Cardo- phenolphthalein formaldehyde resin was studied as a binder of antifriction organoplastics. The role of the phthalide cycle in the structure of the polymer during its curing process is shown. Experimental data on the effect of processing temperature on the tribological and thermofriction properties of organoplastics reinforced with polyoxadiazole fiber are presented.

The paper presents the results of a study of the frictional characteristics of mineral dispersed fillers — graphite and schungite. It is shown that the introduction of a mixture of these dispersed mineral modifiers into phenol-formaldehyde composites reinforced with cotton fabric leads to a significant improvement in tribological characteristics.

Cardo- phenolphthalein formaldehyde resin was studied as a binder of antifriction organoplastics. The role of the phthalide cycle in the structure of the polymer during its curing process is shown. Experimental data on the effect of processing temperature on the tribological and thermofriction properties of organoplastics reinforced with polyoxadiazole fiber are presented.

Poly(arylene ether ketone)s containing pendent bulky cardo groups in the monomer unit, while having a high antifrictionality, do not obey the earlier established regularity of the relationship between chemical structure and friction. The necessity of taking into account the flexibility of macromolecules is an additional factor for these polymers. To XPS study the tribochemical processes of carded polymers, “flexible chain” and “rigid chain” copolyarylene ether ketones (co-PAEKs) were used. It was found that the flexible moieties of the macromolecule favor a decrease in the friction coefficient and an increase in the wear resistance. Impaired tribochemical indices of the rigid cardo polymer are caused by active tribodestruction of phthalimidine groups.

The causes of an abrupt decrease in the wear and in the friction coefficient from 0.6 to 0.24 for poly(arylene ether ketone) copolymers containing 10, 15, and 25 mol % of cardo bisphenol moieties in the main chain have been investigated. The presence of cardo groups in the copolymers promotes an increase in the microhardness from 12 to 22 kgf/mm2 and maintains a high antifrictionality as a parameter that characterizes the dispersion interaction energy contribution to the total energy of the intermolecular interaction. The XPS examination of the copolymers has shown that only in the case of poly(arylene ether ketone) copolymer containing 10 mol % cardo groups, wear products do not undergo any considerable structural changes in the friction process. The studies demonstrated that a significant improvement of friction-and-wear parameters in the case of a poly(arylene ether ketone) copolymer containing a 10 mol % of cardo groups is caused by an optimal combination of increasing microhardness, formation of a discrete surface, and by maintaining a high antifrictionality. With increasing cardo group content in the copolymers to 15 and 25%, a gradual increase in the friction coefficient to 0.5 and 0.75, respectively, was observed.

Methods of modifying polyarylate based on bisphenol A and mixture of iso- and terephthalic acids by a representative of a promising class of polymers — polyarylene ether ketone have been discussed in this article. Comparative thermomechanical and thermofriction tests of two grades of poly(arylene ether ketone)based on bisphenol A and 4,4'-difluorobenzophenone (PAEK-32 and PAEK-34) have been carried out. It has been established that PAEK-34 is the most suitable for modifying polyarylate, which is confirmed by its higher softening temperature and stable friction coefficient at elevated temperatures. The thermomechanical properties and molecular mass distribution of amorphous polyarylene ether ketone before and after pressing have been studied. It has been established that during processing of poly(arylene ether ketone) PAEK-34 it’s molecular weight increases from 123 to 178 thousand a.m.u. with simultaneous change in the character of the molecular mass distribution from bimodal to unimodal. At the same time, there is a sharp decrease in the content of the low molecular weight fraction from 23.32 to 7.2%. Theoretical compatibility of polyarethylene ether ketone PAEK-34 and polyarylate DV based on the theory of solubility of substances has been studied. It was established that mixtures of these polymers are compatible for any components’ ratio according to the calculation results. The thermomechanical characteristics of the mixtures obtained on the basis of polyarylate and polyarylene ether ketone have been evaluated. It has been established that the growth of heat resistance of the mixture during processing is caused by intermolecular interaction of components with the formation of new chemical compounds having a block-type copolymer structure. This was confirmed by the change in the nature of the molecular-mass distribution of the polymer mixture upon the transition of the pressing temperature from 260 °C to 300 °C. It was established that the optimal conditions for the realization of block-copolymer formation reaction are created at 300 °C.

Triboactivity of polymers is studied as a chemical process that significantly affects their friction. The examples are provided which demonstrate the tribochemical activity in linear amorphous polymers, such as polyphenylquinoxalines, polyacrylonitrile, crystalline aliphatic polyamides and polyaramids as well as polyamidoimide binder. The process of self-organization in a heat-resistant composite material based on a phenol formaldehyde polymer is analyzed in detail.

The main reasons reducing the lifetime and failure of implants are tribo-oxidative processes. Stabilizing additives are used to inhibit tribo-oxidative activity and increase the lifetime of the implant. The most common stabilizer is α-tocopherol. The biocompatible stabilizer of a number of flavonoids, dihydroquercetin, was selected as the thermo- and tribo-oxidative stabilizer of UHMWPE. Dihydroquercetin (DHQ) stabilizes peroxide radicals formed as a result of the tribological process (friction of UHMWPE) by detaching a hydrogen atom from OH groups with the formation of a non-reactive phenoxyl radical. A comparative analysis of the samples, stabilized with DHQ and α-tocopherol, was carried out. The samples studied were prepared by direct compression molding at a temperature of 190ºС. The comparative study of thermo- and tribo-oxidative stability of UHMWPE samples modified with DHQ and α-tocopherol evidences that the thermo-oxidative stability induced with DHQ is higher that of α-tocopherol. In the first case the thermal-oxidative stability of the composition is maintained up to a temperature of 230 °C. Evolution of friction compositions at temperatures higher than that of the human body was investigated. Such tests were conducted using a gradual increase in friction velocity. During the tests, an increase in weight of initial UHMWPE and the composition with α-tocopherol induced by tribo-oxidative processes was observed. The introduction of dihydroquercetin, a highly effective biostabilizer of thermal oxidation, leads to the conservation of the original weight of the samples. When selecting a counterbody for the developed composition with DHQ, a study was conducted of friction on steel 3X13 and Ti6Al alloy used in medicine and in endoprostheses of artificial joints. It was found that the best results are obtained in the case of using a steel counterbody.

A general approach to understanding the complex nature of the friction of friction-resistant heat-resistant thermoplastics has been developed. This approach made it possible to idenify two main factors determining the basic character of the friction of these polymers on steel: the dispersion component of the intermolecular interaction energy and the molecular weight. Specific properties of some polymers can be used to refine the friction behavior.

The effect of the molecular weights of amorphous polyarylene ether ketone (PAEK) synthesized by the reaction of 4,4'-difluorobenzophenone with 2,2-bis (4'-hydroxyphenyl) propane (bisphenol A) potassium diphenolate on its tribological characteristics has been studied. In the case of the friction of a sample with M w < 200 × 10 3 Da, its high wear resistance and the coefficient of friction decreased to 0.4, even at high pressures of up to 10 MPa. These properties of high-molecular-weight PAEK are due to the high contribution of the weak dispersion forces into the intermolecular interaction energy of the polymer. Low wear determines the nature of tribodestruction, which, during the process of self-organization, leads to the appearance of a positive gradient in the physicomechanical properties in the surface layers. The XPS study shows that, during PAEK pressing at 260°C, the intensive oxidation of a thin surface layer occurs.

Thermal and tribochemical processes in a phenol formaldehyde composite reinforced with polyoxadiazole fibers and modified with finely dispersed particles of a polyformaldehyde copolymer were studied by mass spectrometry and X-ray photoelectron spectroscopy. Under thermal exposure to polyformaldehyde, the liberated formaldehyde sharply reduces the amount of phenol that is released. In the case of friction, polyformaldehyde is a bifunctional modifier. It forms a discrete surface, which helps reduce the coefficient of friction. The released products can play the role of a "tribochemical lubricant" and, at the same time, a cross-linking agent. Tribological tests of the modified composite showed a decrease in the coefficient of friction (from 0.20 to 0.18) compared with the original composite, and a significant (approximately 2-fold) decrease in the vibration amplitude of the friction coefficient.

Progress in high-tech industry sectors, including aerospace, shipbuilding etc. combined with the implementation of additive manufacturing technologies, leads to more stringent requirements for the performance of composite materials, including thermoplastic-based ones. In order to improve the properties of these materials, addition of various polymeric modifiers, which have different levels of compatibility with the major thermoplastic component, is often required. Polyarylate DV manufactured by NPO “Polymersintez” was selected as major matrix component. It is synthesized via emulsion polycondensation of Bisphenol A and equimolar mixture of isophtalyl chloride and terephthalyl chloride. The compatibility level of modifier with the polyarylate matrix was the main criterion for the modifier selection. It was estimated by calculation from the values of surface tension, molar volume and solubility parameters. Five modifiers were selected: four with polyarylate structure and one is based on polyphenylene sulfide. The effect of compatibility of polyarylates based on polymeric mixtures on their thermomechanical and tribological properties was studied. It has been shown that the most sensitive to changes in the polymer mixtures components chemical structure were tribological characteristics. The presence of compatibility in polymer compositions of polyarylates promotes the improvement of thermo-friction indexes. The co-polymer formed in a mixture of DV-FV polyarylates with a completed process of intermolecular interaction has a stable friction character over a wide temperature range. The stabilization of tribological characteristics in polymer mixtures such as polyarylate-polyphenylene sulfide in the absence of compatibility occurs after additional high-temperature (250 °C) frictional treatment.Forcitation:Sorokin A.E., Krasnov A.P., Goroshkov M.V., Klabukova L.F., Zyuzina G.F. Influence of compatibility in the polyarylate’s blends on friction. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 58-67

The friction of an ultrathin coating (5 nm) formed as a result of the modifier segregation towards the surface of modified epoxy polymer in the form of multiple short chains of Si, F modifier has been investigated in a range of loads from 0.1000 to 0.0005 N. During the investigation of the reverse friction of ceramic (Al2O3) ball on the coating, the sharp decrease in coefficient of friction at a load of less than 0.002 N has been shown, which is probably caused by the change in the mechanism of friction during the transition of friction to the zone of a self-lubricating coating. Under these conditions, the difference between the static coefficient of friction (stop effect) and dynamic coefficient of friction increases.

The effect of ultrasound treatment of expanded graphite (EG) on structure and tribological behavior of PTFE-EG composites filled with 5 mass % of EG is studied. It is found that sonicated EG (EG(S)) increases the friction coefficient of PTFE composite compared to that of the composite filled with the original EG (EG(O)). Filling with EG allows to reduce the wear rate of PTFE up to a factor of approximate to 700 to Kw approximate to 6x10-(7) mm(3)/ Nm depending on the friction conditions. At high sliding velocity causing high frictional heating, the wear rate of PTFE-EG(S) composite is several times higher than that of PTFE-EG(O) owing to reduced thermooxidative stability of both EG(S) and PTFEEGS composite, whereas at friction regimes with small frictional heating the wear rates of the two composites are similar.It is also found that the wear rates reduce with the increasing content of iron carboxylates in the friction layer of the composites, which evolve from interaction of the counterface steel with the products of PTFE tribochemical degradation. The counterface steel is transferred onto the friction surface of the composite specimen in the form of spherical particles of micrometer-nanometer size range according to SEM and electron probe analysis. Chemical bonding of the fine steel particles to the tribochemically modified macromolecules of PTFE reinforces the running film and improves the wear resistance of the composites. Both the content of transferred iron and the wear resistance of PTFE-EG composites increase significantly with the increase in the relative humidity of the ambient air.EG filler aggregates delaminate at friction into thinner platelets of nanographite which may accumulate in the friction surface layer of the composites. Accumulation of the filler is more expressed in highly wear resistant composites and has an additional effect on reduction of the wear rate.

Nanocrystalline graphite samples obtained by the sonication of TEG in water and glycerol have been investigated by XPS and AES. The ultrasonic treatment of graphite leads to the loosening of its edges, increases the number of defects in layers, and promotes the penetration of a modifying fluid into the interlayer space in the peripheral areas. The dissociation on internal defects with the formation of C–OH groups is possible in the case of water. In friction against a thoroughly polished steel surface, modified graphite particles have demonstrated a lower coefficient of friction but a shorter lifetime than original graphite.