Papers by Keyword: Glass Transition Temperature

Abstract: The possibility of using the compositions of BaSO₄-KPO₃-Na₂B₄O₇ system as a glass-solder (frit) material was shown. A glass formation region has been established in BaSO₄-KPO₃-Na₂B₄O₇ system which is located in the borate-phosphate part of the concentration triangle and occupies ~41% of the triangle area. The concentration dependences of linear thermal expansion coefficient (TCLE), the softening temperature and the glass transition temperature was determined and discussed. It is established that the glass formation region, the concentration dependences of TCLE and technological temperatures values are significantly closer to those for CaSO₄-KPO₃-Na₂B₄O₇ system than for MgSO₄-KPO₃-Na₂B₄O₇ system. That may point out at the similar effect barium sulphate and calcium sulphate doping in the sulphate-phosphate-borate systems.

Abstract: Using differential scanning calorimetry, phase transitions in polycarbonate-polytetramethylene oxide block copolymers were studied. It is shown that, depending on the ratio of rigid polycarbonate and flexible polytetramethylene oxide units, block copolymers can be two-phase or four-phase. It is shown that phase transitions in copolymers of a polyester-polyether depend on the ability to crystallize the components.

Abstract: Some properties (enthalpy of formation, glass transition temperature and rheological parameters) of hyperbranched polyglycidol derivatives containing nitrate and azide functional groups were investigated. The dependence of the found properties on the molecular weight, composition and structure of the investigated substances was determined.

Abstract: The paper provides the results of the investigation in the influence of heat treatment on the quality of vehicle component parts made of rigid polyurethane integral foam. The temperature of heat treatment was based on the exo-peak of the first heat cycle in DSC curve, and was equal to 135 °С. At that temperature, the samples were treated for 2-8 hours, and, as a result, they experienced an abnormal exo-effect in the glass transition region, which was indicative of thermal relaxation. The paper shows that the additional heat treatment stage for parts made of rigid polyurethane integral foam results in an increase in molecular mass of polymer, due to a smaller quantity of end groups, and, thus, in an increase in glass transition temperature from 169 °С to 176 °С. An increase in heat treatment time to 6 hours at 135 °С leads to a higher ultimate bending strength, which reaches its maximum, while further heat treatment (up to 8 hours) lowers this value. Therefore, with a higher degree of cross-linking the fracture toughness increases and passes its maximum, after that it starts to decrease, and the material becomes brittle.

Abstract: The change in the elastic-strength and sorption properties of epoxy polymers in the process of natural aging, taking into account the sequence of different climatic seasons effects, was studied. We studied polymers obtained on the basis of low-viscosity epoxy resins and a hardener, which is a mixture of aromatic and aliphatic di-and polyamines, modified by salicylic acid. Differences in the processes of structural relaxation and elimination of the initial nonequilibrium depending on the season of the exposure start are revealed. Mathematical models that describe changes in the elastic-strength properties of epoxy polymers during climatic aging, depending on the accumulated quantitative values ​​of the acting environmental factors, have been developed. For the first time, it was proposed to use as a variable parameter the total duration of time intervals for the studied period the surface temperature of the samples at which exceeded the glass transition temperature.

Abstract: Blended polymer composites are prepared based on linear low density polyethylene (LLDPE) and mixed with polysulfone (PSU) using solvent casting technique. LLDPE is functionalized with carbonyl functional groups to enable it to interact with PSU from the molecular level. Various weight percent of PSU is added into LLDPE to find the optimum weight percent ratio between LLDPE and PSU. The highest glass transition temperature obtained is 47.58°C for ratio LLDPE to PSU of 7:3. In addition, value for decomposition temperature is increased up to 490.16°C with the increasing of PSU content. SEM observation of the blended polymer films shows that glass transition and decomposition temperature depend on morphology of the blended polymers.

Abstract: The influence of SnO₂ on the chemical stability of sodium silicate glasses is investigated. The six glass compositions of ySnO₂–37.9Na₂O–(62.1-y)SiO₂, y=1–8 mol.%, system were synthesized. Thermal behavior of the glasses was studied with the methods of dilatometry and DSC. It is shown that the hydrolytic resistance increases when growing the SnO₂ concentration in the glass composition at constant Na₂O content.

Abstract: Silver nanoparticles (AgNPs) were synthesized by bioreduction method using aqueous extracts of Boesenbergia rotunda as reducing and stabilizing agents. Ultraviolet-Visible (UV-Vis) spectrophotometer was utilized to monitor the qualitative formation of AgNPs. The UV-Vis spectrum showed that the spherical AgNPs with diameter of 20-40 nm were formed. The antifugal activity of synthesized AgNPs was investigated using Candida albicans, which was found that the synthesized AgNPs could be used as effective growth inhibitors. The influence of the incorporation of prepared AgNPs on thermal properties of the acrylic denture base material was investigated. Glass transition temperature of filled acrylic resins was studied using the dynamic mechanical analyzer (DMA). The temperature sweeps were performed with tension mode. Thermogravimetry analysis (TGA) was used to examine effect of AgNP concentration and thermocycling (1250, 2500, 5000, and 10000 cycles) on thermal stability of AgNP filled acrylic resin denture base materials. Glass transition temperature (T_g) of the acrylic resins slightly increase with increasing AgNP contents. TGA results indicated that AgNP retarded thermal degradation of acrylic resin denture material, and thermocycling did not affect thermal stability of AgNP filled acrylic resin denture material.

Abstract: Durability of glass fibre reinforced polymer (GFRP) composite is an important research topic because the changes occur in GFRP composite with ageing can affect its properties and lifetime. For long term use, GFRP composites should be examined in real time and with reasonable in-service environments. However, this is not practical because the time involved would significantly delay product development and therefore, accelerated ageing technique is required. Conditioning in wet and elevated temperatures known as hygrothermal ageing is a very useful technique to evaluate the durability of GFRP composites in a reasonable timeframe. In this work, pultruded GFRP composites were aged in sea water and in dry conditions at 23, 55 and 75°C for 0, 8 and 20 months to assess the changes in shear properties (e.g. short beam shear strength, SBSS and transverse shear strength, TSS) and in glass transition temperature, T_g. After ageing in sea water for 20 months, SBSS was found to retain by about 101, 102 and 95% at 23, 55 and 75°C, respectively. On the other hand, SBSS was retained by around 106% after ageing in dry condition for 20 months at 55 and 75°C. TSS was found to retain by approximately 99, 95 and 91% after ageing in sea water for 20 months at 23, 55 and 75°C, respectively, whereas TSS of dry conditioned samples was retained by about 105 and 107% at 55 and 75°C, respectively. T_g, measured by dynamic mechanical thermal analyser, showed little change both in wet and dry conditions at different temperatures and time.

Abstract: Within this work, it was experimentally verified that the waste from mineral wool board insulation production (WIRG) with high portion of glass recyclate (> 80%) and no organic material seems like ideal filler for polymer grouting materials. The main objective was to develop a progressive grout on epoxy basis with as high content of this secondary raw material as possible, while achieving physical and mechanical properties as e.g. very fast strength increase and high thermal resistance. With regard to the consistency of epoxy grout in the fresh state, three different filling were tested, namely 60%, 65% and 70%. The grout with lower filling is too fluid, and it is also disadvantageous from an economic point of view because a large amount of epoxy resin is used. On the other hand, at higher filing, it is not possible to mix the filler into epoxy resin properly. Setting of an optimal filler content in the mixture was performed mostly on the basis of the results of compressive and three-point flexural strength test. It was found out that the optimal amount of the filler is 65%. In case of the best formulation with optimal filler content (65% WIRG), the thermal resistance was monitored by determination of the glass transition temperature (T_g) by the dynamic mechanical analysis (DMA) method. Furthermore, the optical microscope with high resolution was used to monitor filler distribution and homogeneity of the hardened developed epoxy grout.