Three additional methods were developed with dynamic heating steps at 340◦C and 350◦C which were interrupted by an isothermal segment for 15 min and with heating rates set at 5, 10, 20 and 50 ◦ C/min (Table 4).
The final developed method consists of four segments (Table 4, no. 5). The first step starts with a dynamic heating rate (50 ◦ C/min) from 25 ◦ C and ends with 350 ◦ C. The second step is an isothermal phase at 350 ◦ C for 15 min. The third step is a dynamic heating phase with a heating rate of 50 ◦ C/min from 350 ◦ C until 550 ◦ C. Finally, the atmosphere is switched from the inert gas nitrogen to the reactive gas oxygen. The last step is performed with a heating rate of 50 ◦ C/min until 700 ◦ C by burning the residue.
For method no. 5, the thermal degradation of WPC 1–3 is shown in Fig. 6.
The thermal degradation of all WPC samples differs which can be well seen in the DTG-curves at approximately 500◦C whereas the TGA curves show that only WPC 1 and 2 are similar. In addition, step results analysis shows the differences in composition between all three formulations well. In Table 5 the results of the step separation and weight loss measurements for methods no. 3–5 (Table 4) were compared. In the left column the actual contents (wt.%) of wood flour and polymer are shown and in the remaining columns values of the analyzed average contents and standard deviations are represented. Additionally, the deviations in relation to analyzed and actual contents are listed.