Synthesis And Properties Of Thermotropic Liquid Crystalline Copolyester/Graphene Oxide Composite

Thermotropic liquid crystalline copolyester(TLCP) is a kind of polymer which can exhibit liquid crystalline state at the temperature above its phase transition temperature. Due to its excellent mechanical properties, good thermal stability and superior melt processing property,TLCP has attracted a great deal of interest in the field ranging from scientific to industrial. In order to improve properties of TLCP, researchers have tried many methods. For example, many researchers have done lots of work on the modification of TLCP with nano particles. The thermal stability and mechanical properties of TLCP can be improved by the modification of nano particles, which is important for extending the application domains of TLCP.In this thesis, a kind of TLCP with good properties was obtained by changing catalysts. Then the obtained TLCP was modified by graphene oxide(GO), and the influence of GO on the structure and properties of TLCP was studied. At last, TLCP/GO composite fibers were melt-spun and their morphology and mechanical properties were studied. Specific studies as follows:In this thesis, a series of TLCPs catalyzed by calcium, magnesium and zinc acetate,respectively, were synthesized via “two step method” melt polymerization using4-Hydroxybenzoic acid(HBA) and 6-hydroxy-2-naphthoic acid(HNA) as monomers. Within the three TLCPs, TLCP catalyzed by zinc acetate exhibited high onset degradation temperature,excellent mechanical properties and superior melt flow property. Therefore, TLCP catalyzed by zinc acetate can be used as matrix and its properties can be improved by the modification of nano particles.The surface of GO contains a large number of oxygen containing groups, so GO can be well dispersed in the polymer matrix, and GO showed great potential in the modification of polymers.In order to improve the properties of TLCP, GO was used. In this thesis, a series of TLCP/GO composites with different content of GO were synthesized via in-situ melt polymerization and their structure and properties were studied in detail. The results showed that GO can efficiently improve the degradation temperature of TLCP. Compared to pure TLCP, the onset degradation temperature and the temperature at highest degradation velocity of TLCP/GO composite with0.1wt% GO were increased by 4.4 and 9.4oC, respectively. Moreover, TLCP/GO composites exhibited obvious nematic liquid crystalline texture and good melt flow property when the content of GO was not more than 0.1wt%, this showed that composite materials had good processing properties..Fiber is an important application field of TLCP. In this thesis, a series of TLCP/GO composite fibers with different content of GO were melt-spun and their morphology and mechanical properties were studied in detail. SEM images showed that the surface of fibers was smooth when the content of GO was not more than 0.1wt%. The fibrillar structure was obvious from SEM images of the tearing areas and cross sections and there were no evidence of the agglomeration of GO in cross sections. Two dimension X-ray diffraction(2D-XRD) test results of fibers showed that the degree of orientation of molecular chain in the crystalline region gradually decreased with the increase of the content of GO. The mechanical properties of TLCP fiber can be improved when composed with GO. Compared to pure TLCP fiber, the tensile strength, elongation at break and fracture energy of composite fiber with 0.1wt% GO increased by 29.6, 60.0 and107.4%, respectively.