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. 2021 Aug 21;13(16):2807.
doi: 10.3390/polym13162807.

Hydrophobic Modification of Chitosan via Reactive Solvent-Free Extrusion

Tatiana A Akopova  1 , Tatiana S Demina  1 , Mukhamed A Khavpachev  1 , Tatiana N Popyrina  1 , Andrey V Grachev  2 , Pavel L Ivanov  1 , Alexander N Zelenetskii  1
Affiliations

Hydrophobic Modification of Chitosan via Reactive Solvent-Free Extrusion

Tatiana A Akopova et al. Polymers (Basel). .

Abstract

Hydrophobic derivatives of polysaccharides possess an amphiphilic behavior and are widely used as rheological modifiers, selective sorbents, and stabilizers for compositions intended for various applications. In this work, we studied the mechanochemical reactions of chitosan alkylation when interacting with docosylglycidyl and hexadecylglycidyl ethers in the absence of solvents at shear deformation in a pilot twin-screw extruder. The chemical structure and physical properties of the obtained derivatives were characterized by elemental analysis, FT-IR spectroscopy, dynamic light scattering, scanning electron microscopy, and mechanical tests. According to calculations for products soluble in aqueous media, it was possible to introduce about 5-12 hydrophobic fragments per chitosan macromolecule with a degree of polymerization of 500-2000. The length of the carbon chain of the alkyl substituent significantly affects its reactivity under the chosen conditions of mechanochemical synthesis. It was shown that modification disturbs the packing ability of the macromolecules, resulting in an increase of plasticity and drop in the elastic modulus of the film made from the hydrophobically modified chitosan samples.

Keywords: alkyl glycidyl ethers; chitosan alkylation; hydrophobic derivatives; mechanochemical synthesis; solid state organic reactions.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure A1
Figure A1
Original histograms of number-weighted size distribution of macromolecular associates of (a) N-2-hydroxy-3-(hexadecyl) methyl chitosan (Ch1-L-C16-3s sample, degree of substitution of 0.012) and (b) initial chitosan with degree of acetylation of 0.07 and Mw of 140 kDa (Ch2-LMw sample) in 0.2 wt-% solutions in aqueous acetic acid.
Figure 1
Figure 1
Chemical structure of chitosan.
Figure 2
Figure 2
FT-IR spectra (bottom to top): starting reagents HAGE 16 (C16), HAGE 22 (C22); modifier C22 unreacted after co-extrusion.
Figure 3
Figure 3
FT-IR spectra of the samples (bottom to top): chitosan Ch2-LMw; chitosan Ch1-LMw; fraction Ch1-L-C16-3s.
Figure 4
Figure 4
FT-IR spectra of the samples (from bottom to top): chitosan Ch-HMw; fraction Ch-H-C16-5s; fraction Ch-H-C16-5ins.
Figure 5
Figure 5
FT-IR spectra of the samples insoluble in acidic aqueous medium: Ch1-L-C16-3ins fraction (bottom); Ch2-L-C22-10ins fraction (top).
Figure 6
Figure 6
Number-weighted size distribution of macromolecular associates of native chitosan samples (Ch1-LMw, Ch2-LMw and Ch-HMw) and their N-alkyl derivatives in 0.2 wt-% solutions in aqueous acetic acid.
Figure 7
Figure 7
The proposed schemes of chitosan hydrophobization using hexadecylglycidyl (a) and docosylglycidyl (b) ethers as alkylation agents.
See this image and copyright information in PMC

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