Physical and chemical characteristics of alginate-poly (vinyl alcohol) based controlled release hydrogel

Utilization of natural polymer matrix for preparation of hydrogel can improve the performance of the materials and render them environmentally friendly. In this work, the hydrogel based on alginate-poly (vinyl alcohol) cross-linked by glutaraldehyde (at optimum volume (mL) ratio of 10:10:10, respectively) were prepared using solution mixing copolymerization method. The structural and morphological characterizations of hydrogels were determined by mean of FTIR spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic forces microscopy. The swelling ratio, water retention, and nutrient release of hydrogel were determined by gravimetric method. The synthesized hydrogel showed roughness surface with random and asymmetric pore size distribution and layered structures. The FTIR spectra confirmed the copolymerization of hydrogel that primary occurred through the crosslinking of alginate to poly (vinyl alcohol) via intermolecular hydrogen bond. The X-ray diffraction patterns indicated the predominant amorphous structure of hydrogel. The insertion of nutrient into hydrogel induced the strong interaction between nutrient ions and hydrogel resulted in the enhancement of hydrogel crystallinity and modification of interlayer distance. The nutrient coated hydrogel led to the increase of water absorbency up to 480%. Hydrogels can confine water molecules in their matrices up to 50% within time interval of 2 weeks. The maximum of nutrient released from hydrogel is around 69.25% after observation period almost to 12 days. The insertion of nutrient into hydrogel improved their mechanical properties. These results inferred that synthesized hydrogel is typical of slow released material, which is promising to be applied as an alternative controlled release fertilizer material.