Bark from Nordic tree species – a sustainable source for amphiphilic polymers and surfactants

Many of the amphiphilic molecules, or surfactants, are produced from fossil-based raw materials. With the increasing awareness of the climate situation, focus has shifted toward more environmentally friendly solutions to replace fossil-based products. This has led to more interest towards the forest. The circular bioeconomy is focused on making use of residues and waste and on optimizing the value of biomass over time via cascading. Nowadays, bark is seen as a waste product by industries and mainly incinerated as solid fuel. The bark contains interesting compounds but some of these are only available in low amounts, less than 1 % in the bark, while other components are present in several percentages. However, some of these components are potential candidates for the manufacture of amphiphiles and there seems to be a strong match between bark availability and surfactant demand. The global amount of bark available is approximately 359 million m and more than 10 million m of industrial bark are generated annually in Sweden and Finland. The bark of Norway spruce, Scots pine and silver birch contains approximately 25–32 % of extractives and part of these extractives has a potential as a surfactant backbone. This matches the global surfactant demand of about 15.6 million tons. Therefore, industrial bark has a significant potential value as a raw material source for amphiphilic molecules and polymers. This review focuses on betulin, condensed tannin and suberin. These compounds have been studied on individually and methods to extract them out from the bark are well investigated, but to utilize them as amphiphilic compounds has not been explored. With this review, we want to emphasis the potential of using bark, what today is seen as a waste product, as a raw material for production of amphiphiles. Moreover, a techno-economic analysis has been performed on betulin, tannins and suberin.