Tannin foams are innovative materials obtained exploiting the capacity of tannin for undergoing poly-addition reactions and that of furfuryl alcohol to polymerize under acid catalysis. These materials are known for many years, but only recently they have been systematically studied and many of its properties have been evaluated.
The first generation of the tannin foams have shown good insulation properties and very significant resistance against fire but unfortunately they were produced with around 5% of formaldehyde needed for keeping the network stable and variable amounts of diethyl ether for allowing the blowing at room temperature. These two drawbacks have hindered the development of the foam for industrialization because formaldehyde is almost completely forbidden for inner application while diethyl ether is an easy-burning VOC.
In this study an important upgrading of the original formulation is presented. The synthesis of 100% natural formulation only catalyzed by heat is described. Due to this innovative approach, the toxic chemicals have been replaced with other bio-based resources so that the interest of the insulation industry is arisen again.
In particular, these second generation of foams have confirmed many of the properties of the first generation one with the significant advantages of being easily exploited as core material for many a wide range lightweight sandwich panels. The versatility of the new tannin-furanic formulations allows to produce composite materials with a broad set of decking materials according to performance required for the specific final application.
Key words: Core foams, Lightweight boards, natural resources, Tannin polymer
In very recent years, an innovative material has taken the attention of many scientists all over Europe: Tannin-based foams. This material initially studied from the group of Prof. Pizzi (Meikleham & Pizzi 1994) has started a deeper investigation line in the final years of the last decade (2009a,b). The results obtained in the first years of investigation were extremely interesting for the industrial applications. This material, indeed, presented a highly natural skeletal structure combined with good physical properties and therefore a great amount of research work in this direction was and is still done. For instance, Lacoste et al. were able to produce foams out of pine tannin (2013), Li et al. prepared elastic foams (2013) while Basso et al. (2011) developed a method to produce room-temperature tannin-foams increasing the amount of furanic derivative and consequently the energy of the polymerization process. In the same years the tannin foams were also investigated focusing in the more applicative purpose of producing lightweight panels based on formaldehyde-free tannin foams. Various formulations of formaldehyde-free tannin foams were developed for insulation purposes (Link et al. 2011, Kolbitsch et al. 2012, Tondi et al. 2014).
A general review of these works is presented in this...
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