Rheology and miscibility of thermotropic liquid crystalline polymer blends

Abstract

Steady and dynamic rheological properties of a thermotropic liquid crystalline polymer (TLCP), HIQ45, its blend with a polycarbonate (PC) and with another TLCP (Vectra A950) are presented in this work. Due to the biphasic nature of HIQ45, both complex and steady shear viscosities increase with temperature after 350°C. According to a three-zone model, the dynamic rheological behaviour of HIQ45 is assigned to terminal and plateau zones. Relaxation times derived from the crossover frequencies of G′ and G″ decrease with temperature and show a sharp reduction between 320°C and 340°C. Dynamic rheology of PC shows terminal zone characteristics, and its blends with HIQ45 display PC-dominant dynamic behaviour. These blends were found to be miscible, which is unusual for blends of a TLCP and a thermoplastic. The Cox-Merz rule is followed by PC and HIQ45, but not by the blends. HIQ45 and Vectra A950 form a miscible blend system and its dynamic behaviour, both in the solid state and molten state, is dominated by HIQ45 component. The Cox-Merz rule is not obeyed by Vectra A950 but is for blends with HIQ45. Under steady shear, the blends show a strong negative deviation from the existing models proposed for miscible and immiscible blends. This enhanced synergistic flow behaviour is explained in terms of enhanced alignment and lubrication of the TLCPs on a molecular level.