Monovalent and divalent salt effects on thermogelation of aqueous hypromellose solutions

• Gelation shifted to lower temperature with increasing salt concentrations.
• Gelation temperature is independent of valency of cations and the mole concentration of anions.
• Melting temperature decreased linearly with increasing ion concentration of salts.
• Bound water increased as the salt concentration increased.

The effect of salt on gelation behavior of concentrated low molecular weight Hydroxypropyl methylcellulose (HPMC, Hypromellose) solutions were investigated by using rheology measurements. Various gelation matrices were used to characterize gelation point as a function of salt concentrations. It was found that gelation temperature identified by frequency-independent loss tangents is similar to the gelation temperature at which minimum elastic modulus, G′, occurred during heating process. Thermal analysis showed that the melting temperature decreased linearly with increasing ion concentration of salts. The bound water analysis showed that the bound water increased as the salt concentration increased. Secondary peaks that represent the freezable bound water were also observed for solutions with NaCl and KCl.

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