Simultaneous coupled techniques include sample testing using two (or more) instrumental techniques. Those kind of techniques include coupled thermogravimetry with infrared spectrometry with Fourier transformation (TGA-FTIR), which allow testing of off-gas during thermal degradation. The test sample is heated up at a constant rate, according to a controlled temperature change program and the mass change as a function of the temperature is measured, simultaneously analysing the gas emitted during the thermogravimetric analysis. Alternatively, the sample is kept at a specified, constant temperature, measuring the mass change as a function of time in a specified timeframe, together with simultaneous analysis of emitted gaseous products. The final stage of the measurement is IR spectrum interpretation, from which information about the functional groups and the type of bonds which were present in test gas sample emitted from the degradable material at a given temperature or a given timeframe is obtained.