Development of Coconut Shell Charcoal‐Reinforced Starch Superabsorbent Composites, with the Comparative Study of Epichlorohydrin and Citric Acid as the Crosslinking Agents

Abstract Coconut shell charcoal is explored as filler for the synthesis of starch‐based superabsorbent composites, and the effect of two crosslinking agents, namely epichlorohydrin (EPI) and citric acid (CA), is evaluated. The study investigates how varying filler concentrations influence water absorption, retention, and swelling. The highest water absorption (1462% swelling) is observed with EPI‐crosslinked starch and 0.75 g of filler. The charcoal increases the porosity and free volume of the composites, enhancing water retention. However, excessive filler reduces absorption by increasing rigidity. Compared to epichlorohydrin, CA‐crosslinked composites show lower absorption, with an optimal CA concentration at a 1:1 starch‐to‐CA ratio, resulting in a swelling of 234%. The composites are analyzed using Fourier Transform Infrared (FTIR) and X‐ray Diffraction (XRD) techniques. Their application as water retention agents in plant growth demonstrates a positive impact on shoot height, supporting seed growth. Biodegradability tests reveal excellent performance in CA‐crosslinked samples.