How Different Carryover Pitch Extractive Components are Affecting Kraft Paper Strength

Jussi Lahti; Roman Poschner; Werner Schlemmer; Andrea Hochegger; Erich Leitner; Stefan Spirk; Ulrich Hirn

doi:10.1021/acsomega.1c02579

How Different Carryover Pitch Extractive Components are Affecting Kraft Paper Strength

ACS Omega. 2021 Oct 26;6(44):29350-29359. doi: 10.1021/acsomega.1c02579. eCollection 2021 Nov 9.

Authors

Jussi Lahti^{1

2}, Roman Poschner^{1

2}, Werner Schlemmer¹, Andrea Hochegger³, Erich Leitner³, Stefan Spirk^{1

2}, Ulrich Hirn^{1

2}

Affiliations

¹ Institute of Bioproducts and Paper Technology, Graz University of Technology, Inffeldgasse 23, Graz 8010, Austria.
² Christian Doppler Laboratory for Fiber Swelling and Paper Performance, Boltzmanngasse 20/1/3, Vienna 1090, Austria.
³ Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, Stremayrgasse 9/II, Graz 8010, Austria.

Abstract

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.