Measurement Techniques and Methods for the Pressure Coefficient of Viscosity of Polymer Melts

Table 2

Summary of different measurement techniques.

Type of flow	Drag flow	Pressure-driven flow
Rheometer	Rotational rheometer, rotating cylinder viscometer, sliding plate rheometer, etc.	Traditional standard rheometer	Rheometer with counter-piston device	Rheometer with pressurized exit chamber
Measurement process	Change shear rate and pressure. Then, obtain the master curve by superposition.	Obtain the nonlinear pressure profiles from pressure transducers or from the Bagley plots.	Keep pressure drop (shear stress) constant by adjusting the hydraulic system.	Keep piston speed (shear rate) constant by adjusting the valve at the exit.
Pressurizing medium	Inert liquid, gas	Piston
Typical volume range of loaded sample	Less than 10 cm^3 (only a few cm^3)	About 20 cm^3	Between 10 and 20 cm^3	About 20 cm^3
Advantages	(1) The sample is subjected to even pressure and shear rate.; (2) Data processing is straightforward without any correction.	(1) The shear rate range is wide.; (2) The measurement is direct without the second pressure chamber.	(1) The shear rate range is wide.; (2) It can realize accurate pressure control and constant shear stress control.; (3) Sample consumption is small.	(1) The shear rate range is wide.; (2) It strikes a reasonable balance between complexity and accuracy.; (3) The application of this method is widespread.
Disadvantages	(1) The shear rate range is relatively small. (2) The mechanical configuration of the rheometer is intricate.; (3) It is laborious to load samples and time-consuming to clean the instrument.	(1) The high curvature of the capillary makes it impossible to install the pressure sensor.; (2) The pressure coefficient estimated from the nonlinear pressure profile is unreliable.; (3) The pressure and shear rate are uneven, and the data processing is required.	(1) The application of this precise device is limited due to its high cost and difficult operation.; (2) The pressure and shear rate are uneven, and the data processing is required.	(1) The pressure and shear rate are uneven, and the data processing is required.