# Comparison of the Properties and Structure of Montmorillonite Modified with Polyvinylpyrrolidone
## 3 Results and Discussion
### Thermal Degradation of the Modified MMT Samples  
So, the structure of the MMT/PVP = 1:12 is similar to the MMT/PVP-top, which is logical since their quantitative composition is the same. TGA (Figure 7) confirmed this conclusion. TG curves of MMT (curve a), MMT/PVP-bottom (curve b), and MMT/PVP-middle (curve c) significantly differ from curves of MMT/PVP-top (curve d), MMT/PVP = 1:12 (curve e), and PVP (curve f). Thermal phenomena in the MMT, PVP, MMT/PVP-bottom, MMT/PVP-middle, and MMT/PVP-top are described in detail in the previous work [43]. Thermal destruction of MMT, MMT/PVP-bottom, and MMT/PVP-middle samples occur  
Figure 4: ATR-FTIR spectra of MMT (a) and MMT/PVP-bottom at the MMT:PVP ratio 4:1 (b); 3:1 (c); 2:1 (d), 1:1 (e), 1:2 (f).  
Figure 5: ATR-FTIR spectra of MMT (a) and MMT/PVP-middle at the MMT:PVP ratio 4:1 (b); 3:1 (c); 2:1 (d), 1:1 (e), 1:2 (f).  
during three stages, and PVP, MMT/PVP-top, and MMT/PVP = 1:12 during four stages (Table 2). The mass loss of the MMT/PVP = 1:12 (about 9.5%) is lower in the first two stages of thermolysis (up to temperatures of 345 \({}^{\circ}\)C) compared to the PVP (about 10.8%), MMT/PVP-top (about 11%), and MMT (about 10%) (Figure 7, Table 2). This mass loss is mainly associated with the evaporation of absorbed water and the beginning of oxidation-reduction processes in PVP macromolecules (at the second stage of thermolysis). At the third stage of thermolysis in the range of 345-486 \({}^{\circ}\)C, the MMT/PVP = 1:12 degrades faster than the MMT/PVP-top but slower than the original PVP (mass loss of MMT/PVP = 1:12 is 86.2%, MMT/PVP-top--80.8%, PVP--86.9%). This mass loss is associated with the destruction of PVP macrochains. The mass residue of the samples at 486 \({}^{\circ}\)C is also significantly different: For MMT/PVP = 1:12, it is almost two times smaller (4.3%) than for MMT/PVP-top (8.2%) and two times larger than the original PVP (2.3%). PVP completely burns at 800 \({}^{\circ}\)C. The masses residues of MMT/PVP = 1:12 and MMT/PVP-top samples are about 2 and 4%, respectively, at 980 \({}^{\circ}\)C. Thus, the destruction and dehydration of the MMT crystal lattice at temperatures above 600 \({}^{\circ}\)C occur more intensively in the MMT/PVP = 1:12 than in the MMT/PVP-top. Similar results of accelerated thermal destruction of organically modified MMT are found in many works [47; 48]. The samples MMT/PVP = 1:12 and MMT/PVP-top have different structures and heat resistance, although their quantitative composition is the same. That is, the modified MMT structure and thermal properties significantly depend on the preparation method.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Temperature Range, \({}^{\circ}\)C** & **Mass Loss, \%** & **Mass Residue, \%** \\ \hline  & 25–150 & 9.3 & 90.7 \\ MMT & 150–512 & 2.4 & 88.3 \\  & 512–980 & 2.3 & 86 \\ \hline MMT/PVP-bottom & 25–150 & 3.1 & 96.9 \\ (MMT:PVP = 1:2) & 150–512 & 6.6 & 90.3 \\ \hline MMT/PVP-middle & 512–980 & 4.1 & 86.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of TG analysis for modified MMT samples.  
Figure 6: ATR-FTIR spectra of MMT/PVP = 1:12 (a), PVP (b) and MMT/PVP-top at the MMT:PVP ratio 4:1 (c); 3:1 (d); 2:1 (e), 1:1 (f), 1:2 (g).