Memory Effect and Extrudate Swell

Abstract

The first part of this paper describes an interpretation of extrudate swell with an emphasis on the following aspects: (1) The material behavior in the entrance zone leading to capillary is in transient and not in steady state. (2) The material behavior is predominantly in elognation and not in shear. (3) The deformational memory introduced in this zone is carried into capillary. (4) The material behavior in capillary is the steady state flow with accompanying memory mentioned in (3). (5) The memory is disspitated (relaxation) during the flow. (6) The remaining memory results in extrudate swell after material exist from capillary. (7) Even with a long capillary, the memory does not dissipate completely, because the steady state flow itself maintains certain memory. (8) The extrudate swell is time-dependent and not instantaneous. (9) It is like a creep-recovery. (10) The extrudate swell is related to the normal stresses in the flow through capillary.
The second part of the paper describes various subjects, which are required for the fundamental understanding of the memory behavior and extrudate swell in particular. (11) The deformation associated with extrudate swell is nonlinear. Therefore, a theoretical treatment of nonlinear viscoelasticity is needed. (12) Because the material behavior involves both shear and elongation, the relationship between them must be established. (13) A quantitative description of deformational memory is needed. (14) In the transient behavior a memory is being built and at the same time a part of memory is lost. A “balance sheet” of the memory at any instant of time must be available. (15) Stress relaxation accompanying steady state flow must be elucidated. A use of stress relaxation measurement is proposed as a quantitative means of describing the “memory balance”.