Determination of surface area and pore volume of holocellulose and chemically modified wood flour using the nitrogen adsorption technique

Very low surface area (ca. 0.5 m(2)/g) and a low pore volume (ca. 0.002 cm(3)/g) have been obtained for oven dried wood, using the nitrogen adsorption technique. The microporous structure of wood flour was partially preserved by the solvent exchange drying (SED) employed in this study, in particular when toluene was used as a final solvent. However, the resulted surface area (ca. 6 m(2)/g) and a pore volume values (ca. 0.015 cm(3)/g) indicated that such a structure is in no way representative of a fully swollen cell wall. By using solvent exchange drying (SED), it is possible to preserve the swollen pore structure of holocellulose samples. However, with samples which contain significant amounts of lignin, such as native wood, it is not possible to prevent re-collapse of the pores. This problem arises because as micropore swelling occurs, the surrounding lignin network of the cell wall is stretched. When the molecules occupying the micropores are removed, the lignin returns to its original configuration, re-collapsing the micropores in the process. Chemical modification resulted in significant reduction in surface area and pore volume, possibly a result of pore blocking by the large acyl group.