In this study, basalt fiber-reinforced polymer (BFRP) composites with epoxy matrix, 20 layers, and volume fraction of fibers Vf = 53.66%, were prepared by a hand lay-up compression molding combined method. The fabric of the basalt fibers is in twill 2/2 weave. Through dynamic mechanical analysis (DMA), their viscoelastic behavior at elevated temperatures and in various frequencies was explored, whereas thermomechanical analysis (TMA) took part in terms of creep recovery and stress-relaxation tests. Moreover, the glass transition temperature (Tg) of the BFRP composites was determined through the peak of the tanδ curves while the decomposition of the BFRP composites and basalt fibers, in air or nitrogen atmosphere, was explored through thermogravimetric analysis (TGA). The mechanical behavior of the BFRP composites was investigated by tensile and three-point bending experiments. The results showed that as the frequency is raised, the BFRP composites can achieve slightly higher Tg while, under the same circumstances, the storage modulus curve obtains a less steep decrease in the middle transition region. Moreover, the hand lay-up compression molding hybrid technique can be characterized as efficient for the preparation of polymer matrix composites with a relatively high Vf of over 50%. Remarkably, through the TGA experiments, the excellent thermal resistance of the basalt fibers, in the temperature range 30–900 °C, was revealed.
The V4 countries went through a transformation of their entire economies, including the agricultural sector, in the 1990s. Each of these countries approached the transformation of agriculture differently, but later the V4 countries’ approach to agricultural development was unified by the EU's common agricultural policy. The aim of the paper was to compare the development of the production (sown area and hectare yield) of selected most commonly cultivated crops in Slovak and Czech regions (NUTS 3) in the period between 2004 and 2017. The development of production in these two countries was also evaluated against the trends of V4 countries. Based on these analyses, common and specific agriculture development trends in V4 countries were revealed. A chronological average was used to evaluate the average values of the monitored indicators in the period from 2004 to 2017 in Slovak and Czech regions. To express the development of the given indicators between 2004 and 2017, the change index was used and visualised cartographically. Regression analysis was used to show the development trends of agricultural production in the V4 countries. In general, the agricultural sectors in the V4 countries show similar characteristics with similar trends, and the average hectare yield has a modest growing trend. In terms of the structure of the cultivated plants, the size of the cultivated areas, the volume of production and the average hectare yields, there have been considerable changes to crop farming in Slovak and Czech regions. The study showed that the changes in the agrarian sector after the year 2004 conditioned by the entry of Czechia and Slovakia into the European Union were reflected in a decrease in crop production and an increase in regional disparities. From the point of view of the production indicator expressing the hectare yield of crops, Czechia achieves better indicator values than does Slovakia.
In this study, aramid fiber-reinforced polymer (AFRP) composites were prepared and then postcured under specific heating/cooling rates. By dynamic mechanical analysis, the viscoelastic properties of the AFRP composites at elevated temperatures and under various frequencies were determined. Thermomechanical analysis (TMA), in the modes of creep-recovery and stress–relaxation tests, was also performed. Furthermore, differential scanning calorimetry was also used, and the decomposition of the AFRP composites, aramid fibers, and pure postcured epoxy, in two different atmospheres, namely, air atmosphere and nitrogen (N2) atmosphere, was explored by the thermogravimetric analysis (TGA). From this point of view, the aramid fibers showed remarkably thermal resistance, in N2 atmosphere, and the volume fraction of fibers (Φf) was calculated to be Φf = 51%. In the TGA experiments, the postcured AFRP composites showed very good thermal resistance, both in air and N2 atmosphere, and this characteristic in conjunction with their relatively high T g, which is in the range of 85–95°C, depending on the frequency and the determination method, classifies these composites as potential materials in applications where the resistance in high temperatures is a required characteristic.
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