Self-reinforced composites of polyesters and PET/HBA based LCP (poly(ethylene terepthalate), liquid crystal polymers).

摘要

Unidirectional sheets and fibers of blends of polyesters (PET, PBT, PEN, and copolyester) and LCP based on poly(ethylene terephthalate)/p-hydroxy benzoic acid, PET/HBA were prepared by using a single screw extruder with a static mixer followed by a die. Various operating conditions such as die geometry, die temperature, LCP content, extension ratio, screw speed, and die gap in extrusion were used to find optimum processing conditions required for improvement of mechanical properties of the blends. It was found that the main factors affecting tensile strength and Young's modulus of the polyester/LCP composite blends were the die temperature, LCP content, and extension ratio. These findings correlate well with the degree of micro fibrillation of the LCP phase in the thermoplastic matrix as shown by observation using scanning electron microscopy. Depending on matrix and processing conditions, blends revealed different LCP domain deformation, size, shape, and, consequently, mechanical properties. Among four different polyesters, PET matrix was the most efficient in obtaining uniform LCP phase distribution and large deformation in blends, which led to nanocomposites of PET/LCP blends. However, the blends based on the copolyester matrix showed the best mechanical properties with the addition of LCP phase. Also, the rheological study of pure materials was performed to find the viscosity ratio dependence of components and its relevance to microfibrillation. The mechanical properties and morphology of injection molded bars made by reprocessing fibers at the melt temperature below the LCP melting point were investigated and compared with properties of the original fibers. The latter allowed the author to shed light on the possibility of sustaining LCP microfibrils during the second stage of operation. Among various blends, the LCP fibrils preexisting in PEN/LCP fibers were best preserved in moldings. The addition of the LDPE-based compatibilizer to the injection molding of PET/LCP blend revealed little increase in tensile strength and modulus. The simulation of LCP droplet deformation during fiber spinning of 60/40 PET/LCP and 60/40 PBT/LCP blends revealed a well matched diameter of LCP droplets with experimental results.