Cavitation of Polyethylene During Extrusion Processing Instabilities

Published

December 1, 2002

Author(s)

Y Son, Kalman D. Migler

Abstract

We present observations of cavitation that occur inside a capillary die during extrusion of a polyethylene. This phenomenon is observed over the last 1.5 mm of the capillary tube immediately upstream of the exit. We observe spontaneous formation of voids near the wall that grow to a typical length and width 150 ?m, then shrink down and disappear over a timeframe of approximately 20 ms (milisecond). From velocity measurements of these structures, we conclude that their width in the radial direction is smaller than that in the axial and lateral directions, and that they are near the wall. The shape of the cavities is highly irregular. We assess the roles of extensional stress and shear stress at the exit region and conclude that they are not the direct cause of the cavitation. Rather, we find that the cavitation occurs in conjunction with an upstream rupture of the polymer that occurs in the contraction region leading into the capillary tube (gross melt fracture). We argue that the exit region does however serve as the initiation point of the cavitation, due to a combination of the reduced pressure and extensional shear stress.

Citation

Journal of Polymer Science Part B-Polymer Physics

Volume

40

Issue

No. 24

Pub Type

Journals

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Keywords

Fluoropolymer coating, grossmelt fracture cavitation polyethyle, visual observation

Citation

Son, Y. and Migler, K. (2002), Cavitation of Polyethylene During Extrusion Processing Instabilities, Journal of Polymer Science Part B-Polymer Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852095 (Accessed April 18, 2024)