BLENDS OF THERMOTROPIC LIQUID-CRYSTALLINE POLYESTERS AND POLY(BUTYLENE TEREPHTHALATE) - THERMAL, MECHANICAL, AND MORPHOLOGICAL PROPERTIES

Blends of poly(butylene terephthalate) (PBT) with three different thermotropic liquid crystalline polyesters (TLCPs) were prepared. The first TLCP (HBH-6) consists of diad aromatic ester type mesogenic units and the hexamethylene spacers along the main chain, and the second (TB-S6) is a wholly aromatic polyester TLCP having alkoxy side groups on the terephthaloyl moiety. The last (TR-4,6) is an LC copolymer consisting of triad aromatic ester type mesogenic units and two different spacers; tetramethylene and hexamethylene units. Blends of TLCP with PET were melt spun at different LCP contents and different draw ratios to produce monofilaments. For the HBH-6/PBT and TB-S6/PBT blends, the ultimate tensile strength showed a maximum value at the 5 wt% level of LCP in the blends, and then it decreased when the LCP content was increased up to 20%. On the other hand, the initial modulus monotonically increased with increasing LCP content in all cases. The blends with TB-S6 showed the highest tensile properties of the three blend systems. This can be ascribed to the highest rigidity of the polymer chain, which still carries relatively long alkoxy substituents that promote sufficient adhesion between the LCP and PET matrix. When compared with the PET fiber itself, the fibers obtained from the 5% TB-S6/PBT blend exhibited an improvement in tensile strength by > 250% and in tensile modulus by similar to 200%.