Exploration of effect of delignification on the mesopore structure in poplar cell wall by nitrogen absorption method

As an important commodity wood material, poplar has porous structure, which is worthy of being investigated. Especially, the lignin concentration is closely related to the formation and change of pores. Although a few studies reported the relation between the pore volume and the lignin removal of the ground wood (Stone and Scallan in J Polym Sci C Polym Symp 11(1):13-25, 1965), no information of the distribution of pore sizes versus the whole delignification process steps was reported. This study initially explored the effect of delignification level on the pore size distribution and pore structure in poplar cell walls using nitrogen absorption measurement. It was found that delignification increased the N-2 adsorption amount and specific surface area of poplar. It also caused a large number of mesopores in the cell wall, mainly in the 2-10 nm pore size range, and decreased the average pore size. The whole delignification process can be roughly divided into three major phases, namely, the initial phase, the transitional phase and the stable phase, in which, the change process was not completely uniform. During the delignification, the size of poplar cell wall pores continued reducing, and finally a large number of uniform pores of about 2.1 nm was formed.