Biodegradable Urea-Formaldehyde/PBS and Its Ternary Nanocomposite Prepared by a Novel and Scalable Reactive Extrusion Process for Slow-Release Applications in Agriculture.

Novel binary composite urea-formaldehyde/poly(butylene succinate) (UF/PBS) and its ternary nanocomposite UF/PBS/potassium dihydrogen phosphate (MKP) were prepared by a simple and scalable reactive extrusion approach using methylolurea (MU), PBS, and MKP as the raw materials. The results show that MUs react by melt polycondensation to form UFs with different polymerization degrees at the high temperature in the extruder, giving the two polymer components molecular segment-scale mixing in composites. Meanwhile, MKPs dissolved in the water generated by the melt polycondensation are perfectly confined to the nanometer scale during their precipitation process in ternary composites due to the hydrogen bonding interactions between them and UF and the "cage effect" of UF and PBS macromolecule chains. Both composites have excellent processability, mechanical properties, and slow-release performances. Compared with UF prepared by direct synthesis or reactive extrusion, N release speeds of the two composites are much lower in the early incubation stage but much higher in the subsequent stages; ternary composites can also impart MKP with excellent slow-release properties. This study can provide a good feasibility for large-scale applications of UF-based or PBS-based composites and nanocomposites used as slow-release fertilizers or other products in agriculture or horticulture.