Fabrication and Characterization of Re-Entrant Honeycomb Polyurethane Aerogels

Abstract

In this work, polyurethane aerogels are fabricated in re-entrant honeycomb forms to achieve auxeticity and much higher flexibility than corresponding aerogel monoliths. For this purpose, a set of re-entrant honeycomb-shaped hollow molds is first printed from high-impact polystyrene (HIPS) using a fused filament fabrication technique and subsequently filled with polyurethane sol synthesized from an aliphatic triisocyanate and a diol selected from among butanediol, pentanediol, hexanediol, or octanediol. A sol–gel transition process yields the gel in a re-entrant honeycomb shape, which is isolated by dissolving the HIPS mold and supercritically dried using carbon dioxide. The effects of diol chain length on the properties of aerogels, such as bulk density, pore size, and tensile properties are investigated. The auxetic aerogels show different deformation behavior and much higher elongation at break than dogbone-shaped aerogel monoliths. Such unique properties of auxetic structures can extend applications of aerogels as acoustic absorbers and smart bandages that require high porosity, tunable pore structures, and high flexibility.

Lightweight polybenzoxazole aerogels with high compressive strength, ultralow dielectric constants, and excellent thermal stability

“…[5][6][7] Therefore, polymer aerogels have garnered increasing attention because they have better mechanical properties, processability, and density than inorganic aerogels. [8][9][10][11] It is well known that the mechanical properties and thermostability of aerogels are related to not only their porous structure but also the intrinsic mechanical properties and heat resistance of the materials that make up the aerogels. Polymer aerogels typically operate at lower temperatures than inorganic aerogels because of the poor heat resistance of most polymers.…”

“…5–7 Therefore, polymer aerogels have garnered increasing attention because they have better mechanical properties, processability, and density than inorganic aerogels. 8–11…”

Different Effects of Mixing Manners on the Porous Structures and Dense Films of Waterborne Polyurethane Modified with Recycled Aramid Nanofibers

“…To modify the inherent fragility of the aerogel, ductile polymers, such as poly­(vinyl alcohol) (PVA), , polyurethane (PU), and waterborne polyurethane (WPU), have also been introduced to the composite with rigid ANF networks within porous structures. Inspired by the concept of sustainable development, WPU, the aqueous dispersion of PU colloidal nanoparticles, is more and more used to replace the traditional solvent-borne PU products in various fields to reduce the emission of volatile organic compounds (VOCs). − In addition, the relatively low viscosity of the dispersion significantly reduces the mixing difficulties with ANF. However, as a thermodynamically unstable dispersion, the spatial aggregation of the colloidal particles and the fractal geometry of the condensed network would be quite complex and highly dependent on the external factors triggering destabilization, i.e., the manner used to introduce the 1D nanomaterials.…”

Upcycling of Waste Fabrics into High-Efficiency Air Filters Using Flexible Polyimide Aerogel Coatings

“…Fonner and Jana also identified that poor flexibility of aerogels is a concern for handling of aerogel-coated fabrics as filter media and that not all fabric types can be considered. Recent studies used additive manufacturing tools to circumvent the poor flexibility of aerogels and reported fabrication of complex shape aerogel articles for applications in filtration and thermal insulation. − Kulkarni et al recently reported fabrication of an aerogel filter medium using 3D printing for separation of water droplets from ultralow sulfur diesel fuel and observed an efficiency of up to 97% aided by size exclusion of water droplets by the small pores and adsorption of nonionic surfactants on polymer surfaces.…”