Flame Retardant Thermotropic Liquid Crystal Copolyesters And Their In Situ Composites With PET

Regular structural copolyesters and random copolyesters, derived from 2-(6-oxide-6H-dibenz ( c, e ) ( 1, 2 ) oxa phosphorin-6-y))-l,4-dihydroxyphenylene, 4-hydroxybenzoic acid, terephthalic acid and isophthalic acid, were synthesized by solution polycondensation and melting polycondensation, respectively. Their structures and basic properties, such as thermal behavior, crystallinity, liquid crystallinity, thermal stability and thermal degradation kinetic were investigated by FT-IR, elemental analysis, differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), wide-angle X-ray diffractometry (WAXD), and hot-stage polarizing optical microscope. The Tg values of the copolyesters are about 190?. The Tm or flow temperatures (Tf) of the copolyesters are varied with the composition of comonomers. Relative lower flow temperatures (say, 290 ?) were obtained. The schlieren textures were observed, and banded textures appeared after a slightly shear force was exerted. The copolyesters are thermotopic and nematic. The decomposing temperatures (Td 5%) in nitrogen are about 450 ?. The average activation energy of thermal degradation is 186.7kJ/mol, and the degradation process follows FI model, i.e. random nucleation with one nucleus on the individual particle. The copolyesters possess excellent flame retardancy, and LOI is 72.The flame retardancy, isothermal crystallization behaviors, morphology and mechanical properties of PET/LCP blending systems were investigated. LCP improved the flame retardancy of PET and increased the char residues. DSC and WAXD measurements showed that LCP acts as the nucleating agents and accelerate the crystallization rate of PET. Ellipsoidal and short fibrous structures are observed by SEM in extruded strands of the blends. The tensile strength of extruded strands of the blends increased with increasing LCP content. When the LCP content is 15 weight percent, the tensile strength of the PET/LCP in situ composite, which has a LOI value of 32, increases by 1.5 times than that of PET...