Abstract: A solid state extrusion process extrudes a semi-crystalling polymer billet through a die at the end of a pressure chamber. The temperature of the die is controlled so that a thin surface layer of the polymer profile being extruded is melted to form a thin, smooth surface layer on the profile of reduced orientation and increased toughness and which is substantially free of surface imperfections.

Abstract: In a solid state extrusion process a semi-crystalline polymer billet in a pressure chamber is forced through a die at the end of the chamber, with the polymer passing through the die at a temperature between 30.degree. C. below the alpha-crystalline temperature and the melting point of the polymer to form an oriented polymer profile. The pressure chamber is heated to about 0.50-0.95 of the melting point of the polymer and the die is heated to about 0.65-1.2 of the melting point of the polymer, with the die preferably being heated to at least 5.degree. C. warmer than the billet. A haul off stress on the profile extruded from the die is maintained between at least 0.5 MPa and a maximum amount without plastic deformation of the extrudate to obtain an oriented profile having a cross-sectional area greater than 0.5 cm.sup.2 at an extrusion rate greater than 0.5 m/min.

Abstract: A process, apparatus and product related to extrusion or other deformation of solid thermoplastic polymers includes using a die or other deformation devices that have an interior passageway of changing cross-sectional shape commencing with an inlet of compact cross-section and ending with an outlet corresponding to the angular shape of the final extruded profile. The die passageway is divided into at least two consecutive stages including a first stage having an interior contour adapted to transform the polymer billet at a low deformation ratio into an intermediate cross-sectional shape proportional in shape to, but greater in cross-sectional area than, the final angular shape and a second stage having an interior contour adapted to transform the intermediate shape to the desired final shape with substantial longitudinal orientation of the polymer, but without substantial lateral shear deformation.