Twin screw extruder for processing mixtures of plastics and natural fibers has screw profile for repeated compression and relaxation along the screw length and vacuum evacuation

摘要

The closely intermeshing extruder screws have a profile along their length designed to compress and relax the polymer and fiber mixture at least five times. Volumetric compression in the screw is not less than1.5 and relaxation not more than0.8. Vacuum is applied to the interior of the barrel in the relaxation zones to extract volatiles and water vapor. In the front screw segment pressure is increased to force the molten plastic and fiber mixture through a die at the front of the barrel. Feeding of the extruder is via a stuffing hopper whose screw speed and torque can be adjusted to vary the degree of filling in the feed zone. Stuffing screw speed can be controlled so that the main extruder can be driven at a constant torque. An Independent claim is included for a process using the extruder in which: a) a mixture of undried natural fibers and plastics is conveyed and mixed in a hopper; b) fed by a stuffing screw into twin plasticizing screws of the main extruder; c) degassed and compressed and relaxed at least five times; d) extruded through a die.