Lignin
Also searched as: lignification, monolignol polymer, woody polymer, phenylpropanoid polymer
A cross-linked aromatic polymer in plant cell walls that stiffens and waterproofs tissue; in bast fibers it helps bind cells together and affects stiffness, color and processing.
In detail
Lignin fills spaces in secondary cell walls between cellulose microfibrils and hemicellulose, making woody tissue rigid, water resistant and harder for microbes to break down. It forms by oxidative coupling of monolignol radicals, so unlike cellulose or proteins it has no regular repeating sequence. Wood is heavily lignified, whereas textile bast fibers such as flax contain only a few percent, found partly in the outer secondary wall layer. Retting, scutching and chemical degumming aim to free fibers from the woody core and reduce the non-cellulosic material, including lignin, that would otherwise make yarn coarse and stiff.
The science and numbers
Lignin is assembled from three monolignols, p-coumaryl, coniferyl and sinapyl alcohols, which enter the polymer as p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units. They differ in the number of methoxy groups on the aromatic ring, which affects how they can couple. Oxidized monolignol radicals join in several bond types, giving a heterogeneous network, and plants also incorporate minor phenylpropanoid units such as hydroxycinnamyl aldehydes and p-coumarates. In flax fiber, reported compositions are about 2 to 5% lignin alongside roughly 64 to 78% cellulose and 12 to 17% hemicellulose. In jute, transgenic suppression of monolignol biosynthesis genes lowered fiber lignin by about 13 to 14% relative to controls, showing that the pathway can be targeted to ease fiber processing.
A practical example
A researcher compares two batches of hemp from the same field, one well retted and one under-retted. The under-retted batch feels stiffer and splits only into coarse strands, and chemical analysis shows more residual lignin and pectin holding its fiber bundles together. The comparison shows that processing, not just plant species, determines how much lignin reaches the yarn and how finely the fiber can be divided.
What to distinguish
Lignin is not cellulose and is not a textile fiber on its own. A reported lignin content depends on the analytical method, such as acid-insoluble residue, and on whether whole stems or isolated fibers were analyzed, so figures from different studies may not be comparable. Research into lignin-derived materials or low-lignin crops says nothing about what is in a particular commercial fabric.
Origins and history
The name is built on the Latin lignum, wood. Once Payen had isolated cellulose from plant tissue in 1838, chemists turned to the other substances that held woody tissue together, and lignin became defined largely as what must be removed to obtain clean cellulose. Chemical pulping for paper and dissolving pulp still works mainly by stripping it out. Its exact structure proved hard to pin down because it forms by radical coupling rather than by a templated process.
Related terms
Sources & further reading
- Scientific Reports: Modification of monolignol biosynthetic pathway in jute, different gene, different consequence
- IntechOpen: Chemistry of lignin
- Cellulose (Springer): Extraction of cellulose fibers from flax and hemp, a review
- PubMed: The development, differentiation and composition of flax fiber cells
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.