Cellulose & lignin
Two polymers, one tree: the hydroxyl chemistry that makes cellulose useful is the same chemistry that makes it vulnerable to water.
Wood is a composite of two polymers with opposite characters. Cellulose provides strength: crystalline microfibrils with a dense hydrogen-bond network. Lignin provides protection: an amorphous aromatic resin that makes wood durable — and makes it difficult feedstock. Nearly all the processing in this cluster is an attempt to separate the two without ruining either.
The cluster’s recurring ideas: the same hydroxyl chemistry that bonds paper together and builds barrier films also draws in water — the useful property and the application limit are one and the same. Lignin’s heterogeneity: assembled by template-free radical polymerisation, it forces depolymerisation to race recombination, and only part of its linkages can ever be won. And the logic of the kraft process: what dominates is not the cleanest chemistry but the one that closes its own reagent-recovery loop.
Start with cellulose, fibres & wood chemicals: it sets the structural vocabulary every other page leans on.
Articles 10
| Wood, cellulose and recalcitrance Wood is a fibre-reinforced composite built to refuse enzymes its sugar, and every industrial route to cellulose pays the same bill: the selectivity of delignification. |
| Nanocellulose: CNC, CNF and BNC Dividing cellulose until its internal surfaces become the product — and the same surface physics that makes it valuable makes drying nearly irreversible. |
| Nanocellulose as a diffusion barrier Crystalline cellulose blocks oxygen because the molecules have nowhere to dissolve and no free volume to diffuse through — and it admits water for exactly the same chemical reason. |
| Where paper's dry strength comes from Paper is held together almost entirely by hydrogen bonds that water outbids one for one — and every dry-strength additive either adds bond sites or enlarges the area where bonds can form. |
| Sizing paper against capillary suction Unsized paper is a bundle of micron-scale capillaries that drinks by Lucas–Washburn suction; sizing is the craft of turning the contact angle so the suction works backwards. |
| Why enzymes prebleach but cannot bleach Bleaching enzymes work by clearing access to lignin, not by removing it — and the same size constraint that makes them gentle makes a fully enzymatic bleach impossible. |
| The aromatics locked in lignin Lignin is the only large-scale renewable aromatic feedstock — and its central problem is a race: every bond cleaved to free a monomer is a chance for the fragments to weld back together. |
| Carbon fibre from lignin Carbon fibre strength is graphitic crystals aligned along the axis, and lignin — the cheapest aromatic feedstock there is — is an amorphous pitch with no way to align itself. |
| Non-wood fibres and grown packaging Sheet-making physics does not care what the fibre is — fibre geometry does — and the niches of grass paper, algae paper and mycelium packaging are the exact shape of their raw material's geometry and economics. |
| Why lignin comes first now Kraft chemistry turned lignin into fuel by accident of process; organosolv fractionation reverses the accident, and every downstream lignin market inherits the sulfur-free backbone that survives it. |