Rheological and mechanical properties of semiflexible thermotropic polyesters and their blends with engineering plastics = 유연 열방성 폴리에스터 및 엔지니어링 플라스틱과의 블렌드에 과한 물성 및 유변학적 성질

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Thermotropic liquid crystalline polyesters(LCPs) were prepared by melt polymerization and they have flexible spacers inserted between mesogen units. The number of carbon units in a flexible spacer was controlled. Their thermal properties as well as mesophasic behavior were investigated by using differential scanning calorimetry and polarizing microscope. Fibers were made from pure semiflexible polyesters and their blends with engineering plastics and their mechanical properties and morphology were observed by using tensile tester, scanning electron microscopy and wide angle X-ray diffractometer. Rheological properties of nematic melts were measured with rheometrics dynamic spectrometer and capillary-tube viscometer. The thermotropic polyesters were confirmed to have a nematic phase by showing strong stir-opalescence, strong birefringent and thread-like testures. Teh molecular weights of polyesters were enough high to form high-strength and modulus fibers. SALS patterns revealed that the scattering elements of the melts had rod-like shapes. The apparent viscosity of nematic phase of LCPAL showed a dependence on the tube diameter and an yield stress in the low shear rate region called Region I. The dynamic data of homopolymer and copolymer showed that LCP melts were differ from flexible chain polymers in a sense of having a quite long relaxation time, which was estimated from viscosity and elasticity. In addition, they show the occurrence of yield stress, strain amplitude dependence of complex viscosity and the disappearance of Newtonian region in the flow curves. All of the LCPs exhibited good spinnability in nematic melt states because LCPs have sufficiently long relaxation times for the orientation of molecules and keep the orientation during fiber formation and good mechanical properties in a tensile test because of high crystallinity and orientation to the fiber axis. From the morphology of thermotropic polyester fibers, we could delineate the hierarchical s...
Chung, In-Jae정인재
한국과학기술원 : 화학공학과,
Issue Date
61329/325007 / 000845176

학위논문(박사) - 한국과학기술원 : 화학공학과, 1989.8, [ xiv, 247 p. ]

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