**4.2. X-ray diffraction**

**3.6. Mechanical properties**

and frequencies.

**4. Results and discussion**

**4.1. Fourier transform infrared spectroscopy**

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

For the "Temperature ramp" mode, the temperature ranged from 275 to 300°C/min, oscilla-

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

The presence of montmorillonite in the polymer matrix was checked by FTIR analysis (see **Figure 1**, only PMAA-ClNa and Cl15A data are presented here). FTIR spectra of Cloisites show the presence of clay characteristic peaks, confirmed also by the literature data [12, 15]. For all four types of montmorillonites, around 3633 cm−1 we noticed the OH stretching of latex water. The peak from 1011 cm−1 with a shoulder at 921 cm−1 was attributed to Si–O stretching vibration while the Si–O bending vibration was identified in the 400–600 cm−1 area, more exactly 518 cm−1 and 454 cm−1. The difference between the ClNa and the modified clays (Cl30B, Cl15A and Cl20A) is given by the presence of additional peaks at 2926 cm−1 and 2852 cm−1, specific for quaternary ammonium salts. As for the pure PMAA, its spectra reveal the characteristic peaks around 3000 cm−1 corresponding to the O–H stretching vibration and at 1737 cm−1 associated to CO group stretching vibration. At the wavelength of 2960–2875 cm−1, the peaks for stretching vibration of methyl and methylene groups were found [16]. The absence of vinyl group stretching vibration at 1628–1692 cm−1 indicates that the polymerization occurred [15]. Referring to the spectra of Salecan, a broad peak was identified at 3329 cm−1, being characteristic for O–H stretching vibration, as well as the intermolecular hydrogen bonding of the polysaccharide [17]. Peaks from the 800–1100 cm−1 area are assigned to polysaccharide structure and include C–OH stretching in the glucopyranose rings. More specifically, the band at

the sample. The measurements were repeated for three times.

152 Current Topics in the Utilization of Clay in Industrial and Medical Applications

tion amplitude of 20 μm, 1 Hz frequency and 0.5 sampling.

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

Salecan. These results along with the literature data [3] prove that the Salecan had an amorphous structure. From the spectrum of pure PMAA hydrogel, it could be seen that the PMAA showed prominent diffraction peak posited around 2θ = 15°, suggesting the high crystallinity. The peak form and angle value are later noticed in the composites containing PMAA, with a slight loose in intensity due to the presence of Salecan and/or unmodified/modified clay.

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

XRD data of ClNa show the characteristic peak at 2θ = 7.3°. This peak is preserved in PMAA-ClNa spectra with a slight displacement at a lower angle (2θ = 6.7°). In the case of PMAA-ClNa-Salecan, the peak registered a decrease in intensity and was shifted to 2θ = 5°. The narrow, intense peak of ClNa present in PMAA-ClNa structure stands for a microcomposite, tactoid structure, while the decrease in intensity and broadening of the same peak in the PMAA-Salecan-ClNa hydrogels proves a highly intercalated network. The XRD pattern of Cloisite 30B

the PMAA-Cl30B composite as well as in the spectra of the final PMAA-Cl30B-Salecan hydrogel. A decrease in diffraction intensity and sharpness of the Cloisite peak in the composites leads to the conclusion that the montmorillonite tends to spread into an intercalated structure.

defined crystalline nature of Cloisites. The Cloisites have a tendency of spreading leading to slight intercalated layered structures of the PMAA-Cloisites and PMAA-Cloisites-Salecan,

The conclusion was deducted from the examination of Cloisite peaks that suffered an enlargement and decrease in intensity. From the all abovementioned Cloisites, Cloisite Na and Cloisite 30B seemed to have the highest degree of intercalation, whereas Cloisite 20A and Cloisite 15A formed only microcomposites (tactoid structure). What is interesting to notice is that in case of ClNa, the tactoid structure was perfectly preserved when PMAA-ClNa composites were synthesized but spread and turned into an intercalated-exfoliated structure once Salecan was added. As for other Cloisites, we do not have the same observation, for all of them, a little more intercalated morphology is noticed rather for PMAA-Cloisite composites

The thermal stability of the synthesized PMAA/Salecan hydrogel and hydrogel nanocomposites (PMAA/Salecan/clay) were examined by TGA analyses. Three steps of weight loss were registered (see **Figure 3**) with two maximum decomposition temperatures. The first weight

The second and third steps are assigned to PMAA decomposition as well as the degradation of the main skeleton of Salecan. At this point, the polymer backbone is destroyed. Regarding the samples of nanocomposites obtained in the presence of simple/modified montmorillonite, some changes of the thermal stability of final materials were registered. These modifications were due to the presence of quaternary ammonium salts [4], more evident in the case of Cl15A and 20A. It is worth to mention that when Salecan was added, semi-interpenetrated networks were obtained, and the systems behave as homogenous architectures. Thus, the

loss is a result of water volatilization and the degradation of organic compounds [20].

, respectively. This was in conformity with the literature data [19] and stands for well-

As for Cl20A and Cl15A, the characteristic diffraction peaks were identified at 2θ = 3.5<sup>o</sup>

. The same angle value of this peak is noticed in

http://dx.doi.org/10.5772/intechopen.74478

and

155

reveals the main diffraction peak at 2θ = 4.9<sup>o</sup>

than for final PMAA-Salecan-Cloisite hydrogel.

**4.3. Thermal-gravimetric analysis**

more obviously for the Cl15A.

2θ = 2.3<sup>o</sup>

**Figure 2. I.** XRD results. I PMAA/ClNa/PMAA-ClNa/Salecan/PMAA-Salecan/PMAA-Salecan-ClNa; **II.** PMAA/Cl30B/ PMAA-Cl30B/Salecan/ PMAA-Salecan/ PMAA-Salecan-Cl30B; **III.** PMAA/Cl20A/PMAA-Cl20A/Salecan/PMAA-Salecan/ PMAA-Salecan-Cl20A; **IV.** PMAA/Cl15A/PMAA-Cl15A/Salecan/PMAA-Salecan/PMAA-Salecan-Cl15A; **A**: Wide angle; **B:** Low angle.

Salecan. These results along with the literature data [3] prove that the Salecan had an amorphous structure. From the spectrum of pure PMAA hydrogel, it could be seen that the PMAA showed prominent diffraction peak posited around 2θ = 15°, suggesting the high crystallinity. The peak form and angle value are later noticed in the composites containing PMAA, with a slight loose in intensity due to the presence of Salecan and/or unmodified/modified clay.

XRD data of ClNa show the characteristic peak at 2θ = 7.3°. This peak is preserved in PMAA-ClNa spectra with a slight displacement at a lower angle (2θ = 6.7°). In the case of PMAA-ClNa-Salecan, the peak registered a decrease in intensity and was shifted to 2θ = 5°. The narrow, intense peak of ClNa present in PMAA-ClNa structure stands for a microcomposite, tactoid structure, while the decrease in intensity and broadening of the same peak in the PMAA-Salecan-ClNa hydrogels proves a highly intercalated network. The XRD pattern of Cloisite 30B reveals the main diffraction peak at 2θ = 4.9<sup>o</sup> . The same angle value of this peak is noticed in the PMAA-Cl30B composite as well as in the spectra of the final PMAA-Cl30B-Salecan hydrogel. A decrease in diffraction intensity and sharpness of the Cloisite peak in the composites leads to the conclusion that the montmorillonite tends to spread into an intercalated structure.

As for Cl20A and Cl15A, the characteristic diffraction peaks were identified at 2θ = 3.5<sup>o</sup> and 2θ = 2.3<sup>o</sup> , respectively. This was in conformity with the literature data [19] and stands for welldefined crystalline nature of Cloisites. The Cloisites have a tendency of spreading leading to slight intercalated layered structures of the PMAA-Cloisites and PMAA-Cloisites-Salecan, more obviously for the Cl15A.

The conclusion was deducted from the examination of Cloisite peaks that suffered an enlargement and decrease in intensity. From the all abovementioned Cloisites, Cloisite Na and Cloisite 30B seemed to have the highest degree of intercalation, whereas Cloisite 20A and Cloisite 15A formed only microcomposites (tactoid structure). What is interesting to notice is that in case of ClNa, the tactoid structure was perfectly preserved when PMAA-ClNa composites were synthesized but spread and turned into an intercalated-exfoliated structure once Salecan was added. As for other Cloisites, we do not have the same observation, for all of them, a little more intercalated morphology is noticed rather for PMAA-Cloisite composites than for final PMAA-Salecan-Cloisite hydrogel.
