Lignin product guide for industrial buyers
Lignin is the aromatic polymer that gives wood and bark their rigidity. Industrial lignin is recovered from pulping liquors and supplied in several forms that differ in solubility, pH and purity. Unlike lignosulfonates, lignin is not sulfonated, so most grades are insoluble in neutral water. This page explains what lignin is, how the commercial forms differ, and how to choose between lignin and lignosulfonate.
What lignin is
Lignin is one of the three main components of plant cell walls, together with cellulose and hemicellulose. It fills the spaces between polysaccharide fibres, makes the wall rigid and water-resistant, and lets vascular plants transport water under tension. Its name comes from the Latin lignum, wood.
Chemically, lignin is a cross-linked phenolic polymer formed by radical coupling of three monolignols: p-coumaryl, coniferyl and sinapyl alcohol, which appear in the polymer as H, G and S units. Softwood lignin is mainly G; hardwood lignin is G plus S; grass lignin also contains H units. The units are joined by aryl ether (especially β-O-4) and carbon–carbon bonds, producing an irregular polymer with no repeating sequence. This is why lignin’s properties depend strongly on the plant source and the extraction process.
The biosynthetic pathway has been substantially revised in recent decades. Plant cell walls tolerate large variations in lignin content and structure, which opens the way to crops with lignin tailored for processing (Boerjan, Ralph & Baucher, Annu. Rev. Plant Biol. 54:519–546, 2003, doi:10.1146/annurev.arplant.54.031902.134938).
How industrial lignin is produced
| Process | Product | Key characteristics |
|---|---|---|
| Kraft pulping (NaOH + Na2S) | Kraft lignin | Precipitated from black liquor by acidification; soluble in alkali, low sulfur bound as thiol groups; most kraft lignin is burned for mill energy |
| Sulfite pulping | Lignosulfonates | Sulfonated, water-soluble across the pH range; see lignin vs lignosulfonate |
| Soda pulping (non-wood) | Soda lignin | Sulfur-free; from straw, bagasse and other annual plants |
| Organosolv and biorefinery pretreatment | Organosolv or hydrolysis lignin | Lower-modified, higher-purity lignins; an active development area |
The expansion of cellulosic biorefineries has created new opportunities to turn lignin into value-added products. These include carbon fibres, engineered plastics and thermoplastic elastomers, polymeric foams, fuels and commodity chemicals (Ragauskas et al., Science 344:1246843, 2014, doi:10.1126/science.1246843).
Green Agrochem lignin grades
Typical values from the current TDS documents. Batch results are on the shipment COA.
| Parameter | Lignin, acidic powder | Kraft lignin, alkaline powder | Lignin, liquid alkaline | Non-soluble lignin |
|---|---|---|---|---|
| Document | GAC-L | GAC-L | GAC-L | GAC-L-Non-soluble |
| Appearance | Black-brown powder | Brown powder | Black-brown liquid | Black-brown powder |
| Lignin content | 80% min | 80% min | 80% min | 50% min |
| pH | 4–7 | Around 9 | Around 9 | 4–6 |
| Water solubility | 0% (insoluble) | Soluble in alkaline media | Supplied as alkaline solution | Insoluble (100%) |
| Moisture / solids | Moisture around 10% | Dry matter around 95% | Solids around 50% | Moisture around 15% |
| Reducing sugar | Not stated | Not stated | Not stated | 0% |
Packaging: 20 kg or 25 kg woven bags with liner for powders; other packaging on request.
Lignin or lignosulfonate?
| Requirement | Usually better choice | Why |
|---|---|---|
| Water-soluble dispersant (concrete, dyes, pesticides) | Lignosulfonate or sulfonated lignin | Sulfonate groups give solubility and charge |
| Phenolic resin or adhesive partial replacement | Kraft or alkaline lignin | Reactive phenolic structure, no sulfonate |
| Carbon materials, fillers, composites | Lignin (acidic or kraft) | Higher carbon content, lower hydrophilicity |
| Binder in water-based processes | Lignosulfonate | Dissolves and forms adhesive bridges on drying |
| Alkaline formulations | Alkaline lignin powder or liquid | Soluble at high pH |
When lignin is sulfonated, molecular weight and degree of sulfonation largely determine dispersant efficiency. Sulfonated products can make some composites more hydrophilic, and for flocculant use they usually need cross-linking to raise molecular weight (Aro & Fatehi, ChemSusChem 10:1861–1877, 2017, doi:10.1002/cssc.201700082).
Qualification checklist
- Define the function: resin replacement, filler, carbon precursor, dispersant raw material or binder.
- Confirm form and solubility at your process pH.
- Request lignin content method, ash, sulfur, moisture and particle size for the exact grade.
- Test reactivity or compatibility in the actual formulation at laboratory scale.
- Check consistency across several lots before scale-up.
Documents and supply
Batch COA, TDS, SDS, samples, packaging options and quotations are available on request from info@greenagrochem.com. Related: lignin as a biopolymer, lignin vs cellulose.