*3.1. FT-IR Analysis*

The FT-IR spectra of the ST, SA, SAP, SAPC and KL are shown in Figure 1. The FT-IR spectrum of ST is shown in Figure 1a, peaks at 1158, 1081 and 1005 cm−<sup>1</sup> were the stretching vibration of the C-O-C bond [30,31]. After polymerization, these peaks shifted and weakened. As shown in the spectra of SA (Figure 1b), the strong bands at 1610 and 1410 cm−<sup>1</sup> were due to the asymmetric and symmetric stretching vibrations of -COO<sup>−</sup> groups, respectively [32]. The peak at 1032 cm−<sup>1</sup> was related to the stretching vibration of C-OH [33], which moved to 1030 cm−<sup>1</sup> and 1036 cm<sup>−</sup>1, respectively, after polymerization, and the intensity of this peak weakened significantly. Figure 1c shows the FT-IR spectrum of SAP, the absorption peak at 3469 cm−<sup>1</sup> was attributed to the stretching vibration of -OH, and three new peaks appeared at 1711, 1567 and 1409 cm<sup>−</sup>1. The peak at 1711 cm−<sup>1</sup> may be related to the ester group formed during graft polymerization. Also, the new absorption at 1567 and 1409 cm−<sup>1</sup> could be ascribed to the asymmetric and symmetric stretching of -COO−, respectively. These results showed that both ST and SA were involved in the grafting reaction. In the infrared spectrum of KL (Figure 1e), the absorption peaks of -OH were observed at 3696-3621 cm−<sup>1</sup> [25]. As revealed in Figure 1d,e, the -OH peak shifted from 3469 cm−<sup>1</sup> to 3457 cm−1, and a characteristic Si-O peak was observed at 471 cm−1, which indicated that -OH on KL was also involved in the reaction.

**Figure 1.** FT-IR spectra of (**a**) starch (ST), (**b**) sodium alginate (SA), (**c**) superabsorbent polymer (SAP), (**d**) superabsorbent composite (SAPC) (4 wt. % KL) and (**e**) kaolin (KL).

#### *3.2. Morphology*

The appearance of SAPC at different states is exhibited in Figure 2a,b. The dried SAPC was a light-yellow solid, while the swollen SAPC was a transparent hydrogel. The volume of dried SAPC was significantly smaller than fully swollen SAPC.

**Figure 2.** Digital images of (**a**) dried SAPC (80 mesh) and (**b**) swollen SAPC. SEM of (**c**) SAP and (**d**) SAPC (4 wt. % KL); the scaling bars are 2 μm.

SEM of dried SAP and SAPC are shown in Figure 2c,d. The surface of SAP was compact and smooth, making it not conducive to the liquid entering into the polymer network. By contrast, after addition of KL, the surface of SAPC displayed a more rough and loose morphology with porous structure.

#### *3.3. XRD Analysis*

The XRD patterns of KL, SAPC and SAP are shown in Figure 3. The strong peak of KL at 2θ = 12.59◦ had an interplanar distance of d = 0.702 nm. This peak shifted to 2θ = 12.44◦ (0.711 nm) in SAPC due to the intercalation of KL by polymer network. No obvious peaks were observed for SAP due to the amorphous structure. In contrast, SAPC showed the typical crystallite reflections associated with KL, which indicated that KL was uniformly dispersed in the polymer matrix, and an amorphous superabsorbent composite was synthesized.

**Figure 3.** X-ray diffraction XRD patterns of (**a**) KL, (**b**) SAPC (4 wt. % KL) and (**c**) SAP.

#### *3.4. TGA Analysis*

The TGA curves of SAP and SAPC (4 wt. % KL) are shown in Figure 4. In the range from 35 to 203 ◦C, the minor weight loss of SAP and SAPC was mainly ascribed to the evaporation of adsorbed moisture and bound water. The weight loss of SAP and SAPC at 203–343 ◦C were related to the dehydration of saccharide rings and breaking of the C-O-C bond in ST and SA chain. Also, the weight loss from 343 ◦C to 416 ◦C corresponded to the decomposition of the carboxyl groups of the copolymers. The major mass loss of SAP and SAPC occurred in the temperature range of 416-480 ◦C and 416-495 ◦C, which was due to the decomposition of the 3D network structure. It is noted between 343 and 495 ◦C that the decomposition rate of SAP was obviously higher than that of SAPC. Additionally, the weight residual of SAPC was 49.5%, 6.4% higher than that of SAP. These facts seem to indicate improved thermal stability of SAPC compared to that of SAP, probably owing to the heat dissipation impedance effect of KL.

**Figure 4.** Thermal gravimetry analysis (TGA) curves of (**a**) SAP and (**b**) SAPC (4 wt. % KL).
