posted on 2021-10-26, 23:43authored byJussi Lahti, Roman Poschner, Werner Schlemmer, Andrea Hochegger, Erich Leitner, Stefan Spirk, Ulrich Hirn
We present how harmful
different wood extractives carried over
to paper mill with unbleached softwood Kraft pulp are for the strength
of packaging papers and boards. The investigations were done by simulating
industrial papermaking conditions in laboratory-scale trials for handsheet
production. It was found that fatty acids are the most relevant compounds
in the carryover pitch extractives (CPEs), as they readily interfere
in fiber–fiber bonding strength, control the properties of
CPE micelles, and are furthermore the most abundant compounds. Addition
of cationic starch improved strength and evened out the strength differences
of handsheets with different CPE compounds. Oleic acid (unsaturated
fatty acid) was an exception, as it was above average harmful for
paper strength without cationic starch and also heavily impaired the
functioning of cationic starch. As a whole, these findings demonstrate
that fatty acids, especially unsaturated ones, are the most relevant
CPE compounds contributing to the reduced efficiency of cationic starch
and decreased strength of unbleached softwood Kraft paper. This makes
the cleaning of process waters by precipitating CPEs on the pulp fibers
harmful for paper strength.