Study On The Preparation And Performance Of OZnAl-LDH/polyimide Composites Aligned By Magnetic Field

The performance of inorganic/organic nanocomposites is not only associated tothe nature of inorganic fillers, but also closely related to the existence state anddistribution of inorganic fillers in polymer matrix. When inorganic fillers and organicmatrix were identified, inorganic fillers were aligned in the polymer matrix by usingof certain technology, and then the aligned nanocomposites were obtained. In contrastto classical nanocomposites, the aligned nanocomposites possess enhanced optical,magnetic, electrical, and thermal properties. The aligned nanocomposites have thepotential applications in the areas such as magnetic recording materials, molecularseparation, biomedicine, and electromagnetic wave absorption and so on. Recent workhas mainly focused on the alignment of linear and spherical nanoparticles.Nonetheless, how to align non-magnetic lamellar materials such as layered doublehydroxides and lamellar clays remains a big challenge.In this work, under the controlling of magnetic field, magnetic LDH was alignedin the polymer matrix, and the properties of the materials were studied in detail. Thefollowing was the main contents of this work:(1) Magnetic Fe3O4nanoparticles used as magnetic partilces was coateduniformly on the lamellar of LDH modified with organic sulfonate(or sulfate) bycoprecipitation method firstly, and then the lamellar LDH with magnetic andhydrophobic properties was used as filler and composited with polyamic acid(PAA)by intercalating-in situ polymerization. Thereafter an external magnetic field wasapplied to control the alignment of magnetic OZnAl-LDH in the PAA matrix. Alignedmagnetic OZnAl-LDH/PI nanocomposites were obtained finally after imidization ofmagnetic OZnAl-LDH/PAA nanocomposites at high temperature.(2) The morphology and structures of the magnetic ZnAl-LDH, magneticOZnAl-LDH and composite films, and the orientation of magnetic OZnAl-LDH in thePI matrix were studied by the X-ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR) and so on. The characterizationdemonstrated that, the intercalated or exfoliated magnetic OZnAl-LDH could beoriented very well in the PI matrix, and the orientation of magnetic OZnAl-LDHsheets in the PI matrix could be controlled by varying the direction of magnetic field.(3) The ultraviolet-visible spectroscopy (UV-Vis), mechanical properties (tensilestrength), thermal properties (TGA) and magnetic properties (VSM) of the compositefilms were studied in detail, respectively. The study on UV-vis and mechanicalproperties of the composite films indicated that the materials shown obviousanisotropy. And the temperature at5%weight loss of the composite films was allhigher than500°C on the whole, and the films still had excellent thermal properties.But more amount of modifier inserted in the interlayer of LDH was useful forpreparation of exfoliated composites, neverthless it was not beneficial to theimprovement of thermal performance of nanocomposites. VSM results manifestedthat the composite films were superparamagnetic materials, and the films wereexpected to be applied as a soft magnetic composite materials.