Abstract
The supercooling behavior of three thermotropic liquid crystalline polymers (TLCP's), 60 mole% p‐hydroxybenzoic acid and 40 mole% poly(ethyleneterephthalate), 60/40 PHB/PET, 80 mole% p‐hydroxybenzoic acid and 20 mole% poly(ethyleneterephthalate), 80/20 PHB/PET and a copolyester of 73 mole% p‐hydroxybenzoic acid and 27 mole% of 2‐hydroxy‐6‐naphthoic acid, Vectra A900, was studied by means of both rheological and thermal methods. 60/40 PHB/PET and Vectra A900 exhibited a degree of supercooling as high as 80°C while there was only 20°C of supercooling for 80/20 PHB/PET. The degree of supercooling for the blends of 60/40 PHB/PET and 80/20 PHB/PET also decreased with the increase in 80/20 PHB/PET content. The increase in G′ as the temperature decreased was more gradual for 60/40 PHB/PET and Vectra A900 than that for 80/20 PHB/PET, which was beneficial from a processing point of view. The solidification of the LCP melt was attributed to both the crystallization and the freezing of the mesophase. The degree of crystallinity for all three TLCP's was very small, less than 5%, as measured by the DSC. It was found that both 60/40 PHB/PET and Vectra A900 showed an induction period of a few minutes during solidification while 80/20 PHB/PET solidified continuously at the test temperature. Therefore, 60/40 PHB/PET and Vectra A900 seem to be more suitable for use in processes such as blow molding and film blowing than 80/20 PHB/PET.