LLDPE/POE Matrix Composites With Photocatalytic And Microwave Absorbing Properties

The thesis reported preparation and characterizationof low density polyethylene (LLDPE)/ethylene- octene copolymer (POE) matrix composites with photocatalytic and microwave absorbing properties.Using tetrabutyl titanate as the precursor of titanium, visible-light-driven titania photocatalysts co-doped with boron and nitrogen, with boron and ferrum and cerium, and titania/silica photocatalysts co-doped with boron and ferrum were prepared by sol-gel routes, in which boric acid and ammonium fluoride, boric acid and ferric nitrate and cerium nitrate, and boric acid and ferric nitrate and ethyl silicate were the sources of dopants, respectively. The prepared photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffusive reflectance spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption-desorption isotherm and scanning electron microscopy (SEM). The decomposition of phenol or 2, 4-dichlorophenol under visible light irradiation was used as probe reaction to evaluate their photocatalytic activities, which were compared with the photoactivity of merchandise titania P25. The results show that the doping can retard the transformation from anatase to rutile at elevated temperatures, that nonmetal boron and nitrogen atoms or boron atoms are weaved into the crystal lattice of titania, resulting in the decreases of band gap, red-shift and visible-light-driven photoactivity, whereas ferrum and cerium atoms or ferrum atoms present in the forms of FeO/Fe₂O₃ and Ce₂O₃/CeO₂ or FeO/Fe₂O₃ and disperse in TiO₂, which can prohibit recombination of the photo-generated electrons and holes, increasing photo quantum efficiency and improving the photoactivity, and there are intimate molecule-level interactions between titania and silica, which are in favor of the preparing the photocatalysts with big surface area. The synergistic effects of co-doping are responsible for the visible light response and high photoactivity.Using microporous film prepared from LLDPE/POE/CaCO₃ as substrate, titania film with photocatalytic property was prepared by dipping. The morphologies were observed by SEM. Degradation of formaldehyde under ultraviolet radiation or visible illumination was used to evaluate the photoactivity of photocatalytic films. The results show that the photocatalytic property of P25 film under ultraviolet radiation is superior slightly to that of boron-nitrogen co-doped titania film, whereas the photocatalytic property of boron-nitrogen co-doped titania film under visible illumination is obviously higher than that of P25 film.Polymer matrix microwave absorbing composites were prepared by melt blend using LLDPE and POE as matrix, and carbonyl iron powder (CIP), short carbon fiber (SCF), multi-walled carbon nanobute (MWCNT) and carbon black (CB) as absorbents, respectively. The absorbing properties and electromagnetic parameters of microwave absorbing composites were measured by a scalar network analyzer and a vector network analyzer, respectively. The microwave absorption mechanisms of composites prepared with different absorbents were discussed. The morphologies were observed by SEM and TEM. The results show that the absorbing peak moves to the low frequency as absorbent content in composites increases when absorbent and thickness of composites are fixed, that there is the corresponding optimum content of absorbent in order to gain the best absorbing effectiveness. The microwave absorption can be attributed to a combining contribution of the dielectric loss and magnetic loss for LLDPE/POE/CIP composites, and the dielectric loss for LLDPE/POE/SCF,LLDPE/POE/MWCNT,LLDPE/POE/CB andLLDPE/POE/CB/CaCO₃ composites. The absorbents and filler (CaCO₃) are well dispersed in polymer matrix, demonstrating that LLDPE/POE matrix composites can be fabricated by melt blending. The simulation calculation show that the absorbing peak moves to the low frequency as thickness of composites increases when absorbent and content of absorbent in composites are fixed.