Synthesis of cellulose microfibrils embedded carboxymethyl tamarind kernel gum hydrogels for water retention and controlled urea release in agricultural applications.

Cellulose microfibrils (extracted from agricultural waste rice straw) embedded carboxymethyl tamarind kernel gum (CMTKG) hydrogels were synthesized. In this process, freeze-thaw technique was utilized to reorganize and align the cellulose fibers, followed by chemical crosslinking to induce the gelation reaction of the highly absorptive polymer, CMTKG, which was crosslinked around the cellulose microfibrils. The design of the hydrogel is intended to achieve two main objectives. First, the cellulose microfibrils function as a microchannel for transporting water and plant nutrients. Second, hydrogel accommodates and retains the water and plant nutrients, aiding in the controlled release of the fertilizer. The hydrogel exhibits a swelling capacity as high as 15,359 % at 10 °C. When hydrogels are incorporated into soil at a concentration of 0.1 % (w/w), they can help retain water in the soil for up to 56 days. The release of urea was also demonstrated, with about 95 % of urea being released after 8 days in water and 34 days in soil. Urea release behavior in water follows purely Fickian diffusion, while the Higuchi model best describes urea release behavior in soil. Based on the outcomes of the kinetics models, it can be concluded that urea molecules are uniformly distributed within the hydrogel and that the release process is primarily governed by diffusion rather than by degradation or erosion. The degradation study of the hydrogel in soil further supports the kinetic results.