Direct ink write (DIW), an additive manufacturing method, offers several advantages over more traditional extrusion and injection molding: abilities to produce 1. large, porous polymeric parts with complex geometry and spatially dependent properties due to variations in structure, porosity, or material composition and 2. highly filled polymers without exotic processes or high pressures; room temperature fabrication; and reduced waste material. However, low yield stress thixotropic inks typically require polymers &lt;100kg/mol to avoid post-extrusion flow resulting from nozzle swell and thixotropic breakdown. However, mechanical properties are highly molecular weight dependent and current DIW ink properties may not be sufficient for some industrial applications. Previous work has demonstrated hydrophobic-treated fumed silica incorporation to the silicone matrix significantly improves performance, exhibiting tensile strength up to 4MPa and 250% elongation at Shore A 50 hardness and 30wt% silica loading. To further improve performance of DIW silicones, covalent incorporation of fumed silica into the silicone cross-link network is desired. This project investigates the effects of varying silica size and vinyl-treating agent on silicone to increase both tensile strength and elongation at Shore A 50 hardness. NMR of initial silica modifications show replacement of surface hydroxyls with vinyl-containing silanes and silazanes. Fully incorporated tensile test samples containing vinyltriethoxysilane-treated silica (BET 250m2/g) increased elongation by about 20%, indicating higher vinyl-treated silica loading may be necessary to increase tensile strength. For other treating agents and higher surface area silica (BET 400m2/g), limited incorporation was observed. To fully incorporate all vinyl-treated silicas, ongoing work is testing more intensive mixing techniques. Results from this project will advance knowledge of silica size and treating agent effects on high performance elastomer properties, enabling tailored elastomer compositions to desired mechanical performances.

Vinyl-functionalized fumed silicas to enable tailored mechanical performance of direct ink write silicone elastomers

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.