Rapid and Energy-Efficient Frontal Curing of Multifunctional Composites Using Integrated Nanostructured Heaters

Current technologies for the manufacture of fiber reinforced polymer composites are energy-intensive, environmentally unfriendly, and time-consuming and require expensive equipment and resources. In addition, composites typically lack key nonstructural functionalities (e.g., electrical conductivity for deicing, lightning strike protection, and structural health monitoring), which are crucial to many applications such as aerospace and wind energy. Here, we present a new approach for rapid and energy-efficient manufacturing of multifunctional composites without using traditional expensive autoclaves, ovens, or heated molds used for curing of composites. Our approach is predicated on embedding a thin conductive nanostructured paper in the composite layup to act as a resistive heater for triggering frontal polymerization of the matrix thermosetting resin of the composite laminate. Upon passing electric current, the nanostructured paper quickly heats up and initiates frontal polymerization, which then rapidly propagates through the thickness of the laminate, resulting in rapid curing of composites (within seconds to few minutes) irrespective of the size of the composite laminate. The integrated nanostructured paper remains advantageous during the service of the composite part by imparting new functionalities (e.g., deicing) to the cured composite, owing to its excellent electrical conductivity and electrothermal properties. In this work, we first study the influence of several composite processing parameters on the electrothermal properties of the nanostructured paper and determine the power required for rapid initiation of frontal polymerization. We then successfully fabricate a 10 cm x 10 cm composite panel within 1 min using only 4.49 kJ of energy, which is 4 orders of magnitude less than the energy consumed by the traditional bulk, oven-curing technique. Detailed experiments are conducted to provide an in-depth understanding of the effect of heater position, tooling material, and input power on frontal curing of composite laminates. The multifunctional response of produced composites is demonstrated by performing a deicing experiment, where a 50 x 50 x 3 mm3 cube of ice is completely melted within 3 min using an input power of 77 W.