Network toughening of additively manufactured, high glass transition temperature materials via sequentially cured, interpenetrating polymers

Abstract

Vinyl ester and epoxy-amine resins are used to produce polymeric materials for numerous commercial and military applications due to their relatively high moduli (>2 GPa), glass transition temperatures (T g s) (≥120°C) and adequate fracture toughness (G 1C ≈ 200-250 J m −2 ). Most commercially available vinyl ester and epoxy-amine resins are typically cured into polymeric materials via traditional manufacturing techniques, such as resin transfer molding and thermal curing. However, additive manufacturing (AM) has gained significant traction as a favorable manufacturing technique over traditional methods due to the ability to create customizable parts with complex geometries on-demand. Manipulation of polymer network connectivity using a dual-cure mechanism of methacrylate free radical cure via stereolithography (SLA) and epoxy-amine thermal cure for the in situ creation of interpenetrating polymer networks (IPNs) for AM was investigated. Resins and formulations of individual monomers bearing both vinyl ester and epoxy functionality were either synthesized or formulated to elucidate the effect of interconnecting the two networks at the molecular level. The formation of a multi-mechanistic, interconnected, sequentially cured IPN via SLA yielded polymeric materials with glass transition temperatures that exceeded 120°C. Polymer network connectivity was shown to have a minimal impact on thermomechanical and thermogravimetric properties. IPN formation was shown to afford materials with high storage moduli (E 0 values as high as 3.2 GPa), tensile strengths (as high as 51 MPa), Young's moduli (exceeding 3.5 GPa) and fracture energies (as high as 790 J m −2 ).

Epoxy‐functional thermoplastic copolymers and their incorporation into a thermosetting resin

“…The reference peak is visible at 5900 cm −1 and is not affected by the polymerization. The amine functionality was used to determine the extents of cure of the epoxy–amine networks 30 . The equation used to quantify extents of cure is given by Equation ().…”

“…The amine functionality was used to determine the extents of cure of the epoxy-amine networks. 30 The equation used to quantify extents of cure is given by Equation (6). A typical preand post-cure FT-IR spectrum is shown in Figure 3.…”

Superior Properties through Feedstock Development for Vat Photopolymerization Additive Manufacturing of High-Performance Biobased Feedstocks

“…Trigonox was employed as thermal initiator to aid in post-curing to achieve a type of dual-cure effect. Photocure followed by thermal cure has proven advantageous for some SLA formulations [16,17,41]. Resin formulations were cured with a metal halide flood lamp followed by thermal post-cure.…”

“…Other investigators have turned to clever methods to allow for AM of high-performance materials, including dual-cure technologies where the vat photopolymerization is mostly relied upon to set the matrix and therefore allowing for the desired geometric shape, but not pivotal in obtaining the high-temperature properties. Worthy of mention is the investigation of Bassett et al, where they developed epoxy acrylate dual-cure interpenetrating polymer networks with reportedly high fracture energies up to 790 J/m 2 while having glass transition temperatures in excess of 120 • C [17]. Zhou et al developed IPN based on tris(2-hydroxyethyl)isocyanurate triacrylate, which, upon photoirradiation, polymerized, imparting green strength into the material while upon post-cure, cyanate esters would react, forming triazole rings enhancing the polymer properties.…”

Special issue: polymers for defense

“…28 Bassett et al, studied a unique approach to toughening additively manufactured networks via the sequential curing of vinyl ester and epoxy resins to form interpenetrating polymers. 29 Strutton et al, report on how particle size effects in aluminum/poly(vinyldene fluoride) filaments can be manipulated to alter the burn rate performance in melt-processed energetic composite formulations. 30 Chemical decontamination and environmental remediation are also important applications for defense.…”