*3.4. Recrystallization of Short-Chain Amylopectin in the TPCS, TPCS-C, and TPCS-HC Films Aged for 15, 45, and 90 Days as Detected through FTIR Analysis*

The FTIR spectra of TPCS, TPCS-C, and TPCS-HC in the range of 900–1200 cm−<sup>1</sup> are shown in Figure 5. Many studies proved that the alteration of short-range molecular order could be obtained from the bands at 1022 cm−<sup>1</sup> and 1047 cm−<sup>1</sup> [45–47]. The number of amorphous regions and crystalline regions was represented by the bands at 1022 cm−<sup>1</sup> and 1047 cm−<sup>1</sup> , respectively. The intensity ratio between the 1047 cm−<sup>1</sup> :1022 cm−<sup>1</sup> (C values) can be used to index the starch crystalline structure region in the amorphous area. The higher the C values, the more organized the TPCS matrix structure. The infrared spectra from 900 to 1200 cm−<sup>1</sup> were deconvoluted, and the 1047 cm−<sup>1</sup> :1022 cm−<sup>1</sup> values were calculated and presented in Table 4. *Polymers* **2022**, *14*, x FOR PEER REVIEW 16 of 21

**Figure 5.** FTIR spectrum scan for neat TPCS, TPCS-C, and TPCS-HC films aged for (**a**) 15, (**b**) 45, and (**c**) 90 days from the range 900-1200 cm<sup>−</sup>1. **Figure 5.** FTIR spectrum scan for neat TPCS, TPCS-C, and TPCS-HC films aged for (**a**) 15, (**b**) 45, and (**c**) 90 days from the range 900-1200 cm−<sup>1</sup> .

**Table 4.** The ratio of 1047 cm<sup>−</sup>1:1022 cm−1 (C value) of TPCS, TPCS-C, and TPCS-HC films after 15, 45, and 90 days of aging. **Days Films 1047 cm−1:1022 cm−1 (C Value)**  15 days TPCS15 0.827 TPCS/5BT15 0.837 TPCS/5NC15 0.815 TPCS/4BT1NC15 0.803 After reaching 90 days of storage, the virgin TPCS film exhibits the highest increase in the C values compared to other films, indicating that the recrystallization of the short-chain amylopectin occurred more significantly. However, by adding a single filler or hybrid fillers, the recrystallization of short-chain amylopectin could be slowed down. The C values of the TPCS/4BT1NC, TPCS/5BT, and TPCS/5NC films have been consistently increased with the increase of storage time, which is in line with the increase in crystallinity percentage measured through the XRD analysis. However, the increase of the C value for TPCS/2BT3NC from 15 to 90 days showed little difference compared to the results

TPCS/2BT3NC15 0.797

TPCS45 0.854

TPCS90 0.870 TPCS/5BT90 0.853 TPCS/5NC90 0.846 TPCS/4BT1NC90 0.823 TPCS/2BT3NC90 0.857

TPCS/5NC45 0.823 TPCS/4BT1NC45 0.815 TPCS/2BT3NC45 0.825

45 days

90 days

obtained through the XRD analysis. The crystalline percentage calculated from XRD suggested that the TPCS/2BT3NC experienced a slow rate of crystal growth from 15 to 45 days, and the growth of crystalline structure was only detected after 45 days. However, the steady increase in the C-value as detected from the FTIR analysis indicates that the TPCS/2BT3NC possessed a consistent growth of crystalline structure from 15 to 90 days. The contradiction between the FTIR and XRD results could be due to the formation of a transcrystalline structure in the TPCS/2BT3NC sample, where the recrystallization of short-range molecular was more sensitive to be detected by FTIR. The transcrystalline structure in TPCS/2BT3NC was only detected in XRD analysis by shifting the peak at 2θ. The transcrystalline does not reflect the intensity of the XRD peak because XRD is more sensitive to detecting long-range molecular crystallized structures [48].


**Table 4.** The ratio of 1047 cm−<sup>1</sup> :1022 cm−<sup>1</sup> (C value) of TPCS, TPCS-C, and TPCS-HC films after 15, 45, and 90 days of aging.
