Options
2001
Journal Article
Titel
Structure-property relationships in extruded starch. 1 supermolecular structure of pea amylose and extruded pea amylose
Abstract
Separated amyloses with different molecular weight distributions were obtained enzymatically from wrinkled pea starch and processed in a multi-zone twin-screw extruder. The crystalline polymorphs, crystallinity and crystallite dimensions of amylose (unbranched molecular starch component) and films extruded from it were investigated by wide-angle X-ray scattering. The starting amylose materials exhibit a crystalline V-A structure with rather large crystallites (9-25 nm) and a degree of crystallinity ranging from 30 and 40%, depending on the history of the amylose sample. The extruded films, on the other hand, recrystallized in the B-type with a slightly higher degree of crystallinity and significantly smaller crystallite dimensions (3-7 nm). In one case, V-H-type crystals were observed. The mechanical properties of the extruded materials were determined in tensile tests. The amylose with the highest molar mass produces films with the highest mechanical performance. As compared with cellulose or synthetic polymer films, the mechanical properties of the amylose films appear to be fundamentally limited by the lack of preferred molecular orientation.