Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures

Abstract

This review presents different chemical modifications of tannins, an abundant source of aromatic biomolecules, to elaborate biobased polymers.

Tannin-based biosorbents for environmental applications – A review

“…The use of petrochemical solvents should be avoided, considering the related negative environmental effects, flammability and toxicity risks. In the last years, new extraction methods have been also developed, such as microwave-assisted extraction (MAE), ultrasoundassisted extraction (UAE) and pressurized liquid extraction (PLE), which can bring important improvements for the extraction of these bio-compounds [16]. Among the various methods that can be found in literature, a simple and eco-friendly procedure should be selected to extract tannins for biosorbents production.…”

“…There are no universal conditions for extracting tannins from vegetable sources [16]. The yield and the composition of extracts depends on the source, type of solvent, extraction time, temperature, solid-liquid ratio, and preparation of the sample, which is commonly milled, used in fresh, frozen or dried state.…”

“…The traditional industrial method for tannin extraction from vegetable matter is exactly based on hot/boiling water, with temperatures ranging from 50 to 110°C, using autoclaves working in counter-current, contact times of several hours (6-10 h) and water/wood ratios equal to 2-2.4 in mass. Tannins are then concentrated, by evaporation under vacuum, to limit the oxidation [16,29].…”

“…On the basis of their structural characteristics, however, a classification into four major groups is preferable: gallotannins, ellagitannins, complex tannins, and condensed tannins [16,17]. Hydrolysable tannins can be fractionated into simple components, by treatment with hot water or by enzymes [17].…”

“…Tannins are inexpensive and ubiquitous natural polymers [14], polyphenolic secondary metabolites of higher plants, mainly present in soft tissues (sheets, needles or bark) [15,16]. After cellulose, hemicellulose, and lignin, tannins are the most abundant compounds extracted from biomass [16], leaves, roots, bark, seeds, wood and fruits [17].…”