Brent A. Petersen MS Thesis, Pulping Characteristics of Young, Genetically Selected Western Hemlock

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Pulping Characteristics of Young, Genetically Selected Western Hemlock

Brent A. Petersen MS Thesis, University of Washington, College of Forest Resources, 1998

Trees for this study were obtained when a hemlock progeny test on Quinault Tribal Lands near Taholah, Washington was thinned. The test was planted on a 4x4 spacing and thinned when 15 years old from seed. Trees were obtained from 23 half-sibling families. Three trees were selected from each of 13 of the fast growing families and two trees were selected from the other 10 slower growing families to give a wide range of growth rates. The major study objective was to focus on the pulping characteristics of the faster growing families. It was also desirable to gather additional information on the overall pulping relationships of young hemlock and gain insights on whether faster growing families deviated from these overall relationships.

Each sample tree was felled and measured for dbh, total height and stem form and the 7 feet above the stump removed for testing. Disks were removed from each end and at BH for determination of specific gravity. Specific gravity was obtained for each disk by water immersion and oven-drying and the results combined to give the composite average for the bolt. The remainder of the bolt was debarked with a power hand planer, chipped with an AcrowoodTM pilot chipper, allowed to reach an equilibrium moisture content of about 10%, and screened on a slotted screen to provide 2-6 mm thick chips.
Pulping was done in a 10 liter Aurora batch digester with an effective alkali charge of 17.5% (Na2O) on oven-dry wood and a sulfidity of 25%. The liquor to wood ratio was 5:1. The digester was heated to 175° C and seven 200 gram samples were randomly assigned and arranged and cooked until an H-factor of 1,575 was achieved. After cooking, the chips were defibered for 2 minutes, washed on a 100 mesh screen and fluffed in a pin fluffer. The pulp was weighed and samples taken to determine moisture content and total yield based on oven-dry wood charged to the digester. The pulp was slushed and screened to remove rejects and determine screened yield. Kappa number was done on 3 subsamples using TAPPI method T236-cm-85. Kappa number is a measure of the degree of removal of lignin. Fiber length was determined by passing pulp samples through a Kajaani fiber length analyzer and coarseness determined.

ANALYSIS

Both ANOVA and regression analysis were used to examine for possible relationships between growth rate, specific gravity, Kappa number, fiber length, and fiber coarseness.

RESULTS

Comparisons of all 23 families versus the 13 fast growing families revealed no unusual deviation of the fast growing families from overall trends. Consequently, the remainder of this article will focus on just the 13 fast growing families which are the ones of greatest interest to managers. Among these, the objective was to determine if there are pulping differences that could be used in making selection decisions or no differences such that the selection could be based primarily on growth.

Wood Specific Gravity

Wood specific gravity was not significantly different among these 13 fast growing families. In part this may reflect the young age of these trees (15 years) which are just transiting from production of juvenile wood where there may not be much differentiation. Also, there may not be much differentiation given that all 13 of these families are fast-growing.

CONCLUSIONS

The 13 fast growing families differed significantly only in total pulp yield. Hence those that were superior in this regard could be candidates for further selection. However, it would be useful to further investigate families that have lower Kappa number and uniform fiber length. Finally, further testing should be done to determine if there are effects in paper making and paper properties.

Yield

There was a statistically significant difference (p = .009) in total yield with 3 families exhibiting higher yield than the others. In general a higher yield family is desirable.
Kappa Number
There was no significant difference among the 13 fast growing families. In general, a low kappa number is desirable. Even though there was no statistically significant difference in Kappa number, mills would prefer families with high yield and low Kappa; some families did have this desirable combination while others either had low yield and high Kappa or high yield and high

Fiber Length

In general, both long length and uniformity of length of fibers are desirable. There were no significant differences among the 13 fast growing families in mean fiber length. However, examination of fiber length distributions revealed that while most had a sharp peak at lower lengths, one family differed from the others by having a much more uniform distribution. These differences may have implications for paper making that were not tested in this study.

Fiber Coarseness

Coarseness is a measure of the ability of fibers to collapse and bond well in paper making. Low coarseness is associated with fibers that perform well. There was no significant difference among the 13 fast growing families in coarseness.