From olive stones waste to valuable resource: Exploring various techniques for cellulose extraction

Cellulose was extracted from olive stones using various extraction techniques, including microwave-assisted extraction (MAE), conventional heating extraction (CHE), hot water extraction (HWE), and ultrasound-assisted extraction (UAE). These methods consisted in sequential acid treatment with hydrochloric acid (HCl), alkaline treatment with sodium hydroxide (NaOH), and bleaching with hydrogen peroxide (H2O2). Among them, MAE and CHE yielded significantly higher extraction yields, while reducing reaction time and solvent consumption as compared to HWE and UAE. NMR and FT-IR analyses confirmed the chemical structure of extracted cellulose and revealed the presence of residual lignin. Furthermore, celluloses obtained through MAE and CHE present higher crystallinity index and enhanced thermal stability as compared to those of HWE and UAE. These findings highlight MAE and CHE as promising techniques for cellulose extraction from olive stones in the context of circular economy, thus paving the way scaling and potential applications in the health and pharmaceutical sectors.