From Bark to Better Materials: Rethinking a Natural Resource

More than just a by-product 

When trees are processed, bark is usually treated as a low-value by-product—often burned or discarded. Yet it makes up a significant portion of every tree and contains naturally occurring compounds with untapped potential. 

Instead of viewing bark as waste, it can be seen as a renewable raw material that can be used in more valuable and sustainable ways. 

What makes bark interesting? 

One of the key components found in bark is tannins. These are natural plant compounds that also occur in everyday products like tea or red wine, where they create a slightly dry, astringent sensation. 

Beyond this familiar context, tannins have useful chemical properties: they can form stable and durable structures. This makes them a promising bio-based alternative to synthetic materials, many of which are currently derived from petroleum. 

A demanding use case: transport surfaces 

In the transport sector, materials are exposed to constant mechanical stress. The interior surfaces of trucks, trains, and shipping containers are typically lined with plywood panels that are coated with protective layers. 

These coatings are essential to ensure durability and long service life. At present, such high-performance coatings are almost exclusively petroleum-based. 

A bio-based alternative 

By extracting tannins from bark, it is possible to develop a fully bio-based coating system for these demanding applications. 

This means that softwood bark is a sidestream, which can be used to replace fossil-based components in industrial coatings, without changing the function of the system. Importantly, this approach has already been successfully demonstrated: at Holzforschung Austria, tannins extracted from bark provided by VTT are further processed by mimicking resin formulations used in traditional petroleum-based systems using only bio-based components. This results in a fully bio-based resin, which is used to impregnate overlay paper. The impregnated paper can then be applied as a high-pressure laminate on transportation plywood. Mechanical performance is evaluated according to European standards and exceeds expectations, making this coating a very promising solution for replacing petroleum-based systems. The already developed formulation of the bark-based resin will be sent to Metsä for validation at industrial scale. Future work will focus on assessing bark extracts obtained under different extraction conditions and with varying compositions in terms of their influence on mechanical properties. 

Using bark as a raw material contributes to better use of existing biomass, reduces waste streams, lowers dependence on fossil resources, and supports a broader shift toward a more resource-efficient and circular use of materials.