Swelling behaviour of calcium pectin hydrogels by thermomechanical analysis in water

Aqueous solutions of pectin annealed at various temperatures at sol state were mixed with CaCl2 solution and calcium pectin gels with various cross-linking ratios were prepared. A thermomechanical analyser (TMA) equipped with a sample holder, which was newly designed at our laboratory was used. The sample holder was immersed in water whose temperature was controlled from 30 to 80 °C. Swelling behaviour of hydrogels during equilibration was measured as a function of immersing time. Creep coefficient was calculated as functions of time and temperature using a compression type probe. The creep coefficient of hydrogels increased with increasing swelling temperature and decreased with increasing cross-linking ratio. Dynamic modulus (E′) was measured in water in a temperature range from 30 to 60 °C. E′ of the gel with cross-linking ratio 0.36 decreased from 5.5 × 104 to 3.5 × 104 Pa with increasing swelling temperature from 30 to 60 °C.