Synthesis and Characterization of High-Performing Sulfur-Free Tannin Foams

Abstract

Tannin foams are green lightweight materials that have attracted industrial interest for the manufacturing of sandwich panels for insulation purposes. However, the dimensions of the cells and the presence of sulfur in the formulation developed until now have discouraged their upscaling. In this work, we present the synthesis and the characterization of the more promising small cell and sulfur-free materials. It was observed that, with respect to standard ones, foams catalyzed with nitric acid present similar physical properties and more phenolic character, which favors the absorption of ionic pollutants. Conversely, the foams blown with aliphatic solvents and surfactants present smaller pores, and higher mechanical and insulating properties, without affecting the chemical properties or the heating value. The combined foam produced with nitric acid as a catalyst and petroleum ether as a blowing agent result in sulfur-free and small cell material with overall improved features. These foams have been produced at 30 × 30 × 3 cm3, with high homogeneity and, to date, they represent the most suitable formulation for industrial upscaling.

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

“…Target pressure was set to 12 psi and the average of 10 measurements was calculated. Cell size and orthotropy were collected and calculated using a Nikon SMZ 1500 transmitted light microscope (Nikon, Tokio, Japan), by conducting at least 50 measurements for each foam as described previously [ 14 ]. Scanning electron microscopy (SEM) images were taken using a Zeiss Ultra Plus field emission scanning electron microscope equipped with an annular backscatter electron detector (Carl Zeiss AG, Oberkochen, Germany).…”

“…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 ].…”

“…One major drawback of these lightweight foams is their brittleness and relatively low mechanical stability. Although more stable foams can be produced by altering the acidic catalyst, blowing agent, or including additives [ 14 ], values higher than 0.2 MPa for compression resistance are hardly reported.…”

Mitigation of Ammonia Emissions from Cattle Manure Slurry by Tannins and Tannin-Based Polymers

“…Tannin-based adhesives have allowed the production of particle boards for interior use with properties comparable with urea-formaldehyde bonded ones [35][36][37] and zero formaldehyde emission [38], while tannin monoliths were applied for carbon-gel production [39][40][41]. In this context, the most attractive products are the tannin foams because, with their strong insulation performance [42], their versatility [43,44], and their outstanding fire resistance [45], they aim to replace synthetic insulation materials such as polystyrene and polyurethane in the green building construction [46,47]. One of the major drawbacks for the tannin foams is that their end-life has not been completely clarified yet.…”

State-of-the-Art Polymer Science and Technology in Italy

“…Conversely, the foams blown with aliphatic solvents and surfactants presented smaller pores, and higher mechanical and insulating properties, without affecting the chemical properties or the heating value. The combined foam produced with nitric acid as a catalyst and petroleum ether as a blowing agent result in sulfur-free and small cell material with overall improved features [10].…”