Tapered barrel screw extruder help!

Hi everyone,
 
I want to fabricate a tapered barrel screw extruder for extruding pcl through a 100 micron nozzle. Please refer the attached diagram. The outer diameter of the larger end is 24mm and is constant. Also, I wish the inner diameter at the larger end to be 14mm. The length of the barrel is 84 mm; you can increase the length if it is to increase the extrusion rate. Can you please tell me what should be the appropriate taper angle so that it extrudes well? Is there any formula to calculate that taper angle?
Thanks a lot in advance.
Regards,
Matthew