Eco-friendly carboxymethyl cellulose hydrogels filled with nanocellulose or nanoclays for agriculture applications as soil conditioning and nutrient carrier and their impact on cucumber growing

In this work, carboxymethyl cellulose (CMC) hydrogels were produced via chemical crosslink with citric acid and filled with nanocellulose (NC), montmorillonite, or vermiculite, in different contents. The FTIR results indicated a strong chemical interaction between NC or vermiculite and the CMC, increasing the hydrogen bond energies by the fillers' participation in the crosslinking, reflecting in the water absorption (WA). Higher filler contents interacted more with the matrix, resulting in a denser hydrogel with lower WA capacity. The montmorillonite did not alter the hydrogels' structure due to its low compatibility with the CMC, doubling the WA values at low contents. The hydrogels' thermal stability was maintained after the fillers' addition. NPK fertilizer was added to selected formulations, and results indicated success in NPK encapsulation. Fertilizer release in water and soil indicated a slow-release, and the rate was dependent on the filler; all fillers showed a low rate than the CMC pristine hydrogel. The Korsmeyer-Peppas model indicated that vermiculite is not adequate for agriculture applications due to the diffusion mechanism, while nanocellulose and montmorillonite showed crucial results for the field. The in vivo tests demonstrate hydrogels' efficiency filled with 3% NC or 1% montmorillonite in the nutrients-controlled release.