The Preparation Of Modified Carbon Nanotubes By Hyperbranched Polyamides With In Situ Polymerization And Its Effect On Properties Of PA6

The carboxyl groups on the surface of multi-walled carbon nanotubes(MWCNTs)were produced by oxidizing MWCNTs using the mixture of sulfuric acid and nitric acid,then tri(3-aminophenyl)phosphine oxide and hexanedioic acid ether were in situ polymerized as A3 and B2 monomers,respectively,in the presence of oxidized MWCNTs to afford hyperbranched polyamides (HBPA) modified MWCNTs(MWCNT-P) in phosphorous pentoxide(P2O5) medium. The overall evidence based on the date of Fourier-transform infrared(FTIR) sepectroscopy, X-ray photoelectron sepectroscopy(XPS),scanning microscopy(SEM), transmission electron microscopy(TEM) and thermogravimetric analysis(TGA) implicates that HBPA were attached to the surface of MWCNTs. The diameter of the modified carbon nanotubes were larger than pristine carbon nanotubes, and the surface of modified carbon nanotubes becomes srough.MWCNT-P filled polyamide-6 (PA6) nanocomposites (MWCNT-P/PA6s) were prepared by melt processing technique.The -dispersion of modified carbon nanotubes in composite materials were studied by scanning electron microscope, the results show that at the low addition amount of modified carbon nanotubes (≤1.0wt%) ,the modified carbon nanotubes can uniformly disperse uniformly in the composite material, but,when the content of carbon nanotubes is higher level(1.5wt%), the dispersion of modified carbon nanotubes in the . composite decreased, modified carbon nanotubes were easy to agglomerate.The non-isothermal crystallization behaviors of PA6 and MWCNT-P/PA6s were investigated by DSC method. Jeziomy equation, Ozawa model and Mo equation were employed to analyze the non-isothermal crystallization date. The results showed that Owaza and Jeziorny equations can deseribe the non-isothermal crystallization poreess,while the Mo equations exhibits great advantages in treating the non-isothermal crystallization kinetics.The nucleation mechanism of the composites was affected by the addition of carbon nanotubes and branched polyamide. XRD was used to study the crystal morphology of the composites. The results showed that the addition of carbon nanotubes changed the crystal form of nylon 6, the crystal morphology of nylon 6 and composite materials were mainly a crystal mainly,which is more stable crystal mainly.The study of the mechanical properties of composite materials showed the addition of carbon nanotubes and hyperbranched polyamide improves the tensile modulus, the flexural strength and flexural modulus of composite materials, but the tensile strength, elongation at and break and impact strength of composite materials decreased, This phenomenon is related to the dispersion of carbon nanotubes and the arrangement of carbon nanotubes in composite materials.The study of flame retardant properties of the composites showed that the limit oxygen index of the composites materials was improved. The flame retardant properties of the composites were related to the amount of the hyperbranched polyamides and carbon nanotubes. The same group of samples, limit oxygen index of the composites increases first and then decreases with the content of carbon nanotube increases ,this is because the carbon nanotubes can be formed carbon layer in the combustion process of composites materials,but higher content of carbon nanotubes can improve the thermal properties of composites,lead to the flame retardant properties of the composites decreased. With the same content of carbon nanotubes composites materials , the limit oxygen index of polyamide increased with the content of hyperbranched polyamides increase,this is because of the high content of hyperbranched polyamide can form a thick carbon layer thick and release more gas that hard to burn in the composite combustion process, so as to improve the flame retardant properties of composite materials.