Structural control of PEG-intercalating Na-bentonite and its influence on the properties of castor oil-based polyurethane coating

Although controlled-release fertilizer (CRF) is a safer and more efficient strategy to administer nutrients for plant growth, it is still a daunting task to reduce the cost and improve the degradability of the synthetic resin coatings. In this paper, an inorganic/organic composite coating for urea fertilizer was prepared from a biodegradable castor oil-based polyurethane (PU) filled with the layered Na-bentonite (Na-BT), which was ultrasonically treated by a series of green PEG surfactants . Synergistically influenced by various intercalation ability, cation-hosting ability and hydrophilicity of the PEGs, the porous structures of the modified Na-BT (MBT) fillers were simply tuned by varying the Mn molecular weights of the PEGs, resulting in the adjustable water swelling and mechanical properties of the MBT/PU composites. Moreover, it was confirmed that the water swelling property played a critical role in controlling the early stage of nutrient release, and the mechanical properties were important for the longevity of nutrient release from the CRFs. The best MBT/PU composite supported a CRF with a long-term release of 75 % in 38 days, which was much longer than the one based on pure PU (20 days).