Influence of storage on the physical and chemical properties of Scots pine bark

Abstract

Bark is currently used mainly to produce energy, but the extraction of valuable compounds before combustion offers an interesting cascading use for debarking biomass. Buffer storage is an inevitable part of bark biomass logistics, but substantial dry matter and extractive losses can degrade the properties and reduce the economic value of the raw material during storage. In this study, moisture and ash content, calorific value, and extractives content and composition of Scots pine (Pinus sylvestris) sawmill bark were determined over 2 months of buffer storage, and the change in energy content during storage was calculated. The results showed that the energy content (MWh m−3) of the bark increased 3% during storage, while at the same time the moisture content decreased 16%. The content of acetone-soluble extractives decreased markedly, with only 56% of the original amount remaining after 8 weeks of storage. In particular, hydrophilic, phenolic extractive compounds were rapidly lost after debarking and piling of the bark. About 60% of condensed tannins (CT) and about 26% of the quantified lipophilic compounds were lost after 2 weeks of storage. The fastest rate of decrease and the most significant changes in extractives content and composition occurred within the first 2 weeks of storage. Utilization of these valuable compounds necessitates fast supply of material for further processing after debarking. The comprehensive utilization of bark requires efficiency at all levels of the supply chain to ensure that tree delivery times are kept short and loss of bark is avoided during harvest and transport.