Foam as a carrier phase: A multipurpose technology for industrial applications: Dissertation

The applicability of foam in paper/board manufacturing processes was studied. The pulp and paper production in Finland has been forecast to decrease by up to a third from 2007 to 2020. The declining trend is mainly due to the weakening of main export markets. (Hetemäki et al., 2009).For the renewal of paper industry new solutions for savings in energy and raw materials are needed. Newly developed materials like nano materials may also challenge the conventional processes. New technologies are needed and the interest towards foam technology is growing. The main focus in this thesis was on foam forming and coating and on nano/microfibrils. The suitability of foam in biosludge treatment was also studied. The work showed that the strength loss due to the bulky structure of the foam formed paper, can be regained by using cellulose microfibrils (CMF) as strength additives, instead of wet pressing or beating. The strength enhancement was received with a lower bulk lost. The studied CMF grades had different responses to the strength properties of the pulps used; bleached soft wood pulp and chemi-thermo mechanical spruce pulp. This indicates that CMF used has to be chosen depending of paper properties needed. Dewatering was more effective due to the porous structure of the foam formed sheets and the formation of the papers better than in water forming, even with 12 mm synthetic fibers. Foam coating applications were done both to dry and wet fiber webs. Two different coating methods were used in the dry web applications.The work showed that using foam it is possible to create thin functional surfaces on paper/board. Titanium dioxide and zinc oxide functionalized cellulose nanofibrils (CNF) created antimicrobial and photocatalytic properties on the paper and grease and water vapour barriers were achieved with polyvinyl or ethylene vinyl alcohol foam. In wet web application done at the former section polymers known to enhance the strength properties of paper were used. Due to foam destruction using vacuums, the whole web structure was treated with the chemical. The enhancement both on wet and dry web strength properties was detected with an increase in the dry matter content of the paper and without bulk lost. In addition to 'a carrier phase' function, the ability of foam to displace liquid water from a porous medium, was investigated. The foam enhanced dewatering in foam forming as well as in foam coating of the wet web. Based on these observations the foam assisted dewatering was studied on biosludge treatment. According to the results, the filtration time was shortened, the filtrate was cleaner and the sludge cake 10% drier. The change in dry solids content was quite small due to the insufficient vacuum level in filtration, 2 kPa. However, the result indicates that with a more efficient filtration vacuum it is possible to use foam to assist filtration. This thesis shows that foam technology offers several benefits for the paper/board industry, and combining it with nanomaterials enables the development of novel paper products.