Thermogelling polysaccharides for aqueous gelcasting -: part 1:: a comparative study of gelling additives

In this work the rheological properties of aqueous solutions of three polysaccharides, agar, agarose, and carrageenan for aqueous gelcasting are studied. Solutions of these additives have been prepared to concentrations ranging from 1 to 4 wt.%. The dissolution and gelling behaviour are studied from the measurements of viscosity as a function of temperature on both heating and cooling. These additives need to be heated at >90 degreesC to dissolve, except carrageenan, where full dissolution is achieved at <70 degreesC. Dissolution temperature and Tg of carrageenan directly depend on concentration and do not change significantly for agaroids. The hystheresis of gelation is much broader for agaroids. The viscosity increases at least 1000 mPa.s on gelation when the concentration is greater than or equal to2 wt.%. Gelation occurs for the three additives in a broad range of pH between 4 and 10. The gels are reversible but the temperature must be maintained above 50 degreesC to prevent gelation. The results show that carrageenan is a suitable candidate for gelcasting since its properties are near to those of agaroids and the cost is lower. (C) 2002 Elsevier Science Ltd. All rights reserved.