Shear induced phase transitions within TLCPs and their effects on the viscosity of PE/TLCP blends

Blending of thermotropic liquid crystalline polymers (TLCPs) with commercial thermoplastics has long been known to lead to viscosity reductions, as well as improved mechanical and barrier properties of the final blend product over the pure homopolymer. The improved processability brought about by the inclusion of TLCPs is beneficial in a number of ways: (i) the power requirements for extrusion are lowered; (ii) hier processing rates are possible; (iii) using TLCPs as reinforcers reduces wear and abrasion processing equipment in comparison with glass fiber reinforcers; and (iv) homopolymers normally processed at temperatures high enough to initiate degradation may be processed at lower, less harmful temperatures. Cogswell et al. were the first to state that for improved melt processing, the TLCP should be in an anisotropic state over the temperature range as the homopolymer is melt processable. However since most commercial TLCPs exhibit nematic phase at temperatures at 300 ℃ or above, due to their wholly aromatic nature, they are not applicable to enhance the processability of molten polyethylene. The present work seeks to demonstrate that: firstly, viscosity reductions in excess of 90 % can be brought about by the addition of a very small amount of TLCP. Secondly, the viscosity reduction can only be achieved when the TLCP is in the nematic phase. Flow induced phase transition into nematic phase is necessary when the TLCP is not in its nematic phase in the quiescent state; and, thirdly, wall slip is negligible for blends containing TLCPs