2.9. Thermal Analyses DSC, TGA and DTG

The device DSC 1 (Mettler-Toledo GmbH, Greifensee, Switzerland) was used to monitor the curing processes by the differential scanning calorimetry (DSC) method. This device provides accurate and reliable results of measuring the enthalpy depending on the temperature for the selected temperature program. The device provides the capability to monitor endothermic and exothermic processes which correspond to the peaks and changes the shape of the DSC curve [80,81]. For each test, the results were obtained in the form of important parameters such as “onset” temperature (T_o), and temperature of peak reached during the reaction (which is also the temperature when the curing is completed) [82]. It is known that linear resin monomers are converted into crosslinking networks during curing. The cure reactions of resins are very complex because many reactive processes occur simultaneously has been studied by means of differential scanning calorimetry [83,84]. Results commonly depend on several factors such as the size of the fillers, the percentage loading and the dispersion of the particles [80,85].

Thermal gravimetric analysis (TGA) can be used to monitor weight changes in a sample as a function of temperature. The technique is primarily used for studying degradation processes, providing information on thermal oxidative degradation rates and thermal degradation temperatures of polymeric materials. The technique is not particularly sensitive to the changes in adhesives and resins due to different states of cure and this is the main reason it has not been developed further for cure monitoring. According to the shape of the TGA curves, the materials determine the rate of the reaction and the temperature of the decomposition processes. From thermal degradation of materials, we can identify thermal resistance [85,86].

Three types of thermal analyzes were used for the samples, namely DSC, TGA together with derivative thermogravimetry (DTG). DTG as a technique was used for identifying and quantitatively analyzing the chemical composition of substances by observing the thermal behavior of a sample as it is heated.

The temperature methodology of the experiment was set according to the needs of practice. The temperature was increased from 25 °C to 105 °C at a heating rate of 10 °C∙min⁻¹. Isothermal part of experiment occurred after reaching 105 °C which lasted 10 min. Upon completion the temperature was raised to 110 °C with a heating rate of 15 °C∙min⁻¹. After achieving the temperature 110 °C the sample was cooled to an operating temperature of 25 °C. TGA was performed in oxygen atmosphere throughout the experiment. As carrier gas was used nitrogen (purity 99%) at DSC method. Gas flow was for both methods 20 mL∙min⁻¹.

The device TGA/DSC1 was employed to measure the changes of mass in the samples and to monitor the temperature processes. TGA measurement was realized in alumina crucible with lids and with diameter of 6 mm and length of 4.5 mm. The total volumes of the crucibles were 70 μL and the lids were pierced. Simultaneously with the thermogravimetric analysis, a DSC measurement was performed. The sample was weighed by scales KERN ABT 220-5DM version 1.2 03/2013 (Kern & Sohn GmbH, Balingen, Germany) into a 100 μL aluminum crucible with a diameter of 6 mm and a height of 4 mm.