Multiscale characterization of effective thermal properties by an asymptotic homogenization method of a biosourced epoxy resin with two porosity levels

This paper has carried out numerical characterizations of effective thermal properties of a new kind of macroporous bio-based epoxy resin. This new kind of material was synthesized by a free-solvent and free-amine-hardener process combining the cationic photopolymerization and the solid porogen leaching technique. In order to determine the effective thermal properties of the material, the asymptotic homogenization method has been used, deriving a cell problem from microscopic thermal equations. By solving this problem on a representative volume element consisting of elementary fillet-edge cubic pore and matrix which have been idealized from experimental pore characterizations, the effective thermal conductivity and diffusivity tensors have been attained. The asymptotic homogenization method revealed the effect of microstructural characteristics via pore arrangements, porosity and pore size on the effective thermal properties of the porous material. This first stage in the material development allows to propose adjustments in the elaboration process to improve the thermal insulation characteristics of a biosourced epoxy resin with two porosity levels. The paper has also provided examples of multilayer walls using the studied epoxy resins as thermally insulating materials. These walls including two or three insulation layers with different thicknesses have been assumed to suffer either a step change or a harmonic variation of the temperature at one side of the walls. Transient thermal responses of multilayer walls to the above thermal excitations have been dealt with by a semi-analytical approach in the context of one-dimension problems.