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 me-chanical 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).

Automated summary

This paper presents a study on the preparation of an inorganic/organic composite coating for urea fertilizer using a biodegradable polyurethane filled with Na-bentonite. The porous structures of the filler were tuned by varying the molecular weights of the PEGs, resulting in adjustable water swelling and mechanical properties of the composites. The water swelling property was found to be critical for controlling the early stage of nutrient release, while the mechanical properties were important for the longevity of nutrient release from the CRFs.