Search

Funding Information: This work was supported by Business Finland corona-co-creation funding for the project Antiviral Fibers?pilot with extracts from Finnish forests (grant: 40699/31/2020). This study was also funded by the Natural Resources Institute Finland?s strategic research funding to the projects ?More, faster, higher quality: potential of short-rotation aspen and willow biomass for novel products in bioeconomy? (AspenWill) and ?Added value potential of new and under-utilized fibre sources in Finnish value networks of green bioeconomy: prefeasibility, prototyping, and market acceptance? (VALUEPOT). In addition, Academy of Finland has supported this study via the project ?Antivirals from Forest Biomasses: Structure, Function, and Applicability? (grant: 342250). Work was also funded by Jane and Aatos Erkko Foundation: Novel probes for discovering antivirals. Publisher Copyright: Copyright © 2021 Tienaho, Reshamwala, Sarjala, Kilpeläinen, Liimatainen, Dou, Viherä-Aarnio, Linnakoski, Marjomäki and Jyske. Earlier studies have shown that the bark of Salix L. species (Salicaceae family) is rich in extractives, such as diverse bioactive phenolic compounds. However, we lack knowledge on the bioactive properties of the bark of willow species and clones adapted to the harsh climate conditions of the cool temperate zone. Therefore, the present study aimed to obtain information on the functional profiles of northern willow clones for the use of value-added bioactive solutions. Of the 16 willow clones studied here, 12 were examples of widely distributed native Finnish willow species, including dark-leaved willow (S. myrsinifolia Salisb.) and tea-leaved willow (S. phylicifolia L.) (3 + 4 clones, respectively) and their natural and artificial hybrids (3 + 2 clones, respectively). The four remaining clones were commercial willow varieties from the Swedish willow breeding program. Hot water extraction of bark under mild conditions was carried out. Bioactivity assays were used to screen antiviral, antibacterial, antifungal,yeasticidal, and antioxidant activities, as well as the total phenolic content of the extracts. Additionally, we introduce a fast and less labor-intensive steam-debarking method for Salix spp. feedstocks. Clonal variation was observed in the antioxidant properties of the bark extracts of the 16 Salix spp. clones. High antiviral activity against a non-enveloped enterovirus, coxsackievirus A9, was found, with no marked differences in efficacy between the native clones. All the clones also showed antibacterial activity against Staphylococcus aureus and Escherichia coli, whereas no antifungal (Aspergillus brasiliensis) or yeasticidal (Candida albicans) efficacy was detected. When grouping the clone extract results into Salix myrsinifolia, Salix phylicifolia, native hybrid, artificial hybrid, and commercial clones, there was a significant difference in the activities between S. phylicifolia clone extracts and commercial clone extracts in the favor of S. phylicifolia in the antibacterial and antioxidant tests. In some antioxidant tests, S. phylicifolia clone extracts were also significantly more active than artificial clone extracts. Additionally, S. myrsinifolia clone extracts showed significantly higher activities in some antioxidant tests than commercial clone extracts and artificial clone extracts. Nevertheless, the bark extracts of native Finnish willow clones showed high bioactivity. The obtained knowledge paves the way towards developing high value-added biochemicals and other functional solutions based on willow biorefinery approaches.

The overall aim of the project was to systematically evaluate the suitability of softwood tannins for wood resin and hot melt applications including the development of adhesive formulations for both applications. Furthermore the aim is to improve the process economy. Therefore, optimizing the extraction step and improving the extraction yield of tannins and the stability of tannins in liquids were project objectives.In the project, VTT Technical Research Centre of Finland Ltd. (coordinator), the Natural Resources Institute Finland (Luke) and the South-Eastern Finland University of Applied Sciences (Xamk) have evaluated technologies for an industrial production method of tannin from softwood bark and performed application tests.The project delivered a realistic estimate of the yield for crude tannin in an industrial set-up. The yield of solubilized material in pilot extractions were up to 14 w% from finely ground spruce bark in a batch process in VTT’s pilot extraction, 10 w% in a batch process with flow through in Luke’s pilot extraction and up to 7 w% in the newly developed continuous extraction using 8% consistency at Xamk. The lower yield compared to up to 20% in the literature, can be partly explained by the fact that bark stream in pulp and saw mills contain substantial amounts of wood. In project samples from a saw mill, 20 % and 30% wood content were estimated for bark from spruce and bine bark, respectively. The yield of crude tannin from pine bark remained lower in pilot extraction trials with 7.8 w% yield. In agreement with earlier findings, the most potential crude tannin extracts from spruce bark contained ~45% phenolic compounds, ~40% carbohydrates and ~5% ash for batch extractions at 90 or 110 °C.An approach to produce a purified tannin product enriched in phenolic compounds was developed. The performed steps were liberation of monosaccharides from the crude tannin by enzymatic hydrolysis of carbohydrates followed by nanofiltration in order to remove the liberated monosaccharides. In total, 50% of carbohydrates were liberated with an enzyme dosage of 10 mg/g DM. The fractionation with a nanofiltration membrane enabled 9-fold concentration of the enzymatically treated crude spruce bark tannin in pilot scale with successful removal of the liberated carbohydrates, resulting in enriched phenolic fraction. However, also the permeate contained some phenols. Thus, both monosaccharides and low molecular weight phenols can pass through NFG membrane, enlarging the average molecular weight of the fraction.In a shelf life study, it was observed that aqueous crude tannin products can be stored at +4°C for a period of 7 months preserving the reactivity against formaldehyde and without notable microbiological growth.The tannins from softwood bark were tested as phenol replacement in phenol-formaldehyde resins (thermosets) for plywood gluing and at a replacement level of 30%, crude pine tannin, the resins showed comparable adhesive bond strength as commercial wood resins in laboratory testing. Even 50% replacement level gave reasonable bond strength. Future work should be directed towards formulation to ensure water resistance. It could be demonstrated that a mixture of tannin and poly(DL-lactide-co-ε-caprolactone) is a potential hot melt adhesive. The copolymer can be used as a hot melt adhesive by itself, but the processability and adhesion towards uncoated boxboard increased with tannins.