Chemical composition of underutilized nipa (Nypa fruticans) frond and its valorization for one-pot fabrication of carboxyl cellulose nanocrystals

This study analyzed the chemical composition of nipa frond (NF) and proved that it consisted of 24.6 ± 0.2 wt% cellulose, 22.4 ± 0.4 wt% hemicellulose, 35.0 ± 0.2 wt% Klason lignin, 2.0 ± 0.1 wt% acid-soluble lignin, 5.4 ± 0.2 wt% soluble organic compounds, and 9.5 ± 0.1 wt% ash. To valorize the lignocellulosic biomass resource, NF was used for one-pot synthesis of carboxyl cellulose nanocrystals (CCNC) using an HNO3–NaNO2 mixture. TEM images revealed that nanocrystals were successfully extracted from NF with a mean diameter of 20 ± 4 nm. In addition, EDX spectroscopy, FTIR spectroscopy, and acid-base titration revealed that carboxylic (-COOH) groups were generated from the oxidation of hydroxylmethyl (-CH2OH) groups on cellulose structures. The discovery of a high carboxyl content of 3.38–5.62 mmol/g (15–25 wt%) in CCNC paves the way for its use as an ion-exchange material.