Finnish softwood bark contains large amounts of water-soluble tannin-polyphenols, which can be used as renewable alternatives to the fossil and toxic phenol compounds widely used in glues. VTT Technical Research Centre of Finland, the Natural Resources Institute Finland (Luke) and the South-Eastern Finland University of Applied Sciences (Xamk) are developing an industrial production method for a polyphenol extraction process as part of the SusBinders project.

Around 3 million tonnes of softwood bark are produced as a side-stream of the Finnish forest industry each year. Most of this bark is burned as is, or as a processing energy source in pulp mills. More efficient use of the bark would generate added-value from Finnish forest biomass and create new business.

Water-based extraction processes are presently used to produce tannin from tropical trees such as acacias. Currently tannins are mainly used for dying leather. Tannins are also suitable for glue applications, although, this use is relatively limited. However, they have huge market potential, since phenol-based glue resins have a global market of around 4 million tonnes per year and a value of EUR 10 billion. Phenolic resins are mainly used as binding agents in the production of plywood and laminates.

The SusBinders project involves the optimisation of extraction processes for separating polyphenolic value components from bark. Suitability of the components for various glue applications is also analysed. Luke is focusing on optimising the extraction process and increasing the scale of production. Xamk is developing a continuous extraction process and is preparing and testing wooden panels glued with tannin-based glues. VTT is developing the purification of tannin extracts and is in charge of formulating the glues and resins. VTT is also assessing the technical and economic suitability and carbon footprint of processes and products and coordinating the project.

The project is being funded by Business Finland for Innovation, the research partners and private enterprises from various parts of the value chain. The total budget for the project component is EUR 728,000. The project, which was started in the summer 2017, will be completed on 31 May 2020.