*3.2. Thermal stability*

TGA analysis was used to study the thermal stability of the PMPC/BNC nanocomposite membranes, as well as of their individual components. Figure 6A shows the thermograms of cross-linked PMPC and neat BNC, while Figure 6B presents the thermograms of PMPC/BNC\_1 and PMPC/BNC\_2 nanocomposites. The thermal degradation profile of the cross-linked PMPC is characterized by two consecutive steps (apart from the dehydration at about 100 ◦C with a loss of *ca*. 7.5%) with maximum decomposition temperatures of 284 ◦C (loss of *ca*. 21%) and 385 ◦C (loss of *ca*. 28%, Figure 6A) corresponding to the pyrolysis of the PMPC skeleton. The thermogram of BNC shows a single weight-loss step with initial and maximum decomposition temperatures of 290 ◦C and 342.5 ◦C (loss of *ca*. 68%, Figure 6A), respectively, allocated to the pyrolysis of the cellulose skeleton [33,34]. PMPC left a residue at 800 ◦C corresponding to about 34% of the initial mass, whereas BNC only left a residue of *ca*. 18% at the end of the analysis.

The thermal degradation profiles of both nanocomposites (Figure 6B) follow a double weight-loss step, aside from the water loss below 100 ◦C (loss of *ca*. 10%). PMPB/BNC\_1 has maximum decomposition temperatures at 290 ◦C (loss of *ca*. 24%) and 382 ◦C (loss of *ca*. 17%) with a final residue of 35%, while for PMPC/BNC\_2 the maximum occurs at 288 ◦C (loss of *ca*. 19%) and 383 ◦C (loss of *ca*. 20%) with a residue of 32% at the end of the analysis (800 ◦C). This two-step pathway is associated first with the simultaneous pyrolysis of cellulose and cross-linked PMPC, and the last stage with only the zwitterionic polymer. This pattern points to the reduction of the thermal stability of the nanocomposites when compared to neat BNC, as already described for other BNC-based nanocomposites containing polymers with lower thermal stability [35]. Even so, the two PMPC/BNC membranes exhibit good thermal stability up to 250 ◦C (Figure 6B).

**Figure 6.** Thermograms of (**A**) cross-linked PMPC and neat BNC, and (**B**) membranes PMPC/BNC\_1 and PMPC/BNC\_2 under nitrogen atmosphere. The inset curves correspond to the derivative.
