*3.5. Tensile Properties and Self-Healing Efficiency of WPU-SS Films*

In addition, the self-healing process of WPU films was evaluated more quantitatively through tensile measurement, and the self-healing efficiency was calculated according to the final tensile stress ratio of the repaired sample to the original sample. Figure 6 reveals the stress-strain curves of the original samples of WPU1, WPU2 and WPU3. The film of WPU1 exhibits a high tensile strength since the hard segment content is relatively high, and the content of carbamate in WPU1 may be more than that in WPU2 and WPU3. On the contrary, WPU2 and WPU3 possesses high soft segment content, and strong molecular weight mobility, so its self-healing performance is also relatively improved.

**Figure 6.** Stress-strain curve of WPU1, WPU2, WPU3.

Figure 7 shows the self-healing efficiency of WPU1 WPU2 and WPU3 under different conditions. The self-healing efficiency of WPU1 is only 29.02% after 4 h at 70 ◦C, while the healing efficiency of the WPU2 and WPU3 films reached 96.14% and 97.28% under the same conditions, respectively. Meanwhile, WPU2 and WPU3 films also had a self-healing efficiency of up to 84.21% and 85.86% after being placed at 25 ◦C for 24 h. The table of repair efficiency changing over time is shown in Table 3. There is no doubt that introducing SS bond endowed the film with excellent self-healing performance. Of course, the content of the soft segment also exerts a certain degree of influence on the repair effect of the film [34,35].

**Figure 7.** Stress-strain curves of WPU1 (**a**), WPU2 (**b**) and WPU3 (**c**) films repaired under different conditions.


**Table 3.** Details of Tensile Results and the Healing Efficiency ofWPU-SS Samples under different conditions.
