| In this thesis, series of Polyimide/organic montmorillonite(PI/OMMT) composites, Polyimide/carbon nanotube(PI/CNT) composites, Polyimide/graphite C3N4(PI/g-C3N4) composites and Polyimide/lead salt of p-Aminobenzoic acid composites(PI/ABA(Pb)) were synthesized. Application of them in shielding was also researched. Structures of these composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance spectroscopy (1H-NMR), elemental analysis and X-ray diffraction analysis (XRD), while their morphology analysis were conducted by scanning electron microscope (SEM). Furthermore, thermal stability of these composites were researched by thermogravimetric analysis (TGA), while mechanical properties of part of composites were characterized by tensile stress test and compression stress test. Last but not least, y-ray spectrometry are used to investigate radiation-proof property of these composites materials.The main research work consists of the following four parts:1) A series of PI/OMMT composites with different content of nano clay were prepared by in-situ intercalation and two step polycondensation.Organic montmorillonite was intercalated into polyimide which formed by polycondensation of ODA and PMDA. Two kinds of molding powder with different sizes were prepared by ball milling and automatic grinder, then the materials were shaped by mould pressing. The experimental results show that:the smaller the particle size and the higher the content of nano clay, the better the shielding effect of materials performed.2) A series of PI/CNT composites with different content of nanotube were prepared by in-situ intercalation and two step polycondensation. Amino carbon nanotubes were linked into polyimide which formed by polycondensation of ODA and PMDA. Molding powder was prepared by ball milling, then the materials were shaped by mould pressing. The experimental results show that carbon nanotubes bonding into polyimide led to the formation of cross-linked structure, which enhanced the effect of radiation shielding material.3) A series of PI/g-C3N4 composites with different content of g-C3N4 were prepared by in-situ compounding and two step polycondensation, g-C3N4 was blended into polyimide which formed by polycondensation of ODA and PMDA. Molding powder was prepared by ball milling, then the materials were shaped by mould pressing. The experimental results show that introduction of g-C3N4 did not change the molecular weight of polyimide significantly, while increased the radiation shielding effect of composites, but the dispersion of g-C3N4 cannot reach the high content.4) A series of PI/ABA(Pb) composites with different content of lead ion were prepared by in-situ two step polycondensation, the two amine monomer lead p-aminobenzoic acetate (ABA(Pb)) was synthesized via ion exchange method and acid-base neutralization method. Polyimide (PI(Pb)) were prepared by a two-step polycondensation approach, starting with ABA(Pb) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) as the diamine monomers, as well as 2,2-bis[4-(3,4-dicarlxyphenoxy)phenyl]propane dianhydride (BPADA) as the dianhydride monomer. The lead ion was introduced into main chain of polyimide, so that Pb element reached the dispersion degree which physical mixture methed cannot realized. Shielding effect of PI/ABA(Pb) composites is superior to pure PI and PI-Pb(NO3)2 which possessing the same lead content. Furthermore, PI(Pb) composites having good thermal stability and mechanical properties.The innovation of this paper lies in:1) Providing various novel polyimide composite materials, expanding their application in radiation shielding field; 2) Exploring the effect of particle size of mould powder on the performance of radiation shielding; 3) Increasing the degree of dispersion of Pb in radiation shielding materials, improving the shielding performance of composite materials based on the traditional radiation element; 4) Geting rid of the use of heavy metals such as lead, in almost of these composites, making meaningful exploration for the development of no pollution, non-toxicmaterial radiation shielding materials. |
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