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.
Highlights
The hydrophobization of polysaccharides is widely used to change their hydrophilic– lipophilic balance and, the rheological properties of their aqueous solutions
We have shown the efficiency of the solvent-free method, which makes it possible to carry out the chemical modification of polymers in the absence of liquid dispersion media as well as any catalysts to obtain hydrophobic derivatives of chitosan
The degree of substitution (DS) of amino groups of chitosan with alkyl substituent for the soluble products was 0.006–0.016, that corresponds to 5–10 hydrophobic moieties per chitosan macromolecule with a degree of polymerization of 500–800 (Ch-LMw samples) and 12 substitutes per macromolecule for Ch-HMw sample with DP of 2000
Summary
The hydrophobization of polysaccharides is widely used to change their hydrophilic– lipophilic balance and, the rheological properties of their aqueous solutions. Lipophilic interaction of the introduced side substituents leads to aggregation of the macromolecules in an aqueous medium, which results in the formation of nanoparticles with a “core-shell” structure, micelles, or gels, depending on the polymer concentration, temperature, number of substituents, and the length of their alkyl chains [1,2,3,4,5] Such derivatives of chitosan are used mainly for the development of amphiphilic drug delivery vehicles [6], for cleaning the water surface from oil contamination, including with subsequent regeneration of oils [7], as separating membranes [8], and for stabilizing oil-in-water emulsions [9,10,11]. The fabrication of composite filaments for 3D printing usually requires several steps of component mixing, and preliminary modification of their chemical structure could facilitate the compatibility of the filler and polyolefin matrix [17,18]
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