Table 1. Occurrence of Lignin Molecular Structures and molecular Weights Following the Various Treatmentsa.
| Lignin sample | B1 | B2 | B3 | B4 | B5 | B6 | B7 |
|---|---|---|---|---|---|---|---|
| Bonding Motif | Abundance (mmol/g)b | ||||||
| Cα-Hα in β-O-4′ structures (excl. α-OEt) | 1.47 | 1.01 | 0.84 | 1.30 | 1.49 | 0.92 | 1.28 |
| Cβ-Hβ in β-O-4′ linked to G/H (incl. α-OEt) | 0.25 | 0.16 | 0.08 | 0.21 | 0.30 | 0.29 | 0.25 |
| Cβ-Hβ in β-O-4′ linked to S (incl. α-OEt) | 0.95 | 0.79 | 0.64 | 0.97 | 0.91 | 0.43 | 0.88 |
| total Cβ-Hβ in β-O-4′ | 1.20 | 0.95 | 0.72 | 1.18 | 1.21 | 0.72 | 1.13 |
| total Cα-Hα in β-O-4′ (incl. α-OEt) | 1.75 | 1.30 | 0.99 | 1.53 | 1.99 | 1.95 | 1.68 |
| β-O-4′ linked to S/(G + H) | 3.80 | 4.94 | 8.00 | 4.62 | 3.03 | 1.48 | 3.52 |
| oxidized (Cα) G units (aver. of C2 and C6) | 0.02 | 0.02 | 0.02 | 0.02 | 0.03 | 0.00 | 0.03 |
| oxidized (Cα) S units | 0.18 | 0.16 | 0.34 | 0.35 | 0.31 | 0.32 | 0.25 |
| Cβ-Hβ in α-oxidized β-O-4′ | 0.01 | 0.01 | 0.01 | 0.00 | 0.03 | 0.12 | 0.00 |
| oxidized Cα S (ox. Cα/aromatic S cont.) | 0.04 | 0.05 | 0.07 | 0.07 | 0.05 | 0.07 | 0.05 |
| oxidized Cα G (ox. Cα/aromatic G cont.) | 0.02 | 0.02 | 0.02 | 0.01 | 0.02 | 0.00 | 0.02 |
| β-5′ (average of Cβ-Hβ, Cα-Hα) | 0.12 | 0.08 | 0.06 | 0.10 | 0.12 | 0.38 | 0.00 |
| β-β′ (average of Cγ-Hγ, Cβ-Hβ, Cα-Hα) | 0.24 | 0.17 | 0.15 | 0.21 | 0.30 | 0.84 | 0.28 |
| β-1′ | 0.00 | 0.01 | 0.00 | 0.01 | 0.01 | 0.25 | 0.00 |
| Cα-ethoxylation in β-O-4′ linkages | 0.28 | 0.29 | 0.15 | 0.23 | 0.49 | 1.03 | 0.40 |
| methylene OEt | 1.11 | 0.74 | 0.68 | 0.92 | 2.09 | 9.81 | 2.73 |
| methyl OEt | 1.00 | 0.74 | 0.65 | 0.92 | 2.21 | 9.38 | 2.62 |
| Lignin End Groups | Abundance (mmol/g)b | ||||||
| p-hydroxycinnamyl alcohol (average of Cγ-Hγ, Cβ-Hβ, Cα-Hα) | 0.05 | 0.02 | 0.01 | 0.02 | 0.08 | 0.00 | 0.00 |
| cinnamaldehyde (average of Cβ-Hβ, Cα-Hα) | 0.06 | 0.02 | 0.01 | 0.01 | 0.01 | 0.00 | 0.03 |
| α methylene | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.02 | 0.00 |
| Hibbert ketone, Hγ | 0.00 | 0.00 | 0.00 | 0.00 | 0.04 | 0.28 | 0.00 |
| Lignin Aromatic Units | Abundance (mmol/g)b | ||||||
| G units (average of C6 and C2) | 1.06 | 0.89 | 1.12 | 1.36 | 1.71 | 1.15 | 1.27 |
| S units (C2.6-H2.6) | 4.01 | 2.95 | 4.27 | 4.90 | 5.85 | 4.34 | 4.79 |
| sum S + G | 5.07 | 3.84 | 5.39 | 6.26 | 7.56 | 5.49 | 6.06 |
| ratio S/G incl. A-oxidized units | 3.88 | 3.42 | 4.04 | 3.80 | 3.54 | 4.05 | 3.88 |
| methoxy groups | 7.20 | 5.24 | 4.23 | 6.06 | 9.02 | 11.46 | 8.14 |
| Lignin Hydroxyl Group | Abundance (mmol/g)c,d,f | ||||||
| aliphatic OH | 3.46 | 3.22f | 3.21 | 3.53e | 3.54 | 1.34 | 2.95 |
| C5 substituted/condensed OH | 1.35 | 1.15 | 1.05 | 1.18 | 1.46 | 2.05 | 1.38 |
| syringyl OH | 0.40 | 0.33 | 0.35 | 0.34 | 0.40 | 0.74 | 0.44 |
| 4-O-5′ | 0.69 | 0.64 | 0.51 | 0.69 | 0.76 | 0.92 | 0.74 |
| 5–5′ | 0.21 | 0.18 | 0.14 | 0.13 | 0.24 | 0.35 | 0.17 |
| guaiacyl OH | 0.54 | 0.50 | 0.46 | 0.49 | 0.61 | 0.68 | 0.51 |
| p-hydroxyphenyl OH | 0.13 | 0.05 | 0.07 | 0.05 | 0.14 | 0.16 | 0.05 |
| carboxylic acid OH | 0.21 | 0.13 | 0.13 | 0.13 | 0.20 | 0.17 | 0.15 |
| total phenolic OH | 2.02 | 1.69f | 1.58 | 1.73e | 2.21 | 2.89 | 1.94 |
| S-OH/G-OH | 0.74 | 0.66 | 0.76 | 0.69 | 0.65 | 1.08 | 0.86 |
| Sugar Units | Abundance (mmol/g)b | ||||||
| β-d-xylopyranoside | 0.04 | ||||||
| C2-H2 in β-d-xylopyranoside | 0.03 | ||||||
| C3-H3 in β-d-xylopyranoside | 0.05 | ||||||
| C4-H4 in β-d-xylopyranoside | 0.05 | ||||||
| C5-H5 in β-d-xylopyranoside (overlap) | |||||||
| Molecular Weightd | |||||||
| polydispersity index (Mw/Mn) | 5.8 | 5.6f | 2.7 | 2.7e | 4.9 | 2.0 | 2.7 |
| Mw (kDa) | 7.20 | 8.00f | 3.55 | 4.40e | 6.10 | 2.70 | 4.40 |
| Mn (kDa) | 1.25 | 1.40f | 1.30 | 1.60e | 1.25 | 1.30 | 1.60 |
| Lignin Aromatic Units by Pyrolysisg | |||||||
| S% | 63 | 61f | 68 | 67 | 37 | 49 | 62 |
| G% | 34 | 36f | 30 | 30 | 60 | 45 | 34 |
| H% | 3 | 3f | 2 | 2 | 3 | 5 | 4 |
a
Error for NMR quantification data was estimated to be ±0.1 mmol/g.
b
From HSQC and quantitative 13C NMR.
c
From HSQC, quantitative 31P NMR, and quantitative 13C NMR.
d
From GPC analysis.
e
Data previously published by Mu et al.14
f
Data previously published by Muraleedharan et al.31
g
From pyrolysis-GC/MS.