Mika Iijima

EFFECT OF ANNEALING ON CALCIUM PECTIN GEL FORMATION BY THERMOMECHANICAL ANALYSIS

Pectin solutions were annealed at various temperatures and time intervals. Calcium pectin gels were prepared by mixing aqueous solutions of pectin and calcium chloride (CaCl2). The degree of Na to Ca substitution (DS) was calculated based on the data obtained by atomic absorption spectrometry. DS increased with increasing Ca content and levelled off at the characteristic Ca content which corresponds to the saturated value assuming all -COOH was converted into -COO2Ca. The characteristic saturated values depended annealing temperature and time at sol state. DS was calculated and it was found that DS decreased with increasing annealing temperature. Viscoelastic properties of gels in water were investigated using a thermomechanical analyzer (TMA). Dynamic modulus increased and tanδ decreased with increasing DS. Swelling ratio of gels decreased with increasing annealing temperature and time at sol state showing a similar tendency to the results of DS. It can be concluded that a large network structure was formed when the samples were annealed at high temperature for a long time at sol state.

Thermomechanical Analysis of Polysaccharide Hydrogels in Water

Application of thermomechanometry to the measurement of hydrogels containing a large amount of water was carried out by static and dynamic methods. A thermomechanical analyzer (TMA) equipped with a quartz compression probe immersed in water was used. Polysaccharide hydrogels containing ca 98% water were measured. Creep of hydrogels in water was analyzed in a stress range from 1.04⋅103 to 5.2⋅103 Pa and loading rate from 0.3⋅103 to 3.0⋅103 Pa min−1.Stress relaxation was measured in compressed ratio range from 0.02 to 0.45 m m−1 and in compressing rate was 0.09 to 0.15 m m−1 min−1. Dynamic viscoelasticity was measured by TMA when dynamic Young’s modulus which was larger than 1⋅104 Pa in frequencies ranging from 0.02~0.2 Hz.