(Left) 3D-printed molecular model of the DCPD monomer resin; (right) a quickly curing custom spiral. Credit: Nature
Some of the main attractions of additive manufacturing include the ability to make complex shapes that elude standard machining or molding operations, and the ability to make small production runs without making expensive molds or fixtures. Researchers at the University of Illinois, Urbana-Champaign have discovered a way of producing shapes from a family of thermoset polymers at significantly lower energy cost.
Their process makes use of a heat-curable monomer (DCPD) that, after curing has started by an external heat source, generates sufficient heat from the exothermic polymerization to sustain the curing process, producing a thermoset. The process is called frontal polymerization, so-named because the reaction moves as a front through the monomer.
(Left) 3D printing of gel solidified immediately following extrusion from print head; (right) rapid FROMP reaction transforms liquid or gel into a thermoset polymer. Credit: Nature
Energy Efficient Custom Shapes in 3D Printing
Typically, these types of resins require the application of pressure and heat to effect the cure throughout the entire curing process, which requires much more energy and equipment. The FROMP (ruthenium-catalyzed frontal ring-opening metathesis polymerization) approach requires less energy and time and eliminates the need for large curing ovens.
Previous to this research, the FROMP technique was not industrially useful because the unheated DCPD resin cured in 30 minutes. By using alkyl phosphite inhibitors, the University of Illinois, Urbana-Champaign researchers were able to extend that time period to 30 hours, allowing enough time to shape the material before starting the frontal polymerization process.
These researchers generated quick-curing, high-quality spiral shapes and carbon-reinforced composite panels, and demonstrated similar mechanical properties to conventionally manufactured materials. Although the FROMP process has not yet been commercialized, this rapid fabrication of parts has a myriad of potential applications, including in the space, aircraft, and automotive industries.