Functionalization of softwood kraft lignin for coating urea as highly efficient nitrogen fertilizer

An industrial softwood kraft lignin (SKL) was blended with polylactic acid (PLA) and used for complex coating of urea as nitrogen fertiliser. The coating was perfumed using a simple and cheap dip-coating technique. The lignin was pre-functionalised via esterification or Mannich reaction. Esterification rendered a lignin derivative with higher hydrophobicity, while the Mannich reaction introduced organically bound nitrogen onto the lignin derivative structure. It was found that the coating resulted in good attachment of the coating layer on the surface of urea pellets. The coating layer was very compact and the wall layer was rather homogeneous and well distributed. The urea coating not only constructed a physical barrier to delay urea dissolution (controlled release), but also supplied chemically slow-release, organically bound nitrogen and biological stabilisation effects. It was found that the Mannich reaction product (ManSKL/PLA) slowed down the urea release more than the PLA coating reference, taking approximately 1m000s or 6.7 times as lon