Nanostructural, Chemical, and Thermal Changes of Oil Palm Empty Fruit Bunch Cellulose Nanofibers Pretreated with Different Solvent Extractions

Abstract

The aim of this study was to analyze the effect of different extraction solvents in cellulose nanofibers (CNFs) isolation and properties, including nanostructures, chemical functional groups, chemical substances, and thermal stabilities. Physical oven-dried CNFs had a varied diameter of self-aggregated nanofibers from 2 to 20 µm with different aggregate shapes of nanofibers, whereas individual nanostructure of CNFs suspension was akin to grape-like flocking nanofibers with a diameter of about 50 nm. FTIR spectra showed that hot water extraction for CNFs isolation was able to remove low-molecular weight carbohydrates (hemicellulose and pectin), whereas ethanol and ethanol/benzene extraction for CNFs isolation was able to remove tannin, fatty acids, and waxes. However, amorphous lignin was still present indicated with IR transmission peak at 1558 cm−1. Carboxylic acids, esters, ketones, and benzoyl units were the chemical compounds of CNFs, indicating the presence of cellulose, hemicellulose, and lignin in which long-chain fatty acids were the most dominant compounds. There were five thermal degradation peaks for ethanol- and hot water-pretreated CNFs thermal stability, whereas ethanol/benzene- and non-extraction-pretreated CNFs had four thermal degradation peaks. Solvent-pretreated CNFs had better thermal stability and higher char residue obtained above 8.51% than that of non-extracted-pretreated CNFs.