Mechanical and structural properties of highly loaded carbon nanotubes/polyamide 6 composites

Abstract

Recently, carbon-fiber composite materials have been attractive to many industries and agencies such as automotive, aerospace, sport equipment manufacturing, Department of Defense, and Department of Energy. These materials show improved mechanicals properties and can be lighter than steel and many other alloys. Carbon nanotubes are structures that present unique chemical and mechanical properties, such has a sp2 hybridization and an elastic modulus of about 1 TPa, which make them a suitable prospective to enhance the properties provided by the carbon fibers. Reported studies have showed that carbon nanotubes can be used as fillers in different polymeric matrices such as epoxy, polyether ether ketone, polycarbonate, polyamides, and others. However, obtaining a good dispersion of carbon nanotubes in the matrix is quite challenging, because their electrostatics forces make them to agglomerate. In order to get a better interaction between the carbon nanotubes and the polymer matrix, many researchers have tried to functionalize the carbon nanotubes surfaces. However, functionalization of the carbon nanotube surfaces might end in reduction of their chemical and mechanical properties. In this study, non-functionalized carbon nanotubes/polyamide 6 composites were fabricated using an innovative method where no solvent is needed. Concentrations of carbon nanotubes (40-65 wt%), higher than ever reported were used to create the composites. Temperatures higher than the melting point of the polymer and pressure was required to fabricate the composites. Pressure levels and processing temperature were found to have a strong effect on the final composites’ structure. For this reason, two different temperatures (280-300 oC), and two different pressures (5 and 10 MPa) were studied. Higher polyamide 6 degradation was found for polymer samples processed under air atmosphere at 300 oC, than for the samples processed under nitrogen atmosphere. Larger number of defects was found for the composites processed at 5 MPa of pressure compared to the ones processed applying a pressure of 10 MPa. An improvement in the polyamide 6 mechanical properties, such as the hardness and the elastic modulus, was found for the carbon nanotubes loaded composites.