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. 2023 Feb 10;15(4):890.
doi: 10.3390/polym15040890.

Highly Branched Tannin-Tris(2-aminoethyl)amine-Urea Wood Adhesives

Bengang Zhang  1 , Xinyi Chen  2   3 , Antonio Pizzi  2 , Mathieu Petrissans  1 , Stephane Dumarcay  4 , Anelie Petrissans  1 , Xiaojian Zhou  3 , Guanben Du  3 , Baptiste Colin  1 , Xuedong Xi  3
Affiliations

Highly Branched Tannin-Tris(2-aminoethyl)amine-Urea Wood Adhesives

Bengang Zhang et al. Polymers (Basel). .

Abstract

Condensed tannin copolymerized with hyperbranched tris(2-aminoethyl)amine-urea formed by amine-amido deamination yields a particleboard thermosetting adhesive without any aldehydes satisfying the requirements of relevant standards for the particleboard internal bond strength. The tannin-triamine-urea cures well at 180 °C, a relatively low temperature for today's particleboard hot pressing. As aldehydes were not used, the formaldehyde emission was found to be zero, not even in traces due to the heating of wood. The effect is ascribed to the presence of many reactive sites, such as amide, amino, and phenolic groups belonging to the three reagents used. The tannin appears to function as an additional cross-linking agent, almost a nucleating agent, for the triamine-urea hyperbranched oligomers. Chemical analysis by MALDI ToF and 13C NMR has shown that the predominant cross-linking reaction is that of the substitution of the tannin phenolic hydroxyls by the amino groups of the triamine. The reaction of tannin with the still-free amide groups of urea is rather rare, but it may occur with the rarer tannin flavonoid units in which the heterocyclic ring is opened. Due to the temperature gradient between the surfaces and the board core in the particleboard during hot pressing, the type and the relative balance of covalent and ionic bonds in the resin structure may differ in the surfaces and the board core.

Keywords: 13C NMR; MALDI ToF; copolymerized networks; tannin; thermoset resins; tris(2aminoethyl)amine; urea; wood adhesives; wood panels.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Basic structure of a condensed tannin flavonoid unit.
Figure 2
Figure 2
TMA curve of the highly branched polymer-modified tannin resin.
Figure 3
Figure 3
TG curves (a) and DTG (b) of T0, T1, T2, and T3 resins in the 50–650 °C temperature range.
Figure 4
Figure 4
FTIR of the hyperbranched reaction product of tris (2–amino ethyl) amine with urea.
Figure 5
Figure 5
FTIR spectra of the highly branched polymer-modified tannin resins.
Figure 6
Figure 6
Chemical species (I–IV) are formed by the reaction of flavonoid units with the free triamine noy yet involved in the hyperbranched network.
Figure 6
Figure 6
Chemical species (I–IV) are formed by the reaction of flavonoid units with the free triamine noy yet involved in the hyperbranched network.
Figure 7
Figure 7
The only cyclic structure detected of the reaction of triamine with urea.
Figure 8
Figure 8
A higher molecular weight structure of the tramine-ureahyperbranched network.
Figure 9
Figure 9
An example of a detected structure with two flavonoid units linked to a triamine-urea hyperbrached network part.
Figure 10
Figure 10
An example of a detected structure with three flavonoid units, one of which a flavonoid dimer linked to a triamine-urea hyperbrached network part.
Figure 11
Figure 11
A rare example of a detected structure in which the amide group of a urea has reacted and linked to a flavoid unit of the tannin.
Figure 12
Figure 12
An example of a flavonoid unit linking two hyperbranched triamine-urea structures.
Figure 13
Figure 13
Cross-polarisation/magic-angle spinning (CP-MAS) 13C NMR spectrum of the reaction of the catechin model compound with hexamethylene diamine at 100 °C, NaOH-catalysed.
Figure 14
Figure 14
Cross-polarisation/magic-angle spinning (CP-MAS) 13C NMR spectrum of the reaction product of mimosa flavonoid tannin with the hyperbranched tris(2-amino ethyl)amine-urea polymer at 100 °C.
See this image and copyright information in PMC

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