*3.2. Mechanical and Thermal Properties*

The addition of TiO2 or functionalisation of TiO2 develops the mechanical tensile characteristics of the polymeric form significantly [19–21]. For example, as displayed in Table 1, increasing the amount of PO4TiO2 in the polymeric film enhanced the tensile strength of the composite films by improving their compatibility. This behaviour can be explained by improving the interaction between functional groups along two polymer backbones, such as ether linkages, hydroxyl groups and the various phosphate groups of PO4TiO2 nanoparticles, via ionic, covalent and hydrogen interactions interfacial adhesion, as compared to the neat membrane.


**Table 1.** Physicochemical parameters of the formulated composite membranes compare to Nafion 117 [1,24].

\* The retained weight of membranes (RW) after immersion for a day in Fenton's reagent.

The TGA of formulated composite films in the presence or absence of PO4TiO2 nanoparticles is shown in Figure 5. Moisture evaporation in all membranes can be defined as the initial weight loss of all manufactured membranes at 150 ◦C (10%) [40]. The following weight loss of composite membranes was demonstrated between (150–300) ◦C range, possibly due to the breakdown of functional groups [41,42]. Finally, from 300 to 580 ◦C, all samples show a significant decomposition, which could be connected to polymeric chain decomposition [43], which began at 250 ◦C for the undoped membrane and began at 310 ◦C with a lower weight % for the doped membranes, with 3 wt percent doping. According to these findings, the addition of PO4TiO2 to composite membranes increases their thermal stability by increasing hydrogen bonding in the composite. Furthermore, the presence of only one endothermic peak in DSC, as shown in Figure 5, demonstrates flawless membrane miscibility, and the removal of this peak at PO4TiO2 (3 wt.%) may be

attributed to constructing new physical bonds (i.e., hydrogen bonds) between the nanoparticles and the polymeric matrix [29]. When a result, as the concentration of the doping agent increased, the melting temperature of the membranes fell. This behaviour may be described by hydrogen bond interactions that partially degrade membrane crystallinity, lowering the melting point and increasing ionic conductivity [29].

**Figure 5.** TGA of PVA/PEO/PO4TiO2 membranes (**left chart**) and DSC of PVA/PEO/PO4TiO2 membranes (**right chart**) curves of nanocomposite membranes.

Table 1 depicts the behaviour of nanocomposite membranes in contact with deionised water. When contact angles are less than 90 degrees, membrane surfaces are deemed hydrophobic, and when they are greater than 90 degrees, they are considered hydrophilic. However, as the doping agent content increases, the composite membranes become less hydrophilic and have a lower hydrophilic quality [26,44]. When the amount of PO4TiO2 in the polymeric blend was increased from 1% to 3%, the swelling ratio and water sorption of the composite membranes were lowered, which is vital because water overload may be avoided [45]. To put it another way, increasing the doping agent in the membrane matrix makes the structure more compact, reducing water overload in the polymeric matrix channels [46,47].
