Journal of Spectroscopy

Research Article

A Simple Approach to Distinguish Classic and Formaldehyde-Free Tannin Based Rigid Foams by ATR FT-IR

Table 2

FT-IR absorption bands of the tannin and furanic polymers.


Peaks (cm⁻¹)	Tannin-formaldehyde polymer (TF)	Polyfurfuryl alcohol (PFA)	Classic TBRF	Formaldehyde-free TBRF	Template compounds^*	Assignments

3545–3405		L			Furfural, furfuryl alcohol, pyrogallol.	O–H stretch.
3280	L		L	L	Phenol, resorcinol, benzyl alcohol, furfuryl alcohol, pyrogallol, catechin, flavonol.	O–H stretch.
3100		S			phenol, benzaldehyde, furfural, furfuryl alcohol, benzofuran, flavonol, diphenylmethane.	C–H stretch. Aromatics, also PFA [22]
2920	M	M	M	M	Methanol, diethyl ether, benzyl alcohol, furfuryl alcohol, catechin, diphenylmethane.	C–H stretch. Aliphatics [22].

1710	L	L	L	L	Benzaldehyde, furan, furfuryl alcohol, benzofuran.	C=O stretch (furan ring opening), formaldehyde activated tannin.
1610	L	M	L	L	Phenol, resorcinol, benzyl alcohol, catechin, benzofuran, flavonol, diphenylmethane.	C=C stretch. Aromatics (6C) [22, 25] also flavonoids [25].
1560		M			Furfuryl alcohol, flavonol, benzofuran, diphenylmethane.	C=C–H stretch. symm. aromatic (in-plane) [26] also furanics [22, 27].
1505		S	M	M	Phenol, guaiacol, benzofuran, furfuryl alcohol.	C=C–H stretch. asym. aromatic (in-plane) [27] also furanics [22, 27].

1450	L		L	L	Resorcinol, benzyl alcohol, benzaldehyde, furfural, pyrogallol, catechin, flavonol, diphenylmethane.	C–H bend. asym. aromatic [22, 28] also flavonoids [29], C–O stretch. Aromatic (6C) [17].
1420		S			Furfuryl alcohol, flavonol, diphenylmethane.	C–H bend. In-plane O-containing aromatics; C=C stretch ring B [25]
1360		S			Benzyl alcohol, furfural, furfuryl alcohol, benzofuran, pyrogallol, catechin, flavonol.	C–H bend. symm. in-plane aromatic conjugated sequences of polymer backbones.
1290	M	S	M	M	Phenol, resorcinol, benzaldeh., pyrogallol, catechin, flavonol.	C–O stretch. Aromatics (6C) [25] (also ring B of flavonoids) [29].
1210	M		S	S	Benzyl alcohol, guaiacol, flavonol.	O–H bend. in-plane deformation.
1160	S	L	M	M	Phenol, resorcinol, guaiacol, furan, furfural, furfuryl alcohol, benzofuran, pyrogallol.	C–O stretch. Aromatics [25, 27] also ring A of flavonoids and also furanics; H–C–C bend. Ring B [25].

1120			M	S	Methanol, diethyl ether, guaiacol, catechin, flavonol.	C–O stretch. Aliphatic, methylene-ether bridges. [27]
1080	L		S		Phenol, resorcinol, benzaldehyde, furfural, furfuryl alcohol, catechin, flavonol.	C–H bend. also ring B of flavonoids [28, 29]; =C–O–C= stretch [17, 27].
1035		S	L	L	Benzofuran.	=C–O–C= stretch [27, 28].Breathing oxoaromatic compounds.
1010	S	M	L		Furfural, furfuryl alcohol, benzofuran.	=C–O–C= stretch [17]. Breathing oxoaromatic compounds, methylene-ether bridges and methoxy activation.

970		M			Resorcinol, furan, furfuryl alcohol, catechin.	C–O stretch. Aromatic (6C) also flavonoids [17, 25, 29] and C–H bend. aromatic Out-of-plane asym.
880		M	S	S	Phenol, furfural, furfuryl alcohol, catechin, flavanol.	C–H bend. out-plane asym., also furanics.
840			S	S	Resorcinol, benzyl alcohol, furfural, pyrogallol.	C–H bend aromatic out-plane asym [28].
810			S		Benzyl alcohol, catechin.	C–H bend. aromatic out-plane symm.
780		L			Benzofuran, naphthalene.	C–H bend. aromatic out-of plane conjugated furanics.
730		S			Resorcinol, benzyl alcohol, difurfuryl ether, furfural, pyrogallol.	C–C–C ring bend. symm., C–H bend. out-of-plane symm. [28]. Also furanics.
680			L		Phenol, resorcinol, benzaldehyde, catechin, flavonol.	C–C–C ring in-plane stretch. C–H bend. out-of plane symm. (6C) [21].
650		S			Methylfuran, naphthalenediols.	C–C–C ring in-plane stretch. Conjugated aromatics.

According to the Spectral Database for Organic Compounds SDBS (http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi).
L = large; M = medium; S = small.