Effect of Flow-Induced Phase Transitions in TLCPs on the Viscosity of PE/TLCP Blends

Abstract

The incorporation of thermotropic liquid crystalline polymers (TLCPs) into engineering thermoplastics has long been known to have viscosity, ηap, reducing effects1,2. For a ηap, reduction to occur the TLCP must have a nematic transition in the same temperature range as that required for processing the thermoplastic3. For extrusion grade high density polyethylene (HDPE) this is 170–190 °C and for the more intractable high molecular mass polyethylene (HMMPE) it is 220–230 °C. Recently B.P. Chemicals Ltd has synthesized some TLCPs based on hydroxybenzoic acid, hydroquinone and sebacic acid which have nematic transitions in these ranges4. Notably, these TLCPs produce ηap, reductions in excess of 90% at very low concentrations in a polyethylene matrix, i. e. 0.2-2 wt%. For the two polymer blend systems, HDPE/TLCP1 and HMMPE/TLCP3, there are different ηap, reducing modes. For HDPE/TLCP1 blend, with the TLCP1 in the fully nematic state at 185C t here i sa clear TLCP1 c oncent ration dependent, critical shear stress, 44–100 kPa, beyond which ηap, reduction takes place5. The contribution of wall slip to the reduction was found to be insignificant