三重耦合改性防止水基聚合物包膜肥料粘连并延缓释放

  【目的】  水基聚丙烯酸酯价格低廉、成膜性好，具有作为控释肥料包膜材料的潜力，但其玻璃转化温度低和耐水性差，导致用其制备的包膜控释肥料颗粒容易相互粘连并且养分释放过快。本研究旨在通过改性措施防止水基聚丙烯酸酯包膜控释肥料的粘连，并提升其控释性能。  【方法】  选用易获取且价格低廉的3种改性剂纳米二氧化硅、FeⅢ-单宁酸配合物和十六烷，通过简单的物理混合方式对水基聚丙烯酸酯进行耦合改性。采用动态热机械性能测定了改性前后包膜材料的玻璃转化温度和储能模量，采用接触角仪和水蒸气渗透装置分别测定了包膜的水接触角和水蒸气渗透率，采用静水溶出法测定了控释肥料的养分释放特征。为了更好地比较耦合改性的效果，将未改性的丙烯酸酯 (PA)、纳米二氧化硅单独改性的丙烯酸酯 (PA+Silica)、FeⅢ-单宁酸配合物单独改性的丙烯酸酯 (PA+Fe) 和十六烷单独改性的丙烯酸酯 (PA+HD)作为对照，分析了包膜材料性质改变对控释肥料养分释放特征的影响。  【结果】  耦合改性后包膜的玻璃转化温度提升了4.4℃，?70°C的储能模量提升了72.2%，水接触角提高了22°，水蒸气渗透率降低了13.6%。以上包膜材料性质的改变不但有效防止了控释肥料的粘连，也将其初期溶出率从未改性的38.29%降低到2.04%，控释期从未改性的8天延长到52天，释放模式也从和作物养分需求不匹配的“倒L”型变为和作物养分需求相匹配的“S”型。耦合改性改善包膜肥料粘连现象的原因为耦合改性将包膜材料的玻璃转化温度从20.40℃提升到了24.80℃。相关分析表明，包膜肥料初期溶出率的显著降低主要是因为FeⅢ-单宁酸配合物所降低的水蒸气渗透率和纳米二氧化硅所提高的玻璃转化温度和储能模量，而控释期的延长主要是由于十六烷所带来的水接触角的上升。  【结论】  采用纳米二氧化硅、FeⅢ-单宁酸配合物和十六烷耦合改性水基聚丙烯酸酯后，有效防止了控释肥料的粘连，显著提升了控释性能，并且该改性方式易于应用到工业生产中，是一种可行的水基聚合物包膜材料的改性方法。

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, FeⅢ-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), FeⅢ-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 FeⅢ-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, FeⅢ-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.