a process for reducing polymer surging , lowering pressure and temperature fluctuations , and reducing polymer degradation while providing good overall throughput rate when plasticating and extruding low bulk density polycarbonate materials . the process involves a two - stage extrusion screw having a feed section with a constant channel depth of at least about 12 percent of the screw diameter and a transition section having a compression ratio of at least about 3 : 1 . thermoplastic low bulk density polycarbonate materials are extruded through a die in the shape of sheets , profiles , or films .