Selective fractioning of Pseudotsuga menziesii bark and chemical characterization in view of an integrated valorization

Abstract

The outerbark of Pseudotsuga menziesii was chemically analyzed after selective fractioning into different particles sizes. Fractionation was selective: after grinding, the coarse fraction (>2mm) was enriched in cork and was obtained in higher yield (53.9%).The mean bark chemical composition was, as % o.d. mass: ash 5.9%; total extractives 26.7%; lignin 29.5% and suberin 22.0%. The fine fraction of bark was richer in extractives (31.7%) namely polar compounds soluble in ethanol and water (29.2%). The content in lipophilic extractives was higher in the coarse fraction (5.5%). The polysaccharides contained glucose (65.7% of total neutral monossacharides), mannose (11.8%), xylose (9.0%), arabinose (7.1%) and galactose (6.5%). The ethanol and water extracts contained phenolics, flavonoids, condensed and hydrolysable tannins. The lipophilic extracts were analysed by GC–MS, directly and after saponification, revealing two major compounds: β-sitosterol and tetracosanoic acid. The fine fraction was enriched in extractives and polysaccharides as well as in inorganics, and impoverished in suberin in comparison with coarse fractions.Milling and fractionation may be applied as pre-treatment for Douglas-fir bark utilization, by separation of cork-rich fractions for cork-based products e.g., composites, and phloem-rich fractions for extraction of polar extractives and further processing of the polysaccharide-lignin matrix under a biorefinery approach.