Additively manufactured thermosetting elastomer composites: small changes in resin formulation lead to large changes in mechanical and viscoelastic properties

Composites with high loadings of the reinforcement phase are interesting systems for vat photopolymerization forms of additive manfuacturing (AM), since AM enables fabrication of complex structures. This work investigates the effect of resin chemistry and addition of solid reinforcement on mechanical, thermal and viscoelastic properties of thermosetting polymer composites at high solid loading (50 vol%) that were fabricated using digital light processing (DLP). Co-monomers that would preferentially interact with the glass surface and act as surfactant-like additives were added to a base urethane acrylate resin system. Better resin wettability led to higher strength of printed composites, while glass transition temperature remained constant across resin formulations in neat and composite specimens. Addition of co-monomers more substantially affected the mastercurves of composites than neat specimens, with co-monomer addition leading to high stiffnesses at high frequencies. We also compare two approaches for tailoring interfacial interactions (modifying the resin formulation and modifying the reinforcement's surface chemistry) and discuss the relative advantages of each for achieving high performance additively manufactured composites. Better resin wettability increases strength and stiffness in high solids loading composites that can be additively manufactured with high resolution.