Mechanical Properties of Liquid Crystal Polymer Fibres
Doctoral thesis, 1992
Fibres of thermotropic liquid crystalline polymers (LCP) and its blends containing a random coil polymer LCP have been spun at low draw ratio at different temperatures and shear rates. Their mechanical properties have been studied in detail.
Fibres of the copolymer hydroxybenzoic acid/hydroxynaphthoic acid (HBA/HNA) obtained high strength and initial modulus with a capillary diameter of 0.161 mm at high shear rates and low draw ratio. The mechanical properties were approximately identical at higher shear rates. The properties are affected by the draw ratio only at lower shear rates. Highest shear rates do not affect the properties but lower shear rates influence the properties negatively.
Mechanical properties of fibres spun from polyethylene terephthalate/hydroxybenzoic acid (PET/HBA) with 60 mole percent HBA and inherent viscosity (I.V.) of 0.7 and 1.04 and PET/80HBA have been compared. The initial modulus is almost equal for the three polymers. PET/60HBA with I.V. 1.04 has the highest strength; considerably higher than PET/60HBA with I.V. 0.7. Elongation at break is highest for PET/60HBA I.V. 1.04; about 3 percent compared to about 1.3 percent of the other two polymers. Decrease of I.V. for PET/60HBA I.V. 1.04 due to thermal degradation is also discussed.
PET/HBA with the flexible segments in its chain has significantly lower mechanical properties than HBA/HNA.
HBA/HNA has been mixed with a random coil copolyester at 10, 20, 30 and 50 percent HBA/HNA. Strength and modulus follow the rule of mixture. After mixing the polymers the matrix polymer showed lower viscosity than the mother LCP and in spite of this, fibres of LCP were developed.
copolymer hydroxybenzoic acid
thermotropic liquid crystalline polymers