Rheology and miscibility of thermotropic liquid crystalline polymer blends

Steady and dynamic rheological properties of a thermotropic liquid crystall ine polymer (TLCP), HIQ45, its blend with a polycarbonate (PC) and with ano ther TLCP (Vectra A950) are presented in this work. Due to the biphasic nat ure of HIQ45, both complex and steady shear viscosities increase with tempe rature after 350 degrees C. According to a three-zone model, the dynamic rh eological behaviour of HIQ45 is assigned to terminal and plateau zones. Rel axation times derived from the crossover frequencies of G' and G " decrease with temperature and show a sharp reduction between 320 degrees C and 340 degrees C. Dynamic rheology of PC shows terminal zone characteristics, and its blends with HIQ45 display PC-dominant dynamic behaviour. These blends w ere found to be miscible, which is unusual for blends of a TLCP and a therm oplastic. The Cox-Merz rule is followed by PC and HIQ45, but not by the ble nds. HIQ45 and Vectra A950 form a miscible blend system and its dynamic beh aviour, both in the solid state and molten state, is dominated by HIQ45 com ponent. The Cox-Merz rule is not obeyed by Vectra A950 but is for blends wi th HIQ45. Under steady shear, the blends show a strong negative deviation f rom the existing models proposed for miscible and immiscible blends. This e nhanced synergistic flow behaviour is explained in terms of enhanced alignm ent and lubrication of the TLCPs on a molecular level. (C) 1999 Elsevier Sc ience B.V. All rights reserved.