Tailored and Integrated Production of Carboxylated Cellulose Nanocrystals (CNC) with Nanofibrils (CNF) through Maleic Acid Hydrolysis

Abstract

This study demonstrates the feasibility of tailored and integrated production of carboxylated cellulose nanocrystals (CNC) with nanofibrils (CNF) from bleached pulp fibers through hydrolysis using a recyclable dicarboxylic acid. Hydrolysis experiments were conducted using ranges of 15–75 wt % maleic acid concentrations, 60–120 °C temperatures, and 5–300 min reaction times. Maleic acid esterified cellulose resulted in carboxylated CNC and CNF. Furthermore, the acid‐hydrolysis solubilized xylan and depolymerized cellulose, which substantially reduced the energy input for the production of CNF through subsequent mechanical fibrillation. A combined hydrolysis factor (CHF), a measure of hydrolysis severity, was developed to map xylan dissolution and cellulose depolymerization over the entire reaction space. It was found that CHF can be used to predict the morphological and chemical properties of the resultant CNC and CNF, independent of the individual reaction process variables. This is important for process scale‐up design in order to tailor the properties of CNC and CNF for specific applications. With the low temperature hydrolysis and low energy input in mechanical fibrillation, along with the recyclability of maleic acid, the presented process has promise of achieving commercial success in the low‐cost and sustainable production of CNC and CNF.

Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

“…Maleic acid was also used for the preparation of CNCs and the pretreatment of cellulose [95][96][97][98]. Wang and coworkers reported the preparation of CNCs using maleic acid to hydrolyze cellulose [95].…”

“…Wang and coworkers reported the preparation of CNCs using maleic acid to hydrolyze cellulose [95]. CNCs were obtained at a low yield, about 5%.…”

High value‐added monomer chemicals and functional bio‐based materials derived from polymeric components of lignocellulose by organosolv fractionation

“…Sulfuric acid and hydrochloric acid are usually applied in the production of CNCs. Dicarboxylic acids such as oxalic acid have also been used, with the advantage of easy recovery by crystallization …”

“…[143][144][145][146][147][148][149][150] Solid dicarboxylic acids can be used to produce CNF from bleached chemical pulp fibers. 146,151 Usually, ligninfree chemical pulp fibers are good feedstocks for producing nanocellulose, but lignin in cellulose nanomaterials showed the potential to improve the thermal stability of nanomaterials, adjusting the polarity and hydrophilicity of cellulose, decreasing the production cost and improving the yields. 152 Lignin-containing cellulose nanomaterials are also expected to generate hydrophobicity and improve dispersion features.…”

“…Dicarboxylic acids such as oxalic acid have also been used, with the advantage of easy recovery by crystallization. 146,151 Cellulose nanocrystals can be applied in many fields. They can work as drug carriers in aqueous suspensions.…”