Isothermal crystallization of concentrated amorphous starch systems measured by modulated differential scanning calorimetry

Citation
P. De Meuter et al., Isothermal crystallization of concentrated amorphous starch systems measured by modulated differential scanning calorimetry, J POL SC PP, 37(20), 1999, pp. 2881-2892
Citations number
36
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
ISSN journal
08876266 → ACNP
Volume
37
Issue
20
Year of publication
1999
Pages
2881 - 2892
Database
ISI
SICI code
0887-6266(19991015)37:20<2881:ICOCAS>2.0.ZU;2-R
Abstract
The slow isothermal crystallization of concentrated amorphous starch system s is measured by Modulated. Differential Scanning Calorimetry (MDSC). It ca n be followed continuously by the evalution (stepwise decrease) of the MDSC heat capacity signal (Cp), as confirmed with data from X-ray diffractometr y, Dynamic Mechanical Analysis, Raman spectroscopy, and conventional Differ ential Scanning Calorimetry. Isothermal MDSC measurements enable a systemat ic study of the slow crystallization process of a concentrated starch syste m, such as a pregelatinized waxy corn starch with 24 wt % water and 76 wt % starch. After isothermal crystallization, a broad melting endotherm with a bimodal distribution is observed, starting about 10 degrees C beyond the c rystallization temperature. The bulk glass transition temperature (T-g) dec reases about 15 degrees C during crystallization. The isothermal crystalliz ation rate goes through a maximum as a function of crystallization time. Th e maximum rate is characterized by the time at the local extreme in the der ivative of Cp (t(max)), or by the time to reach half the decrease in Cp (t( 1/2)). Both t(max) and t(1/2) show a bell-shaped curve as a function of cry stallization temperature. The temperature of maximum crystallization rate, for the system studied, lies as high as 75 degrees C. This is approximately 65 degrees C above the initial value of T-g. Normalized Cp curves indicate the temperature dependence of the starch crystallization mechanism. (C) 19 99 John Wiley & Sons, Inc.