Treatments no. Independent variables  in coded forma Experimental variables in their natural units     SS BT SS BT 1 0 0 85 232.5 2 a 0 60 232.5 3 + + 110 275 4 0 A 85 275 5 - − 60 190 6 A 0 110 232.5 7 0 a 85 190 8 + − 110 190 9  - + 60 275 Treatments No: 1=85 rpm SS & 232.5°C BT; 2=60 rpm SS & 232.5°C BT; 3=110 rpm SS & 275°C BT; 4=85 rpm SS & 275°C BT; 5=60 rpm SS & 19°C BT; 6=110 rpm SS & 232.5°C BT; 7=85 rpm SS & 190°C BT; 8=110 rpm SS & 190°C BT; and 9=60 rpm SS & 275°C BT. SS=Screw Speed (revolutions per minute) and BT=Barrel Temperature.

Table 1: Central composite design (CCD) design of the Extrusion Experiments in their coded form and natural units.