Tailored and Integrated Production of Functional Cellulose Nanocrystals and Cellulose Nanofibrils via Sustainable Formic Acid Hydrolysis: Kinetic Study and Characterization

Abstract

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are of great interest to researchers due to their outstanding properties and wide application potentials. However, green and sustainable production of CNCs and CNFs is still challenging. In this work, the integrated and sustainable production of functional CNCs and CNFs was achieved by formic acids (FA) hydrolysis. Kinetic study for FA hydrolysis of cellulosic pulp was performed to investigate the hydrolysis mechanism. FA concentration of 80–98 wt %, reaction temperature of 70–100 °C, and reaction duration up to 24 h were employed to capture the feature of the coexistence of a diversity of reaction products, i.e., CNCs, cellulose solid residue (CSR), cellulose formate (CF), xylose, glucose, and furfural. The separated CSR was further fibrillated to CNFs by homogenization. It was found that the yield, morphology, crystallinity, thermal stability, and degree of esterification of CNCs and CNFs were significantly affected by hydrolysis conditions (particularly for acid concentration). Detailed characterization indicated that the as-prepared CNCs exhibited high thermal stability (maximal weight loss temperature of 375 °C) and high crystallinity index of 79%. Both the resultant CNCs and CNFs showed good dispersibility in dimethylacetamide due to the introduction of ester groups on cellulose surface during FA hydrolysis. More interestingly, the regenerated CF was also a kind of functional CNFs with more ester groups. These ester groups would enable the CNCs/CNFs to be potentially used in polymeric materials due to the hydrophobic surface. Therefore, this study provided fundamental knowledge for the sustainable and integrated production of thermally stable and functional CNCs and CNFs with tailored characteristics.

Preparation of treelike and rodlike carboxymethylated nanocellulose and their effect on carboxymethyl cellulose films

“…The onset decomposition temperature (T onset ) of CMC A , CMC B , CMCNFs and CMCNCs are 236°C, 244°C, 270°C and 250°C, and the maximum decomposition temperature (T max ) are 284°C, 302°C,306°C and 328°C, respectively. Both CMCNFs and CMCNCs both show good thermal stability due to many unstable hydroxyl groups replaced by thermally stable ester groups, while CMCNCs has better thermal stability because of more amorphous regions hydrolyzed by strong acid 42 …”

“…Both CMCNFs and CMCNCs both show good thermal stability due to many unstable hydroxyl groups replaced by thermally stable ester groups, while CMCNCs has better thermal stability because of more amorphous regions hydrolyzed by strong acid. 42 The TS and EB of the pure CMC film are 30.83 ± 1.61 MPa and 7.15 ± 1.5%, respectively. As for TS property, the performance of the composite film increases firstly, and then decreases with the increase of nanocellulose content.…”

Integrated and sustainable preparation of functional nanocellulose via formic acid/choline chloride solvents pretreatment

“…The total yields of U-NC (U-NC1 and U-NC2) samples were similar to that of B-NC, while the total yields of F-NC (F-NC1 and F-NC2) samples were decreased to 95.3% and 95.2%, respectively. This phenomenon was probably because a small amount of cellulose was hydrolyzed by formic acid during F-DES pretreatment (Lv et al 2019). Moreover, the yields of CNCs in U-NC1 and F-NC1 were 7.1% and 7.8%, respectively, which were about 3 times higher than that of B-NC1 (2.4%).…”

“…Moreover, formic acid is a good hydrogen bond donor, which can mix with choline chloride to produce a new-type DES (F-DES) (Lynam et al 2017). In previous work, the integrated production of NC (CNCs and CNFs) with tailored characteristics was achieved via formic acid hydrolysis plus the followed homogenization, and formic acid was readily recycled by vacuum distillation due to its low boiling point (100.8 ºC) (Lv et al 2019). The integrated preparation of NC (CNCs + CNFs) could get a high yield of NC and reduce the production cost (Chen et al 2016;Wang et al 2017).…”

Preparation of Surface-Modified Nanocellulose from Sugarcane Bagasse by Concurrent Oxalic Acid-Catalyzed Reactions

“…Moreover, such pretreatments might minimize the sizes of the cellulose fibers, thus avoiding clogging of the homogenizer (Li et al, 2012). Hydrolysis with milder organic acids, such as formic acid, has been reported for cellulose pretreatment before the mechanical treatment for nanocellulose production (Li et al, 2015;Du et al, 2016;Lv et al, 2019).…”