Zero-Support 3D printing of thermoset silicone via simultaneous control of both reaction kinetics and transient rheology

Abstract

This article presents a framework for using isothermal curing kinetics and transient rheological data to 3D print a curing thermoset silicone without support. These data are used to determine time and temperature boundary conditions for amount of curing during extrusion and layering of the print. From the time of mixing, rheological data show how the elastic modulus (G′) and yield stress (σy) grow as the number of crosslinks increases. The kinetics data show changes in the rate of curing of the silicone and predict final cure time. Time boundaries for stages of transient curing are reported from heat flow, yield stress, and G′ at the printer operating temperature. These times are used to prevent clogging of the mixing nozzle and ensure layering of unsupported elastomeric silicone. Several models are 3D printed to show the successes and drawbacks of the method within equipment limitations. This framework can be applied to help bound the printable region of other reactive thermoset materials in mixed extrusion systems. By printing without support, this method can produce overhanging and enclosed hollow structures that require minimal postprocessing.