Preparation of modified polylactic acid melt coated urea material and its green coating technique

The low utilization efficiency, residue of coating materials of slow-release fertilizers (SRFs) and use of organic solvents in the coating process a serious negative effect on the environment. In this study, a degradable polymer-coated fertilizer with good slow-release performance was prepared using a two-step melting process. First, Polylactic acid (PLA) was modified with isopropyl tris(dodecylbenzenesulfonyl) titanate (TDBSP), polycaprolactone (PCL) and acetyl tributyl citrate (ATBC) to prepare a slow-release coating material by melt blending. Second, a modified PLA slow-release fertilizer was prepared using the molten coating method. A small amount of TDBSP as a transesterification accelerator improved the low-temperature fluidity of PLA. The effect of TDBSP on the crystallization and branching behavior of PLA was explored by DSC, XRD, POM, and Rheology. SEM indicated that the coating on the surface of the urea pellets prepared by using 18 parts (phr) of the coating material per hundred parts of urea was intact. The soil column leaching experiment indicated that the controlled-release effect of the fertilizer melting coating was significant compared with that of pure urea. Furthermore, the SRF with 21 phr coating exhibited the best slow-release effect, with a nutrient release rate of 13.43 % after a day and a cumulative release rate of 81.08 % after 28 days. The melting method was used to coat urea, avoiding the solvent recovery of the currently used solution method for coating polymer films. Therefore, this is an environmentally friendly method for the preparation of slow-release urea. This study provides a novel concept for the preparation of biodegradable organic coating materials and method for solvent-free melt-coated fertilizers.