High-Volume-Fraction Textured Carbon Nanotube–Bis(maleimide) and −Epoxy Matrix Polymer Nanocomposites: Implications for High-Performance Structural Composites
Ashley L. Kaiser, Cécile A. C. Chazot, Luiz H. Acauan, Isabel V. Albelo, Jeonyoon Lee, Jeffrey L. Gair, A. John Hart, Itai Y. Stein, Brian L. Wardle
Abstract
Polymer matrix nanocomposites (PNCs) incorporating high volume fractions (Vf in excess of 10 vol %) of aligned carbon nanotubes (A-CNTs) are promising for high-performance structural composite applications leveraging texture for multifunctionality and performance-to-weight ratios. However, to enable the manufacturing of scalable structures using A-CNT PNCs, nanoscale confinement and interfacial effects due to high A-CNT content in aerospace-grade polymer matrices need to be better understood. Here, we report the model-informed fabrication of high-Vf CNT PNCs to develop process–structure–property relationships, including a scaled film and laminate technique for A-CNT polymer laminates and the fabrication of microvoid-free and fully infused bis(maleimide) (BMI) and epoxy PNCs with high packing densities (or Vf) of biaxially mechanically densified millimeter-tall A-CNT array reinforcement (1–30 vol % corresponding to the average inter-CNT spacings of ∼70 to 6 nm). A polymer infusion model developed from Darcy’s law accurately predicts the time for resin to infuse into CNT arrays during capillary-assisted PNC processing, corroborated by experimental observations via X-ray microcomputed tomography and scanning electron microscopy showing that a diluted resin with ∼10× lower viscosity than a neat resin is required to obtain complete infusion into high-Vf A-CNT arrays (10–30 vol %). For each tested A-CNT volume percent, the cured PNCs maintain vertical CNT alignment and glass transition temperature, and the decomposition onset temperature remains constant for epoxy PNCs but increases by ∼8 °C for 30 vol % A-CNT–BMI PNCs compared to the neat resin. For both polymer matrix systems, a ∼2× increase in the axial indentation modulus for 30 vol % A-CNT PNCs compared to that of a neat resin is measured, and no significant change in the transverse A-CNT modulus is shown experimentally and via modeling, indicating that reinforcement with A-CNTs at higher Vf values leads to enhanced anisotropic mechanical properties. Through the process–structure–property scaling relationships established here, this work supports the development of next-generation structures comprised of nanomaterials with enhanced performance and manufacturability.