Mid Sweden University

This study was carried out on sheets from spruce CTMP fibers, which are surface treated with a mix of cationic starch and CMC and blended with 20% bleach softwood chemical pulp fibers before handsheets were prepared in a Rapid Köthen sheet former, where the sheets were dried to 40-55% d.c. The sheets were pressed in a hot press nip in a pilot machine with adjustable pressure and heat. Both low and high nip pressure were used in combination with two different nip temperatures, 80°C and 100°C, to achieve sheets in a broad range of densities. The results show that remarkable improvements are possible, both in terms of tensile index (up to 85 kNm/kg) and compression strength, SCT, (up to 38 kNm/kg) on the CTMP-based sheets under optimal conditions at papermaking, i.e. consolidate the sheet structure in a press nip at evaluated temperatures. It is evident from the current study that there is an as of yet unexploited potential in modifying the conditions of papermaking from spruce CTMP furnishes, which can be utilized for the manufacturing of papers with high requirements on strength and stiffness, e.g. packaging papers.