Researchers at the University of Illinois have developed a new polymer-curing process that could reduce the cost, time and energy needed, compared with the current manufacturing process. The findings, reported in Nature, state that the new polymerization process uses 10 orders of magnitude less energy and can cut two orders of magnitudes of time over the current manufacturing process.

The manufacture of high-performance thermoset components currently requires the monomer to be cured at high temperatures (around 180 °C) for several hours, under a combined external pressure and internal vacuum. Such curing generally uses large ovens that scale in size with the component. This traditional curing approach is slow, requires a large amount of energy and involves substantial capital investment.

Frontal polymerization is a promising alternative curing strategy, in which a self-propagating exothermic reaction wave transforms liquid monomers to fully cured polymers. We report here the frontal polymerization of a high-performance thermoset polymer that allows the rapid fabrication of parts with microscale features, three-dimensional printed structures and carbon-fibre-reinforced polymer composites.

Precise control of the polymerization kinetics at both ambient and elevated temperatures allows stable monomer solutions to transform into fully cured polymers within seconds, reducing energy requirements and cure times by several orders of magnitude compared with conventional oven or autoclave curing approaches. The resulting polymer and composite parts possess similar mechanical properties to those cured conventionally. This curing strategy greatly improves the efficiency of manufacturing of high-performance polymers and composites, and is widely applicable to many industries.

—Robertson et al.

This development marks what could be the first major advancement to the high-performance polymer and composite manufacturing industry in almost half a century. The materials used to create aircraft and automobiles have excellent thermal and mechanical performance, but the fabrication process is costly in terms of time, energy and environmental impact. One of our goals is to decrease expense and increase production.

—Scott White, lead author

The research team is part of the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign and includes aerospace engineering professor and lead author Scott White, chemistry professor and Beckman Institute director Jeffrey Moore, aerospace engineering professor and department head Philippe Geubelle, and materials science and engineering professor Nancy Sottos.

There is plenty of energy stored in the resin’s chemical bonds to fuel the process. Learning to unleash this energy at just the right rate—not too fast, but not too slow—was key to the discovery.

—Jeffrey Moore

The new process starts a cascading chemical-reaction wave that propagates throughout the material, White said. Once triggered, the reaction uses enthalpy, or the internal energy of the polymerization reaction, to push the reaction forward and cure the material, rather than an external energy source.

You can save energy and time, but that does not matter if the quality of the final product is substandard. We can increase the speed of manufacturing by triggering the hardening reaction from more than one point, but that needs to be very carefully controlled. Otherwise, the meeting spot of the two reaction waves could form a thermal spike, causing imperfections that could degrade the material over time.

—Nancy Sottos

The team has demonstrated that this reaction can produce safe, high-quality polymers in a well-controlled laboratory environment. They envision the process accommodating large-scale production due to its compatibility with commonly used fabrication techniques like molding, imprinting, 3-D printing and resin infusion.

The US Air Force Office of Scientific Research supported this research.

Resources

• Ian D. Robertson, Mostafa Yourdkhani, Polette J. Centellas, Jia En Aw, Douglas G. Ivanoff, Elyas Goli, Evan M. Lloyd, Leon M. Dean, Nancy R. Sottos, Philippe H. Geubelle, Jeffrey S. Moore & Scott R. White (2018) “Rapid energy-efficient manufacturing of polymers and composites via frontal polymerization” Nature volume 557, pages 223–227 doi: 10.1038/s41586-018-0054-x