Direct writing of continuous carbon fibers/epoxy thermoset composites with high-strength and low energy-consumption

Epoxy resin-based thermoset composites are extensively used in industries with billions of dollars in revenue every year. High-rate manufacturing process is highly sought-after to produce complex composite structures with geometric flexibility and low energy-consumption. This work demonstrates printing and in-situ cure of epoxy resin-based thermosets and composites via self-sustaining frontal propagation. Specifically, latent initiator in the resin formulation was tuned from 2 mol% to 0.05 mol% to lower the frontal propagation temperature from ~290 °C to ~240 °C without decreasing the reaction rate. The epoxy resin was soaked into continuous carbon fiber (CF) tows and then printed through a modified direct ink writing system. Synchronization of the printing process and in-situ frontal curing resulted in continuous CF/thermoset composites (c-CFTC). Both single and dual nozzle print-heads were used to print c-CFTC with tunable fiber volume fractions. As-printed specimens exhibited exceptional tensile strength, 1.15 GPa at 48 vol% fibers and 0.42 GPa at 18 vol% fibers in fiber direction and ~35.5 MPa in transverse direction. The energy consumption of the printing process was also calculated, indicating 3.6 billion kilowatt-hours (kWh)/year energy-saving in comparison to conventional manufacturing processes with hours of high-temperature oven curing, equivalent to the energy consumption of 360,000 US families per year (single US family electric consumption: 10,000 kWh/year). The printing speed was 7.5–13.8 cm/min dependent on the fiber fraction, and thus the production rate was estimated to be 400–800 cm³/hour. Such a high-rate and energy-saving approach could revolutionize the c-CFTC industry and aerospace, automobile, and marine industries with environmental and energy sustainability.