Fast flow behavior of highly entangled monodisperse polymers

A systematic experimental investigation is carried out to clarify the nature of a well-known capillary flow phenomenon in linear monodisperse polybutadienes (PBd). By varying the surface condition and the die diameter, it is alluded that a spurt-like stick-slip transition actually results from a breakdown of chain entanglement between adsorbed and next-layer unbound chains. In other words, the transition is not a manifestation of any constitutive properties, as previously asserted by Vinogradov and coworkers (1984). The melt viscosity dependence of the transition amplitude agrees with a Navier-de Gennes type analysis of wall slip. A comparison between the capillary flow and dynamic shear behavior of the same monodisperse PBd reveals that the interfacial stick-slip transition occurs at a stress level that is only a third of the plateau stress given by the elastic plateau modulus G _N ⁰=1.0 MPa at 40°C. The molecular weight independence of the critical stress for the transition provides a striking contrast with the transition characteristics observed in linear polyethylenes and suggests a different state of PBd chain adsorption on steel surfaces. Received: 2 April 1998 Accepted: 1 June 1998