An investigation of the effect of methyl cellulose and sodium polyacrylate on the hydrosorption properties of a vulcanisate based on chloroprene rubber*

The effect of hydrophilic additives – MC-2000 methyl cellulose and sodium polyacrylate – on the properties of a vulcanisate based on Neoprene W was studied. The rubber mixes were prepared in two stages: at the first stage, hydrophilic additives were introduced into the rubber; at the second stage, the remaining ingredients were introduced. Vulcanisation was carried out at a temperature of 150°C for 30 min. The viscosity of the rubber mixes, M, was measured at 120°C on an MVR 3000 Basic viscometer (MonTech), and the vulcanisation characteristics and vulcanisation rate, v, were measured on an MDR 3000 Basic rheometer (MonTech) at 170°C in accordance with ASTM D2084-79. From the results of these measurements it follows that, with the combined use of methyl cellulose and sodium polyacrylate, there is a synergistic reduction in M and in the vulcanisation rate of the rubber mixes. A vulcanisate containing both hydrophilic additives possesses the best hydrosorption properties and has satisfactory physicomechanical properties (nominal tensile strength, elongation at break, hardness, and tear strength). The values of these properties and their changes on exposure of the vulcanisate to distilled water (70°C, 24 h) meet the requirements laid down for water-swelling rubber sealing elements.

Compatibilising additives for enhancing the interaction at the phase interface in thermoplastic vulcanisates based on rubbers of different polarity and polypropylene*

The possibilities of increasing the interaction between the components of previously developed thermoplastic vulcanisates based on polypropylene and a combination of isoprene and nitrile butadiene rubbers were studied. The morphology of the composites was recorded by means of optical microscopy using an analytical complex based on a Leica DM-2500 optical microscope, a Leica DFC-420C digital high-resolution colour camera with a Peltier cooling system, and a specialised computer desk. The parameters of crystallisation of polypropylene were measured by differential scanning calorimetry using a DSC 204F1 Phoenix instrument (Netzsch). The physicomechanical properties of the vulcanisates were also determined. Maleinised polypropylene, a copolymer of ethylene with vinyl acetate, and their mixtures were used as compatibilising additives. Maleinised polypropylene was introduced together with polypropylene in a quantity of 1–10 parts; no changes in properties were observed with increase in the dosage above 4 parts, so this dosage was used. The copolymer of ethylene with vinyl acetate (1–10 parts) was introduced into the rubber phase at the stage of rubber mix preparation specially to improve the compatibility of polypropylene and nitrile butadiene rubber. The introduction of maleinised polypropylene leads to an increase in the workability and in the level of elastic strength properties, in particular the tensile elastic modulus and hardness. A considerable increase in the uniformity of distribution of components throughout the volume, a finer dispersion of the rubbers in the polypropylene matrix, and a reduction in the number of pores in the material were shown, and also an increase in the degree of polypropylene crystallinity measured under experimental conditions. The most positive effect is observed with the combined introduction of the copolymer of ethylene with vinyl acetate and the maleinised polypropylene: the nominal stress under elongation increases by 34%, and the elongation at break by 15%. The combined introduction of the compatibilising additives improves the compatibility of the components of the system, the phase boundaries become more diffuse, there is a reduction in the optical density of rubber-rich zones, and these zones are penetrated by polypropylene fibrils.

The evolution of morphology during the mechanical ‘plasticisation’ of unfilled vulcanisates of nitrile rubbers*

Optical microscopy was used to investigate features of morphological transformation during the mechanical degradation of unfilled vulcanisates of nitrile butadiene rubbers in a thin mill roll gap and subsequent thermal treatment – revulcanisation without the addition of any components into the degradate. An analytical complex based on a Leica DM-2500 optical microscope, a Leica DFC-420C high-resolution digital colour camera, and a specialised computer desk was used. The influence of the milling time in the 0–40 min range on the morphological parameters and the nature of the fine structure of plasticised specimens was studied. The mechanisms of degradation and structure formation during the plasticisation of vulcanisates were analysed. The formation of an additional three-dimensional skeleton in ‘secondary’ vulcanisates and the build-up of this process with increase in the treatment time of the degradate were found, which may lead to an increase in the mechanical properties to a level exceeding that of the initial vulcanisate. However, increase in compositional inhomogeneity may have an adverse effect on oil resistance.

Rubberised fabric for fuel soft storage tanks*

The kinetics of extraction of dibutyl sebacinate by different grades of motor fuel from rubberised fabric based on a blend of nitrile rubbers SKN-26M and SKN-40M was investigated. The kinetics was determined according to the GOST 9.030-74 standard from the change in weight of the specimen after holding in fuel at 50°C and drying. The change in quality of the fuel after contact with the fabric was recorded from the change in the content of existent gum in fuel according to GOST 1567-97 (ISO 6246-95) and its acidity according to GOST 5985-79 before and after contact with the rubberised fabric. It was shown that the process of extraction proceeds in two stages, the time of the first of which under experimental conditions is not dependent on the type of fuel. The rate of the first stage is much higher than the rate of the second stage. The relation of rates and proportion of extracted fuel at the first and second stages depends on the type of fuel. It can be asserted that the surplus amount of extracted substances is made up of impurities, which include residual monomer or its derivatives and substances used in the synthesis of the rubber. The mechanism of extraction with extractant counterflow into the vulcanisate and its dependence on the grade of petrol is proposed, based on allowance for the diffusion processes in the system.

Principles of the parametric definition of rubbers with allowance for their functional possibilities*

This review describes existing methods of parametric definition of rubbers as structural materials, including the authors’ own methods. The principal features of the non-linear mechanical behaviour of elastomer composites are set out.

Innovative ecological agricultural textiles*

Agricultural textiles are applied as a protective barrier against birds and insects, but also as ground covers against weeds and as protection from environmental factors. To protect plants from insects and other pests, pesticides and other protective agents are also used since a textile barrier is often insufficient or is not feasible. As these products have to be applied regularly, their use is costly and time-consuming. The situation also becomes more complicated when a textile is used to protect the field against other influences (e.g. frost). The application of pesticides and other protective agents in or on to the agricultural textile itself, enabling the active substances to be continuously released by the textile, is a viable alternative. Insecticides used in the agricultural sector pose an environmental problem, which cannot be solved even by incorporating them into textiles. A silica-based, ecological alternative will therefore be presented in this article.

An investigation of the efficiency of heat stabilisers Bisphenol-5 and Vulcanox BKF in the production of nitrile butadiene rubber*

The properties of heat stabilisers Bisphenol-5 [4,4′-bis(2,6-di- tert-butylphenol)] and Vulcanox BKF [2,2-methylene-bis(4-methyl-6- tert-butylphenol)] and their efficiency in stabilising nitrile butadiene rubbers (SKN-1865 and SKN-2665) were investigated. The efficiency of the antioxidants was assessed from the thermooxidative ageing of the rubbers at 150°C over the course of 1 and 3 h. The Mooney viscosity and solubility of specimens with Bisphenol-5 change less during oxidation than those of specimens with Vulcanox BKF. The good stability of the Bisphenol-5 dispersion after additional treatment in a ball mill for 12 h was shown. Stability was assessed from the sedimentation rate of antioxidant particles and from the ratio of sediment to dispersion volume. The vulcanisation time and physicomechanical properties of compounds based on rubbers containing Bisphenol-5 and Vulcanox BKF were compared. The recommended content of Bisphenol-5 in SKN-1865 rubber is 0.23 parts, and in SKN-2665 rubber 0.3 parts. Bisphenol 5 can be recommended as a replacement for imported Vulcanox BKF for the stabilisation of nitrile butadiene rubbers.

Elastomeric heat-shielding materials containing microspheres modified with a heteroorganic modifier*

The changes in the thermophysical and fire- and heat-shielding properties of compounds based on ethylene propylene rubber when hollow aluminosilicate microspheres (MSPs) are introduced were studied. The MSPs were treated with a heteroorganic modifier – phosphorus–boron–nitrogen-containing oligomer (PEDA), which is a combustion inhibitor. The physicomechanical characteristics of the vulcanisates and the magnitude of the Payne effect were determined. The vulcanisates contained 30 parts filler BS 120 and a sulphur vulcanising group, and also 1 part MSPs. The optimum MSP/PEDA ratio was 1:3. The ultra-high-frequency treatment of the mixture of MSPs and PEDA was especially effective. Using a Versa 3D electron microscope, the increase in the diameter of MSPs as a result of modification and the change in the atomic composition of the surface of MSPs were recorded. The modification of MSPs leads to a reduction in the Payne effect, to an increase in the interaction between rubber and filler, to a reduction in density, and to an increase in the cohesive strength. By comparison with a specimen without MSPs, the rate of linear combustion according to GOST 28157-89 decreases by 10%. The modification of MSPs leads to a decrease in this parameter by 5% by comparison with a specimen containing unmodified MSPs. The time of heating to 100°C of the unheated surface of a specimen heated on the other side to 2000°C increases by 50–60% and 11–19% respectively. The resistance to separation under conditions of erosion entrainment increases by 4–7%. The use of PEDA makes it possible to improve the adhesion of coating to substrate. A scheme of the interaction of MSPs and PEDA is put forward.

Assessment of the Fluctuations in the Microstructural Parameters of Cellulose in Wood in an Inhomogeneous Temperature Field

The possibility of assessing the average crystallite size of cellulose in wood by formalised modelling from the magnitude of the potential difference arising in the wood specimen owing to polarisation in a non-homogeneous temperature field is considered.