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Nanostructure of potato starch. II. Structure of a highly crystalline gel obtained by retrogradation using X‐ray diffraction techniques
Author(s) -
Bayer R. K.,
BaltáCalleja F. J.
Publication year - 2007
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.24527
Subject(s) - crystallinity , materials science , lamellar structure , amorphous solid , nanostructure , crystallization , crystallography , annealing (glass) , spherulite (polymer physics) , amylose , crystal (programming language) , chemical engineering , starch , crystal structure , amylopectin , composite material , polymer , chemistry , nanotechnology , organic chemistry , programming language , computer science , engineering
A highly crystalline gel (65% crystal portions) was prepared by retrogradation of injection‐molded potato starch in humid atmosphere. The different components of the nanostructure were identified by means of successive melting processes using “ in situ ” simultaneous wide and low angle X‐ray diffractions. At low temperatures, structural changes such as annealing phenomena or evaporation of water, giving rise to a thickening of the gel, are observed. In the range of 55–75°C, a first transition due to melting of a layered structure of concentric sphere‐like alternating crystalline and amorphous lamellar shells (amylopectine, AP, being the crystalline component) is detected. Analysis of results reveals that the AP crystallization contributes 25% to the overall crystal fraction. A spherulitic structure of alternating radial lamellae from amylose (AM) or AP melts in a higher temperature region between 75 and 86°C. This modification represents the major contribution to crystallinity of about 40%. Unexpectedly, the crystalline blocks of such a structure are abnormally anisometric; i.e., they are thicker than their width. This has been related to a contraction of the AMAP‐co‐spherulite due to an excessive growth of the AP‐shell crystals. The anisometry of the blocks of the AMAP lamellae vanishes at the beginning of the melting of the AP shell crystals, just when the total crystallinity decreases below 50% at 60°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 689–696, 2007