Towards understanding the pressure dependence of hygroscopic water

This paper presents a review of water sorption by cellulose, often referred to as hygroscopic or Brix-free water. Of particular interest is the apparent dependence of hygroscopic water on interparticulate ('effective') stress. The analysis suggests that the level of 25% currently assumed in the Australian industry is reasonable at low fibre compactions but at high compactions a much lower value, approximately 8%, may be more appropriate. It is hypothesised that a link exists between cell wall collapse and the reduction of hygroscopic water with increasing effective stress. It is concluded that hygroscopic water must be defined in terms of temperature, solution concentration, (vapour or) pore pressure and effective stress in the fibre skeleton.