Acrylamide sepiolite based hydrojel composites and their properties

Hydrogels are defined as three dimensional polymeric structures which absorb a large quantity of water or various liquids. Hydrogels are used in many applications due to their main advantages such as high water uptake capacity, responsiveness to external factors (pH, temperature, light, electric and magnetic field etc.), biocompatibility and biodegradability. In the first part of this study, acrylamide (Aam) and N-vinyl-2-pyrrolidone (NVP) based cross-linked hydrogels were synthesized. Hydrogel composites were synthesized adding sepiolite as filler in the second part of the study. In the third part, hydrogel composites were synthesized using alkyl ammonium salt modified sepiolite as filler. Characterization of the hydrogels was carried out with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) analyses and thermogravimetric analysis (TGA). Amorphous structure of the synthesized hydrogels based on XRD analysis and homogeneous dispersion of the fillers in hydrogel network according to SEM analysis were figured out. Moreover, TGA curves showed that sepiolite (SP) or modified sepiolite (MSP) slightly increased thermal resistance of the neat hydrogel. Swelling behaviour of the hydrogels was investigated with tea-bag method. Swelling percentage of the hydrogels in distilled water, NaCl solution and different pH media was calculated. In distilled water, the highest swelling percent (DS%) of the NVP hydrogel, NVP+SP hydrogel composite and NVP+MSP hydrogel composite was determined as 1350%, 1260% and 1610%, respectively. In different pH media, DS% value for NVP+MSP hydrogel composite was specified as 1800% at pH 9. It was observed that the swelling percent of the hydrogels in distilled water increased with increasing temperature and the highest swelling percentage of the hydrogels was reached at 50 °C. The results showed that the hydrogels and hydrogel composites were pH and temperature sensitive materials. Moreover, it was concluded that the swelling percent of the hydrogels increased after the three repeated swelling test and the hydrogels can be used time and again.