Elina Kallio-Sihvonen: Upgrading the performance of high yield pulp

Plastic waste leaking into natural and marine ecosystems, together with emerging packaging directives, underscores the need for bio‑based packaging materials. At the same time, minimizing wood consumption in packaging is essential. Requirements for fiber products have shifted from prioritizing high brightness to prioritizing high strength, which is critical for packaging applications. Generally, high yield pulps are inferior in strength properties and bonding ability to low yield pulps. These considerations make improving the strength of highyield pulps an attractive research topic. 

The objective of this research is to improve chemi-thermomechanical pulp (CTMP) networking and strength properties by peracetic acid (PAA) treatment, with the prospect of using it in molded fiber products. PAA treatment is an interesting fiber modification method because PAA is environmentally accepted, and it is known to react selectively with lignin in wood fibers, and some research suggests that it improves the strength of mechanical pulps. A further objective is to determine the mechanism by which the treatment affects strength. The effect of PAA treatment on the tensile strength of hot-pressed CTMP hand sheets was investigated. To elucidate the treatment mechanism the chemical composition and total fiber charge were analyzed. FTIR and XPS were used to analyze chemical bonds in the fibers and to assess surface chemistry. The analyses show a maximum strength improvement of over 200 % to a level of 70 Nm/g due to the treatment while the yield remains high. Some lignin dissolves, and the fiber charge increases. When the fibers are exposed to high pH, the FTIR spectra indicates reduction of acetyl and/or carbonyl groups in hemicelluloses (xylan).

The project is a collaboration with Kemira Oyj.