Refining characteristics of Northern and Southern bleached Softwood Kraft B. Palmer Tappsa Conference October 2010

1. Refining characteristics of Northern and Southern bleached Softwood KraftB. PalmerTappsa Conference October 2010

2. Objectives • Compare wood and fibre characteristics of Northern and Southern bleached Softwood Kraft • Highlight key differentiating features • Determine the individual refining characteristics

3. Selected fully bleached softwood samples • A rich blend of Pinus patula with the balance Pinus elliotii from Mpumalanga, SA (Classified as P. patula in this study) • A rich blend of Spruce with the balance a mixture of Pines from Scandinavia (Classified as P. mariana in the study) • A rich blend of Douglas Fir with the balance Western Hemlock / Balsam Fir – Canada (Classified as P. menziesii in this study)

4. Work Scope • Stage 1 Determine the anatomy of the predominant wood species and fibre characteristics of the respective pulp samples after Kraft cooking and bleaching. • Stage 2 Compare the refining characteristics of each sample using a standard refining programme • Stage 3 Identify the optimum refining energy and intensity of each sample

5. Stage 1- Introduction to Wood AnatomyJuvenile and mature wood • (a) juvenile core located in interior of tree bole; • (b) properties that increase from juvenile to mature wood; and • (c) properties that decrease from juvenile to mature wood. • Plantation grown trees such as P. patula in the Southern Hemisphere grow rapidly and are harvested at a younger age so that the juvenile portion of the tree is significant. • Saw-mill chips will be sourced from the outer portion of the tree (mature wood)

6. Stage 1 – Introduction to Wood AnatomyEarlywood and latewood • Each annual growth ring contains earlywood, which is laid down in the early part of the growing season and is characterized by large cells with thin cell walls. • Latewood is characterized by small cells with thick cell walls. • Earlywood is low density, latewood is high density wood. • Slow growing softwoods, P. mariana and P. menziesii have a high proportion of latewood.

7. Stage 1- Wood Anatomy resultsFibre diameter P. patula has a relatively high fibre width increasing from pith to bark

8. Stage 1 - Wood Anatomy resultsCell wall thickness Increased latewood growth as tree ages Juvenile wood with a high ratio of earlywood

9. Stage 1 - Wood Anatomy resultsSummary • Significant difference in anatomy noted with the P. patula from the inner to outer tree diameter. • Fibres from the outer diameter will be more difficult to refine than those from the inner diameter. • Important to know the ratio of saw mill chips to whole tree or roundwood in a pulp sample.

10. Stage 1 - Gamma ray densitometry from the bark to the pith 0.85 g.cm3 0.65 g.cm3 0.40 g.cm3 0.40 g.cm3 • P. patula has a low and consistent density at the pith (early wood) with an increased frequency of peaks at the middle to outer layer (late wood) • The P. mariana and P. menziesii also had annual peaks of wood density from the pith to the bark but proportionally there was more latewood than with the P. patula. 0.65 g.cm3 0.40 g.cm3

11. Stage 1 - Fibre characteristics – bleached Kraft

12. Stage 1 - Fibre characteristics – bleached Kraft

13. Stage 1 - Fibre characteristics – bleached Kraft

14. Results – Stage 1Summary of fibre dimensions for each of the pulps • P. mariana • P. patula • P. menziesii

15. Stage 2 - Refining equipmentPilot refiner details Evaluate the comparative refining characteristics of the 3 samples using a laboratory single disc refiner under identical and controlled refining conditions. • 12” single disc pilot refiner • 300 lt capacity @ 3.5% consistency, 1.2 Ws.m, 0 kWh/t – 220 kWh/t • Hydra cycle mode: Fixed intensity (auto gap adjustment), several passes • Ability to establish a refining curve at 5 different energy levels

16. Stage 2 – Refining results Freeness vs. refining energy and associated costs P. Patula exhibits a relatively fast freeness development

17. Stage 2 – Refining results Comparative refined strengths P. menziesii exhibits a higher unrefined tensile Index P. mariana and P. menziesii show a sharp increase in the Tensile index at a higher freeness when compared to the P. patula At a freeness of 450 ml the P. menziesii exhibits a tensile Index 60% higher than that of P. patula

18. Stage 2 – Refining resultsComparative refined strengths • With refining, there is always a compromise between the tear and tensile result. • Ideally, both the tear and tensile should be as high as possible however only one of these two properties can be developed, usually one at the expense of the other.  • It is possible to develop P. patula to a similar tear as the other two but not tensile.

19. Stage 2 – Refining resultsComparative refined bulk properties P. patula has the highest bulk as a result of its comparatively high coarseness

20. Stage 3 – Determine Optimum refining for P. patula • Low intensity refining (0.8 Ws.m) of the P. patula produces the best tensile result for a given tear

21. Stage 3 – Determine optimum refining for P. mariana • When refining the P. mariana, an intensity of 1.6 Ws.m produces the best tear and tensile result • An intensity of 0.8 Ws.m appears to be too low to develop tensile with P. mariana

22. Stage 3 – Determine optimum refining for P. menziesii • When refining the P. menziesii, an intensity of 1.6 Ws.m produces the best tear result and an intensity of 1.2 Ws.m produces the highest tensile.

23. Stage 3 – Summary of refined properties at 450 ml CSF

24. Conclusion • significant differences exist in the wood anatomy and fibre characteristics of the pulp samples both between the three different species and between the two Hemispheres. • Fibre characteristics dictate the manner in which a fibre responds to refining which defines the specific refined pulp properties. • P. patula exhibited a relatively fast freeness development. Conventional thinking would suggest that this was an indication of a weaker fibre. However, this species had a robust morphology compared to the Northern Hemisphere woods. The theory developed in this study suggests that the effect of coarseness and the concomitant number of fibres per gram plays a significant role.