Reference

Cellulose & lignin

The chemistry and processing of cellulose and lignin: nanocellulose, paper additives, lignin as a source of aromatics and carbon fibres.

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.

  • Wood, cellulose and recalcitrance The microfibril-and-matrix architecture of wood, why recalcitrance is a design feature rather than a defect, and why the kraft process dominates despite burning roughly half the wood and the aromatic value of its lignin.
  • Nanocellulose: CNC, CNF and BNC How cellulose nanocrystals, nanofibrils and bacterial cellulose are isolated, why percolated hydrogen-bond networks give useful rheology and reinforcement, and why capillary forces during drying set the logistics limit.
  • Nanocellulose as a diffusion barrier The solution–diffusion physics of gas barriers, why the dense hydrogen-bonded network of CNC and CNF films stops oxygen and oil, why water sensitivity is that same network doing its job, and why defects and humidity are the real limits.
  • Where paper's dry strength comes from Dry strength as hydrogen bonding across a limited bonded area, why water beats those bonds at their own chemistry, and what starches, cellulosic polymers and enzymes actually contribute.
  • Sizing paper against capillary suction Why water wicks into paper, how rosin, AKD and ASA place hydrophobes against the fibre surface, and why sizing trades directly against bonding and paper permanence.
  • Why enzymes prebleach but cannot bleach What xylanase and laccase–mediator stages actually remove — redeposited xylan, hexenuronic acids, surface phenolic lignin — and why the final oxidative chemistry remains chemical.
  • The aromatics locked in lignin Why lignin's radical-coupled assembly makes it intrinsically heterogeneous, how the β-O-4 linkage distribution caps monomer yield, and why depolymerisation versus recondensation governs every valorisation route.
  • Carbon fibre from lignin Why PAN's drawable chains and pitch's liquid-crystal order dominate carbon fibre, what lignin's polyaromatic structure offers and costs in spinnability, voids and variability, and where a cheap imperfect fibre actually fits.
  • Non-wood fibres and grown packaging How fibre length, ash and silica cap non-wood papers at stationery grades, how mycelium replaces sheet formation with grown foams, and where each is genuinely better than wood pulp or expanded polystyrene.