Holzwerkstoff- und Naturfaser-Technologien

Research project

FlammLig - Wood-based materials with integrated flame-retardancy through lignin adhesive

Renewable construction materials make buildings more sustainable. In order to enable a more extensive utilization of wood-based materials in high-rise construction and public buildings, flame-retardant treatment is necessary. In an emergency situation, this helps to prevent fires from spreading. The integration of conventional flame retardants is, however, accompanied by technical disadvantages. The vegetable raw material lignin could be the solution to this problem. In this project, we are developing a bio-adhesive on the basis of lignin, which simultaneously serves as a flame retardant. This adhesive enables the production of flame-retardant wood-based materials without technical disadvantages. Furthermore, we are thereby opening up an ecologically and economically interesting application possibility for lignin.

A piece of wood-based panel measuring 20 x 20 cm, from which a circular, foam-like structure rises in the center, which is heavily charred and blackened.
© Fraunhofer WKI I Torsten Kolb
Flame retardancy is ensured by the expansion and charring of the lignin flame retardant, the so-called “intumescence mechanism”; the example shown here is a fire test from an earlier project.

The flame retardancy of wood-based materials such as OSB, particle board or fiberboard can be achieved in various ways: either on the surface, by coating the wood-based materials, or by mass protection, i.e. the integration of flame retardants into the wood-based materials. A surface protection must be applied retrospectively and leads to optical alterations. Mass protection is therefore attractive for manufacturers and processors.

Inorganic substances such as ammonium polyphosphate, magnesium hydroxide or aluminum hydroxide are often used as flame retardants in the mass of wood-based materials. These flame retardants offer good environmental compatibility and are relatively inexpensive. In order to achieve sufficient flame retardancy, large application quantities are, however, required, as a result of which the mechanical properties of wood-based materials generally deteriorate.

The vegetable raw material lignin could solve this problem, as it has inherent advantageous properties and is available in large quantities. Lignin is one of the three main constituents of wood and a hitherto unused by-product from the paper-production industry. It is known that lignin can be used as both a bio-based flame retardant and - in modified form - as an adhesive. Until now, however, its flame-retardant effect has only been investigated in plastics, not in wood-based materials. 

The flame-retardant properties of lignin are attributable to the fact that it chars when exposed to intense heat. In combination with phosphorus and a gas generator, such as a nitrogen-containing molecule, it can therefore form an intumescent system. Intumescent systems expand in the event of a fire and insulate the wood, as a result of which the fire is considerably decelerated or extinguished. In our project, we therefore initially investigate combinations of lignin, phosphorus and gas-formers and test them regarding their flame-retardant effect.

We subsequently modify the lignin, enabling it to be used as an adhesive in the production of wood-based materials. Advantage: The adhesive which bonds the fibers and/or particles together - which is necessary anyway - provides the wood-based material with the desired flame-retardant effect. There is no need to add a supplementary flame retardant. As a result, the wood-based material retains its high proportion of fibers and/or particles. A flame-retardant on the basis of lignin can therefore be integrated without impairing the mechanical properties of the wood-based materials.

Simultaneously, we are creating a possibility for the high-quality utilization of lignin, which is currently being burned in pulp mills in order to generate energy.

With this project, we are making a contribution towards an increased use of bio-based construction materials and a more efficient utilization of plant-based raw resources such as wood. In doing so, we are supporting the development of a bio-based recycling economy (bioeconomy).

Funding

Official project title:
Machbarkeitsstudie zu flammgeschützten Holzwerkstoffen durch Nutzung von phosphoryliertem Lignin (Feasibility study into flame-retardant wood-based materials through the utilization of phosphorylated lignin)

Funding body: German Federal Ministry of Food and Agriculture (BMEL)

Funding reference: 2220HV032X

Project management: Fachagentur Nachwachsende Rohstoffe e. V.

Duration: 01.02.2020 to 31.10.2021

Funded by the Federal Ministry of Food and Agriculture by decision of the German Parliament
Fachagentur Nachwachsende Rohstoffe e. V. (Agency for Renewable Resources)