Measurements of first and second normal stress differences in a polymer melt

A study of the first and second normal stress differences was made in order to determine the properties for an LDPE melt at high shear rates. Time dependent measurements of N-1 and N-2 were carried out using cone/plate and plate/plate rheometry, in order to extend the shear rate for rotational rheometry up to 120 s(-1). Measurements utilizing the pressure hole method extended the shear rate range to approximately 1000 s(-1). For N-1 there is an overlap in the data, that is within the experimental error, for N-2 the data is inconsistent in behaviour. Both N-1 and N-2 initially demonstrated a power law behaviour, but converged to a plateau at high shear rates. This behaviour is believed to be a true response of an oriented polymer network and not slip. (c) 2007 Elsevier B.V. All rights reserved.