DETERMINATION OF RESWELLING PROPERTIES AND WATER DIFFUSION MECHANISM OF HYDROGEL COMPOSITES

This study focused on acrylamide/N-vinyl-2-pyrrolidone chemically cross-linked hydrogel composites. As fillers, sepiolite and alkyl ammonium salt modified sepiolite were used in the preparation of the hydrogel composites. Characterization of the hydrogel composites was carried out with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses. Swelling of the hydrogel composites as a function of time was investigated with tea-bag method. Reswelling ability of the hydrogel composites was revealed after the three cycles. In the third swelling test, the swelling percentage of the NVP hydrogel was about 1690%. The swelling percentage of the NVP+MSP hydrogel composite increased from approximately 1610% to 1760% after the three repeated swelling tests. The hydrogel composite including modified sepiolite showed higher equilibrium water content (EWC) in the distilled water and at different pHs compared to other samples. The highest EWC value was obtained for the hydrogel composite including modified sepiolite (0.9637) in alkali conditions. Water diffusion mechanism of the hydrogel composites was examined based on the Fickian diffusion index (n). n values of the hydrogel composites were lower than 0.5 which is indication of water diffusion governed by less Fickian diffusion mechanism. The results showed that hydrogel composites can be used in various applications required the reswelling ability and high EWC value.