Hydrothermal treatment of Eucalyptus wood: Effects on Ion permeability and material removing

Abstract

Hemicelluloses, the second most abundant polysaccharides in nature after cellulose, can be used for hydrogels, in packaging-films, or biomedical materials, among other purposes. In the case of eucalyptus wood, glucuronoxylans are the main constituents of hemicellulose. Hot water extraction can be used as a pretreatment for purposes of hydrolysis of the biomass followed by fermentation and also as a previous stage in pulping processes. The influence of auto hydrolysis/extraction has been widely studied for different lignocellulosic materials, but the characteristics of the hydrolyzate and aspects like change in wood permeability have not been analyzed in detail. This paper analyzes the hydrothermal treatment of Eucalyptus grandis chips and slices under mild conditions, considering temperature and time range corresponding to a Pfactor of up to 350. The ion permeability of the treated wood slices and its profile in wood chip, as well as the amount of hemicellulose and lignin dissolved from chips are evaluated. The amount of the hemicelluloses and lignin extracted was increased as treatment was intensified. For a Pfactor higher than 180, the increment in the extracted xylan is clear but the colloidal electric charge in the liquor is reduced due to xylan degradation. Total extracted lignin can be up to 3.0 g/100 g of original wood and the hemicelluloses 6.5 g xylose/100 g of original wood, respectively. The permeability of wood slices is clearly increased by water treatment. In the chip, the diffusion restriction leads to a permeability profile, and the increase at the proximity of the outer faces can be higher compared to that in the chip core.