The use of Arrhenius and WLF kinetics to rationalise the mechanical spectrum in high sugar gellan systems

Small deformation measurements were carried out on high sugar gellan mixtures monitoring the combined effect of temperature and time on the changing viscoelasticity. Horizontal superpositions of mechanical spectra produced double logarithmic plots of shear modulus (10−1 to 107 Pa) versus frequency of oscillation (10−1 to 107 rad/s) covering the relaxation, rubbery and glass transition regions. Gellan forms lightly cross-linked segments which gradually transform the mixture into a gel with a high “sol-fraction”. The transition from the terminal to the rubbery zone is followed by the Arrhenius equation yielding parameters pertinent to the chemical structure of the system. Further cooling sees an exponential development of viscoelasticity which yields a WLF form according to the non-specific function of the free volume theory. Thus the disentanglement of the two processes in the time-temperature continuum is clearly demonstrated. The approach may assist in the purposeful investigation of other sugar/polysaccharide systems.