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

Abstract

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 m3 and more than 10 million m3 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.

Bioactive Fiber Foam Films from Cellulose and Willow Bark Extract with Improved Water Tolerance

“…This view is supported by another research, which argues that the hydrophobic domains of a polyphenolic compound, tannin from Acacia mearnsii bark, are oriented toward the surface while the hydrophilic domains adsorb on cellulose . The bark of various Nordic tree species, in general, is rich in amphiphilic compounds . Similar to any polyphenolic compound, the WBE consists of hydrophilic parts (OH groups) and more hydrophobic parts (aromatic rings).…”

“… 58 The bark of various Nordic tree species, in general, is rich in amphiphilic compounds. 59 Similar to any polyphenolic compound, the WBE consists of hydrophilic parts (OH groups) and more hydrophobic parts (aromatic rings). However, more research is needed to verify the exact mechanism behind the observed synergistic effects of WBE and AKD.…”

Resin acids play key roles in shaping microbial communities during degradation of spruce bark

“…Understanding how it can be degraded in nature by different microorganisms is key for future valorization, for instance using select enzymes, and can also be of high relevance to limit the harmful effects of wood-boring insects. Bark from other species contain other types of extractives, with for example birch bark being enriched in betulin and pine in condensed tannins 41 , and our study sets a basis for investigating whether degradation also of other bark types progresses via initial degradation of key 'gatekeeper' molecules that strongly inhibit the growth of but a few extractive-detoxifying microbial species.…”

“…Spruce is indispensable to the forest industry and is used for pulp and paper production in the northern hemisphere. Looking only at the Nordic countries, bark is an industrial side stream produced in close to 400 million m 3 per year 41 , which today is poorly utilized. Understanding how it can be degraded in nature by different microorganisms is key for future valorization, for instance using select enzymes, and can also be of high relevance to limit the harmful effects of wood-boring insects.…”

Resin acids play key roles in shaping microbial communities during degradation of spruce bark

“…Spruce is one of the dominant tree species in northern hemisphere forests and of high economic value, and its bark comprises around 10–15% of the volume at harvest. In the Nordic countries alone, bark is produced in close to 400 million m 3 per year 5 , but it is largely seen as an industrial side stream and is either left to rot in the forest or burnt for energy at the mill. In addition to wood polymers, spruce bark contains a high amount of lipophilic extractives, mainly resin acids (>10 mg/g dry bark), triglycerides (~8 mg/g), steryl esters (~5 mg/g), fatty acids (~2.5 mg/g), and sterols (~1.3 mg/g) (Fig.…”