“Thermal Fusion–Photo-cross-linking” Decoupling Design to Increase Film Controlled-Release Performance

The use of coated controlled-release fertilizers is an effective approach to reduce nitrogen pollution. Among these, polymer latex coated fertilizers have substantial development potential due to their green production process. During the polymer latex coating process, the ideal film formation involves latex particle fusion followed by cross-linking. However, in practice, the simultaneous cross-linking occurring during the fusion of the film hinders further fusion and limits the extent of cross-linking, making it difficult to control the film structure and adversely affecting controlled-release performance. This study investigates a “thermal fusion–photo-cross-linking” decoupling design to increase film controlled-release performance. 4-Benzoylphenyl methacrylate was introduced into polymer latex. During the fluidized bed spray coating process, thermal treatment was applied to enhance the fusion of latex particles, followed by UV irradiation to initiate cross-linking between carbonyl and C–H groups on polymer chains, achieving a highly cross-linked film. Experimental results showed that at a 4 wt % coating amount, the release period of urea coated with latex reached 60 days, over three times longer than that of the non-decoupled process, significantly increasing film controlled-release performance. This decoupling design offers a novel approach for the development of low-coating, long-release fertilizers.