GLASSY-STATE PHENOMENA IN GELLAN SUCROSE CORN SYRUP MIXTURES

The method of dynamic oscillation was employed to investigate changes in the mechanical properties of deacylated gellan gels in the presence of sucrose-corn syrup blends. The effect of sugar, at concentrations between 0 and 50% in the mixture, is to raise gradually the gelling te mperature and the mechanical strength of the gellan network. However, there is a sharp increase in thermal stability (formation of a structu re at the highest experimentally accessible temperature of 90 degrees C) and substantial reduction in shear modulus development at 60% co-so lute in the system which is discussed in terms of a disproportionate c onformational ordering and diminishing water-supported, intermolecular junction zones of the gellan strands in a low solvent environment. Th e dramatic change in physical properties of the gellan-solute blends a t 90 degrees C produces a spectacular temperature dependence of the in -phase and out-of-phase viscoelastic components during subsequent cool ing. Thus, the high-solids gellan network undergoes transformation fro m a rubber-like consistency to a glassy state in the manner observed f or entangled networks of high molecular weight synthetic polymers. The onset of glass transition is enhanced by increasing amounts of sugars , occurring at about 37 degrees C for the 0.5% gellan plus 85% solute system at an experimental frequency of 10 rad/s, Mechanical spectra of sucrose-corn syrup mixtures at this concentration remain Newtonian at 5 degrees C, the lowest experimentally accessible temperature. Accord ing to the time-temperature superposition principle, vitrification of the above gellan sample commences at approximate to 17 Hz at 90 degree s C. Following the empirical procedure developed by Williams, Landel a nd Ferry, the temperature at which the gellan-solute glass forms (Tg) was found to be close to the vitrification temperature of a sucrose pr eparation at 15% moisture content (approximate to-25 degrees C).