The effects of different types of wet-end added microfibrillated celluloses on the properties of paper made from bleached kraft pulp

This report deals with the impact that different types of wet-end added microfibrillated cellulose (MFC) has on papers made from an unbeaten bleached kraft pulp. The studied MFCs were a refined and enzymatically pre-treated MFC (low anionic charge density), a carboxymethylated MFC (high anionic charge density), and a cationic MFC (high cationic charge density). Different retention strategies were needed to retain the different MFC types. The retention of MFC was determined using sugar analysis of the filtrate. Some experiments were also devoted to dewatering and pressability of wet webs with carboxymethylated MFC. It was shown that dewatering and pressability can be handled with appropriate chemical adjuvants. Laboratory hand-sheets with up to 10 wt-% MFC were made and characterized in terms of their mechanical and optical properties. The results show that enzyme MFC gives somewhat better reinforcement of paper sheets compared to the carboxymethylated and cationic MFCs, which gave identical effects on the mechanical properties and scattering coefficients of the papers.