*6.1. Mechanical Properties Test*

The temperature of the freezer test chamber was set to −25 ◦C, and then the 5 groups of specimens were aged in the freezing test chamber for 18 days, 36 days, 54 days, 72 days and 90 days, respectively. After reaching the aging time, the specimens were taken out and placed indoors for 24 h. The tensile strength, elongation and tear strength were tested by an electronic universal tensile testing machine. The loading speed of the testing machine was set to 500 mm/min [17,18]. The shore hardness tester was used to test the hardness of the specimen [19]. The compression specimen was put into the compression permanent deformer to make its compression rate reach 23–28%. After 168 h of compression, the specimen was immediately released and allowed to recover at room temperature for 27–33 min, and then measured the height of the specimen [20]. The compression permanent deformation was calculated according to Equation (1):

$$\mathcal{C} = \frac{h\_0 - h\_1}{h\_0 - h\_s} \times 100\% \tag{1}$$

where *C*—compression set (%); *h*0—initial height (mm); *h*1—height after recovery (mm); and *hs*—limiter height (mm).
