Study On PET/MMT Nanocomposites With High Molecular Weight And Its Fiber

In this thesis, the PET/montmorillonite(MMT) nanocomposites and pure PET with high molecular weight were prepared by solid state polycondensation(SSP) so as to meet the needs of industrial fiber. The fiber was spun and drawn in proper conditions.The microstructure of PET/MMT nanocomposites was studied. The intercalate, exfoliate and dispersing status action of montmorillonite in PET phase were investigated by X-ray diffraction(XRD), transmission electron microscope(TEM) and scanning probe microscope(SPM). For the first time, the shape of lamellar montmorillonite in PET matrix was observed by the method of SPM, which is more intuitionistic compared with the method of XRD and TEM.The effect of montmorillonite on SSP of PET was investigated by using the methods of the viscosity. The result shows that the montmorillonite nanomaterials can greatly increase the rate of SSP of PET. This has an important meaning to the industrial manufacture.DSC, WAXD and polarizing microscope with hot stage experiments were performed to describe what led the SSP rate acceleration of PET/MMT. It was shown that montmorillonite acted as a very good nucleating agent in PET crystallization process, which results in the lower crystallinity, more small microlites, and more surfaces of microlites. These microlites and richer amorphous region will benefit the polycondensation reaction of PET, the diffusion of volatile by-products, and the approach of the end-groups of PET molecular chains by forming more routeways, which may result in the higher rate of SSP. Both time and temperature of SSP could make the crystalline structure perfection.The influence of montmorillonite and various drawing temperature on the physical and mechanical properties of PET fiber were investigated. The result showedthat the thermal stability of fiber could be improved with drawing temperature increased from 160℃ to 180℃. However, the mechanical properties and orientation of fiber changed little. Montmorillonite could also improve the thermal stability of microstructure in PET fiber. We suggest that the strong coherence of the interfaces between montmorillonite microparticles and PET restricts the motions of PET molecular chains, developing "the special continuous network structure" and effectively prohibiting the thermal shrinkage of PET fiber. The modulus and strength of PET/MMT fiber were lower than those of pure PET fiber. This is probably because the lamellar montmorillonite does not disperse randomly and completely, and besides, the spinning and drawing process in our research is limited to make the montmorillonite layers better oriented along the fiber. PET/MMT fiber is a kind of potential tyre cord with high modulus and low thermal shrinkage.The pyrolysis products of fiber were analyzed by PGC-MS. It showed that the content of CO2 in the pyrolysis products of PET/MMT fiber was relatively higher than that of pure PET fiber, while the content of flammable hydrocarbon was lower, which maybe result in the flame resistance of PET/MMT fiber.