Sustainable Biodegradable Starch–Collagen Polymeric Systems: Preparation, Characterization, and Efficacy for Slow Release of Organic Nitrogen, Phosphorus, and Potassium

The use of biodegradable polymers in slow-release NPK fertilizers is gaining prominence for reducing overdosing, minimizing nutrient loss, and enhancing efficiency. This study prepared modified and unmodified thermoplastic starch (TPS) systems via extrusion, incorporating collagen and potassium phosphate. Controlled-release nutrient systems utilizing nitrogen from an organic source were developed and characterized. The materials were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), contact angle measurements, and biodegradability in the soil. The biodegradability of the polymeric matrix was evaluated through mass loss, with up to 78.9% degradation observed after 60 days for TPS-based systems containing collagen. Structural modifications in the TPS matrix led to changes in crystallinity and hydrophilicity, which directly influenced degradation rates. The nutrient release effect was assessed by monitoring the growth of chili pepper seedlings over 15 days. Seedlings grown in soil containing polymeric systems with 20% collagen or 6.2% urea reached average heights between 5.2 and 7.8 cm, compared to 5.0 cm for the unmodified TPS and 0 cm in treatments with pure urea, which caused seedling mortality. The polymeric systems containing collagen exhibited superior performance as a sustainable nitrogen source, ensuring a slower and more controlled release while yielding positive outcomes for early plant development.