G. Pomar et al., EXTRUDATE DISTORTIONS IN LINEAR LOW-DENSITY POLYETHYLENE SOLUTIONS AND MELT, Journal of non-Newtonian fluid mechanics, 54, 1994, pp. 143-151
The onset of sharkskin and wavy extrudate distortions was studied in a
linear low-density polyethylene which was diluted up to 40 wt.% with
octadecane in order to vary the plateau modulus. The ratio of critical
wall stress to plateau modulus remained constant for the onset of sha
rkskin. The transition to wavy flow occurred at a constant wall stress
, independent of plateau modulus for dilutions up to 30 wt.%, after wh
ich the discontinuity in the flow curve and the transition to the wavy
instability did not occur. The different behavior for the two transit
ions suggests different mechanisms.