Preparation and slow-release property of modified lignin-coated sodium alginate fertilizer core double-layer coated fertilizer

This work prepared a lignin-based double-layer slow-release fertilizer (SRF). We prepared sodium alginate-zinc ammonium phosphate microbeads as the inner core of fertilizer by ion exchange method, cellulose acetate butyrate (CAB) co-blended with degradable material polylactic acid (PLA) as the inner coating, and two chemically modified lignin (sulfonated lignin and epoxy-aminated lignin) as the second coating. The synthesized Materials were characterized morphologically and structurally by FTIR, TG, XRD and SEM. The viscosity, mechanical property, water contact angle, water-holding property, water-retention and slow-release property of the samples were evaluated. PC-SRF, PSC-SRF and PEC-SRF all had superior water-retention and nutrient release property compared to sodium alginate-zinc ammonium phosphate. The release of urea and phosphorus in the single-layer PC-SRF reached equilibrium after 34 and 36 days, and their cumulative release rates reached 87.09% and 86.19%, respectively. The release of urea and phosphorus from the bilayer PSC-SRF reached equilibrium after 38 and 40 days, and the cumulative release rates reached 83.57% and 82.07%, respectively; the release of urea and phosphorus from the bilayer PEC-SRF prepared under the same conditions reached equilibrium after 38 and 42 days, and the cumulative release rates reached 81.47% and 81.66%, respectively. Graphical abstract