Abstract
The rational use of natural resources, including the creation of new and improvement of existing technologies in order to reduce the anthropogenic impact on the environment, is currently an important task. This review covers different methods of softwood bark processing. Bark is used for the production of heat-insulating plates, and also as filler in adhesives and composites. In agriculture, it is used as a mulch. Softwood bark is a valuable raw material for chemical processing. Extractive substances of the bark are of particular interest. Among them, phenolic compounds are very important, in particular of tannin nature, which are used as tanning agents in leather production. Bark is used for the isolation of substances with antibacterial activity for pharmaceutical and nutraceutical applications. Aqueous-alkaline solutions, in particular monoethanolamine, are used as an extracting agent. Currently, tannins have been applied into many different fields, including medicine, food, beverage, the manufacture of ink and adhesives, the dye and tanning industry, plastic resins, water purification, and surface coatings. Tanning extracts obtained as a result of extraction are refined by ultrafiltration. The obtained extracts are of high purity. The extraction residue, the so-called tan, is a promising raw material for obtaining a cellulosic product. In addition to the chemical conversion of tan, biotechnological processing is an alternative option. In the process of tan biodegradation by the microscopic Trichoderma fungus, a biological product trichodermin is obtained, which is used to protect plants from phytopathogens.
Highlights
Tanning extracts obtained as a result of extraction are refined by ultrafiltration
The main forest-forming species in the Krasnoyarsk Territory are conifers; they occupy more than 75.9% of the forested area, which amounts to 9.7 billion m3 ; the share of spruce and fir amounts to 16.0%
The use of monoethanolamine as an additive to the main extraction agent makes it possible to extract from softwood bark, for example, larch bark, up to 50% of phenolic substances, which makes the obtained extracts promising for further processing [96]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The total forest resources of the Krasnoyarsk Territory amount to 164 million hectares [2]. The main forest-forming species in the Krasnoyarsk Territory are conifers; they occupy more than 75.9% of the forested area, which amounts to 9.7 billion m3 ; the share of spruce and fir amounts to 16.0%. The crown, a part of the trunk, top, twigs, stumps, roots, and some foliage are left in the felling area as logging waste. Burning the bark is not cost-effective due to its low heating value and its high ash and moisture content It partially decomposes when stored for a long time, forming phenolic compounds, which are washed off by precipitation and meltwater. The problem of wood waste recycling is a weak point in integrated raw material processing [8,9,10,11]
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