# Comparison of the Properties and Structure of Montmorillonite Modified with Polyvinylpyrrolidone
## 3 Results and Discussion
### Differential Scanning Calorimetry  
The DSC analysis is used to study the thermal behavior of the MMT/PVP = 1:12 and MMT/PVP-top samples. The DSC curves of PVP and the MMT/PVP = 1:12 are very similar (Figures 8 and 9). However, the glass transition temperature of pure PVP is almost 3 \({}^{\circ}\)C higher than that of the MMT/PVP = 1:12 sample (141.7 and 138.9 \({}^{\circ}\)C, respectively). During the first heating of these samples, only one endopeak (in the 34-118 \({}^{\circ}\)C) is observed on the DSC curves, which is associated with the evaporation of moisture. The enthalpy values of these processes in the samples are almost identical (for PVP AH = 359.1 J/g, for MMT/PVP = 1:12 \(\Delta\)H = 355.7 J/g). During the first heating of the MMT/PVP-top sample (Figure 10), two endopeaks (in the ranges of 38-126 \({}^{\circ}\)C and 218-286 \({}^{\circ}\)C) are observed on the DSC curve. Suppose the first endopeak can be explained by the moisture evaporation (\(\Delta\)H = 281.2 J/g). In that case, the second endopeak is most likely explained by the partial destruction of weak physical bonds formed between MMT and PVP (\(\Delta\)H = 16.9 J/g). These endopeaks are absent during the second scan of the sample, which indicates the completion of the above processes. During the cooling of the studied samples (crystallization curve), no thermal processes occur (Figures 8-10), which confirms their amorphous structure. The glass transition temperature of the MMT/PVP-top sample is 144.2 \({}^{\circ}\)C. Therefore, it notes  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Temperature Range, \({}^{\circ}\)C** & **Mass Loss, \%** & **Mass Residue, \%** \\ \hline \multirow{4}{*}{MMT/PVP-top (MMT:PVP = 1:2)} & 25–95 & 7.1 & 92.9 \\  & 95–345 & 3.9 & 89.0 \\  & 345–486 & 80.8 & 8.2 \\  & 486–980 & 4.2 & 4.0 \\ \hline \multirow{4}{*}{MMT/PVP = 1:12} & 25–95 & 6.5 & 93.5 \\  & 95–345 & 3.0 & 90.5 \\  & 345–486 & 86.2 & 4.3 \\  & 486–980 & 2.7 & 2.0 \\ \hline \multirow{4}{*}{PVP} & 25–85 & 8.5 & 91.5 \\  & 85–350 & 2.3 & 89.2 \\  & 350–486 & 86.9 & 2.3 \\  & 486–800 & 2.3 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 7: TGA of MMT (a); MMT/PVP-bottom (b), MMT/PVP-middle (c), MMT/PVP-top (d) at the MMT:PVP ratio 1:2; MMT/PVP = 1:12 (e) and PVP (f).  
significant differences in the thermal behavior of the studied samples of modified MMT. In particular, the glass transition temperature of the MMT/PVP-top sample increased by 2.5 \({}^{\circ}\)C compared to the original PVP, and the MMT/PVP = 1:12 sample decreased by 2.8 \({}^{\circ}\)C. Also, the MMT/PVP-top sample has a significantly lower value of the enthalpy of evaporation of absorbed water than the MMT/PVP = 1:12 and PVP samples, which indicates a different amount and type of evaporated water and correlates with TGA data. Such differences are explained by other physical interactions between PVP macromolecules and exfoliated MMT sheets in these samples and their different structure. Preliminary analyses and SEM confirm such assumptions.  
Figure 8: DSC curves of PVP.  
Figure 9: DSC curves of MMT/PVP = 1:12.