Zum Einflu� von F�llstoffen auf das rheologische Verhalten von hochmolekularen Polyethylenschmelzen

Abstract

For the visualization of polymer flow in the entry region of a capillary, a method has been developed that uses distinct crystallization phenomena of the partially crystalline polymer itself solidifying from a presheared melt. The solid polymer shows so-called flow lines made up of transcrystalline overgrowth on rows of nuclei capable of showing a picture of the past melt-fow streamlines. The development of circulating flow in the entry region of capillaries could be shown with an injectionmolding type LDPE. The higher molecular-weight types appeared to show unstable flow with disappearing circulating flow in the comers even at very low flow rates. The bulk polymer seems to flow into the capillary from certain parts of the reservoir until a critical strain is reached, then snaps back, giving way for the same flow type from another part of the reservoir. The behaviour of the suspensions does not differ in this respect from that of the pure melts.A significant filler influence is, however, shown within the capillary. While unfilled polymer melts reach steady flow conditions only one or two diameters downstream of the capillary entrance, an entry pressure loss increasing with increasing filler content is found in short capillaries (l/d = 5 -15), but not in "no-land dies" (I/d < 1). This seems to indicate a flow hardening mechanism in the region where the steady laminar flow profile develops and which might result from the very high extensional strain (next to instability) in the converging flow of the capillary entrance.

Untersuchungen zum Flie�verhalten verschieden konzentrierter Polyisobutenl�sungen unter hoher Scherbeanspruchung.

“…B. von Bagley und Birks [7], Htirlimann und Knappe [8], Kleinecke [9] u.a. B. von Bagley und Birks [7], Htirlimann und Knappe [8], Kleinecke [9] u.a.…”