Dielectric on-line spectroscopy during extrusion of polymer blends

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.