The glass transition zone in high solids pectin and gellan preparations

Dynamic oscillatory data on deacylated gellan and high methoxy pectin, in the presence of sucrose and glucose syrup, are presented over a wide temperature range. High levels of the co-solute induce a transition from rubberlike to glasslike consistency in the two biopolymers. The time-temperature superposition method is employed to construct composite curves, around the glass transition region, covering a nine-decade frequency range. The shift factors thus derived are fitted against the experimental temperatures using the Williams, Landel and Ferry equation. These observations are interpreted on the basis of the free volume theory which allows calculation of thermal expansion coefficient and fractional free volume parameters, at the glass transition temperatures of the high solids gellan and pectin systems. Values are in excellent agreement with those for synthetic polymers, a result which emphasizes the universal utility of the above approach (experiment and theory) in studying glasses of synthetic or biological origin. (C) 1997 Elsevier Science Ltd.