Parameters of hydrothermal gelation of chitin nanofibers determined using a severity factor

Abstract

The hydrothermal gelation of and -chitin nanofibers (-and -ChNFs) prepared at neutral and acidic pH was conducted by heating them to 120, 160, 180, and 200 °C in a sealed reactor. The optical transmittance and mechanical strength of -ChNFs gelated at the acidic pH were determined for the first time using a severity factor defined as a function of the integrated heating time and temperature. The width of -ChNFs increased after the hydrothermal treatment, indicating that these fibers strongly adhered to each other to form a network structure during gelation. Furthermore, the hydrothermal gelation of and -ChNFs with different degrees of disintegration prepared at the neutral and acidic pH was conducted. It was found that the hydrothermal treatment of -chitin must be performed at the acidic pH to obtain a self-sustaining hydrogel of well-disintegrated NFs. The disintegration of -chitin into NFs occurred more easily at the acidic pH than under the neutral conditions; however, in the latter case, the same disintegration degree of -ChNFs could be achieved by increasing the number of disintegration steps. At the same disintegration degree, the strength of the self-sustaining hydrogel obtained at the neutral conditions was greater than that of the gel prepared at the acidic pH, indicating that the electrostatic repulsion caused by acid addition negatively affected the formation of the hydrogel network structure. To maximize the efficiency of the hydrothermal gelation process, ChNFs should be as thin as possible and electrostatic repulsion forces must be controlled.

Hydrothermal Gelation of Pure Cellulose Nanofiber Dispersions

“…The CNF hydrogels maintained their cylindrical shape over the entire heating time. In previous reports, TOCN and ChNF hydrogels displayed brown discoloration, 10,11,17 although Lewis et al reported hydrothermal gelation of cellulose nanocrystals at 120 °C for 20 h with no discoloration. 18 Herein, the CNF hydrogels were bluish-white with no discoloration (see Figure S1).…”

“…Hydrothermal gelation has been carried out previously with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) as well as α-chitin and β-chitin nanofibers (ChNFs), although many aspects of the process remain unclear. 10,11 In particular, the mechanism of gelation and the impacts of NF morphological features, molecular mass, and concentration on the mechanical strength of the resulting hydrogel are not well understood. In this study, cellulose, which is the most abundant biomass material, was converted to a self-sustaining hydrogel through wet pulverization and hydrothermal gelation.…”

“…This is referred to as hydrothermal treatment, as it uses water in the pressurized liquid phase (above 100 °C). Hydrothermal gelation has been carried out previously with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) as well as α-chitin and β-chitin nanofibers (ChNFs), although many aspects of the process remain unclear. , In particular, the mechanism of gelation and the impacts of NF morphological features, molecular mass, and concentration on the mechanical strength of the resulting hydrogel are not well understood. In this study, cellulose, which is the most abundant biomass material, was converted to a self-sustaining hydrogel through wet pulverization and hydrothermal gelation.…”

Effect of the degree of acetylation on the physicochemical properties of α-chitin nanofibers

“…Chitin has a hierarchical structure based on chitin nanofibers (ChNFs), which has attracted research interest in materials engineering [2][3][4]. Although chitin powder is insoluble in water, ChNFs can be dispersed homogeneously in water, which makes them easy to handle and shape into desired forms [5][6][7]. There are two types of chitin, namely, α-chitin and βchitin, which have different crystalline structures [8,9].…”

Preparation of β-chitin nanofiber aerogels by lyophilization

“…Chitin takes the form of a nanofiber (NF)-aligned polymer chain by biosynthesis [15]. The utilization of chitin NFs (ChNFs) as gel materials is expected to improve the mechanical strength because of their high crystallinity [16,17]. In addition, the biocompatibility and biodegradability of chitin are useful characteristics for various applications [18,19].…”