Tannin-Based Copolymer Resins: Synthesis and Characterization by Solid State 13C NMR and FT-IR Spectroscopy

Abstract

In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials (e.g., adhesives, foams). In the present work we aim to observe the behavior of the extract of Acacia Mimosa (Acacia mearnsii) when reacted with several possible co-monomers at different relative amount, pH and temperature conditions. The more insoluble copolymers obtained with formaldehyde, hexamine, glyoxal, maleic anhydride, furfural and furfuryl alcohol were analyzed through solid state 13C NMR (Nuclear magnetic resonance) and FT-IR (Fourier Transform-Infrared) spectroscopy. The 13C NMR afforded the opportunity to detect: (i) aromatic substitutions and consequent poly-condensations for the majority of the hardeners studied; (ii) acylation for the maleic anhydride and also some; (iii) Diels–Alder arrangements for the furanic co-monomers; the FT-IR spectroscopy suggested that the formaldehyde and hexamine copolymers present a higher cross-linking degree.

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

“…The peak at 40 ppm and the shoulder at 38 ppm belong to the -CH2-next to the aldehyde group that has reacted with the tannin aromatic ring site. The other one possible explanation is that it belongs to -CH2-on the unreacted heterocycle C4 site of the flavonoid [64]. This is, however, unlikely, considering the intensity of the signal in relation to the low intensity of all the other signals of the flavonoid carbons.…”

“…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.…”

Applications of Tannin Resin Adhesives in the Wood Industry

“…Hydrolyzable tannin comprises different types of unit structures, including gallic, digallic, and ellagic acids (see Figure 1), as well as sugar esters, which usually exist in the form of glucose [2,3].…”

Characteristics, Industrial Application, and Prospects of Continuous Extrusion Technology

“…Its yield is second only to cellulose, lignin and hemicellulose. Tannins can be divided into condensed tannins and hydrolysable tannins according to their chemical structure [1][2][3][4] , as shown in Figure 1. Condensed tannins account for more than 90% of the total tannins [4,5] .…”