Effect of component removal upon the porous structure of the cell wall of wood

Abstract

It has been shown by nitrogen adsorption that the removal of lignin and hemicellulose from the middle lamella and cell wall of spruce wood produces pores with a median size in the 20–40 A. range throughout the dissolution process. During both kraft and sulfite pulping, these pores have a total volume which from 90–100% yield equals, from 55–90% yield exceeds, and below 55% yield is less than, the volume of material removed from the wall. The results therefore indicate a swelling of the wall at intermediate yields followed by a contraction below the initial dimensions towards the end of pulping. In accordance with a previously postulated theory of cell‐wall structure based on a multilamellur model, the pores produced by the dissolution of wood components are the slit‐like spaces between adjacent lamellae. Specific surface measurements show that, on this model, the cell wall of water‐swollen wood consists of about 5 lamellae, which subdivide into a total of about 350 lamellae each 35 A. thick at the point of maximum swelling (65–70% yield). Thereafter, towards lower yields, the lamellae start to reaggregate. This technique applied to groundwood pulp shows that the process of splitting the wall into layers may be accomplished to some extent by purely mechanical action.