Measurements of flow-induced orientation and crystallization have been
made on a high-density polyethylene melt (HDPE) undergoing a planar e
xtensional flow in a four-roll mill. The HDPE was suspended as a cylin
drical droplet at the flow stagnation point in a linear low density po
lyethylene (LLDPE) carrier phase. Deformation and crystallization of t
he HDPE droplet phase were monitored using video imaging in conjunctio
n with measurement of the birefringence and dichroism to quantify the
in-situ transformation kinetics. Planar deformation rates along the sy
mmetry axis of the molten HDPE phase were on the order of 0.03 s-1. Me
asurements of the initial transformation rate following flow cessation
at 131.5-degrees-C and 133.2-degrees-C show a dependence on initial a
morphous phase orientation and the total Hencky strain achieved during
flow. The flow-induced crystallization rate is enhanced over the quie
scent transformation rate by orders of magnitude, however, the depende
nce on temperature is less dramatic than expected for a nucleation-con
trolled growth mechanism. Analysis demonstrates that the melting point
elevation model cannot account either qualitatively or quantitatively
for the phenomena observed, suggesting that alternative explanations
for the strong orientation dependence of the transformation rate are n
eeded.