Table 4.
Signal assignment and relative intensities in the FTIR spectra of the lignin samples
| Peak (cm−1) | Assignment | Control | S = 3.6 | S = 3.9 | S = 4.2 |
|---|---|---|---|---|---|
| 3446 | O–H stretching vibration in OH groups (R–OH, Ar–OH) | 14.98 | 14.16 | 15.93 | 22.17 |
| 2925 | C–H stretching vibrations | 18.19 | 11.72 | 11.90 | 14.02 |
| 2849 | 6.73 | 3.83 | 3.67 | 4.95 | |
| 1770 | Unconjugated carbonyl groups (C=O stretch) | 0.70 | 1.22 | 1.56 | 1.65 |
| 1653 | Conjugated carbonyl groups (C=O stretch) | 63.01 | 75.08 | 80.54 | 95.00 |
| 1458 | C–H vibrations in –CH3 | 28.40 | 20.01 | 20.91 | 24.43 |
| 1370 | Phenolic hydroxyl groups (Ar–OH) | 5.32 | 5.03 | 5.20 | 10.93 |
| 1335 | R–OH in the lignin | 6.25 | 3.79 | 3.89 | 4.82 |
| 465 | The 2 or 2, 3, 4 overlay substitution of benzene ring | 404.80 | 408.19 | 421.17 | 569.49 |
The relative intensity was calculated as the ratio of the intensity of the band to the intensity of the band at 1795 cm−1
S stands for the pretreatment severity