Plasma-modified biodegradable coatings for controlled nitrogen release from urea

Slow-release urea based on biodegradable polymers offers a sustainable alternative to conventional formulations, which often causes rapid nitrogen loss and adverse environmental impacts. This study aimed to develop and evaluate novel biodegradable polymer coated urea using polybutylene succinate (PBS), polycaprolactone (PCL), and methylene diphenyl diisocyanate (MDI) as a crosslinker, with or without plasma surface treatment. Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis revealed decreased crystallinity in PCL after MDI crosslinking and plasma treatment, suggesting enhanced polymer interactions and structural modifications within the blend. Nitrogen release dynamics were assessed through a 90-day soil column experiment. Compared with the control, all coated formulations significantly delayed peak of the release of nitrate-nitrogen (NO₃^--N) from 30 days to approximately 70 days after precipitation. At day 90, cumulative NO₃^--N release was 29.8 mg (PBS + PCL + MDI), 26.5 mg (PBS + PCL + Plasma), and 35.9 mg (MDS), compared with 48.6 mg in control. Total nitrogen concentrations showed similar trends, with the MDS (urea coated with PBS/PCL blend treated with both MDI and plasma) treatment achieving sustained release and a 70-day peak concentration (222.0 mg L^-1) versus a 30-day (229.5 mg L^-1) in control. Release profiles were best fitted by a three-parameter sigmoidal model, indicating improved control over nutrient availability. These results highlight the potential of plasma-modified biodegradable polymer-coated urea to provide prolonged and tunable nitrogen release, supporting environmentally responsible nutrient management.