​A 27mm or 34 mm diameter co-rotating twin screw Leistritz extruder with L/D of 40 is used for the foaming experiments.  Polymer is fed into the hopper of the extruder through a solid metering feeder. The blowing agent is injected in the extruder through a syringe pump or a HPLC dual piston at 20 L/D of the extruder, after a complete melting of the material is achieved.  The rest of the extruder is used to mix, pressurize, and cool the blowing agent laden melt before extruding through the die.