Tensile, flexure, and compression properties of anisotropic microchannel epoxy foams

Abstract

This cover by Eric Schmid, David Salem and colleagues shows an SEM of a microvascular epoxy produced by sacrificial removal of PLA fibers. In this example, the microchannel volume fraction is 0.6, and the (18 μm diameter) channels are primarily oriented longitudinally, with fewer microchannels in the transverse direction. Tensile, flexure, and compression properties were characterized and modeled over a wide range of microchannel fractions and different microchannel orientations, demonstrating the ability to engineer the properties of these materials for structural thermal insulation applications, and for applications requiring liquid transport through the polymer for thermal management, self-healing and various biomimetic functions.

Mechanical and thermal properties of microchannel insulating foams comprising a multifunctional epoxy/polyhedral oligomeric silsesquioxane nanocomposite

“…While this may seem minimal, these results are an improvement over those of Bukowczan et al, in which the specific maximum force before breaking increased approximately 5% in polyurethane foams with 15 wt% octa‐POSS 45 . Since the strength of foam generally increases exponentially in relation to the density, improving the specific strength of any material is a great challenge since reinforcement strategies frequently result in increased density 44 . Therefore, an improvement of about 10% at identical microchannel foam densities is in fact a significant achievement in the field, and it was achieved without compromising the thermal insulation capacity of the final foam structure.…”

“…Energy Dispersive X-ray Spectroscopy (EDS) was performed with an Oxford Instrument X-Max 80 mm 2 SDD detector and analyzed F I G U R E 2 Infusion of A, PLA nonwoven microfiber with liquid DGEBF/DDS epoxy forms a B, solid PLA/epoxy composite after the resin is cured. The PLA fibers are then selectively dissolved, leaving the C, epoxy foam microchannel structure, with this particular image demonstrating microchannel bulk volume fraction of 0.6 with templated microchannels in a [0/90] configuration; Image C is adapted from 44 [Color figure can be viewed at wileyonlinelibrary.com] using the AZtec microanalysis system. EDS of carboncoated specimens was conducted in tandem with microimaging using a Zeiss Supra 40 variable-pressure fieldemission SEM under 10 keV acceleration voltage.…”

“…This resin was degassed and then infused by Vacuum Assisted Resin Transfer Molding (VARTM) at 105 C into a microfiber layup as described in previous reports, with the fiber layup then being sacrificed post-cure to create the desired microchannel structures. 43,44 DGEBF/ POSS/DDS epoxy solid panels (not foams) were also fabricated in a variety of ratios by casting in an aluminum mold; these samples were used for resin characterization prior to analysis of the final foam structures.…”

“…[40][41][42] Inspired by the wide variety of successful POSS demonstrations, octa-functionalized glycidyl POSS has been explored, in the present study, as an additive to the DGEBF ( Figure 1B) and diaminodiphenyl sulfone (DDS) ( Figure 1C) epoxy resin system ( Figure 1D) recently utilized in the fabrication of microchannel foams for mechanical thermal insulation. 43,44 These foams contain pore structures in the form of hollow microchannels with engineered microchannel orientations created via extraction of thermoplastic templating fibers after curing of the infused thermosetting epoxy resin (for reference, these materials are shown in Figure 2). Based on literature reports, addition of POSS to the epoxy-based foam matrix is anticipated to not only improve the thermal stability 25 and mechanical performance, 45 but also the resistance to UV degradation.…”

“…Infusion of A, PLA nonwoven microfiber with liquid DGEBF/DDS epoxy forms a B, solid PLA/epoxy composite after the resin is cured. The PLA fibers are then selectively dissolved, leaving the C, epoxy foam microchannel structure, with this particular image demonstrating microchannel bulk volume fraction of 0.6 with templated microchannels in a [0/90] configuration; Image C is adapted from 44 [Color figure can be viewed at wileyonlinelibrary.com]…”