Jl. Willett et al., EXTRUSION OF WAXY MAIZE STARCH - MELT RHEOLOGY AND MOLECULAR-WEIGHT DEGRADATION OF AMYLOPECTIN, Polymer, 38(24), 1997, pp. 5983-5989
Waxy maize starch was extruded initially using a co-rotating twin-scre
w extruder. This extrudate was then equilibrated to either 18 or 23% m
oisture content, and subsequently re-extruded in a single-screw extrud
er at either 110 or 130 degrees C to characterize the melt viscosity.
The melts exhibited shear thinning behaviour under all conditions; the
power law index m increased with temperature, but did not significant
ly change with moisture content. Molecular weights of selected samples
were measured by multi-angle laser light scattering (MALLS) in dimeth
yl sulfoxide/water (90/10 v/v). The initial extrusion pass reduced the
molecular weight from 336 x 10(6) to 40 x 10(6). Molecular weight red
uctions during the second pass increased with increasing specific mech
anical energy, and were less drastic than the initial drop. The observ
ed M-W values display a semi-logarithmic dependence on the specific me
chanical energy, with r(2) = 0.925. Specific mechanical energy can the
refore be used to estimate molecular weight degradation, regardless of
variations in extruder type or conditions during multiple passes. Mol
ecular weight distributions determined using gel permeation chromatogr
aphy correlated well with the single-point molecular weight determinat
ions. (C) 1997 Published by Elsevier Science Ltd.