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

Area of Science:

• Materials Science
• Polymer Chemistry
• Chemical Engineering

Background:

• Epoxy foaming is complex due to simultaneous curing and gas loading.
• Chemical blowing agents pose environmental concerns, limiting epoxy foam development.
• Achieving optimal curing stages is crucial to prevent cell coalescence and ensure expansion.

Purpose of the Study:

• To develop an environmentally friendly method for epoxy foaming.
• To investigate solid-state carbon dioxide (CO2) foaming of epoxy resins.
• To control the density and cellular structure of fabricated epoxy foams.

Main Methods:

• Pre-curing diglycidylether of bisphenol-A (DGEBA) epoxy and polyamide hardener mixtures into solid-state sheets (preEs).
• Absorbing CO2 into preEs using an autoclave under pressure.
• Free-foaming absorbed preEs in a conventional oven at various temperatures, followed by post-curing.

Main Results:

• PreEs exhibit a unique behavior where storage modulus decreases then increases upon heating due to further curing.
• Epoxy foams with densities ranging from 0.32-0.45 g/cm³ were fabricated from preEs with a storage modulus of 4 × 10⁴-1.5 × 10⁵ Pa at 30 °C.
• Foam cell morphologies included star polygon, spherical, and irregular shapes.

Conclusions:

• Solid-state CO2 foaming is a viable technique for producing epoxy foams.
• This method offers control over foam density.
• The process circumvents the environmental issues linked to traditional chemical blowing agents.