MALDI-TOF and 13C NMR Analysis of Tannin–Furanic–Polyurethane Foams Adapted for Industrial Continuous Lines Application

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 OPEN ACCESSPolymers 2014, 6 2986 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.

Preparation and Characterization of Condensed Tannin Non-Isocyanate Polyurethane (NIPU) Rigid Foams by Ambient Temperature Blowing

“…First of all, the peaks belonging to the tannins are relatively small. One can, thus, distinguish the shoulder at 157 ppm of the tannin C5 and C7, the wide peak at 153-155 ppm both belonging to the C9 of flavonoid units, and possibly the C=O of a urethane linkage does contribute [24]. The small peak/shoulder at 150 ppm more clearly belongs to a urethane linkage.…”

“…Furthermore, some foreseeable species in the preparation of the co-reaction of tannin-based biomass foam are shown in Table 3. In general, as shown in Figure 4, four types of flavonoid units are involved in the formation of condensed tannin-derived oligomers, i.e., Fisetinidin, Robinetinidin, Catechin, and Delphinidin, respectively [24,50,58]. The tannin-derived products will originate from the combination of these units with each other and with other reagents.…”

“…They are assigned to some tannin-hexamine reaction products. 13 C NMR is a useful technique to investigate the composition of the foams prepared [24,64,65]. The 13 C NMR spectrum of a tannin-based NIPU foam (T-Fs-7) is shown in Figure 6.…”

Furfuryl Alcohol a Versatile, Eco-Sustainable Compound in Perspective

“…In a related work, Basso et al successfully developed mixed phenolic-polyurethane-type rigid foams using tannin-furfuryl alcohol natural materials co-reacted with polymeric isocyanate which the method can be adapted for industrial continuous lines production, thus, opening up new possibilities for large-scale manufacture of these sustainable foams. The underlying technology for such tannin-based foams is on a self-blowing process with mild exothermic reaction due to the self-condensation reaction of the FA under acidic conditions thereby initiating rapid evaporation, at ambient temperature, of the organic volatile during hardening [136]. Similarly, relative low cost furanic foams (consisting only of FA systems) exhibiting excellent thermal stability under high temperatures has been investigated.…”

Vegetable Tannin as a Sustainable UV Stabilizer for Polyurethane Foams

“…[19,22,23] and constitute more than 90% of the world production of tannins. Due to its chemical structure (Figure 1), which constitutes a high amount of multiple phenolic hydroxyl groups, they could be used as a platform for producing reactive polyhydroxyl chemicals [24,25] and, hence, for precursors in polymer synthesis.…”