Process Optimization of Neem (Azadirachta indica) Oil Extraction using a Semi-Automated Screw Expeller for Coating Applications

Abstract

Neem (Azadirachta indica A. Juss.) oil is a renewable feedstock for eco-friendly coatings due to its high oxidative stability and bioactive content. Its industrial adoption in sub-Saharan Africa is limited by low extraction efficiency and variable quality. This study optimized oil recovery using a locally developed semi-automated expeller integrating microwave-assisted pre-treatment with mechanical pressing. A Box–Behnken design within Response Surface Methodology assessed the influence of moisture content (4–12%), microwave duration (2–4 min), feed rate (10–20 kg/h), and screw speed (20–60 rpm) on yield and oil quality. Models exhibited excellent predictive accuracy (R² > 0.99, p < 0.0001), identifying optimal conditions of 7.23% moisture, 2.93 min microwave exposure, 14.68 kg/h feed rate, and 39.65 rpm screw speed, producing 40.43% oil. The extracted oil demonstrated low acid (3.29 mg KOH/g) and peroxide values (2.25 meq O₂/kg), moderate iodine value (83.0 g I₂/100 g), high oxidative stability (6.5 h), thermal resistance (248.5°C), and retained unsaturated and bioactive compounds. The process improved yield, energy efficiency, and processing time, highlighting neem oil’s suitability for sustainable coatings and circular bioeconomy applications.