Title
Study of the effect of mechanical treatment and supercritical CO₂ extraction on aspen BCTMP by surface charge measurements and SEM
Authors
KART KARNER RASMUS TALVISTE KARIN VIIPSI MATTI ELOMAA and URVE KALLAVUS

Received June 5, 2013
Published Volume 48 Issue 5-6 May-June
Keywords SEM, surface charge, cellulose, titration, supercritical CO₂, electrolyte, polyelectrolyte, p-DADMAC, aspen, aspen pulp fibres, BCTMP, thermo-mechanical treatment, fibre surface

Abstract
Cellulose is the most abundant organic polymer and is utilized in many forms in industry. Sustainable use of materials includes the utilization of renewable resources like cellulose and selecting methods that allow saving energy and avoiding pollution. Because a complete purification of cellulose demands a lot of energy and chemicals, there are many products in which cellulose is used only partly purified. For example, products like bleached chemi-thermo mechanical pulp (BCTMP) have been developed to be used as a component in paper making. In this article an attempt to further refine aspen BCTMP is reported. The aim is to find an energy effective and environmentally friendly way to affect the surfaces of BCTMP fibres, in other words, to peel and fibrillate the pulped aspen wood cells. Agitation in a bag mixer and supercritical carbon dioxide (scCO2) extraction were selected as methods to treat the fibres. The effects of the treatment were analysed by the surface charge measurement and scanning electron microscopy (SEM). The surface charge of pulp fibres is important as it influences interfibre and fibre-additive interactions in the pulping process, as well as in other applications. In this work, the effect of mechanical treatment scCO2 extraction on the surface charge of aspen BCTMP was evaluated. Dried and ground BCTMP was dispersed in water, treated with a BagMixer (BM) with a nylon separator, extracted with scCO2 with and without ethanol-water co-solvent. The influence of 1% sodium hydroxide was also studied. Polyelectrolyte titration was used to measure the surface charge. The processes were carried out at various times and in different order of succession. A relatively high surface charge was gained by a gentle mechanical and chemical treatment. SEM analysis showed the relation of surface fibrillation to the surface charge of the fibres. Washing with sodium hydroxide removed both the fibrils from the surfaces and the surface charge. The results can be used as a guide to further fibrillation of aspen BCTMP for various applications. Fibrillated intermediates are aimed for processing to, for instance, aerogels and other nanostructured materials.