Fig. 7
From: Green construction and release mechanism of lignin-based double-layer coated urea
Release mechanism of nitrogen in the LDCU. Initial state of LDCU in water (a1); During the initial stage, the hydrone squeezed into the urea core through permeation and diffusion (a2); During the urea dissolution stage, the dissolution of urea led to an increase in osmotic pressure and swelling of the coating layer (b); During the third stage, the nutrients of urea were released in large quantities through the dissolution process, resulting in a decrease in osmotic pressure (c)