Enhancing Film Cross-Linking through VTES Copolymerization in Polymer Latex for Increasing Controlled-Release Performance of Film-Coated Fertilizer Granules

To increase the controlled-release performance of film-coated fertilizer granules using polymer latex as a coating reagent, increasing the cross-linking density of the film during spray coating is crucial. In this study, vinyltriethoxysilane (VTES) was incorporated into styrene-acrylate copolymer latex, with film cross-linking achieved by the condensation of silanol groups derived from the hydrolysis of VTES. VTES-copolymerized latex-coated urea granules were prepared by spray coating in a fluidized bed. The film cross-linking density and controlled-release performance were significantly increased. The structural characteristics of the film cross-linked network were theoretically calculated and analyzed. The cross-linked network with high cross-linking density had a smaller size of mesh structure, significantly reducing the free volume of the film and increasing the diffusion resistance of nutrients. The urea diffusion coefficient across the planar film decreased from 2.74 × 10–15 to 0.125 × 10–15 m2/s when the VTES copolymerized ratio reached 10%. At a low coating amount of 4 wt %, the release period of the film-coated urea granules increased to 32 days, surpassing that of the reference sample by over 300%.