# Preparation and Characterization of Hybrid Nanocomposites for Dental Applications
## 3 Results and Discussion  
### Characterization of Nanofilers  
Figure 1 displays scanning electron microscopy (SEM) images of HNTs (a), modified HNTs with gelatin (b), and silane-modified ATH (c). As one can see in SEM images (a) and (b) the surface of the modified HNTs with gelatin became rough compared with the raw HNTs. Therefore, the results demonstrated that gelatin was successfully grafted on the surface of HNTs. The SEM image (Figure 1a) of HNTs reveal that the majority of HNTs existed in a tubular shape. The presence of short tubular HNTs, semi-rolled HNTs, and sheet-like HNTs were visible. A mean particle size of ca. 1.5 \(\upmu\)m and lengths ranging from 500 nm to 3 \(\upmu\)m were determined. In turn, the morphology of the as-received silane-modified ATH observed by SEM (Figure 1c) was similar to the ones obtained from the manufacturer and provided in the technical data sheet. Particles were not uniform in shape and they exhibited an almost smooth surface. The above-mentioned observations were further confirmed by FTIR and TGA analyses (Figure 2). Figure 2a illustrates the TGA curves of pristine HNTs and gelatin-modified HNTs. In the curve of pristine HNTs nanotubes, one major mass loss was resolved in the temperature range of 380-600 \({}^{\circ}\)C. This mass loss has been assigned to the dehydroxylation of structural Al-OH groups of halloysite [54; 55]. Another mass loss, observed in the range 23-120 \({}^{\circ}\)C, corresponded to the loss of adsorbed water (surface and interlayer) [54]. On the other hand, for the gelatin-modified HNTs, three mass losses were resolved. The first mass loss in the range 23-125 \({}^{\circ}\)C was due to physically adsorbed water, the second mass loss occurring from approximately 250-400 \({}^{\circ}\)C was due to decomposition of the grafted gelatin [56], and the last mass loss over the range 435-675 \({}^{\circ}\)C corresponded to dehydroxylation of the residual structural Al-OH groups. Thus, one can make an important conclusion, that HNTs have been successfully modified with gelatin, which will also be evidenced by the FTIR analysis. Figure 2b presents the FTIR spectra of the pristine HNTs and gelatin-modified HNTs. Both pristine HNTs and modified HNTs showed strong peaks at 3697 and 3615 cm\({}^{-1}\), respectively, which correspond to the stretching vibration of Al-OH groups in the inner surface; at 1028 and 909 cm\({}^{-1}\), peaks corresponded to Si-O stretching and Al-OH bending vibrations, respectively [57]. Meanwhile, minor peaks at 2932, 2359, 1680, and 1540 cm\({}^{-1}\), corresponding to C-H stretching vibration, carbonyl group [58], hydrogen bonding of COOH groups [59], N-H bending vibration [60], and C-N stretching vibration [61], respectively, could be seen in the gelatin-modified HNTs spectrum rather than in the spectrum of pristine HNTs. As mentioned above, thermal properties of modified nanofillers are related to the nature of surfactants used. Therefore, on TGA curves for pristine ATH and silane-modified ATH (Figure 2c),  
Figure 1: SEM micrographs of: HNTs **(a)**, HNTs-g **(b)**, and ATH-sil **(c)**. Figure 2: TG curves **(a)** and FTIR spectra **(b)** of pristine HNTs and gelatin-modified HNTs; TG curves **(c)** and FTIR spectra **(d)** of pristine ATH and silane-modified ATH. one can observe clear differences. For pristine ATH, two mass losses were visible: The first one, in the temperature range of 20-165 \({}^{\circ}\)C, corresponded to the loss of adsorbed water [62], and the second major mass loss, in the temperature range of 180-600 \({}^{\circ}\)C, corresponded to the decomposition of surfactant molecules [63]. In turn, the silane-modified ATH decomposed in one major step; however, its decomposition temperature was improved by about 20 \({}^{\circ}\)C. It was especially well observed at the derivative curve of TG, where the maximum thermal decomposition was shifted from 288 \({}^{\circ}\)C (pristine ATH) to 300 \({}^{\circ}\)C for the modified ATH. Moreover, a very high char residue value for both fillers was observed.