RHEOLOGICAL PROPERTIES BASED OF NA-CMC AND CHITOSAN POLYELECTROLYTE COMPLEXES

Аннотация

Complex coacervate hydrogels formed by sodium carboxymethyl cellulose (Na-CMC) and chitosan were prepared and analyzed for rheological behavior over broad ranges of concentration (1–4% w/v), pH (7–18), and temperature (30–60 °C). Viscosity measurements under steady shear revealed pronounced non-Newtonian (shear-thinning) flow behavior for all samples, with higher polymer concentrations yielding dramatically increased zero-shear viscosity and stronger shear-thinning character. Oscillatory tests showed that low concentrations (∼ 1%) behaved as viscous liquids (loss modulus G'' exceeding storage modulus G'), whereas at 4% a weak gel-like network formed with G' approaching or exceeding G'' at higher frequencies. The rheological properties were highly sensitive to pH: near-neutral pH enabled electrostatic intermolecular associations between the anionic Na-CMC and cationic chitosan, resulting in maximum viscosity and viscoelastic moduli. Increasing pH beyond ~8 caused a sharp drop in viscosity and G', as chitosan became deprotonated and the polyelectrolyte complex disintegrated, leaving a solution with properties approaching those of Na-CMC alone. Temperature elevations from 30 to 60 °C reduced solution viscosity by roughly 2–3 and slightly decreased viscoelastic moduli,consistent with thermal disruptionof polymerinteractions and decreased solvent viscosity. These results illustrate how polymer concentration, pH, and temperature co-modulate the flow and viscoelastic properties of Na-CMC/chitosan complexes. Mechanistically, the strong pH- responsiveness is attributed to the polyelectrolyte nature of the constituents: only within a certain pH window are both polymers sufficiently charged to form extended ionically-crosslinked networks. The findings deepen our understanding of biopolymer complexation and provide quantitative guidance for tuning the rheology of Na-CMC/chitosan systems in applications ranging from injectable hydrogels and controlled drug release matrices to sustainable thickening agents. Key words:Na-CMC, hydrogels, chitosan, polyelectrolete complexe, biopolymer, rheometr.