(a) The plots in Figure Q2(a) were produced from rheological measurements carried out on a commercial grade of polyethylene at 180°C using a slit-die rheometer fitted with pressure transducers along the flow length of the die channel. The dimensions of the die channel were: Depth 1 mm; Width = 15 mm; Length = 20 mm Verify whether the polymer melt obeys the power law relationship by calculating the power law index at each shear rate. (Note that the shear stress at the wall of the channel of a slit-die can be calculated by using the equation derived for a circular die, replacing the radius with depth.) (10 marks) (b) Explain how a wall slip analysis can be performed for rheological measurements using a capillary rheometer, illustrating the fundamental principles. WALL PRESSURE (MPa) 60 40 20 Apparent Shear Rate 80 55 A Die Entry A ° 10 DISTANCE FROM ENTRY (mm) (10 marks) OTD Die Exit B 20