The formation of pores in the cell wall

The purpose of this study was to determine how pores in the fibre cell wall are formed and modified in common pulp fibre processing operations. The po re measurements were done with a novel technique: thermoporosimetry. This t echnique is based on the fact that water in small pores has a depressed mel ting temperature. Solute exclusion was also used. Three fractions of water inside the cell wall were found: freezing and nonfreezing water thought to be in relatively small pores (micropores) and bulk water in relatively larg e pores (macropores). It was found that only micropores are present in wood and mechanical pulp fibres. Macropores are formed by the dissolution of li gnin and hemicelluloses in chemical pulping. Beating and hornification affe ct mostly the volume of macropores, with comparatively little effect on mic ropores.