Room-Temperature Self-Expanding Biobased Epoxy Foams with Reprocessability and Improved Fire Behavior

Fully bio-based, self-expanding epoxy-acid foams were developed in this work. The strategy employs phosphoric acid (PHO) as a curing agent and expansion activator in a vegetable oil-based epoxy formulation. This approach relies on the exothermicity of the epoxy-acid reaction to simultaneously drive curing and gas generation, enabling a self-sustained foaming process under ambient conditions. Two formulations were studied: one containing only phosphoric acid (ESBOPHO) or a mixture with tartaric acid (ESBOTARPHO). While ESBOPHO rapidly reached temperatures of 80 °C, the hybrid system exhibited moderate exothermicity (around 35 °C), allowing for better processing control and morphological homogeneity. Compression molding and rheological measurements highlighted better thermal/hydrolytic stability and reprocessability for the hybrid system. Cone calorimetric tests revealed that tartaric acid reduced the peak heat release by 27% and total heat release by 49%, validating these foams as potential sustainable and safe insulators with a high carbonaceous residue content.