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

Abstract

Chitosan is typically produced by the deacetylation of the chitin biopolymer. Its molecular weight (Mw) is a function of the chitin source and the deacetylation conditions. It remains a challenge to both control the Mw of chitosan and obtain good monodispersity, which are essential for optimal function of chitosan in different applications. This study explores the use of mechanochemistry and aging as effective methods toward the controlled reduction of the Mw of commercial high Mw chitosan (HMwChs) with phosphoric acid, where Mw was measured by gel permeation chromatography (GPC). In comparison to conventional solution-based methods, this new mechanochemical method features improved process mass intensity in comparison to conventional techniques and affords low Mw chitosan (LMwChs) samples in a range of 200 to 19.5 kDa, with a polydispersity down to1.8.

Mechanochemical and aging-based reductive amination with chitosan and aldehydes affords high degree of substitution functional biopolymers

“…S4.2 †), respectively. Although there was a rising trend in the efficiency of the imine reduction, the prolonged milling up to 90 min caused a significant rise in instrument temperature, from room temperature (25.4 °C) to 40.6 °C after 90 min and 50.5 °C at 180 min, as seen in our previous work, 39 which we thought would make the rationalization of mechanochemical vs. thermal effects difficult to disentangle beyond 90 min milling. Therefore, we turned to aging to seek improved DS.…”

“…Previously, we observed similar positive effects for aging on polysaccharide transformations. 38,39 This mechanochemical and aging-based reductive alkylation of Chs with furfural and NaBH 4 showed great simplicity in achieving near complete DS, distinguishing 3 from 2 , in which the functionalization resulted in a mixture of SB and reduced amine. The method eliminated the repeated dissolution, refluxing, and pH adjustment steps that were widely employed in previously reported solution-based methods of similar modifications.…”

“…36,37 Our group has developed a workflow using the combination of mechanochemistry and aging to extract chitin from crustacean wastes; 35 deacetylate chitin into Chs; 38 and hydrolyze Chs to achieve controlled molecular weight. 39 Similarly, Van Poucke et al recently reported a synthesis of water-soluble N -sulfonated Chs by mechanochemistry. 40…”

“…36,37 Our group has developed a workflow using the combination of mechanochemistry and aging to extract chitin from crustacean wastes; 35 deacetylate chitin into Chs; 38 and hydrolyze Chs to achieve controlled molecular weight. 39 Similarly, Van Poucke et al recently reported a synthesis of water-soluble N-sulfonated Chs by mechanochemistry. 40 Imine, or Schiff-base (SB), formation is one of the most studied functionalization of Chs and has led to applications that harness its bioactivities, [41][42][43][44][45] capability as catalyst support for chemical synthesis, [46][47][48] ability to absorb heavy metal ions, 49 and sensing capability.…”

Mechanochemical Hydrolysis of Polysaccharide Biomass: Scope and Mechanistic Insights

“…[84] The mechanical treatment also depolymerizes chitosan (weight-average molecular weight: M w 2000 kDa) to a lower molecular-weight chitosan (M w 80-900 kDa) in the presence of H 3 PO 4 . [86] Figure 7. Mix-milling treatment for contact formation.…”