VALORISATION OF LIGNOCELLULOSIC WASTE MATERIALS: TANNINS AS A SOURCE OF NEW PRODUCTS
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - Poster (CPD&E - P)
Keywords: tannin extraction, lignocellulosic wastes, adhesives, antioxidants
The increase in environmental awareness and in petroleum cost has raised the interest in the exploitation of renewable resources, such as lignocellulosic materials, for the development of new products and processes with a lower environmental impact. Moreover, the valorisation of wastes from industrial productions constitutes a new challenge of economically sustainable and environmentally friendly processes.
Eucalyptus globulus wood, one of the main forest species in Galicia (NW of Spain), is mainly used to produce cellulose pulp and wood panels. In both cases, bark is separated as a waste and used as fuel. On the other hand, chestnut (Castanea sativa) consumption in the food industry involves about 10000 t/year to produce derivatives such as marron-glacé, chestnut purée, etc. In the peeling stage chestnut shell is separated and also used as fuel.
In this work, tannins extracted from both industrial lignocellulosic wastes under different conditions, 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.
Chemical composition of both lignocellulosic materials was determined. Chestnut shell contains more extracts and lignin but less carbohydrates and ash than eucalyptus bark. The influence of extraction conditions (type and concentration of alkaline chemicals in aqueous solution and temperature) on extraction yield and Stiasny number, tannin content (hide-power test), total phenols content, FRAP (Ferric reducing/ antioxidant power) antioxidant capacity and molecular weight distribution of the extracts was analysed. FTIR spectra of crude materials and the extracts obtained were compared.
Extraction yield was significantly greater for chestnut shell than for eucalyptus bark. For both materials the highest extraction yield was obtained using 10% NaOH and the lowest using water (49.4 and 8.7% for chestnut shell and 18.9 and 6.8% for eucalyptus bark). However, water extracts showed the best properties. The Stiasny number, the total phenols content, the tannin content and the antioxidant capacity decreased when the alkalinity of the solution was increased. With respect to the influence of temperature, an increase from 70 to 90ºC implied, for all the alkaline compounds used, not only an increase in the extraction yield but also an improvement in the extract properties. For both materials linear relationships with high correlation coefficients were found among Stiasny number, tannin content, total phenols content and antioxidant capacity of the corresponding extracts.
Molecular weight distribution was in most cases bimodal for chestnut shell extracts whereas eucalyptus bark extracts showed multimodal distributions. Molecular weights of chestnut shell extracts were significantly higher than those of eucalyptus bark extracts. Both number and weight average molecular weights of the extracts diminished when increasing the severity of the alkaline extraction.
For both materials, extraction at 90ºC with a 2.5% sodium sulphite aqueous solution has been selected as extraction yield increased significantly with respect to the extraction with water and the characteristics of the extracts remained almost constant. On the other hand, it can be concluded than chestnut shell tannin extracts, due to their significantly higher polyphenols contents, offer much better properties than eucalyptus bark extracts for all the applications proposed.
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Presented Wednesday 19, 13:30 to 15:00, in session Chemical Product Design & Engineering - Poster (CPD&E - P).
