Edinburgh Napier University

  Capillary breakup extensional rheometry
of semi-dilute hydroxyethyl cellulose (HEC) solutions
was performed under several step-stretch conditions.
The resulting parameters, i.e. terminal steady state
extensional viscosity (gE) and the timescale for
viscoelastic stress growth, commonly referred to as
the extensional relaxation time (kE) were found to be
sensitive to the step-stretch conditions. The kE
decreased with increasing step-strain as opposed to
the gE. Prior to the filament break-up, a ‘bead-onstring’
instability was observed close to the mid-plane.
It is believed that this instability originated from the
accumulation of viscoelastic stresses near the filament
neck leading to the ‘elastic recoil’ of the extended
polymer chains. The reasons for this belief are
discussed in detail with the perspective of the past
literature. Such type of flow instability has been
reported for the first time for a cellulosic system.
Various dimensionless numbers were plotted for the
HEC solutions and compared with those obtained from
past studies for various biopolymers as well as
synthetic polymers.