School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe occurrence of brittleheart in Eucalyptus regnans and its effect on various wood properties( 1990)This project is mainly concerned with a description of anatomical and ultrastructural characteristics of cell wall deformations in brittleheart of E. regnans, development of methodology for quantification of percentage of broken fibre pieces (PBFP) in E. regnans, and physical and anatomical properties of E. regnans in relation to the occurrence of brittleheart. Two 1939 regrowth E. regnans butt logs and one mature growth E. regnans butt log removed from a tree approximately 120 years old were used in the study. The anatomical and ultrastructural characteristics of cell wall deformations were examined with bright field, polarized light, and scanning electron microscopy. The microscopic compression lines were found to consist of slip planes, minute compression failures, corrugations, and buckles. The width of microscopic compression lines along the longitudinal fibre axis ranged from one single fold in the cell wall up to 7 times the average fibre width. The length of the microscopic compression lines ranged from ones which only crossed a few fibres to ones which crossed up to 200 fibres. The severity of microscopic compression lines appeared to be dependent on the type of cell wall deformations and degree of compaction in the deformed zone. In the methodology studies it was found that for a pulp sample prepared from a 2 mm by 2 mm by 15 mm wood chip approximately 400 cellular elements in 8 out of 16 areas on a slide needed to be counted in order to obtain PBFP with less than 10% error. For macerated thin sections, all the cellular elements on 2 slides each carrying about 600 fibres and fibre pieces needed to be counted. A highly significant correlation was found between the length of microscopic compression lines per unit area and the microscopically determined PBFP. A highly significant correlation was found between the theoretical PBFP and the microscopically determined PBFP. These findings confirm that maceration of wood containing cell wall deformations results in broken fibres and verifies the validity of the maceration technique for quantifying the amount of microscopic compression lines. PBFP was found to increase with macerating time. A maceration time around 10 hours appears sufficient to cause fibres having cell wall deformations to break but longer times cause fibres without cell wall deformations to also break due to overmaceration. A significant relationship was found between PBFP determined after 5 hours and after 10 hours of maceration at the same temperature. It was found that parameters extracted or derived from cell length distributions produced by the Kajaani FS-200 may be used to determine the amount of fibre fragments in pulp samples. These parameters were the high peak, the length weighted average, and the mass weighted average of the cell length distributions for pulps which had PBFP greater than 10. Based on the maceration technique, brittleheart was detected in both the mature and the 1939 regrowth logs. Brittleheart was more severe and occupied a larger area in the mature growth than in the regrowth wood. The PBFP was found to be mostly below 5 in the regrowth wood although relatively high PBFP values of 21 and 30 were observed. PBFP values as high as 85 was found in the mature growth wood. In general, PBFP was found to be higher nearer the pith, decreasing toward the bark, and dropping to zero before reaching the two-thirds theoretical point where the stress is assumed to be 0. A large circumferential variation in PBFP was observed in four adjacent growth rings of the mature log. A large variation in PBFP was also found within a volume of 1000 mm^3 for both the mature and the 1939 regrowth wood. The earlywood PBFP was found to be significantly higher than the latewood PBFP for the mature and regrowth logs. A total of 72 green and 132 12% MC Izod specimens were prepared from the two 1939 regrowth logs and tested for impact strength. The mean Izod value was found to be 9.9 ft.lb for the 132 12% MC Izod specimens and 9.2 ft.lb for the 72 green Izod specimens. For side-matched Izod specimens, the mean Izod value was found to be 9.2 ft.lb at green and 9.7 ft.lb at 12% MC and the mean for the 12% MC specimens did not reflect the expected increase in strength with moisture loss. Excessively low Izod values (eg. 1.8 ft.Ib) were found in the 12% MC Izod specimens located near the pith. For 76 12% MC Izod specimens, their PBFP, fibre length, and specific gravity were also measured. Significant relationships (p=0.01) were found between Izod values and specific gravity, PBFP, and fibre length for these 76 12% MC Izod specimens. Specific gravity and fibre length positively contribute to the impact strength whereas PBFP negatively affects the impact strength. Brash-break specimens showed a low mean Izod value, a low mean specific gravity, the presence of brittleheart, and a short mean fibre length.