Characterisation of carboxymethylcellulose-based superabsorbent polymer hydrogel for slow-release of nitrogen-phosphorus-potassium fertiliser

The application of superabsorbents in agriculture can improve the soil moisture retention capacity as well as can increase the soil infiltration. It is also reported that slow-release technology can increase fertiliser utilization efficiency and reduce economic losses. However, the information about superabsorbent with slow-release NitrogenPhosphor-Potassium (NPK) fertiliser and their characterisation are still limited. Carboxymethylcellulose-based super absorbent polymer hydrogel for slow-release of NPK fertiliser was made. Carboxymethylcellulose (CMC) made from Oil Palm Empty Fruit Bunch (OPEFB) was graft polymerized with acrylic acid (AA) to synthetise a super absorbent polymer (SAP) hydrogel. The NPK fertiliser is added to the CMC during the synthesis of the SAP hydrogels. To finding out how much compound fertiliser can coat the SAP hydrogel, the mass of fertilisers added was varied from 2.5 g, 5.0 g, 7.5 g, 10.0 g, and 12.5 g. The SAPs hydrogels carrying the slow-release NPK fertiliser is called SAP-NPK. The SAP-NPK products are characterised by SEM to show their morphology. Their structures are analysed by FTIR, and their capability to absorb water is determined through polymer swelling tests. The biodegradable tests, soil tests, and organoleptic tests are also carried out to complete the quality data of the SAP-NPK. The research results showed that the more NPK fertiliser carried by the SAP hydrogels, the ability of SAP-NPK to absorb water and their flexibility tend to decrease and easily degraded. The morphology of the SAP-NPK has a rougher surface than pure SAP hydrogel, but both have the same colour. Data of soil tests describe that SAP-NPK products vary in their pH and soil water content and their C, N, P, and K element contents.