TEMPO-catalyzed oxidation of oil palm empty fruit bunch (EFB): influence of ozonation and alkali-extraction of EFB on structures and properties of oxidized products and nanofibrils

Oil palm empty fruit bunch (EFB) was sequentially treated with ozone, 5% NaOH, and ozone to prepare EFB-derived materials, i.e., Oz-EFB, Ex-Oz-EFB, and Oz-Ex-Oz-EFB, respectively. The original EFB and EFB-derived materials were subjected to TEMPO-catalyzed oxidation (TEMPO: 2,2,6,6-tetramethylpiperidine-1-oxyl radical) in water at pH 10. Mass recovery ratios, carboxy contents, neutral sugar compositions, degrees of polymerization ( DP ), and solid-state structures of the oxidized products were studied for preparation of carboxy group-rich products. The mass recovery ratio linearly decreased, in turn carboxy group content linearly increased, and molar mass mostly decreased with an increase in NaOCl added in oxidation. When Oz-Ex-Oz-EFB was oxidized with NaOCl of 5 mmol/g-sample, oxidized products with mass recovery ratios of 81% and high carboxy contents of 1.6 mmol/g were obtained without significant depolymerization. The TEMPO-oxidized Oz-Ex-Oz-EFB product with a carboxy content of 1.6 mmol/g was converted to mostly individualized TEMPO-oxidized cellulose nanofibrils with homogeneous ∼5 nm in width and lengths >500 nm by ultrasonication in water. Therefore, the EFB-derived and TEMPO-oxidized cellulose nanofibrils are possibly used as carboxy group-rich bio-based nanomaterials for thickeners with unique shear-thinning behavior, Pickering emulsion stabilizers, nanocomposites with various polymer matrices. • TEMPO-catalyzed oxidation in water at pH 10 was applied EFB-derived materials. • Carboxy content increased and mass recovery ratio decreased with increasing NaOCl. • Degree of polymerization of oxidized products decreased with increasing NaOCl added. • TEMPO-oxidized cellulose nanofibrils with homogeneous ∼5 nm widths were obtained. • Average lengths of unique and carboxy group-rich cellulose nanofibrils were >500 nm.