Effects of extrusion variables and chemicals on the properties of starch-based binders and processing conditions

The effects of extrusion variables (moisture, screw speed, and temperature) and chemicals (urea and sodium bicarbonate) on the properties of starch-based binders (water absorption, bulk density, binder yield, expansion ratio, solubility, pH) and processing conditions (die temperature and pressure, feed rate, and specific mechanical energy) were studied using a central composite design. All quadratic regression models, except the models for bulk density and pH, were significant at the P less than or equal to 0.06 level. These models can predict the binder properties and processing conditions when extrusion variables and the chemical concentrations are known. Optimum combinations of the chemical concentrations (g/100 g of starch) and extrusion variables to achieve high water absorption in the binders were 15-20 g of urea/100 g of starch, 0-4 g of sodium bicarbonate/100 g of starch, 35-40 g of moisture/100 g of starch, 100-120 rpm screw speed, and 185-215 degrees C barrel temperature. The molecular degradation of the starch occurred during extrusion, especially when the moisture content of starch was <30 g/100 g of starch.