Preparation and characterization of novel cellular/nonporous foam structures derived from tannin furanic resin

Abstract

Recently, tannin furanic resin-based foams exhibiting excellent properties have been developed. However, its friability and thermal insulation must be improved prior to industrialization. Therefore, the tannin preconcentrate from wood bark obtained via liquefaction was mixed with furfuryl alcohol in the presence of a catalyst, surfactant, and solvent. This process includes instant in situ formation of a resin matrix, followed by spontaneous molding and curing to yield a distinct cellular/nonporous structure. Further, the cell structure, mechanical strength, friability, thermal insulation, and fire resistance properties of this material were investigated. Results indicated that the developed material displayed a distinguished bilayer structure in the form of a cellular layer crossing the interface into another nonporous layer, as revealed via scanning electron microscopy imaging. In addition, the porosity of the cellular layer was considerably lower than that observed in case of standard tannin foam. Mechanical testing demonstrated a compression strength of 0.183 and > 50 MPa (there is no yield point for the nonporous layer), and internal bond strength of 0.014 and 0.61 MPa for the cellular and nonporous layers, respectively. Rupture was always observed to occur in the cellular layer rather than at the interface. The limiting oxygen index of the cellular layer was approximately 24.51 %, which is comparable to that of the nonporous layer (28.32 %). Based on thermogravimetric analysis (TGA), the overall foam structure can easily decompose into a final residual mass of 2.8 %. Regardless, compared with other tannin foams prepared in the traditional manner by adding a foaming agent, this material exhibited superior friability resistance and thermal insulation, as corroborated from the thermal conductivity measurement (0.0239 W/m K along with an abrasion fraction of 16.49 % after friction, indicating strong durability against abrasion.