The impact of low consistency refining of eucalyptus species on the fibre morphology and strength properties of pulp.
It is a well-known fact that the selection of the raw material and how it is further treated within the stock preparation system has a major affect on the quality of paper obtained. While the pulp selection is important for a good product, the refining treatment received by that pulp is the determining factor for the properties of the product. It is for these reasons that it is interesting and beneficial to study the pulp quality and refining results. The focus of this research work was to study the behaviour of selected clones of Eucalyptus materials from different site indices under different refining conditions. Poor and good sites were investigated. The strength properties of the resulting refined pulp were investigated. The project was conducted in three phases with the focus of the project being phase 3. The work began with refining of commercial Eucalyptus pulp obtained from Mondi Richards Bay (phase 1). The objective here was to get an understanding of the influence of the various parameters affecting refining. This knowledge could then be used on a more focused research program on the well defined pulps with limited refining variables being considered. The results indicated that of the three variables investigated (i.e. stock flow rate, stock consistency and refiner speed of rotation) the parameter speed of rotation gave the most repeatable results when varied and also resulted in the largest range of refining intensity (SEL) achievable compared to the variation of the other two parameters. It was decided that the work on the different pulps investigated in phase 3 would be carried out using the parameter speed of rotation to vary the SEL and multiple passes through the refiner to vary the specific refining energy (SRE). A comparison between the refining characteristic of bleached and unbleached pulp was carried out (phase 2). It was seen that there were differences in the refining characteristics between bleached and unbleached pulp. These differences however, occurred in a predictable manner. This indicated that with further investigations on the differences in refining characteristics, it would be possible to extend the results obtained from refining studies using unbleached pulp to what can be expected from the refining of bleached pulp. Phase 3 of the project considered the refining of different pulps. Two different clones of Eucalyptus (GU A380 and GC G438) each from two site indices (good and poor), were selected to provide raw materials having different wood anatomy. These were pulped under similar cooking conditions using the kraft pulping process. The kappa numbers were in the range of 18 to 21. The refining trials were then conducted to determine how the different pulps affected the refining process and also how the refining process affected the pulp properties. Refining was carried out at three different refiner speeds. It was seen that for the overall results SRE was a good predictor of all the pulp properties measured except for the tear. The pulp fibre length was able to predict the tear best. It was seen that refining higher intensities reduced the SRE required to obtain a pulp freeness of 400 ml.