Structure-property relationships in extruded starch, 1 - Supermolecular structure of pea amylose and extruded pea amylose

Separated amyloses with different molecular weight distributions were obtai ned enzymatically from wrinkled pea starch and processed in a multi-zone tw in-screw extruder. The crystalline polymorphs, crystallinity and crystallit e dimensions of amylose (unbranched molecular starch component) and films e xtruded from it were investigated by wide-angle X-ray scattering. The start ing amylose materials exhibit a crystalline V-A structure with rather large crystallites (9-25 nm) and a degree of crystallinity ranging from 30 and 4 0%, 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 performan ce. As compared with cellulose or synthetic polymer films, the mechanical p roperties of the amylose films appear to be fundamentally limited by the la ck of preferred molecular orientation.