**10. Chemical Analysis**

*10.1. Energy-Dispersive Spectrometer Analysis*

The changes in the content of C and O elements (wt %) in the rubber waterstop samples are shown in Table 3.



It can be seen that increasing the aging time led to a decrease in the C element and a concurrent increase in the O element in the rubber waterstop. In the low-temperature air environment, the content of the C element decreased by 4.77% while the content of O element increased by 45.0% after 72 days; the oxidation reaction suddenly became faster from 72 days to 90 days, the content of C element decreased by 13.98% and the content of the

O element increased by 105.0% after 90 days. In the low-temperature water environment, the content of C element decreased by 4.16% while the content of the O element increased by 61.19% after 90 days. Intramolecular reactions can occur in vulcanized rubber polymers due to the polyunsaturated property and the short distance between the double bonds. In the aging process of these polymers, the C–C double bond breaks and forms hyperoxidehydroperoxides, which leads to the decrease in the C element and the increase in the O element on the rubber surface.

Figure 9 shows the change curve of the C and O element content with aging time under three different environments. The x axis represents the aging time, and the y axis represents the content of the elements. Compared with the natural environment, the oxidation reaction of the rubber waterstop in the low-temperature environment was slower. This indicates that low temperature is helpful to alleviate the aging of rubber and the weakening of the adhesion of the rubber matrix.

(**a**) Change curve of C element (**b**) Change curve of O element

**Figure 9.** Change curve of element content.

*10.2. Fourier Infrared Spectroscopy-Attenuated Total Refection Analysis*

The infrared spectra of the rubber waterstop in low-temperature air environment and low-temperature water environment after 18 days, 36 days, 54 days, 72 days and 90 days are shown in Figures 10 and 11.

**Figure 10.** Infrared spectra of low-temperature air environment.

**Figure 11.** Infrared spectra of low-temperature water environment.

Figure 10 presents the infrared spectra of the rubber waterstop under a low-temperature air environment. In the ATR-FTIR spectra, the peak at 2900–2800 cm−1, 1430 cm−<sup>1</sup> and 1372 cm−<sup>1</sup> was assigned to C–H stretching vibrations of –CH2–, –CH3–. The peaks at 1640 cm−<sup>1</sup> and 878 cm−<sup>1</sup> were defined as =C–H stretching vibration of the cis-1,4 structure, while the peak at 1443 cm−<sup>1</sup> was assigned to deformation vibration absorption of –C–O–. It shows that the C–H bond and =CH slowly weaken, and –CO– appears on the molecular chain. The most obvious change was the stretching vibration peak of hydroxyl (O–H) at 3500–3200 cm−1. After 54 days, the peak intensity sharply increased, and then slowly increased. According to the changes of the above spectral peaks, it can be concluded that the double bond of the rubber waterstop slowly decreases and the product of the vicinal diol obviously increases after aging in the low-temperature air environment, which is consistent with the aging law in the natural environment.

In the low-temperature water environment, the infrared spectrum of rubber after aging is similar to that in the low-temperature air environment. With the increase in aging time, the peak intensities of –CH3– at 2915 cm−<sup>1</sup> and 2841 cm−<sup>1</sup> and C=C at 1640 cm−<sup>1</sup> and 878 cm−<sup>1</sup> decreased slightly, while the peak intensities of –CH2– at 1430 cm−<sup>1</sup> and CH3 at 1372 cm−<sup>1</sup> increased slightly. The peak value of –C–O– group at 1002 cm−<sup>1</sup> obviously decreased, and the change in peak value at 3237 cm−<sup>1</sup> was the same as that in the dry environment.

From the analysis of Figures 10 and 11, it can be found that during the low-temperature aging test, the basic structure of the rubber and the position of the characteristic peak do not significantly change before and after aging, which indicates that during the lowtemperature treatment process of 0–90 days, the basic chemical structure of the rubber waterstop was not obviously damaged or the damage is relatively small.
