Extrusion instability flow test

The experiments of unstable flow and melt fracture show that when polymer melt is extruded from die, when the extrusion rate (or shear stress) exceeds a certain critical shear rate (or critical shear stress), it is prone to elastic turbulence, resulting in unstable flow and rough surface of the extrudate.

With the increase of extrusion rate, wave shape, shark skin shape, bamboo joint shape and spiral shape may appear successively, resulting in completely irregular melt fracture.

Schematic diagram of unstable flow extrudate appearance.

(1) Although there is no unified understanding about the mechanism of unstable flow, various assumptions believe that this is also the manifestation of the elastic behavior of polymer melt.

(2) As far as the melt fracture phenomenon is concerned, it is definitely related to the nonlinear viscoelasticity of the melt, the orientation and de orientation of the molecular chain in the shear flow field (the hysteresis of conformation change and molecular chain relaxation), entanglement and de entanglement, and external process conditions.

(3) From the point of view of deformation energy, the elastic energy storage capacity of polymer melts is limited. When the rate of external force is very large, and the deformation energy given to the melt by the outside world is far beyond the limit that the melt can bear, the excess energy will be expressed in other forms, in which the generation of new surface and the consumption of surface energy is one form, that is, the occurrence of melt fracture.

Optional as an option for capillary rheometer

Quick acquisition pressure sensor

Time resolution 10-5 s

Pressure resolution 0.01 bar

(small pressure fluctuations can be detected directly)

The stress test data is of equal interval time, and Fourier transform can be used

For analysis

Front end dimension 2,5 mm

Small die size