| Jack pine is one of the most widespread commercial tree species in Canada, however, for a long time, the utilisation of Jack pine in high-yield pulping has been limited because of such characteristics as high extractive content, high fibre wall thickness of summer wood and high summer/spring wood ratio, causing some well-known problems such as pitch deposits, high energy consumption and poor strength properties. In order to facilitate the potential utilisation in mechanical pulping industry, we propose a new mechanical pulping method combining selective refining with chemical treatment on the long fibres as one alternative process to the conventional mechanical pulping of Jack pine. The two-stage screen equipped with a 0.25mm smooth hole basket was used to separate thermomechanical pulp from primary-stage refining into long-fibres fraction and short-fibre fraction. At the end, the chemically treated long fibres were combined with the non-treated short fibres to rebuild the initial pulp.;The results of preliminary experiments show that selective refining could be used to produce acceptable Jack pine mechanical pulp. Compared to whole-pulp refining, selective refining can facilitate the development of fibres. Moreover, selective refining with chemical treatment, particularly pulp sulfonation, produces a pulp with a better tensile strength because of the introduction of more acidic groups into the fibres, while consuming less refining energy.;Through the optimization of sulfonation condition prior to selective refining of long fibres, mathematical models were set up to evaluate the impacts of sulfonation variables on refining energy, fibre characteristics and paper properties during selective refining of Jack pine. With these models, the optimal sulfonation conditions for Jack pine long fibres were determined: 4% of sodium sulfite, 30 minutes of sulfonation time and pH of 11 at the temperature of 130°C. Under these conditions, the results predicted by the models generally demonstrate a good correlation with the experimental results.;Both TMP and CTMP could be obtained by selective refining and whole-pulp refining, however, more reduction of refining energy can be achieved by using selective refining compared to whole-pulp refining. Such reduction could be associated with the more intense forces applied on long fibres under less protection of short fibres through the selective refining. In comparison to whole-pulp refining, selective refining can produce a pulp with higher physical strength and lower brightness than whole-pulp refining except for CTMP with sodium sulfite. This could be involved with more flexible and conformable fibres because of higher water retention value and lower coarseness by selective refining, which could be related to fibres' peeling-off and splitting without shortening the fibres.;In this thesis, three series of independent experiments were carried out to better understand the application of selective refining on Jack pine and the corresponding refining mechanism. The viability of selective refining on Jack pine was firstly evaluated; also, the comparison of different impacts from various chemical treatments on selective refining was performed to well select the chemical product which is more suitable to Jack pine. Subsequently, to maximize the advantages and to minimize the disadvantages of selective refining with chemical treatment, the optimization of chemical treatment was done to obtain the optimal conditions for the chemical treatment and to define the effects of independent variables on refining energy and paper properties. Finally, various mechanical pulps produced by selective refining and whole-pulp refining were compared in terms of specific refining energy, physical properties and optical properties as well as fibre surface properties to further identify the difference existing between the two refining processes.;Fibre surface analysis by XPS indicates that selective refining can produce a pulp with higher 0/C values by exposing more cellulose and/or hemicellulose and less surface coverage of extractives in comparison to whole-pulp refining, which makes fibres more hydrophilic. The observation of MEB confirms that fibre development mechanism between selective refining and whole-pulp refining is different. For selective refining, the splitting and rupture along the axis of the fibres can be observed more frequently; however, the delamination of fibres to remove the porous layer of middle lamella is more evident for whole-pulp refining.;Keywords: Jack pine, Long fibres, Fractionation, Chemical treatment, Pressure screen, Selective refining, Whole-pulp refining, Mechanical pulp, Sulfonation, Optimization, Surface analysis. |
