Changes in sugar composition, chemical structure, and molar mass of oil palm empty fruit bunch during ozonation, NaOH-extraction, and re-ozonation treatments

An oil palm empty fruit bunch (EFB) sample was sequentially treated with ozone, 5 % NaOH, and ozone again under environmentally friendly and mild conditions to prepare cellulose-rich materials from agricultural EFB wastes. The ozonated, 5 % NaOH-treated, and re-ozonated products (O₃-EFB, Ex-O₃-EFB, and O₃-Ex-O₃-EFB, respectively) were obtained at mass recovery ratios of 83 %, 65 %, and 50 %, respectively, based on the dry mass of the raw EFB. The O₃-EFB and Ex-O₃-EFB samples maintained their original stick-like fiber bundle morphologies. In contrast, the O₃-Ex-O₃-EFB sample exhibited mostly individualized fibers. The relative glucose unit content increased from 39 % EFB to 79 % in O₃-Ex-O₃-EFB after removal of non-cellulosic components. The O₃-Ex-O₃-EFB contained a carboxy-group content of 0.37 mmol/g, which could be used as electrostatic adsorption sites of cationic compounds, nanoparticles, and metals by ion-exchange in aqueous systems. Ozonation remarkably depolymerized the cellulose molecules. However, this sample exhibited a broad molar-mass-distribution characteristic of the EFB sample, which are advantageous for better mechanical properties. The solid-state ¹³C NMR spectra of the EFB samples showed the removal of acetyl ester groups in hemicelluloses and lignin during sequential treatment. Based on the results obtained in this study, suitable and unique application fields of EFB samples, different from wood chemical pulps, are provided.