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Abstract
To investigate the acid-base and amphoteric properties of carboxymethylchitosan (CMCh) synthesized from silk industry waste (tivit), as well as to evaluate its thermal stability. CMCh was obtained from tivit through chitin extraction, deacetylation and carboxymethylation steps. The degree of substitution was DS = 0.67 (potentiometric titration). Amphotericity was studied by potentiometric titration (determination of and ), solubility measurement in the pH range 4-10, and ζ-potential (electrophoretic light scattering). Thermal stability was studied by TGA/DSC in an inert atmosphere ( , 30-600 °C, 10 °C/min). Structure was confirmed by FTIR and elemental analysis. Potentiometric titration revealed two dissociation constants: = 3.2 ± 0.1 (carboxyl group) and = 6.8 ± 0.1 (amino group). The isoelectric point was pI = 5.0. CMCh solubility was minimal at pH 5.0 (42%) and exceeded 95% at pH > 7.0. ζ-potential changed from +25 mV (pH 3.0) to -25 mV (pH 9.0), ensuring colloidal stability (|ζ| > 20 mV). TGA showed = 232 °C, = 298 °C, and a residue of 23% at 600 °C (carbonized matter). DSC revealed an endothermic peak at 85 °C and exothermic peaks at 302 °C and 450 °C. CMCh from tivit exhibits pronounced amphoteric properties with an isoelectric point at pH 5.0. Thermal stability is sufficient for use in drilling fluids (up to 150°C) and biomedical materials. The results justify the use of CMCh as a pH‑sensitive and heat‑resistant polymer.
References
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