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 (O 3 -EFB, Ex-O 3 -EFB, and O 3 -Ex-O 3 -EFB, respectively) were obtained at mass recovery ratios of 83 %, 65 %, and 50 %, respectively, based on the dry mass of the raw EFB. The O 3 -EFB and Ex-O 3 -EFB samples maintained their original stick-like fiber bundle morphologies. In contrast, the O 3 -Ex-O 3 -EFB sample exhibited mostly individualized fibers. The relative glucose unit content increased from 39 % EFB to 79 % in O 3 -Ex-O 3 -EFB after removal of non-cellulosic components. The O 3 -Ex-O 3 -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 13 C 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. • Sequential O 3 -5 % NaOH-O 3 treatment increases cellulose content of EFB from 39 to 79 %. • O 3 -Ex-O 3 -treated EFB exhibits mostly individualized fibers by delignification. • O 3 -Ex-O 3 -treated EFB contains a high weak acid-group content of 0.37 mmol/g. • Degree of polymerization drops from ∼2000 for EFB to ∼330 for O 3 -Ex-O 3 -treated EFB. • 13 C NMR spectra show efficient removal of acetyl groups and lignin during treatment.