A plastication unit for an injection molding machine, combining a heated plastication barrel with an entrance port and an exit port on opposing ends of the barrel; a hopper positioned to deliver ingredients to be compounded for injection molding to the entrance port of the barrel; and a helical plastication screw rotatably carried within the barrel and running the length of the barrel between the entrance and exit ports, which is operable to rotate and transmit the ingredients along the length of the barrel; wherein the plastication screw has at least one axial fluted extensional mixing element segment and the ingredients include at least one polymer for injection molding. Methods for injection molding with the plastication unit of the present invention and articles formed by the inventive methods are also disclosed.