**3.6. Mechanical properties**

Dynamic mechanical analysis (DMA) was performed using the DMA-Q 800 device (TA Instruments New Castle, DE, USA). Freeze-dried hydrogels were analyzed in "Temperature Ramp" mode and swollen hydrogels in DMA Multi-Frequency-Strain "Frequency sweepisothermal." Dual cantilever-powder clamp was used for freeze-dried hydrogels and compression clamp was used for hydrogels. Hydrogels disk were cut with an eyelet (part of DMA-Q 800 Dynamic Analyzer compression set) before analyses, the dimensions of the analyzed specimens being about 12.5 mm diameter. Rectangles of 60 mm × 12.77 × 2–3 mm were used for lyophilized hydrogels. These were then measured with a caliper in order to enter the initial values. "Isothermal" mode was carried out at 30°C with 4 μm oscillation amplitude for 120 min from 0.1 to 10 Hz at 11 frequencies (frequency sweep segment repeat for 10 times). A 14.5 mm compression plate was used for all samples. A 0.01 N compressive static force was applied to the specimen to ensure that the upper compression plate did not lose contact with the sample. The measurements were repeated for three times.

For the "Temperature ramp" mode, the temperature ranged from 275 to 300°C/min, oscillation amplitude of 20 μm, 1 Hz frequency and 0.5 sampling.

1039 cm−1 was related to C–OH stretching in the glucopyranose ring, a broad, weak peak at 896 cm−1 suggested that D-glucopyranose had a β-configuration whereas the almost unidentifiable peak at 818 cm−1 confirmed the presence of small amounts of α-glucopyranose form. Analyzing the spectra of the nanocomposites that have the modified montmorillonite as a component, alterations were noticed but also the preservation of some characteristic peaks. For instance, specific clay bands were observed. The Si–O–Si stretching vibration shifted from 1011 to 1050 cm−1 and the peaks from 400 to 600 cm−1 suffered a bathochromic shift. In the hydrogels, we found the Si–O bending and stretching vibration at 463 and 622 cm−1,

**Figure 1.** FT-IR spectra of the pristine clay/PMAA/PMAA-Cloisite/Salecan/PMAA-Salecan/PMAA-Salecan-Cloisite

The Effect of Clay Type on the Physicochemical Properties of New Hydrogel Clay Nanocomposites

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For the composites prepared using modified montmorillonites, the bands at 2856 and 2925 cm−1 state that the quaternary ammonium salts are present in the network. At the same time, PMAA peaks were identified. Thus, we have C═O group stretching vibration, moved from 1737 to 1697 cm−1(much lower intensity for 20A and 30B Cloisites), and the stretching vibration for methyl and methylene groups that slightly shifted to 2996–2925 cm−1 [18].

In a comparative analysis of PMAA and PMAA-Salecan bands, we noticed a change in the 2942 cm−1 peak. In the hydrogel structure, the peak broadens and suffers a decrease in sharpness, which can be explained by the formation of the intercalated structure between the poly-

The fact that within the final structure, we find the skeleton of the compounds, we started with, serves as proof that the synthesis of semi-IPN hydrogels went successfully. The slight changes in wavelength and intensity could be explained by the interactions between the com-

XRD analysis was carried out in order to investigate the type of morphology of the clays, we study as well as the structure of final composites materials. According to the recorded data (**Figure 2**, I–IV), a broad peak centered at 2θ = 20° was observed in the XRD patterns of

ponents of the hydrogels with the obtaining of a complex compact structure.

respectively.

exemplified for ClNa and Cl15A.

mer and the polysaccharide.

**4.2. X-ray diffraction**

DMA-Q 800 used Universal Analysis 2000 for calculating dynamic mechanical properties and exports the data for plotting the investigated properties as a function of time, temperature and frequencies.
