Separation of the variables of time and temperature in the mechanical properties of high sugar/polysaccharide mixtures.
Experimental results from previous studies were analyzed in order to separate the dynamic mechanical properties of high sugar/polysaccharide mixtures into a basic function of temperature alone and a basic function of time alone. In doing so, the energy of vitrification as derived from the Williams, Landel, and Ferry equation, and the distribution function of relaxation times were used. It was found that the temperature course of vitrification depends on the nature of the polymer and the composition of the mixture. Thus, at the same level of cosolute, the glass transition temperature of the mixture is determined by the structural behavior of the macromolecule and, it appears, that cation-mediated associations--for example, of kappa-carrageenan--are more efficient "vitrifiers" than the neutral associations of agarose. Regardless of the glass transition temperature, vitrification requires five times the activation energy of elementary flow in the melt or of the viscoelastic relaxation in the rubbery state. In the region of long time scales of measurement, the time function is determined by the molecular weight distribution and the ability of the polysaccharide to form a three-dimensional network. In the area of short times, free volume effects leading to vitrification are similar for all materials.
Kasapis
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Department of Food Science and Nutrition, College of Agriculture, Sultan Qaboos University, Al-Khod, Sultanate of Oman.
Sworn
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D002241:Carbohydrates / Q000737:chemistry*; D004548:Elasticity; D019563:Mechanics; D011134:Polysaccharides / Q000737:chemistry*; D012212:Rheology; D013696:Temperature; D013997:Time Factors; D014783:Viscosity
D002241:Carbohydrates; D011134:Polysaccharides