Dielectric spectroscopy is a technique which is still hardly used for on-li
ne characterization of polymers. in this article we describe its use at med
ium frequencies (between 10 Hz and 1 MHz) for on-line monitoring of the mor
phology of polymer blends during extrusion. A sheet extrusion die containin
g two electrodes, made it possible to perform the dielectric on-line analys
is.
A blend of a thermotropic Liquid Crystalline Polymer (LCP) dispersed in pol
ypropylene was used to follow the change in shape and co-continuity of the
LCP phase with increasing extrusion speed. The creation of a more fibrous s
tructure at higher shear rates was demonstrated by the dielectric technique
as well as by SEM analysis.
A blend of a thermotropic liquid crystalline polymer dispersed in polystyre
ne was chosen to study the evolution of the size of the LCP inclusions with
increasing extruder speed. The Bottcher-Trukhan relation enabled us to con
vert the dielectric data to values of the particle size and a decrease in s
ize with increasing shear rate was found. This was confirmed by SEM microgr
aphs.
The experiments and analysis presented in this article show that dielectric
spectroscopy proves to be a valuable tool for on-line characterization of
the microstructure of polymer blends. (C) 1999 Elsevier Science Ltd. All ri
ghts reserved.