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

The 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 variation of filler concentration is done to study the effect of concentration on absorption, and the highest water absorption, water retention, and swelling were observed with starch crosslinked by EPI and 0.75g filler with a % swelling of 1462%. With the introduction of filler, the porosity is increased, and void space is available for water absorption and retention. The porosity of composites increased due to the coconut shell charcoal filler acting as a spacer between the crosslinked matrix, increasing the free volume available. However, excessive filler dosage increases the structural rigidity and reduces the water absorption capacity. Compared to epichlorohydrin, the CA shows less water absorption, and the variation of CA concentration is done to evaluate the optimum dosage of CA in the formulation. The optimum dosage of CA was observed to be a 1:1 ratio of Starch to CA, with the sample having 0.75g filler, giving the highest % swelling of CA crosslinked composites of 234%. The synthesized composites are also evaluated for Fourier Transform Infrared Radiation (FITR) and X-ray 2ϴ Diffraction (XRD) analysis. The synthesized superabsorbent composites are explored for their effect in aiding plant growth, and the study reported a considerable positive effect of an increase in the height of the shoot considerably via utilizing the composites as a water retention agent to aid seed growth. The biodegradability study reported excellent biodegradability in the case of the CA crosslinked samples.