Bark of siberian conifers: Composition, use, and processing to extract tannin

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.