Valorisation of lignocellulosic waste materials: Tannins as a source of new products

Tannins extracted from lignocellulosic industrial wastes, eucalyptus bark and chestnut shell, under different conditions (type and concentration of alkaline chemicals in aqueous solution and temperature), were analysed in order to establish their properties for different potential applications including: their use as phenol substitutes in the formulation of adhesives for wood derivatives and as chrome substitutes in leather tanning, and as a source of alternative antioxidants. Extraction yield was significantly greater for chestnut shell than for eucalyptus bark and the corresponding extracts showed much better properties for the uses proposed. For both materials the highest extraction yield was obtained using 10% NaOH and the lowest using water, however, water extracts showed the best properties. Extraction at 90oC with a 2.5% Na2SO3 aqueous solution has been selected as the optimum as extraction yield increased significantly with respect to the extraction with water and the characteristics of the extracts remained almost constant.