Tree bark characterization envisioning an integrated use in a biorefinery

Abstract

Tree barks are considerable waste streams in forest industries, and a potentially interesting resource for biorefineries. Barks of six relevant tree species, namely poplar (Populus × canadensis), black locust (Robinia pseudoacacia), red oak (Quercus rubra), willow (Salix sp.), Corsican pine (Pinus nigra subsp. laricio) and larch (Larix decidua) were anatomically and chemically characterized. Anatomical analysis illustrated the structural heterogeneity of the different barks with occurrence of various cell types and their arrangement in phloem, periderm and rhytidome. Summative chemical analysis showed a high extractives content (14-30 wt%) for all barks. Black locust bark presented a substantial suberin content (10 wt%). The lignin content was similar for most barks (22-29 wt%), except for Corsican pine bark (45 wt%). Analytical pyrolysis demonstrated that softwood bark lignin was mostly G type with a small amount of H units, whereas for hardwood species S, G and H units were present, with low S/G ratios (0.3-0.7). The cell wall structural polysaccharides were rather low. Total monosaccharides ranged from 35 to 44 wt%, with glucose being predominant for almost all barks, followed by xylose in hardwood and mannose in softwood barks. Identification of the lipophilic extractives highlighted the predominance of resin acids for softwood barks, and fatty acids and triterpenoids for all barks. Analysis of the polar bark extracts revealed large variations in the content of phenolics (265-579 mg gallic acid equivalent/g extract), flavonoids (177-391 mg catechin equivalent/g extract) and condensed tannins (88-670 mg catechin equivalent/g extract). Furthermore, the polar extracts presented a high antioxidant potential (500-1209 mg trolox equivalent/g extract), as determined by the FRAP assay. Additionally, a very strong antioxidant activity (AAI > 2), as evaluated by the DPPH assay, was observed for all barks. In summary, the results highlight the marked anatomical and chemical interspecies variability in barks, thus suggesting the need for tailored biorefining approaches.

Quercus rotundifolia Bark as a Source of Polar Extracts: Structural and Chemical Characterization

“…The lipophilic content of bark is also of high interest due to its application in food-and medicine-related areas, and compounds such as sterols and triterpenes were also found, for example, in Q. faginea bark [23]. Furthermore, recent studies on the potential for biorefineries of oak barks highlighted Q. rubra, Q. laurina, and Q. crassifolia due to their chemical compositions (e.g., [24][25][26]). This diversity of organic and inorganic components is related with their structural and physiological functions, namely the phenol-based compounds for oak wood durability and biotic defense of oak trees [27].…”

Depolymerisation–hydrogenation of condensed tannins as a strategy for generating flavan-3-ol monomers

“…Larch ( Larix decidua ) bark – of which the composition was determined in an earlier study – was selected because of its high amount of ethanol and water soluble extractives. 45 To obtain a crude extract, we performed a Soxhlet extraction of this ground bark (<1 mm) using methanol as solvent (solid/liquid ratio of 21.4 g L −1 ). After exhaustive extraction (4 h of extraction, ∼4 cycles per h), the extraction yield was 22.5 wt% (relative to the larch bark).…”

Fire Retardancy of Cementitious Panels with Larch and Spruce Bark as Bio-Admixtures

“…The MC of panels made out of larch bark is generally higher in comparison to those of spruce bark. The test specimens of spruce bark achieved a total average MC of 13.15%, compared to 15.17% for larch bark ( Table 2 ) due to the differences on chemical composition: 28.8% lignin and 36% polysaccharides for larch bark [ 40 ] and 26.9% lignin and 47.9% polysaccharides [ 41 ] for spruce bark.…”