Foam forming technology enables utilization of long fibers

A lot of effort has been put to improve the efficiency of paper- and board making processes. Main goal has been to reduce raw material consumption and to improve energy, water and raw-material efficiency. Foam forming has been studied as one opportunity. In foam forming fibres are dispersed into aqueous foam, which reduces fibre flocculation and thus improves the quality of the product. This can lead to excellent formation and bulky structure but simultaneously reduces the strength properties of paper or board. In this study the effects of addition of tempo-oxidized cellulose nanofibrils (CNF) on foam formed paper strength properties have been studied on pilot-scale paper making environment. Cellulose nanofibrils were prepared in a pilot-scale from never dried bleached hardwood kraft pulp, which was chemically pre-treated to improve the functionality of the cellulose nanofibrils. Tempo-mediated oxidation was used as a cost effective method prior to mechanical fibrillation. The pulp had a total charge of 1 mmol/g and the hydrogel was prepared by feeding the fiber suspension once through a microfluidizer. The pilot trials reported in this paper were run with kraft and CTMP pulps by using both foam and water forming. The foam was generated in a tank and the machine was run in a gap mode. The running speed of pilot machine was 400 - 600 m/min. The results showed that the addition of 2-6 % of CNF into kraft and CTMP pulp furnishes could improve paper tensile strength properties 22-36 % and z-strengths 14-50 % and simultaneously maintain excellent formation. These results support our view that tempo-oxidized CNF can be used as a strength additive in foam formed papers.