Characterization of reinforced structural composites with carbon nanotubes grown directly on the fibers/fabrics using the Poptube Approach

Abstract

Carbon nanotubes (CNTs) are ideal candidates for the reinforcement of the matrix and interphase zone in polymer matrix composites (PMCs), due to their ability to more effectively bind the reinforcing fibers to the matrix material. This can lead to the enhancement of several critical composite properties – including interfacial shear strength and interlaminar fracture toughness – that are typically associated with a composite material’s resistance to delamination. Direct dispersion of CNTs into the matrix of the composites has been shown to be very difficult. A more effective way to reinforce PMCs using CNTs is to grow CNTs directly on the reinforcing fibers. To this end, a novel technique used to grow CNTs directly on carbon fibers has been developed at The University of Alabama and Auburn University. This method, referred to as the PopTube Approach, uses microwave irradiation to grow CNTs at room temperature in air, without the need for inert gas protection or additional feed stock gases. The simple nature of the PopTube Approach lends itself to large-scale, high-yield manufacturing that can be done in a cost effective manner. However, before this technique is developed beyond the laboratory scale, its effectiveness as a route to produce CNT-reinforced composites must be evaluated in a comprehensive manner. The objective of this work is to do just that – characterize the mechanical properties of CNT-reinforced composites produced via the PopTube Approach. A systematic experimental program is carried out to provide a comprehensive assessment of the effects of the PopTube Approach on a wide range of composite mechanical properties. Results show that the PopTube Approach provides for enhanced resistance to delamination with respect to several different loading events. Fractography studies are used to qualitatively understand the mechanisms responsible for these improvements in delamination resistance on the micro-scale. Results also suggest that improvements in delamination resistance via CNT reinforcement may come at the expense of the tensile properties of PMCs – which gives rise to the conclusion that in practice, the degree and manner of CNT reinforcement in PMCs should be carefully considered on an application-by-application basis. Together, the collection of studies performed herein provides a wide-ranging quantitative and qualitative assessment of the effects of the PopTube Approach CNT reinforcement scheme on the mechanical properties and behavior of polymer matrix composites.