Table 2.
Infrared bands and related molecular bond assignments
| No. | Bands (cm−1) | Band assignments (References) | PCA factora |
|---|---|---|---|
| 1 | 805 | Vibration of mannan in hemicellulose and CH out of plane bending in phenyl rings (Evans et al. 1992) | PC1 |
| 2 | 825 | CH out of plane bending in guaiacyl units (Faix 1991) | PC3 |
| 3 | 860 | C–H out of plane in position 2, 5, and 6 of guaiacyl units (Faix 1992; Boeriu et al. 2004) | PC3 |
| 4 | 900 | CH deformation of beta-glycosidic linkages in cellulose (Evans et al. 1992; Faix and Böttcher 1992) | PC1 |
| 5 | 945 | O–H out of plane deformation in carboxylic acid (Shearer 1989) | PC2 |
| 6 | 960 | CH out of plane deformation in lignin (Popescu et al. 2007; Gandolfo et al. 2016) | PC3 |
| 7 | 985 | CO stretching in cellulose (Herrera et al. 2014) | PC1 |
| 8 | 1005 | C–O stretch in cellulose (Liang and Marchessault 1959) | PC1 |
| 9 | 1025 | C–O stretching in primary alcohols in cellulose (Popescu et al. 2007) | PC1 |
| 10 | 1055 | C–O stretching of secondary alcohols (Faix 1991) | PC1 |
| 11 | 1105 | C–O–C stretching in cellulose and hemicellulose (McCann et al. 1992; Zhang et al. 2010) | PC1 |
| 12 | 1155 | C–O–C asymmetric stretching in cellulose and hemicellulose (Faix and Böttcher 1992; Popescu et al. 2007) | PC1 |
| 13 | 1185 | C–O stretching in Cellulose (Zhou et al. 2015) | PC1 |
| 14 | 1225 | OH vibration in guaiacyl ring, C–C, C–O, and C=O stretches in lignin (Chen et al. 2010; Zhou et al. 2015) | – |
| 15 | 1265 | C–O vibration in guaiacyl rings (Popescu et al. 2007; Chen et al. 2010) | PC3 |
| 16 | 1315 | CH2 wagging in crystalline cellulose (Colom and Carrillo 2005; Popescu et al. 2007) | PC1 |
| 17 | 1335 | CH of methyl groups in methoxy in amorphous cellulose (Colom and Carrillo 2005; Popescu et al. 2007) | – |
| 18 | 1360 | C–H deformation in cellulose and hemicelluloses (Evans et al. 1992; Mohebby 2008) | PC1 |
| 19 | 1385 | C–O stretching in cellulose and hemicellulose (Labbé et al. 2006) | – |
| 20 | 1405 | C=O in carboxylic groups in carboxylic acid, ester (Zhang et al. 2010) | PC2 |
| 21 | 1425 | C–H asymmetric deformation in methoxyl, aromatic skeletal vibrations, lignin (Faix 1992; Popescu et al. 2007) | PC3 |
| 22 | 1465 | C–H asymmetric deformation in methoxyl for lignins, asymmetric in—CH3 and CH2 in pyran for hemicellulose (Popescu et al. 2007; Chen et al. 2010) | PC3 |
| 23 | 1510 | C=C stretching of the aromatic ring, C=O bond vibrations in extractive compounds (Popescu et al. 2007; Zhou et al. 2015) | PC3 |
| 24 | 1590 | Skeletal vibrations from the C–C (Kubo and Kadla 2005; Vahur et al. 2011) | PC3 |
| 25 | 1610 | C=O stretching conjugated to the aromatic ring, and in carboxylic groups in lignin, carboxylic acid, ester compounds (Zhao et al. 2014) | – |
| 26 | 1635 | Absorbed O–H and conjugated C–O in polysaccharides (Genest et al. 2013; Karunakaran et al. 2015) | – |
| 27 | 1655 | Absorbed O–H and conjugated C–O in polysaccharides (Genest et al. 2013; Karunakaran et al. 2015) | – |
| 28 | 1690 | C=O vibration in carboxylic group in resin acid (Mizzoni and Cesaro 2007; Vahur et al. 2011) | PC2 |
| 29 | 1730 | C=O carbonyls in ester groups and acetyl group in xylan (Bodirlau and Teaca 2009; Zhou et al. 2015) | PC1 |
aBand assignment related to PCA factors (see Fig. 3: PC1 for polysaccharides, PC2 for terpenoids and PC3 for lignin)