Dissolving pulps, i.e. pulps consisting mainly of cellulose and only of traces of hemicellulose and lignin, are used as raw material for regenerated cellulose fibres. The intense chemical treatments of wood carried out to produce the dissolving grade pulps, result in removal of most hemicellulose and lignin from the wood fibres and consequently increase the fibre porosity [1,2]. However, the cell wall pores only exists in the water swollen state and collapse to non-porous solid when dried [1,3]. The fibre pore structure is relevant to almost all aspects of cellulosic fibre processing. Mechanical forces cause internal bonds in the fibre cell wall to break, allowing the cell wall to expand, increasing its accessibility, flexibility and shrinkage potential in drying. The fibre cell wall pore structure also affects the action of cellulolytic enzymes having size similar to the pores in the cell wall of chemical pulp fibers. Any changes in the cell wall pore structure through e.g. mechanical processing of fibers can thus influence the surface area that is accessible to enzymes. Only basic aspects of the cell wall pore size distribution, swelling and, most recently, fibril level swelling have been described so far in connection to enzymatic hydrolysis of cellulosic fibres. In this presentation the effects of the mechanical and enzymatic pre-treatments on the pore structure and alkaline solubility of dissolving grade pulp are discussed based on recent findings. Formation of micro- and macropores in the pulp fibres during mechanical shredding was found to correlate with the susceptibility of the fibres to enzymatic hydrolysis [4]. The fibre porosity development during the processing was studied by a modified solute exclusion approach, which revealed differences between the effect of mild enzyme or acid hydrolysis on the pore structure of fibres. The dissolution of the modified fibres in NaOH/ZnO was evaluated and found to correlate with overall pore volume and accessible surface area analysed by the modified solute exclusion method. References: 1. Pönni R et al. 2013. Carbohydrate polymers 93:424-429. 2. Sixta H. 2006. Pulp Properties and Applications in Handbook of Pulp. Sixta H (ed), Wiley-VHC GmbH &Co KGaA, Weinheim 1009-1067. 3. Oksanen T. et al. 1997. Holzforschung 51:355-360. 4. Grönqvist, S. et al. 2014. Cellulose, article in press.

Porosity development of dissolving pulp during mechanical and enzymatic processing

249th National Meeting (2015)

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