Abstract

The development of efficient and sustainable catalysts for solid propellants remains a challenge due to the tradeoff between energetic performance and environmental compatibility. In this work, lignin-functionalized magnetite nanoparticles (Fe3O4@Lig) were synthesized via a co-precipitation and oxidative functionalization route and evaluated as catalytic additives for the thermal decomposition of potassium nitrate (KNO3) and a sorbitol-based "candy" propellant (KNO3/SB). The structural and magnetic characterization (Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Vibrating Sample Magnetometry (VSM)) confirmed successful lignin grafting, with an average particle size of 6.4 +/- 1.2 nm and superparamagnetic behavior (Ms = 36 emu g-1). TGA and differential scanning calorimetry (DSC) revealed that Fe3O4@Lig decreased the KNO3 decomposition temperature by up to 37 degrees C and reduced the activation energy from 202 to 159 kJ mol-1. In KNO3/SB formulations, the additive lowered the main decomposition temperature from 365 to 276 degrees C and increased the total heat release from 614 to 1453 J g-1. The synergistic effect between the Fe3O4 core and lignin shell enhances electron transfer and thermal conductivity during oxidation, promoting faster and more energetic combustion. These findings position Fe3O4@Lig as a promising, low-cost, and bio-derived catalyst for improving the combustion efficiency of environmentally benign solid propellants.