Fibers spun from poly(ethylene terephthalate) blended with a thermotropic liquid crystalline copolyester with non-coplanar biphenylene units

To investigate the potential of a fully aromatic, amorphous thermotropic liquid crystalline polyester (CPHNA60) as the in situ reinforcement component for poly(ethylene terephthalate) (PET) fibers, blends containing up to 10 wt% of CPHNA60 were prepared, characterized and spun into fibers. DSC measurements of the blends revealed a nucleating effect of CPHNA60 and rheology investigations showed a decreased melt viscosity even at 0.5 wt% CPHNA60 content. Blend fibers were spun at temperatures between 270 and 290°C and successively cold and hot drawn. As-spun fibers showed an increase in Youngʹs modulus with increasing CPHNA60 content to 5.8 GPa at 10 wt%. After a two stage drawing process, moduli up to 22.6 GPa at 3 wt% load level were measured while maintaining ultimate strength values around 1 GPa. This correlates to an increase in modulus of 22%. SEM experiments of as-spun fiber fracture surfaces showed uniformly dispersed CPHNA60 fibrils within the PET matrix with aspect ratios around L/D=25.