Study on the melt fracture of metallocene poly(ethylene‐octene) in capillary flow

Abstract

Shear viscosity and melt fracture of a metallocene poly(ethylene-octene) were studied using a capillary rheometer and dies with different lengths. The true wall shear stresses determined at zero die length showed a dip at high shear rates. The shear viscosity was derived from the true wall shear stress. With increasing shear rates, the extrudate staged from smooth to three types of melt fracture with regular patterns, and then turned into irregular shapes. Three types of regular melt fractures-sharkskin, helix, and spiral (in sequence)-were observed with an increase of the shear rates. The wavelength of the regular melt fracture was measured from extrudates, and the corresponding frequency was calculated. The frequency increased at elevated melt temperatures. Both shear viscosity and frequency at different temperatures correlated well by using the timetemperature Williams-Landel-Ferry (WLF) superposition. Additionally, it was found that the frequency decreased slightly for a longer die but it increased when the shear rate went up. Three frequency functions were associated with three melt fracture patterns, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: [903][904][905][906][907][908][909][910][911] 2005

Effect of short‐chain branching on melt fracture behavior of metallocene and conventional poly(ethylene/α‐olefin) copolymers

“…Moreover, recent development of metallocene catalyst technology makes it possible to produce a tailored ethylene/α‐olefin copolymer at a commercial scale. Since metallocene polymers have a narrower molecular weight distribution (MWD) compared with conventional polyolefins obtained by Ziegler‐Natta catalyst, flow instabilities often take place early and limit the production speed [15–17].…”