Introduction

The growing global demand for food has intensified agriculture, leading to issues such as poor fertilizer efficiency, pollution, and agro-industrial waste. While mismanaged waste contributes to environmental degradation, it also presents a renewable source for biodegradable biopolymer production. This study aimed to develop bioplastic matrices from agro-waste materials—soy and pea protein isolates (SPI and PPI), cassava flour, and defatted rice bran and the mixes of these last three with SPI in a 1:1 ratio—via compression molding at 1100 bar, incorporating ferrous sulfate (5 wt%) as a micronutrient for controlled-release fertilizer (CRF) applications.

Methods

Physicochemical characterization was conducted using Fourier Transform Infrared Spectroscopy (FTIR), and the microstructure was analyzed through Scanning Electron Microscopy (SEM). Mechanical performance was evaluated via dynamic compression tests, including strain and frequency sweep assays. Water uptake capacity (WUC) was measured, and iron release was quantified in both aqueous and soil media by measuring the conductivity of water and the leachates after watering with 20 mL of water, respectively. Biodegradability was assessed under composting conditions.

Results

PPI-based matrices exhibited superior mechanical properties, with higher viscoelastic moduli and enhanced stability compared to the other systems made, showing values of elastic modulus (E’) around 8 MPa, whereas the other systems present values below 7 MPa. Moreover, the addition of SPI further improved the mechanical behavior of all formulations, increasing the values of E’ to those of SPI but increasing instability. In terms of water absorption, PPI-based systems showed strong potential for horticultural use, with a WUC of about 210%. Iron release extended beyond one month, ensuring sustained micronutrient availability during critical plant growth stages.

Conclusions

Bioplastic matrices from agro-waste, particularly those with PPI, demonstrated adequate mechanical strength, water absorption, and prolonged iron release. These characteristics highlight their promise as sustainable controlled-release fertilizers in agriculture.

Aknowlegments

PID2021–124294OB-C21; SOL2024-31712