Bridging the Gap to Higher Performance Silicone Elastomers for Direct Ink Write

Additive manufacturing via direct ink write (DIW) offers several advantages over traditional manufacturing processes, such as the ability to fabricate polymeric components of complex geometry with spatially dependent properties and reduced waste production. Formulation science is critical to new DIW feedstock development as typical inks must exhibit low yield stress thixotropy while avoiding nozzle swell and post-extrusion flow. These ink properties result from the intertwined effects of reinforcing filler, thixotropic additives, polymer molecular weight, catalyst type, and target mechanical response. For DIW silicones, some standard systems that retain ultimate tensile strength (UTS) of ca. 5MPa and 150 - 350% elongation with varying hardness (ca. 20 - 60 ShoreA) set a baseline from which higher performance feedstocks can be developed.<br/><br/>One approach to enhance silicone mechanical response is to chemically graft functional groups to the fumed silica surface, such as vinyl groups that enable covalent silica bonding to the polymer crosslink network. Systematic variations of polymeric components and in-house surface functionalized silica enable both control over cured mechanical properties in a new set of silicones (achieving ca. 8MPa UTS, 400 - 1200% elongation, and 20 - 50 ShoreA hardness) and direct comparisons across treatment type systems. When aggregated, these comparisons begin a detailed, empirical detangling of the reinforcing filler's roll in silicone performance from other formulation components that will aid more streamlined development of future generations of printable silicones.<br/><br/>This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.