Extraction and analysis of carboxycellulose nanofibers from virgin plant fibers using updated TEMPO-mediated oxidation

Abstract

TEMPO-mediated oxidation is the most popular approach to extracting carboxylated cellulose nanofibers (CNFs) from cellulose fibers (pulps). In this study, we have demonstrated the modified TEMPO/NaBr/NaClO oxidation method to extract CNFs from virgin (untreated) jute fibers which were not undergone any pretreatment process (e.g., delignification and pulping) before introducing the TEMPO-oxidation process. This one-pot approach combines the steps of delignification/pulping and cellulose oxidation. Three CNFs with different degrees of oxidation (carboxylate content of 1.18, 0.175, and 0.131 mmol/g) were prepared by the addition of varying amounts of NaClO (i.e., 48, 32, and 24 mmol/g, respectively), where the content of NaClO was found to affect the delignification efficiency of raw fibers. In specific, CNF (0.131 mmol/g) possessed residual lignin of 2% and hemicellulose of 2.5%; CNF (0.175 mmol/g and 1.18 mmol/g) retained lignin of 1.9% and hemicellulose of 2.3%. The results indicate that using excess NaClO could lead to the generation of nitroxonium ions, which selectively oxidize the hydroxyl groups in cellulose, hemicellulose, and lignin. As a result, the excess usage of NaClO (32–48 mmol/g) during the TEMPO/NaBr/NaClO process was more effective in delignification and hemicellulose removal. FTIR, ¹³C CPMAS-NMR, WAXD, contact angle, AFM, TEM, and BET techniques were used to characterize all extracted CNFs. All CNFs showed an average L of 1000 nm and a width of 6 nm.