Release performance for K and Mg from alkaline lignin / polyvinyl alcohol cross-linked slow-release film fertilizer.

In order to improve the utilization of industrial alkaline lignin and expand its application scope, with alkaline lignin and polyvinyl alcohol ( PVA) as primary materials, formaldehyde as crosslinker, potassium sulfate and magnesium sulfate added, alkaline lignin/ PVA cross-linked slow-release film was prepared by casting. The reaction film was characterized by FTIR-ATR. Release performance for K and Mg from alkaline lignin/ PVA cross-linked film was measured by leaching experiment. The results showed that: (1) the absorption peak was at 3 260 cm-1, and vanished at 1 332.57 cm-1, and became larger between 1 145.51 - 983.52 cm-1, which indicated that the cross-linking reaction occurred between alkaline lignin and PVA with formaldehyde. (2) Compared with the cross-linked PVA film, the addition of alkaline lignin was unfavorable for the K release, while the appropriate amount of alkaline lignin was in favor of Mg release. The content of alkaline lignin can be 20%. With the increase of formaldehyde content, the accumulative release rate of K decreased. The appropriate amount of formaldehyde was in favor of Mg release, while the more formaldehyde reduced the Mg release performance of the films. The suitable amount of formaldehyde for Mg slow release was 3.59%. The mechanism of the slow-release film on K mainly resulted from the physical barrier effect of molecular structure. While for Mg slow-release, in addition to a physical barrier effect of molecular structure, is was also from the chelation of lignin. (3) The kinetic data of the K cumulative release rate was fitted with four fit models. The best-fit model for K release was the Higuchi model and the value of R2 was 0.994 1, which indicated that the release mechanism of K followed Fick diffusion. However, the best-fit model for Mg release was the Ritger- Peppas model and the value of R2 was 0.974 2. The release index (n) of Ritger-Peppas model for the Mg cumulative release rate was 0.5n1.0, and the slow-release mechanism of Mg was the synergy of Fick diffusion and dissolution.