Study On Preparation And Properties Of Multi-walled Carbon Nanotubes/Polyimide Composites Films

Carbon nanotubes(CNTs)are the ideal filler of composites because of their outstanding physical and chemical properties.Aromatic polyimides(PIs)are well known as functional materials with high thermal resistance and thermal stability,low dielectric constant,and excellent mechanical strength.With rapid development of modem technology and science,higher standard has been put forward about the properties of polyimides.There are more and more applications of composites base on organic polymer and inorganic nanoparticle,so preparing CNTs/PI nanocomposites materials is an effective way to improve the properties of polyimides.In this thesis,we had prepared MWNTs-s-PI and MWNTs-g-PI composites films through in situ polymerization and sol-gel polymerization,respectively.The structures of these composites were confirmed by FT-IR,UV-vis,XRD and TEM.The mechanical property,thermal property,solar absorptance and solar reflectance of these composites films were compared and discussed roundly.The main content of this thesis is listed below.1.There are some impurities such as catalysts(Fe),amorphous carbon and ash in MWNTs,which were purchased from the Nanotech Port Company.These impurities can be effectively removed by sonication in aqueous HCl solution(12 mol/L)for 2 hours.In a typical method to prepare MWNTs-COOH,MWNTs were suspended in an aqueous HNO₃ solution(2.6 mol/L)and refluxed for about 48 h.During this time,there can be attached enough carboxylic acid groups on the surface of MWNTs-COOH,and hold perfectly structure.2.MWNTs-s-PI composites films had been prepared using in situ polymerization with the starting materials of pure MWNTs,diamine monomers(ODA)and dianhydride monomers(ODPA).The resulting composites films exhibited excellent mechanical and solar absorptance properties.The tensile strengths and Young's modulus of MWNTs-s-PI composites films improved 8.8 MPa(6.8%)and 0.3 GPa(11.5%)at 0.5 wt%content compared to pure PI films' 129.2 MPa and 2.6 GPa,respectively.Also,the solar absorbabilty improved from 17%to 65%at 2 wt%content.However,the glass transition temperature of the composites films decreased from 267.5℃to 250.1℃ (decrease 17.4℃,6.5%)at 2 wt%content.3.MWNTs-g-PI composites films had been prepared using sol-gel polymerization with the starting materials of MWNTs-COOH,diamine monomers(ODA)and dianhydride monomers(ODPA).The MWNTs-g-PI composites films exhibited more excellent mechanical and solar absorptance properties than MWNTs-s-PI composites films.The tensile strengths and Young's modulus of MWNTs-s-PI composites films improved 28.4 MPa(22.4%)and 0.95 GPa(38%)at 0.5 wt%content compared to pure PI-NH₂ films' 127 MPa and 2.5 GPa,respectively.However,the mechanical strengths decreased when the content is more than 0.5 wt%.The solar absorbabilty of MWNTs-g-PI composites films improved from 17.1%to 79.9%at 2 wt%content,but the glass transition temperature of the composites films decreased from 256.1℃to 251℃(decrease 5.1℃,2 %)at 2 wt%content.