Waterborne butyl methacrylate (co)polymers prepared by pickering emulsion polymerization: Insight of their use as coating materials for slow release-fertilizers

Abstract

A new approach for preparing slow-release membranes encapsulated diammonium phosphate (DAP) fertilizer with waterborne polymers is presented. Latex dispersions based on butyl methacrylate (BMA) and 2-(perfluorohexyl)ethyl acrylate (PFA) were successfully synthesized by emulsion (co)polymerization using starch nanocrystals (SNC) as a sole pickering surfactant. A conversion degree around 98% was reached, while the solid content was close to 20 wt%. The particle diameter distribution of PBMA homopolymer and P(BMA-co-PFA) copolymer dispersions as well as the water contact angle measurements and thermal properties were investigated and showed that the incorporation of PFA units in PBMA enhanced the thermal stability and the hydrophobic character of the copolymer. The use of these (co)polymers as fertilizer coatings was explored. Scanning Electronic Microscopy (SEM), Electronic Diffraction X-ray (EDX) and mapping were performed to study the morphology of the coated fertilizer granules and revealed the formation of a cohesive film with a good adhesion between DAP fertilizer and coating films. The evaluation of the release of nutrients (N, P) was monitored by UV–Vis spectroscopy. Compared to uncoated DAP granules which the total release was obtained after less than 2 h, the P release profiles of the coated fertilizers reached the equilibrium stage after 28 and 50 h when the DAP was coated with PBMA and P(BMA-co-FPA), respectively. Indeed, the time to reach the maximum N release concentration was 13.5 and 16.0 times lower than the corresponding uncoated DAP when the DAP was covered with PBMA and P(BMA-co-FPA), respectively. These results indicated significant slower nutrients (P and N) release properties to enhance the efficiency of fertilizer use and minimize adverse environmental effects, and to match with the nutrient demand during crop growth.