Superabsorbent polymer nanocomposites as water reservoir for the sustained release of active agents

Globally, 80% of all farmlands is rainfed, making irregular rainfall regimes a significant threat to food security. Farmers urgently need technologies that minimize water loss toalleviate yield loss in times of drought. Fertilizers and plant protection products (PPPs)are crucial for improved yields. However, the bulk application of these agrochemicals can lead to environmental leaching due to runoff and evaporation. Sustained delivery canimprove the efficiency of agrochemicals.To address the above-mentioned challenges, we propose superabsorbent polymer (SAP)nanocomposites as underground water reservoirs with the ability to integrate water andactive agent delivery. SAPs absorb water during rainfall and release it during dry spells.Composite SAPs can allow sustained delivery of agrochemicals, prevent their runoff due to heavy rainfalls, and keep them closer to the root area for optimum plant uptake.In this study, fertilizer-SAP composites containing 17 wt% micronutrients have achievedsuperior water absorption capacities of 1460-1630 g/g, compared to 500 g/g for traditional SAPs.Commercial SAPs have very limited biodegradability. Developing biodegradable SAP formulations is important to combat plastic accumulation in agricultural lands. There is a lack of studies on bio-SAPs with 25-70 wt% biomaterial contents. We have incorporated 5-60 wt% carboxymethyl cellulose (CMC) into an otherwise polyacrylate-based SAP formulation. A maximum water absorption of 600 g/g was achieved with SAP containing 10 wt% CMC. Up to 40 wt% CMC, SAPs exhibited waterabsorption comparable to commercial SAPs. SAPs with 40 wt% or more CMCbiodegraded completely by cellulase enzyme within 3 days.