Insights into hydrophobic (meth)acrylate polymers as coating for slow-release fertilizers reduce nutrients leaching

Abstract

To solve the problem of low utilization rate of conventional fast water-soluble release fertilizers and to minimize their negative impact on the environment, slow-release fertilizers (SRF) have emerged as sustainable solution to limit their losses, reduce fertilizers dosage and improving crop production. In this study, new hydrophobic (meth)acrylates polymers (poly(2,2,2-trifluoroethyle methacrylate)(PTFEMA) and poly(2-(perfluorohexyl)ethyl acrylate) (PPFEHEMA)) with different fluorinated side chains were synthesized by free radical polymerization and used as coatings for SFR. These polymers were characterized by 1H and 19F NMR, FTIR, WCA, TGA and DSC. Compared to PTFEMA, PPFEHEMA with a higher content of F atoms content displayed improved thermal stability and an elastomer property (Tg= -10 °C) leading a satisfactory film formation. Indeed, contact angle measurements (WCA) were carried out on films of both materials, PPFEHEMA with WCA= 109° indicated a highly hydrophobic character with an excellent water-repellent surface, resulting in a coating layer. The use of these polymers as SFR coatings was explored using dip-coating. SEM and EDX mapping were performed to study the morphology of the coated fertilizer granules and showed the formation of a cohesive film with good adhesion between the DAP fertilizer and the coating films, limiting water diffusion. The N, P nutrients release profile was studied, the corresponding release time increased with the coating thickness (single layer: 1L or second layer: 2L). Compared to uncoated DAP granules which is totally solubilized after less than 2 h, DAP coated with 2 L of PPFEHEMA has the slowest N and P nutrients releases, the time to reach the maximum N and P releases were 30 and 38 times higher than that of uncoated DAP. The significant delay in the release of nutrients from the DAP coated with PTFEMA and PPFEHEMA is consistent with the nutrient demand during crop growth and increases the efficiency of fertilizer use and therefore enhancing agricultural productivity.