Abstract
With increasing demand of alternatives to oil-based lightweight materials, the development of tannin-based foams is getting more and more attention. In this paper, an alternative to traditionally used solvent-evaporation in the production of tannin-foams is presented. Mixing the tannin-furanic resin with different amounts of ionic and non-ionic surfactants at high agitational speed allows for the formation of highly porous, mechanically stable tannin-foams. Investigations on the influence of surfactant type and ingredient ratios on the foaming behavior and properties of the final foams were conducted. Materials obtained via this route do present extraordinary compression resistance (about 0.8 MPa), good thermal insulation (40 mW/m·K) and are suitable as a wastewater treatment agent at the end-of-life. It was shown that during mechanical blowing, homogeneous cross-sections and almost perfectly round pores form, leading to the high compression resistance. Investigations by means of Fourier transform infrared and 13C nuclear magnetic resonance spectroscopy show that the milder reaction environment leads to more linear poly(furfuryl alcohol)-tannin chains. This new type of tannin foam allows for use in various different fields of application ranging from durable building insulation to wastewater treatment.
Highlights
In the past years different research groups around the world presented multiple formulations towards tannin-based rigid foams
Surfactant concentration is expressed as wt. −% based on the weight of tannin and furfuryl alcohol
40 g of tannin, a to furfuryl alcohol (T/F)-ratio of 1.6, and a T/A-ratio of 2.5. Results of these investigations are shown in form of a heat map in Figure 1, indicating the quality from the foams obtained by mechanical agitation
Summary
In the past years different research groups around the world presented multiple formulations towards tannin-based rigid foams 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]. 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
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