Wondering what is lignin used for? Most of it is burned as fuel in pulp mills, while a small share becomes dispersants, concrete additives, adhesives and other products.
Lignin is part of the wider what is the bioeconomy story, because it is a plant-based material that industry is still learning to use well.
| Item | Value |
|---|---|
| Lignin in softwood | 25% to 31% |
| Lignin in hardwood | 16% to 24% |
| Lignin produced worldwide each year (pulp industry) | Approximately 50 million tons |
| Share of that lignin burned for steam and energy | 98% to 99% |
| Share turned into lignosulfonates | 1% to 2% |
The figures come from a BioResources review of kraft lignin. Estimates differ between studies and change over time, so check the source before you rely on them.
What lignin is and where it comes from
Lignin is an aromatic polymer found in the cell walls of plants. It helps give wood and stalks their stiffness. In wood, the review reports that lignin makes up 16% to 24% of hardwood and 25% to 31% of softwood.
Its structure is messy. The same review notes that lignin has a heterogeneous chemical structure and high polydispersity, which can lead to undesirable properties that affect its use in new products. The exact makeup also varies with the plant: softwood, hardwood or grasses.
Industry meets lignin mainly as a by-product of making paper pulp. In the kraft process it is the main organic component of black liquor, the dark liquid left after wood chips are cooked.
The review calls lignin the second most abundant biopolymer after cellulose. It describes lignocellulosic biomass as the most abundant renewable material in the world, with three main components: cellulose, hemicellulose and lignin.
That abundance is the reason people keep asking what lignin is used for. A material that is produced in large quantities by the pulp industry, and that is renewable, is hard to ignore when fossil fuel prices and environmental rules push industry toward plant-based inputs.
The three components play different roles:
- Cellulose is the fiber that paper and many bio-based products are made from.
- Hemicellulose is a related carbohydrate fraction that can be turned into sugars.
- Lignin holds the structure together and is the part with an aromatic, phenol-like chemistry.
Is lignin mostly burned?
Yes. The review states that approximately 50 million tons of lignin are produced worldwide annually, and that 98% to 99% of it is incinerated to produce steam and process energy.
This is not simply waste. In kraft mills the lignin acts as a fuel feedstock, and the burning powers the mill itself. Burning it also helps the mill recover pulping chemicals and reduce its need for outside energy.
The catch is that burning gives the lignin only its fuel value. Many researchers see that as a missed chance, since lignin is one of the few abundant natural sources of aromatic chemical structures.
Main uses beyond fuel
The best-established product is the lignosulfonate, made from lignin in sulfite pulping. The review says only 1% to 2% of the lignin goes into chemical conversion to make lignosulfonates, and that in sulfite mills the lignin is sold after a minor chemical treatment.
Lignosulfonates have a wide range of uses, according to the review:
- dispersants and surfactants
- animal feed
- pesticide formulations
- petroleum drilling additives
- stabilizers in colloidal suspensions
- plasticizers in concrete mixtures
Kraft lignin is a newer candidate. The same review says it can be used as dispersants, technical carbons such as carbon fibers, transportation fuels, bioplastics and adhesives. It adds that technological hurdles remain and that several industrial tests must be developed before these uses are viable.
Two routes therefore dominate today. Kraft mills burn lignin for energy, and sulfite mills sell it as lignosulfonate. Possible kraft-lignin uses, including technical carbons and bioplastics, still need technical work, according to the review.
When you see a claim that lignin is “a new wonder material”, read it with that split in mind. The established market is small and specific, while the larger opportunities are still being tested.
Lignin in materials and plastics
The review lists adhesives among the possible uses of kraft lignin. It is also studied as a filler or building block in plastics. If you want the wider picture of plant-based plastics, see the guide to types of bioplastics.
Carbon fiber is another goal. As the review notes, however, this and other uses still face technical hurdles.
Adhesives deserve a closer look. The review lists adhesives among the kraft lignin uses it considers possible, and lignin’s phenolic hydroxyl groups are the chemical feature that makes this plausible. The same review also lists bioplastics, which is the other materials route to watch.
In practice, technological hurdles and the need for industrial tests limit these possible uses of kraft lignin.
Why lignin is hard to use and what comes next
Lignin does not behave like a single, pure chemical. Its structure depends on the raw material and on the extraction method, which means each technical lignin has different properties.
That variability makes consistent products difficult. A buyer wants the same quality every time, and lignin from different plants and mills rarely offers that.
There is also a trade-off for mills. Because the review says nearly all lignin is burned for steam and energy, taking lignin out of the furnace means a mill must find other energy or accept less of it. Any new use has to be worth more than the fuel value it removes.
Three questions help you judge any proposed lignin product:
- Does it work as well as the fossil-based product it replaces?
- Can the supplier deliver the same lignin quality every time?
- Is it worth more than the energy value lost by not burning the lignin?
Lignin is also a candidate for the integrated plants discussed in the guide on what is a biorefinery. In that model, cellulose, sugars and lignin each become separate products instead of lignin being treated as a leftover.
For a reader new to the subject, the takeaway is simple. Lignin is plentiful and chemically interesting, but today it mostly serves as mill fuel. The growth areas are the ones where its aromatic structure can replace something made from fossil sources.
Watch for two signals as the field develops: reliable, repeatable lignin grades, and products that reach a commercial scale instead of staying at the trial stage.
Frequently asked questions
What is lignin made of?
Show answer
Lignin is an aromatic polymer built from phenolic units linked together in a complex network. Its exact composition varies between softwood, hardwood and grasses.
Is lignin the same as lignosulfonate?
Show answer
No. Lignosulfonate is a product made from lignin recovered from sulfite pulping, used as a dispersant, a concrete plasticizer and in other roles.
Why is most lignin burned?
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Burning provides steam and energy for the pulp mill. Higher-value uses face technical hurdles, so only a small share of lignin goes to chemical products.
Can lignin be used in concrete?
Show answer
Yes. The review lists plasticizers in concrete mixtures among the uses of lignosulfonates.
