Lignin-Based Nanolayers Create Nearly Invisible, Light-Responsive Coatings

Researchers from VITO and Vrije Universiteit Brussel (VUB) have developed an ultrathin coating from lignin. The team calls the material LignoGlow. It combines water resistance and mechanical strength with natural fluorescence. Possible uses include protective coatings, decorative surfaces, security features and smart packaging.

From Wood By-Product To Functional Coating

Lignin is a renewable polymer found in wood and other plant matter. Pulp and paper mills produce large amounts of it as a by-product, yet most of it is simply burned for energy instead of being put to better use. Higher-value applications, such as resins and advanced materials, are now emerging.

The researchers took a different approach: they first broke lignin down into smaller fragments (depolymerization), then chemically modified it and combined it with a glycerol-based ingredient (another renewable resource) to create a liquid resin that hardens under UV light.

The team created continuous coatings between approximately 170 and 1,690 nanometres thick. The tested formula contained 40% modified lignin and 60% glycerol-based material.

The renewable content depends on the source of the other chemicals. The lignin component in this study contained about 75% biobased ingredients. According to the researchers, fully renewable chemicals could raise this figure to 100%.

Almost Invisible In Daylight

Lignin has a natural brown colour. This can restrict its use on surfaces that require a neutral appearance. However, very thin LignoGlow coatings become almost invisible in normal daylight.

The thinnest layer looked similar to untreated glass. Thicker coatings developed a light yellow colour.

LignoGlow also repelled water and remained stable up to about 270°C. The researchers applied it to glass, metal, wood, rubber-like materials and hydrogels. They also transferred free-standing films onto curved and uneven surfaces.

Tests on steel showed moderate adhesion. Therefore, the team must improve and test the bond for each practical application.

Fluorescence Without Added Dyes

LignoGlow glows under UV light without any added dyes or inorganic pigments; the effect comes from the lignin itself. Designers could use this to create hidden patterns that stay out of sight in daylight but appear under certain UV wavelengths. Potential applications include anti-counterfeit labels, information displays, and decorative finishes, adding a light-responsive feature to products and packaging.

The team also coated water-rich hydrogels with the nanolayers, and the coatings stayed intact and kept glowing even when submerged in water.

LignoGlow remains a proof of concept. More research must confirm its durability and performance in industrial settings. Still, the study shows a new use for lignin. It turns this common plant-based resource into a thin, functional surface while using very little material.

Source: ACS Applied Materials & Interfaces
Images: VITO