Abstract
Mixed phenolic-polyurethane-type rigid foams were developed using tannin-furfuryl alcohol natural materials co-reacted with polymeric isocyanate in the proportions imposed by the limitations inherent to continuous industrial plants for polyurethane foams. A variety of different copolymerization oligomers formed. Urethanes appeared to have been formed with two flavonoid tannin sites, mainly at the flavonoid hydroxyl group at C3, but also, although less, on the phenolic hydroxyl groups of the flavonoid oligomers. Urethanes are also formed with (i) glyoxal in the formulation, be it pre-reacted or not with the tannin; (ii) with phenolsulfonic acid and (iii) with furfural. This latter one, however, greatly favors reaction with the A-ring of the flavonoids through a methylene bridge rather than reaction with the isocyanate groups to form urethanes. All of the materials appeared to have co-reacted in a manner to form urethane and methylene bridges between all of the main components used. Thus, the tannin, the furfuryl alcohol, the isocyanate, the glyoxal and even the phenol sulfonic acid hardener formed a number of mixed species linked by the two bridge types. Several mixed species comprised of 2, 3 and even 4 co-reacted different components have been observed.
Highlights
Nowadays, there is an increasing demand for natural-based products in industrial applications, due to environmental issues and the depletion of non-renewable raw materials
The tannin was only used as an additive, but the finding of its co-reaction opened the way for the formulation of mixed copolymerized tannin–furanic–polyurethane foams in which the tannin and the furanic material are reacted, such as phenolic foam, while simultaneously reacting with an isocyanate
Tannin-furanic-polyurethane foams adapted for industrial continuous line application have been developed and applied, opening up new real possibilities for their large-scale manufacture
Summary
There is an increasing demand for natural-based products in industrial applications, due to environmental issues and the depletion of non-renewable raw materials. Increasing interest has been shown for these tannin-derived materials by foam manufacturing polyurethane companies because of their fire resistance and environmental-friendliness [6,7,8,11,12]. Some elastic foams obtained by partial co-reaction of a tannin as an additive to a mixture of components used for polyurethane foams has been described [15]. In this previous work, the tannin was only used as an additive, but the finding of its co-reaction opened the way for the formulation of mixed copolymerized tannin–furanic–polyurethane foams in which the tannin and the furanic material are reacted, such as phenolic foam, while simultaneously reacting with an isocyanate. The present paper describes this development, the type of reaction products obtained and the obtained foam’s characteristics
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