High‐Humidity Shaker Aging to Access Chitin and Cellulose Nanocrystals**

Abstract

To unlock nature's potential for functional biomaterials, many efforts have been devoted to isolating the nanocrystalline domains within the supramolecular structure of polysaccharides. Yet, low reactivity and yield in aqueous systems along with excessive solvent usage hinders its development. In this report, the first solvent‐free pathway to access carboxylated chitin and cellulose nanocrystals with excellent mass balance is described, relying on a new method coined high‐humidity shaker aging (HHSA). The method involves a mild grinding of the polysaccharide with ammonium persulfate followed by an aging phase under high‐humidity and on a shaker plate. Insights into the mechanism were uncovered, which highlighted the unique role of high humidity to afford a gradual uptake of water by the material up to deliquescence when the reaction is complete. This process was then validated for direct synthesis of nanocrystals from biomass sources including crab and soft wood pulp.

Controlled Chitosan Molecular Weight Reduction by Mechanochemical and Aging-Based Phosphoric Acid Hydrolysis

“…Water, either from the 85% H 3 PO 4 solution or the native chitosan and/or absorbed from the humid environment, drives the hydrolysis reaction catalyzed by local acidic protons in the chitosan–H 3 PO 4 mixture and allows the reaction to progress within the reaction mixture. This mechanism is reminiscent of work previously reported by our group on chitin oxidation with ammonium persulfate in solid-state, high humidity aging conditions …”

“…This mechanism is reminiscent of work previously reported by our group on chitin oxidation with ammonium persulfate in solidstate, high humidity aging conditions. 40 Advantage of the Method. We compared the MABPAH process for chitosan treated with 85% H 3 PO 4 with a solutionbased method of H 3 PO 4 -catalyzed chitosan hydrolysis reported by Jia and Shen.…”

“…Besides reactions happening during mechanical treatment, the concept of aging has been introduced, in which reactions take place in the solid phase, after an initial mixing phase . These solid-state methodologies are well suited in the context of biomass conversion, especially because such starting materials tend to be insoluble and have shown great promise in the context of chitin extraction , and conversion. , Mechanochemistry has been used for the deacetylation of chitin into chitosan in a process pioneered by Yan and co-workers . Chitin was ball-milled with solid NaOH to trigger both amide deacetylation and the nucleophilic attack of the chitin glycosidic bonds by hydroxide ions .…”

Cleaner production of cellulose nanocrystals and calcium sulfate whiskers: Process design and life cycle assessment

“…Consequently, the commercialization of CNCs is mainly restricted by high cost and severe environmental issues. Recent advances for the cleaner production of CNCs have been summarized in our latest review, 14 primarily covering sustainable raw materials and clean production processes, for example, nonsolution‐based extraction process (HCl vapor hydrolysis 15 and ammonium persulfate oxidation combined with high‐humidity shaker aging 16 ). However, newly developed materials and processes are not applied in the current industrial production of CNCs, 12 because their scalability requires further verification.…”

Controlled Chitosan Molecular Weight Reduction by Mechanochemical and Aging-based Phosphoric Acid Hydrolysis

“…36 These solid-state methodologies are well suited in the context of biomass conversion, especially because such starting materials tend to be insoluble, 37 and have shown great promise in the context of chitin extraction, 38,39 and conversion. 39,40 Mechanochemistry has been used for the deacetylation of chitin into chitosan in a process pioneered by Yan and co-workers. 41 Chitin was ball-milled with solid NaOH to trigger both amide deacetylation and the nucleophilic attack of the chitin glycosidic bonds by hydroxide ions.…”