Experimental investigation of the physical foaming of tannin-based thermoset foams

Abstract

The physical foaming of thermosetting biosourced formulations, mainly based on tannin extracts and furfuryl alcohol, was investigated in-depth with a specially designed setup. Mass loss, volume expansion, and temperature measured at the bottom, in the middle and at the top of foams were continuously monitored during their preparation, from the first moment after the liquid formulation was poured into a mould until the final foams hardened and dried. Correlations were found between the observed phenomena. Thus, successive foaming mechanisms involving: (i) phase change of the blowing agent at 55°C, (ii) pore opening at a critical inner pressure, which induced 4% mass loss, and (iii) surface evaporation, could be elucidated and were discussed. The effects of the amounts of blowing agent on the one hand, which increases foam expansion, and of polymerisation catalyst on the other hand, which reduces the induction time, were also investigated, leading to some shifts in the aforementioned phenomena. The present results are certainly relevant to other self-foaming formulations based on thermosetting polymers such as traditional polyurethanes expanded by physical foaming with pentane.

Tannin-Furanic Foams Formed by Mechanical Agitation: Influence of Surfactant and Ingredient Ratios

“…This interesting and almost completely bio-based [ 1 ] material has sparked the interest of the industry as an alternative to oil-based insulation foams [ 2 , 3 ], as well as due to their excellent thermal insulation values [ 4 ] and outstanding fire retardant behavior [ 5 , 6 ]. The majority of these foams is obtained by evaporation of a low boiling point solvent and simultaneous hardening of the polymer [ 7 ], which is in most cases is tannin-furfuryl alcohol, with [ 6 , 8 , 9 , 10 , 11 ] or without formaldehyde [ 2 , 5 , 12 , 13 , 14 , 15 ] or other hardeners [ 16 , 17 ]. Some studies were conducted using an oil emulsion templating method to produce monoliths [ 18 ] or to employ ethoxylated castor oil as the foaming agent [ 19 , 20 ].…”

Progress in Bio‐Based Phenolic Foams: Synthesis, Properties, and Applications

“…With this setup, continuous monitoring of the expansion, temperature at different positions, and the changes of mass of the foam all along its growth is possible. This study provides a new method for foam optimization [131].…”

Comparing Condensed and Hydrolysable Tannins for Mechanical Foaming of Furanic Foams: Synthesis and Characterization

“…Tannin foams can be easily produced using condensed tannins (mimosa, quebracho, pine and spruce) [ 12 , 31 , 32 ]. Conversely, hydrolysable tannins are much less reactive and little research was conducted on their use for polymerization processes.…”