Connection of water permeability with a number of physical properties of polymers

Currently, methods for predicting the properties of polymers are very popular, since they simplify the work of synthetic chemists. Instead of lengthy and time-consuming experiments, many properties of polymers can be predicted in advance based on their chemical structure. Naturally, such tasks must be computerized so that the properties are predicted after the chemical structure of the repeating polymer unit is displayed on the display screen. This is the so-called direct task. The inverse problem is more complex and interesting. It consists in entering the intervals of the desired characteristics into the computer. Then computer synthesis of polymers possessing these characteristics are realized. The work consists in writing a computer program that allows the computer synthesis of polymers of different classes with specified intervals of water permeability. These classes include polyurethanes, polysulfones, polysulfides, polyethers and polyesters, polyamides, polyketones and polyethyrketones, polycarbonates, polyolefins, vinyl polymers, polystyrene, acrylic and methacrylic polymers. On the basis of this program, water permeability compatibility diagrams are constructed with various physical characteristics of polymers – glass transition temperature, temperature of the onset of intensive thermal degradation, cohesion energy, density, solubility parameter (Hildebrand parameter)

Assessment of the reliability of bent reinforced concrete elements under corrosive effects

The main problem of reducing the reliability and durability of reinforced concrete structures is the corrosion of concrete and reinforcement of operated buildings and structures. Calculation of structures made of reinforced concrete, taking into account environmental influences, is complicated by the stochastic nature of the parameters of corrosion processes. The conducted studies are aimed at solving the problem of improving the methodology of the probabilistic approach to the calculation of corrosion-damaged reinforced concrete elements. The article considers a probabilistic assessment of reliability for the most common bent reinforced concrete elements, taking into account corrosive wear and the time factor. The modeling of the effect of corrosion processes on the stress-strain state of a reinforced concrete element was carried out using the concrete deformation diagram, which takes into account the decrease in strength characteristics with an increase in the concentration of an aggressive medium in concrete. The scheme of propagation of an aggressive environment in concrete is adopted according to the diffuse front method. Corrosion processes in reinforcement were taken into account by reducing the effective cross-sectional area of reinforcing bars. The change in the properties of steel (its embrittlement) with an increase in the concentration of an aggressive medium was not taken into account. Reinforcement corrosion was simulated after the incubation period, after the concentration of the aggressive medium on the surface of the reinforcing bars reached a critical value. The determination of the moment of the onset of the limit state in the element was carried out on the basis of a nonlinear deformation model at each point of the section of the element to achieve the maximum possible tensile or compression strains in concrete and reinforcement. To solve the problem of reliability assessment, the method of statistical modeling implemented in a specialized software package was used. To apply this method, according to previous studies, the probabilistic parameters of all random variables were taken: mathematical expectation and standard deviation. Based on the results of the reliability assessment, graphs of the decrease in the reliability of a bent reinforced concrete element from the time of exposure to an aggressive environment were obtained

Water absorption of wood-polymer composites of savewood

The materials based on wood-polymer composites (WPC) in the form of decking boards are produced, in which wood filler is partially replaced by mineral one. WPC materials manufactured by Savewood using a matrix polymer of polyvinyl chloride (PVC) have good mechanical properties, low abrasion and satisfactory resistance to climatic influences. However, they have relatively high water absorption, the task of reducing which is relevant not only in Russia, but also in other countries where there are constructions of facilities operating in outdoor environmental conditions. The modification of such materials in this work was carried out by replacing part of the wood filler with the mineral filler, which is CaCO3 (chalk). Partial replacement of wood flour with mineral filler resulted in a marked reduction in swelling from 1.25 to 0.01%. In this case, the modulus of elasticity is increased from 2260 to 2880 MPa, tensile strength from 30.5 to values of 16.7 ÷ 32 MPa. The specific impact strength varies from 8.90 to 7.74 kJ/m2. The optimal ratio of wood and mineral fillers is 60/40%

Stress-optical coefficients of copolymers

The stress-optical coefficient Cσ of copolymers based on cured epoxy resins has been calculated. Calculations were made for epoxy resins based on bisphenol A and aliphatic and aromatic diamines. The Cσ values are in the range of 91.6÷103 weight percent. All calculations were carried out using the Cascade computer program (developed by INEOS RAS). The investigated structures of cured epoxy resins are obtained from industrial components. High Cσ values make it possible to confidently use the mentioned network polymers in the photoelasticity method, from which models of full-scale building structures can be made

Newest models and calculation schemes for quantitative analysis of physical properties of polymers

New models and calculation schemes have been developed for the quantitative analysis of a number of physical properties of polymers — glass transition temperature, flow temperature of polymer nanocomposites, thermal conductivity, boiling point of polymer solutions, water absorption and water permeability of polymers and nanocomposites, strength, viscosity, storage and losses moduli, refractive index and dielectric constant. All calculation schemes are based on the structure of linear and cross-linked polymers; their degree of crystallinity, free volume, the effect of temperature, the composition of copolymers and homogeneous mixtures of polymers, the concentration of nanoparticles, their shape, size distribution, orientation angles, the structure of polar groups grafted to the surface of nanoparticles, the energy of intermolecular interactions are taken into account. All computational schemes are computerized and allow calculations to be carried out automatically after the introduction of the structure of a repeating unit of polymer unit into the computer, as well as the shape and size of nanofillers

Study of the abrasion resistance of wood-polymer composites and mixtures of ABS-plastic with polyvinyl chloride

The abrasion of materials based on blends of ABS plastic with polyvinyl chloride (PVC) as well as terraced boards based on wood-polymer composites (DPC) has been studied. The measurements were carried out on a drum-type machine, and on a Taber's abrasimeter. For blends of ABS plastic with PVC at abrasion path length 600 m wear is 0.85%. For terracotta boards based on WPC, the wear during the test (loss of mass) was 0.0042 g. The abrasion of the sample was 9.29×10-5 g/cm2. Thus, the obtained blends should be recommended for application for floor coverings, since they possess negligible abrasion

Preparation and properties of hybrid materials for high-rise constructions

The theme of the research is important because it allows to use hybrid materials as finishing in the high-rise constructions. The aim of the study was the development of producing coloured hybrid materials based on liquid glass, a polyisocyanate, epoxy resin and 2.4-toluylenediisocyanate. The detailed study of the process of stress relaxation at different temperatures in the range of 20-100°C was provided. The study found that the obtained materials are subject to the simplified technology. The materials easy to turn different colors, and dyes (e.g. Sudan blue G) are the catalysts for the curing process of the polymeric precursors. The materials have improved mechanical relaxation properties, possess different color and presentable, can be easily combined with inorganic base (concrete, metal). The limit of compressive strength varies from 32 to 17.5 MPa at a temperature of 20 to 100°C. The values σ∞ are from 20.4 to 7.7 MPa within the temperature range from 20 to 100°C. The physical parameters of materials were evaluated basing on the data of stress relaxation: the initial stress σ0, which occurs at the end of the deformation to a predetermined value; quasi-equilibrium stress σ∞, which persists for a long time relaxation process. Obtained master curves provide prediction relaxation behavior for large durations of relaxation. The study obtained new results. So, the addition of epoxy resin in the composition of the precursor improves the properties of hybrid materials. By the method of IR spectroscopy identified chemical transformations in the course of obtaining the hybrid material. Evaluated mechanical performance of these materials is long-time. Applied modern physically-based memory functions, which perfectly describe the stress relaxation process

The Criteria for Assessing the Safety of Buildings with a Reinforced Concrete Frame during an Earthquake after a Fire

In the paper, there was researched sensitivity of the criteria for evaluation of seismic resistance of reinforced structures (modes and frequencies of oscillations, displacements, and strains) in relation to various position of fire impact as exemplified by three-span five-storey reinforced concrete space frame. The relevance of the study is justified, the degree of the problem’s development is grounded. There were analyzed the main lines of the research connected with experimental and numerical testing of both discrete structures and full-sized buildings. Numerical analysis was conducted by means of the software complex Ansys, the linear-spectral method was used. Fire impact is simulated by means of damages to reinforced concrete members in one of the building’s units. 16 variants of points of fire outbreak were considered. According to the calculation results, it was stated that for all the variants of fire outbreak frequencies of self-oscillations for reinforced concrete frames after the fire had been found lower than for the non-damaged frame. The modal analysis has shown that the type of longitudinal and bending oscillations had undergone changes. The maximum amplitude of frames’ oscillations after the fire was found insignificantly lower than for the non-damaged frame. Within the floor of fire outbreak location, the displacement increased immensely so that led to failure to comply with the value of inter-floor shifts and the increase of the 2nd order effects. Redistribution of bending moments in reinforced concrete framings was observed. The loading in damaged members decreased due to the members’ strain capacity whereas the extra loading is added to the adjacent members. If compared with the case of the frame non-damaged by fire, overloading of columns can reach up to 20%. Conceptual description of fracture behavior of the frame is outlined assuming its non-linear behavior. The possible lines of further development are set for the methods of seismic analysis of the buildings with reinforced concrete frame after the event of fire

Calculation of the viscosity of dispersions of nanoparticles with a polymer adsorption layer in a melt

As a result of theoretical analysis of the influence of the chemical structure of the polymer and the chemically modified surface of nanoparticles, it was shown that it is possible to predict the dependence of the viscosity of the polymer melt on the concentration of nanoparticles, their size, and the molecular weight of the polymer. Two situations have been analyzed where a strong intermolecular interaction between polymer chains and polar groups located on the surface of nanoparticles is absent, and when a strong intermolecular interaction between polymer chains and polar groups located on the surface of nanoparticles takes place

Sturm-Liouville Problem with Mixed Boundary Conditions for a Differential Equation with a Fractional Derivative and Its Application in Viscoelasticity Models

In this study, we obtained a system of eigenfunctions and eigenvalues for the mixed homogeneous Sturm-Liouville problem of a second-order differential equation containing a fractional derivative operator. The fractional differentiation operator was considered according to two definitions: Gerasimov-Caputo and Riemann-Liouville-Visualizations of the system of eigenfunctions, the biorthogonal system, and the distribution of eigenvalues on the real axis were presented. The numerical behavior of eigenvalues was studied depending on the order of the fractional derivative for both definitions of the fractional derivative