New Insights on Expandability of Pre-Cured Epoxy Using a Solid-State CO2-Foaming Technique

Abstract

Foaming an epoxy is challenging because the process involves the curing reaction of epoxy and hardener (from monomer to oligomer, to a gel and a final three-dimensional crosslinked network) and the loading of gas phase into the epoxy phase to develop the cellular structure. The latter process needs to be carried out at the optimum curing stage of epoxy to avoid cell coalescence and to allow expansion. The environmental concern regarding the usage of chemical blowing agent also limits the development of epoxy foams. To surmount these challenges, this study proposes a solid-state CO2 foaming of epoxy. Firstly, the resin mixture of diglycidylether of bisphenol-A (DGEBA) epoxy and polyamide hardener is pre-cured to achieve various solid-state sheets (preEs) of specific storage moduli. Secondly, these preEs undergo CO2 absorption using an autoclave. Thirdly, CO2 absorbed preEs are allowed to free-foam/expand in a conventional oven at various temperatures; lastly, the epoxy foams are post-cured. PreE has a distinctive behavior once being heated; the storage modulus is reduced and then increases due to further curing. Epoxy foams in a broad range of densities could be fabricated. PreE with a storage modulus of 4 × 104–1.5 × 105 Pa at 30 °C could be foamed to densities of 0.32–0.45 g/cm3. The cell morphologies were revealed to be star polygon shaped, spherical and irregularly shaped. The research proved that the solid-state CO2-foaming technique can be used to fabricate epoxy foams with controlled density.

Foaming epoxy-amine-carbamate: The effect of different neat amines on rheological and cellular morphology

“…10 at appendix. The gel point is determined as the intercept between the storage modulus and the loss modulus [5, 16]. All three compounds do not gel after 2 h of pre-curing at 60°C (Fig.…”

“…Epoxy foam can be produced from a mixture of resin and chemical blowing agents [1][2][3] and by solid-state foaming with physical blowing agents [4][5], with chemical blowing agents [6] or even without blowing agent [7]. Epoxy foam is also fabricated by applying an aqueous emulsion-template [7].…”

High-Strength and Shape-Memory Epoxy Cellular Material with Wood-Like Architecture

“…In particular, epoxy cellular plastics, , one of the most commonly used cellular plastics, have drawn considerable attention for their excellent mechanical properties. Especially, epoxy cellular plastics with excellent compression resistance, low weight, and thermal stability are broadly applied in marine equipment, aircraft, − and vehicles. − During the past decades, many foaming technologies, such as chemical, solid-state, and CO 2 foaming, , have been developed to manufacture epoxy cellular plastics in the industry. However, it remains a great challenge to realize unique porous structures through these conventional production processes .…”