Temperature and pressure inside a twin screw pilot-scale extruder (Clextral BC 45) were measured. The product -maize starch, and screw configuration -transport elements and one reverse screw element before the die, were chosen to be very simple. Axial profiles were determined: the increase in temperature up to 150-200°C is linked with the position of the reverse screw element, the increase in pressure up to 50-80 bar was mainly due to the die. Of the process variables studied, water content and feed rate had the greatest efect. When feed rate and screw speed were changed simultaneously in order to keep the fill fraction constant, the temperature remained steady whereas pressure at the die increased, changing the equilibrium point of the machine.

Interpretation of these observations is suggested in terms of conduction, convection, friction, shear and pressure build-up in polymer flow.