Том 49, № 4 (2017)

Composite fibers were prepared by solid-state dissolution of cellulose in N-methylmorpholine-N-oxide with added tetraethoxysilane (TEOS). It was shown that adding TEOS to the cellulose matrix increased up to 16% the fiber carbon residue during heat treatment. Bonds formed between Si and C during their high-temperature treatment according to IR spectra of the composite cellulose fibers. The thermal behavior of the fibers was studied using TGA and TMA. The fiber morphology and the structure of the Si-containing additive particles were examined using SEM and TEM. The mechanical properties of carbon fibers prepared from cellulose-hydrate and composite fibers were compared.

A method for chemical deposition of thin copper coatings on lavsan fibers was developed using reduction of copper salts in alkaline solution in the presence of complexants. Sodium borohydride was used as the reductant. A nondestructive method for preliminary modification of the lavsan fibers with surface polar groups was found. Studies of the effect of the copper-salt anion on fiber metallization found that the use of copper acetate was most effective. X-ray phase analysis and electron-probe microanalysis found that the formed coating consisted of pure copper without impurities of oxides or other elements. SEM studies of the surface morphology of the copper-coated fibers showed that the obtained continuous coating consisted of Cu crystal agglomerates of dimensions ~500 nm. The metallized lavsan fibers had high electrical conductivity.

The influence of aflammit KWB on the processes occurring during the pyrolysis of a modified material is established. The optimum parameters for the process of modification of cellulose fabric with a phosphorus-containing flame retardant aflammit KWB and a cross-linking reagent quecodur DM 70 were determined to ensure the following: chemical interaction of the modifying agents, production of materials with a reduced flammability and limiting oxygen index of more than 30 vol. %, no deterioration of strength properties, a flame retardant effect, and resistance to multiple wet treatments.

On the example of ten variants of fabrics of different fibrous compositions, the features of the weathering mechanism of aging were investigated in the conditions of exposure in different latitudinal regions – the Leningrad, Kursk and Rostov regions. Using the local hydrometeorological monitoring data, the accuracy and objectivity of the assessment of weathering resistance was determined employing the insolation indices (Ii). It was revealed that the spread of the indices for one variant of fabric exposed in different geographic locations did not exceed 0-2 units (0 – 6.2% of the measured value), which confirms the accuracy of the method, its universality, and reproducibility of the results. The kinetics of the decrease in the strength of fabrics was studied as a function of the time and exposure season, from the total solar irradiance in the range from 0 to 13100 MJ/m². Weathering resistance depends not only on the type of fiber, but also on the density of the fabric and on the fabric finish. Among the ten variants studied, polyamide and polyester fabrics proved to be less weather-resistant, their Ii was 7-9 units; for mixed cotton polyester, the Ii was 22-24; for half-linen canvases, it was 12-13. Dense cotton fabrics with water repellent or flame retardant finishes had Ii values of 24-44. An approximate calculation of the duration of permissible weathering exposure for a continuous multi-month and intermittent seasonal exposure schedule is given as an example.

The influence of heat treatment on the properties of carbon fibers based on polyparaphenylene-1,3,4-oxadiazole was studied. Dependences of mass loss, shrinkage, linear density and electrical resistance of carbon fibers on the final heat treatment temperature were obtained. It is shown that a decrease in the heating rate leads to an increase in the carbon residue and the linear density of fibers, and a decrease in shrinkage and electrical resistance. It was found that at a final heat treatment temperature of 900 °C for a heating rate of 5 °C/min, the volume resistivity of the elemental carbon fiber material is 2.8 ± 0.2 mΩ.cm. Increasing the final heat treatment temperature and reducing the heating rate leads to an increase in the uniformity of the distribution of electrical resistance along the fiber.

Questions related to mathematical simulation and systems analysis of mechanical relaxation and creep of polymer materials are considered. Based on this discussion a prediction of relaxation and deformation processes of differing degrees of complexity, from simple relaxation with constant deformation and simple creep with constant load to compound processes of reverse relaxation and deformation-reduction processes with multi-stage deformation and loading, is presented.

A comparative analysis of the control law applied to complex dynamic objects that exhibit drift and lag is performed. The selection of a proportional–integral–derivative control law based on transient processes with optimum performance indicators is evaluated. An estimate of the external disturbances of the system is given and the advantage of the selection arrived at is proved.