Table 1 FT-IR analysis of WPC derived from AL, DA, LHW and AFEX pretreatment
Wavenumber/cm−1 | Origin | Attribution and description of FT-IR absorption | Wavenumber cm−1 | |||
|---|---|---|---|---|---|---|
AL-WPC | DA-WPC | LHW-WPC | AFEX-WPC | |||
3200–3400 | O–H | Wide absorption band, aliphatic and aromatic O–H stretching | 3308 | 3308 | 3308 | 3308 |
3350–3200 | CONH2 | [36], N–H absorption, double peak | NA | NA | NA | 3210 and 3348 |
2908–2992 | CH3, CH2 | Aliphatic and aromatic O–H stretching | 2925 | 2925 | 2925 | 2939 |
1650–1660 | CONH, CONH2 | C=O stretching vibration | NA | NA | NA | 1654 |
1610–1550 and 1420–1300 | COO– | Carboxylate | 1567 (1410) | 1567 (1410) | 1567 (1410) | 1567 (1410) |
1600 (1450) | Ar | Aromatic hydrocarbon | 1600 (1450) | 1600 (1450) | 1600 (1450) | 1600 (1450) |
1507–1515 |  | Aromatic skeletal vibration; G > S | 1509 | 1509 | 1509 | 1509 |
1267 | O–, CO–O | G ring and acyl-oxygen bond CO–O stretching vibration | NA | NA | 1267 | NA |
1237–1241 | OCH3 | Methoxyl, C–C and C–O stretching vibration; C]O stretching vibration (condensed G > etherified G) | 1235 | NA | 1239 | 1236 |
1168–1170 | COOC | HGS characteristics; conjugated ester-based C=O stretching vibration | NA | NA | NA | 1169 |
1126–1127 | C–H, C–O | C–H aromatic-plane bending vibration, characteristics of S ring; coincide with secondary alcohol C–O stretching vibration | 1127 | 1126 | 1126 | 1127 |
1035–1045 | C–H, C–O | C–H aromatic in-plane bending vibration, G > S; primary alcohol C–O stretching vibration | 1042 | NA | 1042 | 1038 |
834–835 | C–H | S ring C–H out-of-plane bending vibration | 835 | NA | NA | 835 |