Аннотация:Chitin or poly(β(1-4)-N-acetyl-D-glucosamine) is one of the most abundant
polysaccharides found in nature. It is well known that chitin cannot be dissolved in common
solvents. This obviously limits practical utilization of this material. Additionally, the Ndeacetylated
derivative of chitin – chitosan, can be dissolved in aqueous solutions only with a
pH<6.5. Carboxymethyl derivative of chitin is water-soluble in a wide pH interval and
exhibits low toxicity, biodegradability and biocompatibility. Due to such unique combination
of properties carboxymethyl chitin (CMC) found wide application in various areas of biology
and medicine: controlled drug delivery systems, biosensors, bone repairing, wound healing
and etc. For chemical CMC modification, in particular, polymer-similar transformations it is
necessary to realize CMC polyelectrolyte macromolecules behavior at different pH media
during such modification.
Considering it, various forms of 6-O-carboxymethyl chitin (degree of substitution 1.0)
have been obtained: acidic form (CMC-H), salt form (CMC-Na) and mixed form with equal
(50%) share of CMC-H and CMC-Na links in CMC chain. Structure and properties of these
CMC forms and films on their basis were investigated.
The absorption bands with the maximum at 1733 and 1567 cm-1 in FTIR spectra of
CMC-H confirmed the presence of C=O bond in the carboxylic groups and carboxylate-ions,
correspondingly. In contrast to that, intensity of characteristic absorption peak at 1563 cm-1
(C=O in the carboxylate-ion) of mixed form is significantly reduced; at the same time in
CMC-Na FTIR data the spectral sings of such band are absent.
Comparative study using TGA showed that CMC hygroscopicity is significantly depend
on CMC form. So, the most hygroscopic CMC-Na is able to absorb 20% mass. of water at
room temperature, at the same time this index for CMC-H was 9% mass. and for mixed form
– 13% mass. Beginning decomposition temperature of CMC for acid form CMC-H was
197ºС, for mixed form – 221ºС and for CMC-Na – 262ºС. Apparently, the presence of free
carboxylic groups in acid form CMC-H promotes such reactions as decarboxylation,
formation of anhydride bonds and etc., accompanying the thermal transformations of the
polymer.
Analysis of data on the mechanical strength investigation of CMC films showed that
index of elastic modulus for CMC-H film was higher than for CMC-Na film. Such difference
is possibly due to additional intermacromolecular hydrogen bonds formation in CMC-H as
compared to CMC-Na form.