Research On Functionaliztion Of Multi-walled Carbon Nanotubes And Poly(Aryl Ether Nitrile) Composites

Poly(aryl ether nitrile)s are a well known class of engineering thermoplastics.Owing to their outstanding chemical properties (radiation resistance, low flammabilityand toxic gas emission), very good mechanical properties, high heat resistance, highthermal stability, and good molding workability, PEN can find their potentialapplications in aerospace, military and electronic areas. In a long term, the high cost ofproduction and poor processibility of PEN are the main problems that limit theirapplications in engineering thermoplastics. In our previous works, we have exploredlow-cost PEN copolymers with different structures which can satisfy different demands.Also, the phthalonitrile prepolymer is used (BPH) as plasticizer to improve theprocessibility of the PEN. Besides, the application of engineering thermoplastics issignificantly depended on the mechanical properties, electronic properties and thermalstability. Therefore, to expand their applications such as in aerospace and electronicareas, many researchers try to obtain the PEN with high performance by modification,thus becoming a type of multifunctional engineering materials.Carbon nanotubes(CNTs) are viewed as one-dimension materials and haveattracted much attention both from scientific and industrial interests due to theirexcellent chemical and physical properties such as high strength, high aspect ratio andlight quality. The incorporation of small amount of carbon nanotubes into the polymermatrix is founded to significantly influence mechanical properties, thermal properties,barrier properties, crystallization behaviors, rheological behaviors, dimensional stabilityand flame retardance. Thus polymer/carbon nanotubes nanocomposites have drawngreat attention from the academia and industry. The poor dispersion of carbonnanotubes and the poor interfacial interaction between carbon nanotubes and polymermatrix greatly affect the physical properties of polymer/carbon nanotubes composites.However, surface functionalization of CNTs is an effective way to solve these problems.In this dissertation, different kinds of functionalized multi-walled carbonnanotubes(MWCNTs) were prepared and then compounded with poly(aryl ether nitrile)resin to produce MWCNTs/PEN composites. The structure, shape, surface propertiesand dispersion morphology will affect the mechanical properties, rheological behaviors,dielectric properties and thermal stability, and further affect processing and application of the polymer materials. In this dissertation, the relationship between structure andproperties of polymer nanocomposites was discussed. The effect of structure,morphology, surface properties and dispersion state in the PEN matrix on the physicalproperties was systematically investigated. In summary, this dissertation is composed offour parts as follows:Firstly, MWCNTs were successfully functionalized with4-aminophenoxy-phthalonitrile to produce nitrile functionalized MWCNTs(MWCNTs-CN), and werethen compounded with poly(aryl ether nitrile)(PEN) to fabricate MWCNTs-CN/PENnanocomposites. FTIR, TGA and TEM were used to characterize the structure andmorphology of the nitrile functionalized MWCNTs, and its effect on the dispersion ofMWCNTs in PEN matrix, mechanical properties, rheological behavior, dielectricproperties and thermal stability was investigated. The results showed that the dispersionof MWCNTs in PEN matrix and the interfacial interaction between MWCNTs and PENwere improved via nitrile functionalization. Compared with the pure PEN matrix, thetensile strength and tensile modulus of PEN nanocomposite with2wt%MWCNTs-CNincreased by21.3%and21.7%, respectively. Besides, the surface of the nitrilefunctionalized MWCNTs contains a lot of nitrile groups which can promote theadhesion with PEN chain through polar interaction, thus enhancing the interfacialcompatibility. Therefore, as concluded from the rheological results, the addition of lowweight content of the nitrile functionalized MWCNTs can greatly improve the storagemodulus and complex viscosity. In addition, the dielectric and thermal stability werealso greatly improved.Secondly, the nitrile functionalized MWCNTs can be further modified throughchemical reaction to produce phthalocyanine functionalized MWCNTs (MWCNTs-Pc),and were then compounded with poly(aryl ether nitrile)(PEN) to fabricateMWCNTs-Pc/PEN nanocomposites. FTIR, UV-VIS, Raman, TGA, TEM and SEMwere used to characterize the structure and morphology of phthalocyaninefunctionalized MWCNTs. It is found that the surface of MWCNTs was coated by theorganic layer after functionalized by the phthalocyanine and parts of the MWCNTs wereinterconnected. The surface functionalization promotes the entanglement actionbetween the MWCNTs-Pc and PEN chain, which efficiently transfer loading betweenMWCNTs and PEN matrix, thus greatly improving the mechanical properties.Compared with the pure PEN matrix, the tensile strength and tensile modulus of PEN nanocomposite with2wt%MWCNTs-Pc increased by21.8%and40.4%, respectively.The phthalocyanine functionalized MWCNTs improve the dispersion of MWCNTs inPEN matrix and the interfacial interaction between MWCNTs and PEN, thus efficientlyenhanced the storage modulus and complex viscosity. In addition, the interconnectedMWCNTs can further promote the formation of conductivity network, whichsignificantly improve the dielectric properties of PEN nanocomposites.Thirdly, MWCNTs/Fe3O4hybrids were prepared via covalent method and thencompounded with poly(aryl ether nitrile)(PEN) to produce PEN/MWCNTs/Fe3O4nanocomposites. FTIR, DSC, XRD, SEM and TEM were employed to characterize thestructure and morphology of the MWCNTs/Fe3O4hybrids. It is found that the Fe3O4nanoparticles were uniformly formed on the surface of the MWCNTs via covalentmethod. The density and the diameters of the Fe3O4nanoparticles can be controlled bychanging the precursor concentration. Owning to the surface modification of MWCNTswith Fe3O4nanoparticles, the contact area between the MWCNTs and PEN matrix weregreatly improved, which efficiently transfered the loading and significantly enhancedthe mechanical properties of PEN nanocomposites. Compared with the pure PEN matrix,the0.5wt%MWCNTs/Fe3O4reinforced PEN nanocomposite, the tensile strength andtensile modulus increased by19%and42%, respectively. Besides, the Fe3O4nanoparticles can efficiently fill the interspace between MWCNTs which promoted theformation of the conductivity, and thus significantly improved the dielectric propertiesof PEN nanocomposites. In addition, the incorporation of MWCNTs/Fe3O4alsoimproved the rheological properties and thermal stability.Finally, the PEN nanocomposites with nitrile functionalized MWCNTs,phthalocyanine functionalized MWCNTs and MWCNTs/Fe3O4were fabricated,respectively. The structure and morphologies of the three types of functionalizedMWCNTs were discussed and their effects on the mechanical properties, rheologicaland dielectric properties were investigated. The results indicated that the three types offunctionalized MWCNTs showed different structure, morphologies and surfaceproperties, which affected the different reinforcement efficiency and finally resulted inthe different mechanical properties, rheological and dielectric properties.