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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 UF/PBS (urea-formaldehyde/poly(butylene succinate)) and its ternary nanocomposite UF/PBS/MKP (potassium dihydrogen phosphate) 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 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 nanometer scale during their precipitation process in ternary composite due to the hydrogen bonding interactions between them and UF and "cage effect" of UF and PBS macromolecule chains. Both of the two 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 composite can also impart MKP excellent slow-release properties. This study can provide a good feasibility for large-scale applications of UF-based or PBS-based composites and nano-composites used as slow-release fertilizers or other products in agriculture or horticulture.