Source-dependent structural and pH-responsive swelling properties of bentonite/cellulose/alginate hydrogel beads derived from agricultural biomass residues

Agricultural biomass residues are abundant and renewable feedstocks for the development of cellulose-based functional biomaterials. However, direct comparisons of cellulose-rich fractions derived from multiple agricultural biomass sources within the same hydrogel formulation and under identical fabrication conditions remain limited. This study investigated the structural and swelling properties of bentonite/cellulose/alginate (BT/CL/ALG) hydrogel beads prepared from eight agricultural residues: coffee pulp, mango leaf, corn cob, corn leaf, corn husk, corn stalk, sugarcane leaf, and bagasse. The biomass residues were subjected to combined alkaline hydrogen peroxide (AHP) pretreatment to obtain cellulose-rich fractions, which were subsequently incorporated into a sodium alginate matrix with bentonite clay and crosslinked with Ca²⁺. The resulting materials were characterized by compositional analysis, FTIR, XRD, SEM, and TGA/DTG. AHP pretreatment resulted in substantial cellulose enrichment, with the highest cellulose contents observed in corn stalk (76.0%) and bagasse (70.4%). FTIR and XRD analyses indicated changes in the chemical structure and relative crystalline organization of the biomass following pretreatment, while SEM revealed source-dependent morphological changes. The resulting hydrogel beads exhibited differences in swelling behavior, with swelling capacities measured at 144 h ranging from 218.57% to 419.83% in deionized water. Under PBS conditions, all hydrogel beads exhibited pH-responsive swelling, with greater swelling at pH 9 than at pH 3. The highest swelling capacity was observed for the corn-leaf-derived hydrogel at pH 9 (2245.85%). Overall, the findings demonstrate that agricultural biomass residues can provide cellulose-rich feedstocks for the preparation of BT/CL/ALG hydrogel beads with source-dependent structural and swelling characteristics.