Degradation of Chitosan by Hydrothermal Process in the Presence of Sonication Pre‐Treatment with Supercritical CO₂ as Pressurized Fluid

Abstract

Summary For chito oligomer production, the efficient hydrolysis of chitosan to smaller substances is important. The focus of this study is to explore the formation and changes in the chitosan degradation product and properties after chitosan hydrolysis in subcritical water. The hydrothermal process was pressurized by supercritical CO2 used as the pressurized fluid and catalyst. Pre‐treatment sonication was also used to change the molecular weight of the chitosan. The effect of the reaction time on the formation of various products and chitosan residue was studied. The chitosan was pre‐treated by sonication at 60 °C for 120 min before subjected to the hydrothermal process at 200 °C and pressure of 23 MPa for 3‐5 min. The chitosan water slurry of 1 wt % in a batch reactor was rapidly heated to the reaction temperature for a specific time. After the reaction, the product was rapidly cooled in a cooling medium. The total yield reached about 15% based on the initial chitosan at 200 °C in 5 min. Upon an increase in the reaction time, the side group of monomers (NH2 or N‐acetyl) tended to be attacked and replaced by OH to produce glucose and also partially degrade into 5‐HMF. The hydrothermal process had no significant effect on the chitosan structure except for the changes in the inter‐ and intramolecular hydrogen bondings of chitosan and the degree of crystallinity of the chitosan residue in the range of 19.2 to 28.9%.

Biobased Nanographene Oxide Creates Stronger Chitosan Hydrogels with Improved Adsorption Capacity for Trace Pharmaceuticals

“…The broad peak in the range from 3500 to 3000 cm –1 indicating a hydroxyl peak became broader and weaker as compared to the spectra of the original biopolymers (Figure a), which is ascribed to the decrease of aliphatic hydroxyl functionalities and formation of some carboxylic acid units during the formation process of 5-HMF and its further polymerization process to carbon nanospheres (CN). As found previously, the side group −NH 2 on the glucosamine can be replaced with OH ions to form glucose in an acid environment with H 2 O as catalyst . The formed glucose will further degrade to 5-HMF.…”

Porosity‐Induced Improvement in KOH Activation of Chitin Nanofiber‐Based Porous Carbon Leading to Ultrahigh Specific Capacitance

“…When used as carbon precursors, monosaccharides [16,31] and polysaccharides [32,33] typically undergo a decomposition mechanism involving the formation of 5-hydroxymethylfurfural (5-HMF) and other organic compounds during hydrothermal treatment, which then repolymerize to form the solid called hydrochar. [25,34] Chitin and chitosan are assumed to follow a decomposition mechanism similar to that of cellulose, with nitrogen-containing compounds present in both the organic and aqueous phases after HT. [35,36] To confirm this, HMs without PSL (HMÀ Px) were observed using scanning electron micro-scopy (SEM) (Figure 1a).…”

The degradation of cellulose in ionic mixture solutions under the high pressure of carbon dioxide

“…Although the acid used in cellulose hydrolysis is simple, there are some serious problems, such as use of water, corrosion of equipment, generation of huge amounts of waste, disposal of waste, and recycling of solvents, making this method unattractive. 9,10 Moreover, long exposure of cellulosic materials to mineral acids can lead to further degradation. Another method widely applied in industries is enzymatic cellulose degradation, although it requires a long processing time.…”