Moderate-temperature Curing of Epoxidized Soybean Oil for Highly Efficient Coated Fertilizer

The use of bio-oil-based polymers in fertilizer coatings has drawn significant academic interest. However, the challenge remains to eliminate toxic chemicals while enhancing comprehensive properties. This study focused on synthesizing a degradable polymer from epoxidized soybean oil (ESO) without organic solvent at low temperature (120°C), accomplished through a modified curing agent (MCA). This MCA was made of an acidic eutectic mixture of phthalic anhydride (PA) and its glycerides, produced from inexpensive, low-toxic phthalic anhydride and glycerol. The process utilized a small quantity of zinc acetate (0.5 wt%) to facilitate the formation of phthalic triglyceride in the MCA and mitigate PA sublimation, resulting in the enhanced cross-link degree, superior mechanical properties and hydrophobicity of the ESO-based resin (ESOR). Under optimal preparation conditions, the solvent-free ESOR-coated fertilizer exhibited an extended longevity of 53 days, with an 80 % phosphorus release. This coating material can undergo hydrolytic degradation in soil and in-situ conversion into carboxylates. These findings hold significant potential for advancing the applications of ESOR in green and sustainable agriculture.