Spray-dried lignocellulosic microparticles as bio-based carriers for nutrient release of monoammonium phosphate

The global shift toward sustainable agriculture drives the development of enhanced efficiency fertilizers (EEFs) based on biodegradable materials. This study investigates kraft lignin (KL) and sodium lignosulfonate (LS), two byproducts of the pulp and paper industry, as matrices for the controlled or slow release of monoammonium phosphate (MAP). Lignin-based microparticles were produced via spray-drying, an industrially scalable, solvent-free encapsulation method, to assess how lignin macromolecular structure and processing influence nutrient delivery. Structural and morphological analyses confirmed the formation of spherical, single-phase lignin-MAP microparticles. KL-based particles, which are more hydrophobic and structurally condensed, exhibited higher uniformity and lower agglomeration than the hydrophilic LS-based particles. Thermal and structural characterizations (TGA, FTIR, XRD) revealed physicochemical interactions, likely involving hydrogen bonding, between MAP and the lignin matrix formed during atomization and drying, which were not observed in conventionally dried controls. Nutrient-release assays demonstrated a sustained MAP release, which was further extended by incorporating cellulose microfibrils (CMF). The ternary KL-CMF-MAP system delayed MAP release by up to 50% compared to the KL-MAP system, indicating a synergistic effect between lignocellulosic components. Overall, spray-drying offers an efficient and environmentally friendly approach to engineering lignin-based nutrient carriers without the need for chemical modification or toxic solvents. The resulting microparticles demonstrate strong potential as standalone EEFs or as nutrient-rich fillers in biodegradable polymer coatings, supporting fertilizers technologies that align with current sustainability frameworks.