Y. Martinez Rubi, M.B. Jakubinek, C.T. Kingston, B. Ashrafi, A.J. Paleo, B. Krause, P. Pötschke, G. Palumbo, J. McCrea, R. Pallotta, H. Katugaha
National Reseach Council Canada,
Canada
Keywords: carbon nanotubes, flexible thermoelectric, large scale, nanocomposite, fabrics
Summary:
Carbon nanotubes (CNTs) have long been considered promising for development of advanced composite materials, due to their extraordinary properties along with low density. For some applications, composite materials with high nanotube content are often necessary in order to achieve mechanical, thermal or electrical conductivity requirements. Various applications of free-standing CNT sheets and their polymer composites have shown promise at the laboratory scale; however, scalable integration and fabrication methods remain active challenges to meet the technology readiness level for commercialization. We have developed a solution-based method for the production of such nanocomposites in the form of nonwoven fabrics using a thermoplastic polyurethane (TPU).1 Appropriate selection of the solvents and optimization of a TPU solvent/non-solvent volume ratio enhanced interactions between CNTs and polymer chains in solution, improved CNTs disentanglement, and significantly reduced the filtration time for a fast recovery of composite sheet of controlled composition. The method provides for controlled adsorption of TPU on the nanotubes surface for tailoring of the nanotube:polymer ratio (composition) and nanocomposite properties (e.g. conductivity, strength, toughness and adhesion). The resulting prepreg-like fabrics can be handled and employed analogously to other fabric and prepreg materials. Multiwall-CNT (MWCNT)–TPU fabrics have been layered, laminated or infused to produce thick nanocomposites, or integrated with conventional composites, for a series of multifunctional composites demonstrations (e.g., electromagnetic shielding, heating, flame resistance).2 Most recently, the thermoelectric properties of single-wall-CNTs (SWCNT)–TPU composites fabricated by this method were evaluated, achieving significant advantages relative to pristine SWCNT buckypaper sheets (BP) in terms of strength and stretchability (Figure 1).3 In particular, the SWCNT–TPU nanocomposite with a 50/50 wt % ratio composition (equivalent to 15 vol % of SWCNTs) shows a power factor (PF) of 57 μW m–1 K–2, slightly higher compared to the PF of the SWCNT BP prepared under the same conditions (54 μW m–1 K–2), while its mechanical properties significantly increased (e.g., ∼7-, 25-, and 250-fold improvements in stiffness, strength, and tensile toughness, respectively). The developed SWCNT–TPU sheets also compare favorably to other CNT-based polymer composites in the literature. The present approach represents a feasible route to obtain flexible and stretchable p-type components for energy harvesting modules based on the thermoelectric effect. To address the scalability challenge, we have partnered with the Canadian company Integran Technologies through the Innovative Solutions Canada (ISC) Program to translate this batch filtration method to a roll-to-roll fabrication process. The new fabrication process will enable both larger-scale, continuous fabric production – an essential step for industrial application – as well as direct deposition onto other substrates and production of other high-nanomaterial content nanocomposites