Table 2.
Comparative properties of softwood and hardwood lignins. *
| Softwood Lignin | Hardwood Lignin |
|---|---|
| Lignin content is ~ 28% | Lignin content is ~ 20% |
| Lignin dissociates faster in solution | Lignin dissociates slower in solution |
| Lignin self-associates greater in solution | Lignin self-associates less in solution |
| Harder to breakdown lignocellulosic biomass | Easier to breakdown lignocellulosic biomass |
| Coniferyl alchol primarily (~80%) | Coniferyl (~56%) and Sinapyl (~40%) alcohols |
| Guaiacyl (coniferyl alcohol derived) G-lignin | Guaiacyl-Syringyl (G-S) lignin; Syringyl is sinapyl alcohol derived lignin |
| Gymnosperms | Angiosperms, Dicotyledons |
| Molecular mass is larger than hardwood lignin | Molecular mass is lower than softwood lignin |
| Branching is higher | Branching is lower; Lignin is more linear |
| Cross-links are greater | Cross-links are fewer |
| C-C bonds are greater | C-C bonds are fewer |
| 5' Linkages more common | 5' Linkages less common |
| –OCH3 content is ~20% | –OCH3 content is ~14% |
| β-O-4 ether bonds are lower | β-O-4 ether bonds are higher |
| β-β and β-5 bonds are higher | β-β and β-5 bonds are fewer |
| Deconstruction is harder | Deconstruction is easier |
| Lignin is condensed | - - - - - |
* p-Coumaryl alcohol (p-hydroxyphenyl) derived lignin (H-Lignin) is more common among Graminaceous plants (grasses). The –OCH3 content is nearly zero in H-lignin. Monocotyledon angiosperms contain G-S-H lignin. Guaiacyl unit has one methoxy group whereas syringyl unit has two methoxy groups.