Surface modification of pyrophyllite for optimizing properties of castor oil-based polyurethane composite and its application in controlled-release fertilizer

The high cost and difficulty in sustainability have hindered the wide application of the general synthetic resins in the controlled-release fertilizers (CRF). Here, the degradable castor oil-based polyurethane (PU) was filled by the natural pyrophyllite (PY) powders, which were pre-modified with few amount (≤0.5 %) of NDZ-201 coupling agent though a simple and economic mechanochemical method. Furthermore, the composite materials of PU and the modified PY (MPY/PU) with enhanced comprehensive properties were prepared and applied in CRF. Moreover, the release behaviors of the coated fertilizers were investigated while tuning the addition amount of modifier or the filling amount of MPY, and it was confirmed that the release performance was highly depended on the hydrophobic and mechanical properties of the composite coating. As a result, the best optimized MPY/PU coating exhibited significantly superior performance to the pure PU materials, and the duration of 80 % nitrogen release was more than 40 days. This confirms that the MPY/PU composite is a promising coating material for the CRF granules.