Depolymerization of barley starch during extrusion in water glycerol mixtures
1997
Myllymaeki, O. | Eerikaeinen, T. | Suortti, T. | Forssell, P. | Linko, P. | Poutanen, K.
For the purpose of producing thermoplastic starch, barley starch was extruded in mixtures of water and glycerol in a twin-screw extruder equipped with a specially constructed slit die. The process parameters - water feed (15-25 g/min), glycerol feed (15-25 g/min), barrel temperature (150-200 degree C) and screw speed (272-400 rpm) - were varied according to a statistical experimental design consisting 28 trials. The values of the process parameters were selected to lie within ranges technically feasible with the equipment. Starch amylopectin was clearly depolymerized. Intrinsic viscosities decreased from 230 mL/g to about 150 mL/g. The tensile strength depended only on glycerol content in the experiment area, varying from 4,5to 16 MPa. The specific mechanical energy consumption was 87-240 Wh/kg. In all trials, water had only a slightly greater effect than did glycerol on the dependent variables. All the models of dependent variables were statistically very significant. In the experiment range used it was possible to produce thermoplastic starch with relatively high molar mass and mechanical strength.
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