Optimization of water absorption properties of superabsorbent double-network hydrogel biochar composites / Nur Ellydia Mohamad Gustie Noorambia

Agriculture sector contributes a lot in the economic expansion of the country due to the extensive land and biodiversity. Plant growth is affected by many factors such as the temperature fluctuation due to climatic change, as the heat stress directly affect the agricultural productivity. Frequent irrigation is needed to maintain the soil moisture to support the plant development. Hydrogels are three-dimensional crosslinked polymer networks, which contain a huge amount of water and can be used as carriers for various active ingredients including fertilizers. Hydrogel-based controlled-release fertilizers (CRFs) absorb and retain irrigation water as well as simultaneously supply the nutrients to the plants. Superabsorbent double-network hydrogel-biochar composites (DNHBCs) based on polyacrylate were synthesized in this study via solution polymerization method and cyclic freeze-thaw by using different concentrations of poly(vinyl alcohol) (PVA), N,N-methylenebisacrylamide (MBA) crosslinker and palm kernel shell biochar (BC). The DHNBCs were characterized using Attenuated Total Reflection-Fourier Transform Infra-Red (ATR-FTIR) and Thermogravimetric Analyzer (TGA). Water absorption properties of the superabsorbent DNHBCs were optimized by using Response Surface Methodology-Central Composite Design (RSM-CCD) by varying MBA, PVA and BC concentrations. The PVA and MBA contents of the DNHBC showed significant effects on the water absorption capacity of DNHBC but not the BC concentration. Increasing BC wt% tends to increase the water absorption of the resultant DHNBC, however higher PVA concentration tends to reduce the hydrogel’s water absorption. DNHBC-R1 and DNHBC-R7 not only possess high water absorption at 328.28 g/g and 309.08 g/g, respectively, but they also maintain high structural integrity and stability indicating their potentials as multi-functional controlledrelease fertilizer (CRF) candidates. The equilibrium water absorption capacities of the DHNBC-R1 and DHNBC-R7 varied in different aqueous media and ionic strength, with decreasing water absorption capacity with increasing ionic strength. The research theme is aligned with Sustainable Development Goal No. 2 (SDG 2) aiming to end hunger, achieve food security, improve nutrition and support sustainable agriculture by 2030.