Poly (vinyl alcohol)/glutaraldehyde/Premna oblongifolia merr extract hydrogel for controlled-release and water absorption application

Abstract

Fertilizer leaching and water slack are the most problems predominantly found in the agriculture practices. Many efforts have been done by promoting a medium for controlling fertilizer release and water retaining in vicinity of plant and soil. In this work, a biodegradable Premna Oblongifolia Merr (POM) extract/polyvinyl alcohol (PVA) composite based hydrogel for controlled-release and water absorption application has been prepared. The hydrogel composite was successfully synthesized through solution mixing of POM and PVA with an aid of crosslinking agent (glutaraldehyde) at optimum composition in volume ratio of 5:5:9, respectively. In particular, the fertilizer (Zinc nitrate) solution was incorporated into hydrogel matrix for controlled release study. The structural morphology of hydrogel composite was investigated by means of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. The water absorption capacity and fertilizer-controlled release behaviour of hydrogel composite were evaluated by gravimetric and atomic absorption spectroscopy techniques, respectively. The FTIR spectra showed the evidence of copolymerization of hydrogel precursors, indicated by the shifting of peak intensity and position of several functional groups (O-H, C-H sp3, C=O, C-N, C-O) as a result of interaction between POM extract and PVA moieties which predominantly occurs through intermolecular hydrogen bonding. In particular, the crosslinking of PVA and POM extract mediated by glutaraldehyde was evidenced by the appearance of new peak for -C-O-C moieties owing to the formation of hemiacetal bridges in between polymer backbones. The insertion of fertilizer into hydrogel matrix was sharpen the peaks of hydrogel moieties and led to new peak appearance at 1384 cm−1 (NO moieties), correspond to the interaction with zinc ions. The X-ray diffraction confirmed the modification of structural morphology of hydrogel with fertilizer insertion as indicated by the slight shift of interlayer distance of polymer matrices. The hydrogel composites showed the large water absorption capacity up to 550 % and could retained water in its matrix for almost 3 weeks. Absorption and released studies indicate that the micronutrient interacts chemically with a surface functional group of hydrogel. The released micronutrient should come from the second and the upper layer where it occurs only at high concentration. These results offer the promising applications for the controlled-release and water absorbent materials.