Study On The Struction And Properties Of Multi-walled Carbon Nanotube/bismaleimide Composites

This thesis focuses on the preparation and characterization of multi-walled carbon nanotubes (MWNTs)/bismaleimide (BMI) composites.Three different kinds of diamide (1,2-diaminoethane(DME), 1,10-diaminodecane(DMD) and 4,4'-diaminodiphenylmethane (DDM) were grafted onto multi-walled carbon nanotubes (MWNTs) via acid-thionyl chloride route, respectively , and the corresponding functionalized MWNTs were coded as DME-MWNTs, DMD-MWNTs, and DDM-MWNTs/BMI, respectively. These functionalized MWNTs were characterized by Fourier transform infrared spectrum(FTIR), Raman spectrum, transmission electron microscopy (TEM), Element analysis(EA), Energy Dispersive X-ray Analysis (EDAX) and scanning electron microscopy(SEM), etc. The results indicate that acidification of MWNTs can get ride of impurity and cut MWNTs into small size. Moreover, diamine can easily covalently bonded on the surface of MWNTs after activated by thionyl chloride.Two processing methods were used to prepare MWNTs/BMI composites, and the the dependence of processing methods on the properties of the composites were studied. Results showed that comparing with composites made by solution process, the composites by melting process have better mechanical properties. Therefore, the melting process is a better method to prepare MWNTs/BMI composites.The dependence of the surface properties and content of MWNTs on mechanical properties of MWNTs/BMI composites is studied. Results showed that the surface properties of MWNTs determine their dispersity in the matrix of composites, and thereby affecting the properties of composites. The addition of MWNTs as received (p-MWNTs) exhibits a negative effect on the mechanical of BMI resin within the range of p-MWNTs content used in this study because of their large scale of aggregation in the matrix. While amdio-MWNTs have functionalized group in the surface, so they have better dispersity in the matrix. Note that there has a optimum content of DME-MWNTs to obtain optimum impact strength of DME-MWNTs /BMIcomposites. The addition of too much DME-MWNTs tends to lead their poor dispersity in BMI matrix and thus resulting in very poor impact strength of composites, which is lower than that of pure BMI resin.The effect of structure of diamines used to prepare functionalized MWNTs on the impact strength of MWNTs/BMI composites is investigated. Comparing the impact strength of composites with the same content of functionalized MWNTs, they have following order: DME-MWNTs/BMI> DMD-MWNTs/BMI> BMI> DDM-MWNTs/BMI..The dependence of the nature and content of MWNTs on dynamic mechical properties of MWNTs/BMI composites have been studied. Within the whole range of test temperature, the stortage modulus of DME-MWNTs/BMI composite is lower than that of pure BMI resin, while the DMA curves of DME-MWNTs/BMI composite and DMD-MWNTs/BMI composite are quite similar.TGA analyses show that DME-MWNTs/BMI composite has better thermal stability than BMI resin within the temperature range from room temperature to 500°C, and the maximum thermal degradation temperature of DME-MWNTs/BMI composite is 12°C higher than that of pure BMI resin, while the thermal stability the former is slightly lower than that of the later when the temperature above 500°C. In addition, the degradation activation energy (Ea) were calculated by both Friedman non-isothermal and isothermal methods, results shows that the Ea values ofcomposites were lower than that of BMI resin.