Thermoreversible gels of hydrophobically modified hydroxyethyl cellulose cross-linked by amylose

Aqueous mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) or unmodified hydroxyethyl cellulose (HEC), with amylose (AM) or potato amylopectin (PAP), have been investigated by rheology, turbidity, and H-1 NMR measurements. It is concluded that the AM molecules cross-link HMHEC chains by forming helical inclusion complexes with the hydrophobic side chains of HMHEC, leading to thermoreversible, elastic, and thixotropic gels at ambient temperatures. The complexation ability, the setting-melting temperature of the AM-HMHEC complexes, the strength of the association, and the viscoelastic behavior of the gels vary with the polymer concentrations, the pH, and the preparation method. AM-HMHEC complexes were obtained at a pH range of 7-12.5, but a maximum storage modulus was observed at pH approximate to 10. The AM-HMHEC complexation is modified or completely abolished by the addition of surfactant. A weak synergistic interaction was found for mixtures of PAP with HNIHEC. No complexation was observed between HEC and either AM or PAP.