Objectives Ethyl cellulose is widely available and degradable, making it a promising green candidate for controlled - release coating materials. However, its inadequate flexibility and hydrophobicity result in a shorter nutrient - release duration when used as a coating for controlled - release fertilizers. This study preliminarily explored the modification methods of ethyl cellulose.

Methods Triethyl citrate (TEC) was chosen as a plasticizer, alongside cost-effective and readily available nano-silicon dioxide or nano-titanium dioxide, to modify EC via physical blending. Six different samples were prepared: unmodified ethyl cellulose (EC), EC modified with TEC alone (EC+TEC), EC modified with nano-silicon dioxide alone (EC+SiO₂), EC modified with nano-titanium dioxide alone (EC+TiO₂), EC modified with TEC and nano-silicon dioxide (EC+TEC+SiO₂), and EC modified with TEC and nano-titanium dioxide (EC+TEC+TiO₂). An electronic universal testing machine was used to measure the mechanical properties of EC before and after modification, while a differential scanning calorimeter (DSC) was employed to determine the glass transition temperature of the coating materials. Thermogravimetric analysis (TGA) was conducted to assess thermal stability, pyrolysis temperature, and mass loss mechanisms. Additionally, a contact angle meter and water vapor permeability tester were used to measure water contact angles and water vapor permeability rates of the coating materials, respectively. The nutrient release characteristics of the controlled-release fertilizers were evaluated through a static water dissolution method. Finally, the impact of changes in coating material properties on the nutrient release profile of the controlled-release fertilizers was analyzed.

Results After coupling ethyl cellulose (EC) with triethyl citrate (TEC) and nano-titanium dioxide (EC+TEC+TiO₂), the processing temperature increased from 16.7℃ to 32.9℃ compared to unmodified EC. The hydrophobic contact angle rose from 70.9° to 78.6°, while the corresponding water vapor permeability rate decreased from 2.86×10⁻³ g/(m day) to 1.86×10⁻³ g/(m day). Consequently, the controlled release period extended from 3 days to 14 days.

Conclusions Coupling triethyl citrate and nano-titanium dioxide to modify ethyl cellulose significantly improved the controlled-release properties of the coating. However, further extension of the release period is still required to meet nutrient demands throughout the entire crop growing season.