Poli(Vinil Alkol) Kil Nanokompozitlerinden Hibrit Hidrojel Hazırlanması
Özet
Preparation and development nanofilled polymer composites from clay/polymer nanocomposite have been started in the 1950s and became a popular subject in parallel with increasing of applications in industry and academic studies. In the following years, studies are increasing to gain more specific and expanded properties of polymer/clay by enhancing the interaction between polymer chains and clay layers.
Poly(vinyl alcohol) (PVA) is a polimer which is synthetic, non-toxic, water soluble, having high hydrophilic properties. It can easily be converted to film and has high water absorbtion attribute, so have reached vast application fields in industry. Montmorillonite (MMT) is a natural and layered clay which is the most popular filler of this kind of polymers.
In this thesis we aimed to prepare and characterize Na-MMT/PVA hybrid hydrogel nanocomposites by adding nano size Na-MMT clay to PVA matrix.
First at all (%0, 2, 5, 7) Na-MMT/PVA mixtures have been prepared by solution intercalation method with different mass ratios. Freezing and thawing processes were applied to prepared the mixtures. Then crosslinked hybrid hydrogel films were obtained by irradiating the mixtures to 20 kGy in 60Co gamma source.
Then, formation of hybrid hydrogel film nanocomposites and nanocomposite structure were characterized XRD (X-ray diffraction), TEM (Transmission Electron Microscopy),
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AFM (Atomic Force Microscopy), PALS (Positron Annihilation Lifetime Spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy).
The gelation and swelling behaviour of hybrid hydrogel films were also investigated. At the last step, with the aim of investigating physical and thermal behaviour of Na-MMT/PVA hybrid hydrogels, mechanical (stress-strain) and thermal (TGA) tests were made and corresponding changes were studied in more details.
The structural characterization of Na-MMT, 20 kGy irradiated PVA and Na-MMT/PVA hybrid hydrogel film samples were performed by ATR-FTIR spectroscopy. The spectral subtraction of clay-free PVA from 20 kGy irradiated Na-MMT/PVA hybrid hydrogel film samples results in a spectrum which shows that the intensity of characteristic Si-O stretching peaks were increased with an increase in clay amount for hybrid hydrogel film samples which is prepared by the addition of Na-MMT clays with concentrations of 2%, 5% and 7% (weight percentage-with respect to polymer) to the PVA matrix.
According to XRD and TEM results, hybrid hydrogel samples with base exfoliated morphology (specially at %2Na-MMT/PVA) were observed. It is also found that the amount of intercalated Na-MMT in %5-7Na-MMT/PVA hybrid hydrogels is increased as clay ratio increased.
In AFM measurements, surface of PVA and hybrid hydrogel samples (%2 ve%5 Na-MMT/PVA) were scanned. According to the results surface of hybrid hydrogel film samples (%2 ve%5 Na-MMT/PVA) were smoother than pure PVA samples.
In PALS mesurements, crystalline and amorphous regions of the pure PVA showed decreased radius of free volume holes with the addition of clay. According to these results more compact structures were formed.
The gelation percentage of hybrid hydrogel samples was observed to increase compared to pure PVA and in equilibrium percent swelling values of hybrid hydrogel samples were found to decrease compared to the pure PVA.
In TGA experiments, it was observed that the thermal stability of clay contaning MMT/PVA hybrid hydrogel samples were not affected adversely with reference to clay-free PVA samples.
In mechanic test measurements, Na-MMT/PVA hybrid hydrogel samples showed better E-Modulus values (%2Na-MMT/PVA: +%206, %5Na-MMT/PVA: +%300, %7Na-MMT/PVA: +%356) and Yield Stress values (%2Na-MMT/PVA: +%7, %5Na-MMT/PVA: +%11.3, %7Na-MMT/PVA: +%12.23) than pure PVA. According to the results, improvements were obtained in mechanic properties of composite samples.
