Study On Preparation And Properties Of Polyimide Nanocomposites Reinforced By Functionalized Graphene Nanosheets

Polyimide（PI） materials are widely used in heat resistant plastic, integrated circuit, gas separation membrane, aerospace and other fields because of their high resistance to temperature, high insulation, excellent mechanical properties, and so on. However, The low properties of pure PI can not meet the requirements. By incorporating modified fillers into polyimide matrices, which can achieve an effective combination at the nanoscale, lead to enhancing thermal, mechanical properties and electrical conductivity of the nanocomposites. Graphene is one of the common reinforced nanofillers, but it easy to agglomerate in matrices because of its strong interaction between layers. Graphene oxide（GO） covalently bonded a large number of oxygen functional groups on the surface, which provides a lot of reaction sites for the surface functionalization on the GO. Hence, Surface modification on the GO by covalent modification can lead to a good compatibility between GO and matrices. Both the homogeneous dispersion and strong interfacial interaction between the graphene oxide and polymer matrix are essential for achieving the high performance polyimide nanocomposite materials. In this thesis, series of functionalized graphene oxide/polyimide composites were prepared by in situ polymerization and thermal imidization. The morphologies and structure of nanofillers, properties of the polyimide composites were characterized and extensively studied, The main research works in three aspects were carried out:（1） Functionalized graphene oxide（FGO） nanosheets was prepared by GO modified with cyclohexyl isocyanate（CI）, and the nanosheets showed good dispersibility within matrices. The adding of FGO greatly affected the macroscopic properties of the PI composites. The tensile strength and tensile modulus of composites enhanced 56.5% and 43.8% with 2.0 wt% FGO. In addition, the thermal stability and hydrophobic properties of the PI nanocomposite distinctly increased due to the incorprating of FGO.（2） A series of polyimide nanocomposites were prepared by incorporating various loading content of octadecylamine（ODA） functionalized graphene nanosheets（ODA-fGO）. Due to the homogeneous dispersion of ODA-fGO and strong interaction between ODA-fGO and PI, the obtained nanocomposites showed improvement effects of mechanical properties, electrical and thermal conductivity. Compared with PI, the tensile strength of composites enhenced 30.58 MPa, and tensile modulus improved 1.54 GPa, the electrical and thermal conductivity increased 1011 times and 3 times by incorporating 3 wt% ODA-fGO.（3） Amino groups functionalized graphene oxide（GO-NH₂） were obtained through covalent functionalization on surface of GO with p-phenylenediamine, which can be uniformly dispersed in the matrix because of the change of GO surface properties. Strong interface interaction was generated through covalently bonded between the amino of modified GO-NH₂ and PAA matrices, which greatly reinforced the mechanical properties, heat resistance and hydrophobic properties of composites（PI/GO-NH₂）. In comparison with PI, the tensile modulus and tensile strength of PI/3% GO-NH₂ nanocomposites improved by 63% and 54.5%, respectively. Contact angle increased 20° than, and the heat-resistance propertie of composites was enhanced obviously. Moreover, PI/3% GO-NH₂ composites showed more excellent comprehensive properties than PI/3% GO.