Influence of cracks in wood chips on characteristics of pulp produced from those chips

Benjamín Petržela

Master's thesis

Abstract:

The master's thesis deals with the influence of cracks in wood chips and examines selected characteristics of pulp produced from those chips. A key aspect of this paper is the development of a reproducible laboratory method for the analysis and quantification of cracks in wood chips for academic and professional use. The thesis was carried out in collaboration with Mondi Group. Two sets of wood chip samples taken from the Mondi Štětí production plant were analysed in the thesis, where the first set of samples was chipped with a sharp knife and the second set of samples was chipped with a dull knife. An image analysis method for quantifying cracks in wood chips was subsequently developed on these samples. The samples were processed into pulp using a process corresponding to the production process of the Kamyr-line production line at Mondi Štětí. The produced pulp was further subjected to the examination of selected characteristics such as unscreened yield, shive´s content, screened yield, kappa number, residual alkali, and Zero-span fibre strength. Results of the study compare two sets of samples cut with a dull and a sharp knife, representing samples with larger and smaller amounts of cracks presence. These results demonstrate that the cracks in wood chips influence the properties of pulp produced from these chips. It was proven that a larger number of cracks in the chips can positively affect the pulp production process in terms of efficiency and time consumption. A greater presence of cracks in the sample cut with a dull knife resulted in a decrease in H-factor by -8,16% at the same desired kappa number target. The unscreened yield was increased by 1,50% in the sample with a greater presence of cracks at the same target kappa number. An attachment to the thesis is the developed laboratory method for image analysis of cracks in wood chips. This method was used to determine the proportion of the chip crack area, resulting in a 0,79% greater proportion of crack area in the sample cut with a dull knife compared to the sample cut with a sharp knife. The developed laboratory method can serve as a basis for academic and professional purposes in researching this issue.

Keywords

papermaking, residual lignin, microcracks, pulping liquor

Language used: English

Date on which the thesis was submitted / produced: 7. 4. 2024

Thesis defence

• Date of defence: 27. 5. 2024
• Supervisor: Ing. Ing. Štěpán Hýsek, Ph.D.
• Reader: Tomáš Pipíška, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Master programme:
Wood Engineering