of the final material, graphite foil. Analysis of the results has shown that a decrease in the acid concentration of a solution leads to an increase in the intercalation stage. Weight gains due to the formation of oxygen-containing groups and the introduction of water and acid were reduced by this effect, whereas the yield of the final product (thermally expanded graphite) increased. Foil made of thermally expanded graphite obtained from intercalated compounds of high stages had greater electrical conductivity. An improvement in the conductive properties of the material implies that there should be fewer defects in its structure.

The paper presents a comparative study of the influence of various flame retardants on the process of thermo-oxidative decomposition of ethylene vinyl acetate. The degree of influence of different groups of flame retardants on the thermal stability of the polymer composition, on the processes of ethylene vinyl acetate degradation at different stages in a wide temperature range is described. It was found that the flame retardants used tend to increase the thermal stability of the polymer composition, shift the intervals of polymer decomposition to a higher temperature region, while reducing the value of mass loss. Flame retardants form refractory and highly condensed phases that affect the process of outgassing during decomposition of polymer compositions.

The physical and mechanical properties and structural condition of flexible graphite foils produced by processing natural graphite with nitric acid, hydrolysis, thermal expansion of graphite and subsequent rolling were studied. The processes of obtaining materials and changing their characteristics has been thoroughly described and demonstrated. The structural transformations of graphite in the manufacture of foils were studied by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). A decrease in the average size of the coherent scattering regions (CSR) of nanocrystallites was revealed during the transition from natural graphite to thermally expanded graphite from 57.3 nm to 20.5 nm at a temperature of 900 °C. The rolling pressure ranged from 0.05 MPa to 72.5 MPa. The thickness of the flexible graphite foils varied from 0.11 mm to 0.75 mm, the density—from 0.70 to 1.75 g/cm3. It was shown that with an increase in density within these limits, the compressibility of the graphite foil decreased from 65% to 9%, the recoverability increased from 5% to 60%, and the resiliency decreased from 10% to 6%, which is explained by the structural features of nanocrystallites. The properties’ anisotropy of graphite foils was studied. The tensile strength increased with increasing density from 3.0 MPa (ρ = 0.7 g/cm3) to 14.0 MPa (ρ = 1.75 g/cm3) both in the rolling direction L and across T. At the same time, the anisotropy of physical and mechanical properties increased with an increase in density along L and T to 12% with absolute values of 14.0 MPa against 12.5 MPa at a thickness of 200 μm. Expressed anisotropy was observed along L and T when studying the misorientation angles of nanocrystallites: at ρ = 0.7 g/cm3, it was from 13.4° to 14.4° (up to 5% at the same thickness); at ρ = 1.3 g/cm3—from 11.0° to 12.8° (up to 7%); at ρ = 1.75 g/cm3—from 10.9° to 12.4° (up to 11%). It was found that in graphite foils, there was an increase in the coherent scattering regions in nanocrystallites with an increase in density from 24.8 nm to 49.6 nm. The observed effect can be explained by the coagulation of nanocrystallites by enhancing the Van der Waals interaction between the surface planes of coaxial nanocrystallites, which is accompanied by an increase in microstrains. The results obtained can help discover the mechanism of deformation of porous graphite foils. The obtained results can help discover the deformation mechanism of porous graphite foils. We assume that this will help predict the material behavior under industrial operating conditions of products based flexible graphite foils.

C/C materials represent as materials with specific performance, therefore they are applied in various industries. It is essential to figure out the paths to predict, to provide and to enhance their properties to obtain high performance products. It is well known that strong matrix/reinforcer adhesion provides better strength utilization and therefore better properties for the majority of composite materials of all types (Heim in Compos Part B Eng 54:365–370, 2013), (Hancock and Cuthbertson in J Mater Sci 5:762–768, 1970), (Yang et al. in Polymers 13:2764, 2021). However some researchers note that strong adhesion in the materials that are exposed to high temperatures leads to cracking and significant properties degradation (Vignoles et al. in The Control of interphases in carbon and ceramic matrix composites, Wiley, Hoboken, 2012), (Zhang et al. in Compos Struct 340, 2024). In this work, the effect of the pyrocarbon layer applied on the surface of carbon fibers used for reinforcement of formaldehyde novolac resin based carbon/carbon (C/C) material prepregs was investigated. For the first time we used this effect to prove that lower matrix/reinforcer adhesion in C/C materials prepregs leads to better material behavior during pyrolysis, which results in higher mechanical properties of the pyrolised samples in comparison with the samples demonstrating stronger matrix/reinforcer adhesion. The prepregs were thermally treated at various temperatures, the physical and mechanical performance evolution of the prepregs at different carbonization stages were analyzed. Comparative study of the features of the prepregs with pyrocarbon coated and uncoated carbon fiber as a reinforcement were carried out. The damping effect of the pyrocarbon on the fiber surface were advertised, allowing to mitigate the carbonization-caused effects. The prepregs reinforced with pyrocarbon-modified carbon fibers demonstrated lower cracking performance and higher mechanical performance comparing with the uncoated fiber reinforced prepregs.

This study investigates the tribological properties of graphite foils (GF) with densities of 1.0, 1.3, and 1.6 g/cm3, produced from purified natural graphite of different particle sizes (40–80 μm, 160–200 μm, >500 μm). Surface roughness was measured after cold rolling and friction testing at static (0.001 mm/s) and dynamic conditions (0.1 Hz and 1 Hz). Results showed that static friction tests yielded similar roughness values (Sa ≈ 0.5–0.7 μm, Sq ≈ 0.5–1.0 μm) across all densities and particle sizes. Dynamic friction tests revealed increased roughness (Sa from 0.7 to 3.5 μm, Sq from 1.0 to 6.0–7.0 μm). Friction coefficients (µ) decreased with higher sliding speeds, ranging from 0.22 to 0.13. GF with 40–80 μm particles had the lowest friction coefficient (µ = 0.13–0.15), while 160–200 μm particles had the highest (µ = 0.15–0.22). Density changes had minimal impact on friction for the 40–80 μm fraction but reduced friction for the 160–200 μm fraction. Young’s modulus increased with density and decreased with particle size, showing values from 127–274 MPa for 40–80 μm, 104–212 MPa for 160–200 μm, and 82–184 MPa for >500 μm. The stress–strain state in the graphite foil samples was simulated under normal and tangential loads. This makes it possible to investigate the effect of the anisotropy of the material on the stress concentration inside the sample, as well as to estimate the elasticity modulus under normal compression. Structural analyses indicated greater plastic deformation in GF with 40–80 μm particles, reducing coherent-scattering region size from 28 nm to 24 nm. GF samples from 160–200 μm and >500 μm fractions showed similar changes, expanding with density increase from 18 nm to 22 nm. Misorientation angles of GF nanocrystallites decreased from 30° to 27° along the rolling direction (RD). The coherent scattering regions of GF with 40–80 μm particles increased, but no significant changes in the coherent scattering regions were observed for the 160–200 μm and >500 μm fractions during dynamic friction tests. Microstrains and residual macrostresses in GF increased with density for all fractions, expanding under higher friction-induced loads. Higher values of both stresses indicate a higher level of accumulated deformation, which appears to be an additional factor affecting the samples during friction testing. This is reflected in the correlation of the results with the roughness and friction coefficient data of the tested samples.

Synthetic graphite of complex fractional composition was mixed with phenolic resin as a binder and pore-forming component. The mixtures were pressed and subsequently heat-treated to obtain porous matrices. The structural transformations of phenolic resin by heating up to 900 °C in oxygen and inert gas media were studied and the patterns of amorphization of fixed carbon formed on the walls of the pore system during carbonization were investigated. We found regularities in the changes in matrix volume density in the function of the open porosity and the average pore diameter. It is shown that, in order to obtain graphitized carbon matrices with a density of 1 g/cm3 and an open porosity of at least 50%, it is necessary to introduce no more than 20% of phenolic resin into the molding powder with an equal content of 60, 100 and 250 μm graphite fractions. This allows for high intensity and completeness of bulk silicon infiltration.

The paper presents the results of a study of the effect of the composition of PVC compound on the heat resistance of fire-retardant materials based on it. The study was carried out on the example of PVC suspension grades of different molecular weight and with different content of the plasticizer. As a result, it was shown that the heat resistance of fire-retardant materials filled with oxidized graphite is significantly affected by both the content of the plasticizer and the molecular weight of PVC. There is also a dependence of the change in the heat resistance of fire-retardant materials on the viscosity of the polymer matrix.

An automated system for measuring the thermal conductivity of functional and structural materials was developed. The main building blocks of the setup are the following: heating unit and cooling unit creating a heat flux gradient in the test sample; thermal resistances for temperature registration and control; and thermal pads for better contact between parts of the setup and the sample. The effect of the thermal conductivity of thermal pads and thermal resistances on the distribution of thermal fields in the developed setup was studied by computer modelling. A control software for the measuring setup was developed based on the hardware implementation of the steady-state Fourier’s law-based method for the determination of thermal conductivity. The stopping criterion for the setup control software is the equality of heat fluxes in the heating and cooling units, as well as the stability of the thermal conductivity coefficient readings. The testing and calibration of the device were carried out using a sample of pure aluminum (99.999 wt.% Al). It was found that the experimental value of the thermal conductivity coefficient of the aluminum sample at room temperature (T = 22 °C) is <λ> = 243 ± 3 W/m·K. This value of the thermal conductivity coefficient is consistent with the literature data and experimental values obtained by the laser flash method, which ranges within λ = 210–260 W/m·K.

Graphite intercalated compounds (GICs) with different stage numbers are prepared chemically from highly oriented pyrolytic graphite (HOPG), natural flaked graphite (FG) and nitric acid. Exfoliated graphite samples (EG-T) are synthesized from GICs via water treatment followed by thermal shock. The aim of this work is to investigate the dependence of the inner EG-T pore structure on the extent of oxidation and type of graphite by processing scanning electron microscopy (SEM) micrographs of EG-T cross sections. A procedure is developed on the basis of a deep convolutional neural network that speeds up image processing with no appreciable loss of accuracy. A strong correlation is found between EG-T pore structure parameters, the depth of oxidation, and the type of graphite.

The process of thermal oxidation decomposition of phthalonitrile resins which had been post-cured at various temperatures (603 K, 623 K and 648 K) was studied using dynamic and isothermal measurement modes. It was shown that the degradation process is a complex branched four-stage process. We have concluded that the first stage is an nth order reaction with autocatalysis. The second stage is described with the expanded Prout-Tompkins equation which corresponds to an autocatalytic solid-state reaction caused by the formation of im-perfections at the reaction surface. The third and fourth stages are also reactions of the nth order. The phtha-lonitrile resin post-cured at 603 K exhibited better thermal stability than the resins post-cured at 623 K and 648 K based on the activation energies of the 1st stage - 132 kJ/mol, 104 kJ/mol, and 106 kJ/mol respectively. These data were confirmed by comparable experimental activation energy values (111 kJ/mol, 87 kJ/mol, 86 kJ/mol respectively) and changes in mass loss and flexural strength values determined during long-term thermal aging in the temperature range of 553-623 K. It was shown that the phthalonitrile resin post-cured at 603 K with the initial flexural strength of 107 MPa is suitable for long-term application at temperatures up to 573 K.

This work concerns the thermal-oxidative aging behavior of phthalonitrile thermosets and composites at 280-350 degrees C. The easy-to-process resin containing bis(3-[3,4-dicyanophenoxy]phenyl)phenyl phosphate with APB as curing agent and the resin-based composites post-cured at 330 degrees C, 350 degrees C, and 375 degrees C were studied. The phthalonitrile thermosets post-cured at 330 degrees C retained flexural strength of 77 MPa after 200 h of thermal aging at 280 degrees C and 37 MPa (40%) after the same time at 300 degrees C while the resins post-cured at 350 degrees C and 375 degrees C lost over 80% of the flexural strength in these experiments. The same trend of faster oxidation of the samples post-cured at higher temperatures was observed for the composites. For the first time, crosslinking reactions were observed during the aging, despite the aging temperatures being below the Tg of thermosets. Thus, the work shows a high long-term thermal oxidative stability of the studied phthalonitrile resins at temperatures up to 300 degrees C and fast destruction of the materials at 350 degrees C despite the resin decomposition temperatures determined by dynamic TGA being over 500 degrees C. The work has shown the negative effect of high-temperature post-curing on the operating properties of the phthalonitrile composites as constructive materials for long-term application at elevated temperatures.

Introducti on. In the last few years, plasticized PVC filled with intumescent materials was used as a passive fire protection component. Important characteristics of such materials are physical and mechanical properties, degree and temperature profile of foaming and flammability. These characteristics significantly depend on the properties of the polymer matrix of the intumescent material. In this paper, the relationship between the composition of PVC compound and the properties of flame-retardant materials based on it is investigated. Materials and m ethods of research. Intumescent flame-retardant materials based on PVC compound of different compositions were used in this paper: with changes in the molecular weight of PVC and plasticizer content in the composition of the PVC compound. The PVC compound was obtained by intensive mixing of PVC powder with a plasticizer and a complex stabilizer. The flame retardant material was obtained by dry mixing powders of PVC compound, elastomeric component, flame retardant and intumescent material, followed by extrusion of the mixture through a flat slot die. A set of properties was determined for the obtained materials: density, hardness, tensile strength and elongation, heat resistance, degree of foaming in the range of 300 – 800 °C , flammability, fracture surface morphology, melt flow index. Results and their discussion. The paper presents the results of the study of physical, mechanical and thermal properties of the flame retardant materials and their flame retardant effectiveness. It was found that tensile strength when introducing fillers into polymer material decreases by 20 – 62 %, which is typical for fillers with low adhesion to the polymer. At the same time, hardness increases up to 32 %. The viscosity of the polymer matrix at the base of the flame retardant material determines the process of its foaming. Conclu sions. For the flame retardant materials based on PVC compound, the following is observed: 1) reduction of physical and mechanical properties relative to the polymer material; 2) the presence of oxidized graphite in the composition of the flame retardant material determines the decrease in the thermal resistance of the polymer matrix when producing fire-retardant materials; 3) viscosity of polymer base in the composition of the flame retardant material is an indicator that determines the change in heat resistance and degree of foaming.

Graphite intercalated compounds (GICs) with different stage numbers were prepared from highly oriented pyrolytic graphite (HOPG) and nitric acid using a chemical method. Exfoliated graphite (EG-T) was synthesized from GICs by water treatment followed by thermal shock. The effects of the graphite oxidation depth on the EG-T thermal expansion coefficient, volatile content, and total porosity were examined. However, the main purpose of this work was investigation of the dependence of the inner EG-T pore structure on the level of oxidation. Thus, we studied the micro- and mesopore structure and specific surface area by nitrogen porosimetry and the modern 2D-NLDFT method to calculate the pore size distribution and pore volume. As well, we performed a mercury porosimetry experiment to determine the macropore characteristics. We examined the pore space using a number of scanning electron micrographs of EG-T particle cross-sections using an image processing technique. In this way we showed the strong correlation between the EG-T pore structure parameters and oxidation depth of graphite.

Phthalonitrile resins (PN) are known for their incredible heat resistance and at the same time poor processability. Common curing cycle of the PN includes dozens hours of heating at temperatures up to 375 °C. This work was aimed at reducing processing time of phthalonitrile resin, and with this purpose, a novolac oligomer with hydroxyl groups fully substituted by phthalonitrile moieties was synthesized with a quantitative yield. Formation of the reaction byproducts was investigated depending on the synthesis conditions. The product was characterized by 1H NMR and FT-IR. Curing of the resins with the addition of different amounts of novolac phenolic as curing agent (25, 50 and 75 wt.%) was studied by rheological and DSC experiments. Based on these data, a curing program was developed for the further thermosets' investigation: hot-pressing at 220 °C and 1.7 MPa for 20 min. TGA showed the highest thermal stability of the resin with 25 wt.% of novolac (T5% = 430 °C). The post-curing program was developed by the use of DMA with different heating rates and holding for various times at 280 or 300 °C (heating rate 0.5 °C/min). Carbon and glass fiber plastic laminates were fabricated via hot-pressing of prepregs with Tg's above 300 °C. Microcracks were formed in the CFRP, but void-free GFRP were fabricated and demonstrated superior mechanical properties (ILSS up to 86 MPa; compressive strength up to 620 MPa; flexural strength up to 946 MPa). Finally, flammability tests showed that the composite was extinguished in less than 5 s after the flame source was removed, so the material can be classified as V-0 according to the UL94 ratings. For the first time, fast-curing phthalonitrile prepregs were presented. The hot-pressing cycle of 20 min with 150 min free-standing post-curing yielded composites with the unique properties. The combination of mechanical properties, scale-up suitable fast-processing and inflammability makes the presented materials prospective for applications in the electric vehicle industries, fast train construction and the aerospace industry.

Features of utilizing materials based upon thermally expanded graphite (TEG) as barrier materials in electric baths are considered in the article. Experience of industrial application of a graphite foil barrier layer for protecting the refractory part of reduction cells, and advantages and disadvantages of a graphite foil barrier material are analyzed. An area for improving the properties of the barrier materials with the help of antioxidation impregnation is proposed.