Effects of mechanical and chemical treatments on the pore-size distribution in wood pulps examined by inverse size-exclusion chromatography

The inverse size-exclusion chromatography technique (ISEC) has been adapted with a column packing procedure which allows virgin, never-dried wood pulps to be examined for effects of different mechanical and chemical treatments on the fibre swelling (pore volume and pore-size distribution). The reproducibility was high (+/-2-4%) for chemical pulps, and satisfactory (+/-4-8%) for mechanical pulps. Effects of beating, lignin content, recycling and the nature of the counter-ion on pore-size distribution were studied. The new technique allowed a better and more complete understanding of how pore sizes were affected by the different treatments. The apparent pore-size distribution shifted from mainly small pores in an untreated TMP pulp, towards larger pores with a lower proportion of smaller pores for an unbleached kraft pulp. This trend was even more pronounced for a bleached kraft pulp. Recycling of pulps caused irreversible partial pore collapse.