Triple coupling modification to prevent adhesion and delay the release of waterborne polymer coated fertilizer

  Objectives  Waterborne polyacrylate is an attractive candidate for coating fertilizers because of its low price and excellent film-forming property. However, its low glass transition temperature and poor water resistance lead to adhesion and poor controlled-release of nutrients, which affect its performance. In this study, we attempt to modify the properties of waterborne polyacrylate to prevent adhesion and delay the release of nutrients from controlled-release fertilizer coated with it.【 Methods 】The coupling modification was accomplished by blending three modifiers: nano-silica, Fe^Ⅲ-tannic acid complexes, and hexadecane with waterborne polyacrylate simultaneously. The dynamic mechanical analyzer was used to measure the coating materials’ glass transition temperature and storage modulus before and after modification. The coatings’ water contact angle and water vapor permeability were investigated by the contact angle meter and water vapor permeation device. Unmodified polyacrylate (PA), nano-silica modified polyacrylate (PA+Silica), Fe^Ⅲ-tannic acid complexes modified polyacrylate (PA+Fe), and hexadecane modified acrylate (PA+HD) were used as controls to understand the effect of modifiers better. The static water dissolution method was used to determine the nutrients release profile of the controlled release fertilizers. The effects of altered coating properties on the nutrient release profiles of controlled-release fertilizers were investigated.【 Results 】After coupling modification, the glass transition temperature for coating increased from 20.40℃ to 24.80℃, the storage modulus at ‒70℃ was enhanced by 72.2%, the water contact angle of the coating increased by 22°, and the water vapor permeability decreased by 13.6%. These modifications effectively prevented adhesion of the controlled-release fertilizer and reduced preliminary solubility from 38.28% to 2.04%. Consequently, the longevity of the controlled-release coated fertilizer extended from 8 to 52 days, and the mode of release changed from inverted “L” to “S” type. The decreased preliminary solubility of the controlled-release fertilizer was mainly related to the decrease of water vapor permeability caused by Fe^Ⅲ-tannic acid complexes and increased glass transition temperature and storage modulus, resulting from nano-silica. Moreover, the increased water contact angle due to hexadecane was responsible for the prolonged release longevity. 【 Conclusions 】 After coupling modifications of water-based polymer with nano-silica, Fe^Ⅲ-tannic acid complexes and hexadecane, the adhesion of controlled-release fertilizer was effectively prevented, with improved fertilizer performance. Finally, we recommend this method for improving fertilizer performance because it is easy to scaleup for industrial production.