Current issue: 54(3)
Under compilation: 54(4)
Birch wood is used widely in wooden structures where mechanical strength is needed. The aim of the research was to study the influence of the relative share of mechanically weak tracheids, and length of the wood fibers on specific gravity and bending strength of downy birch (Betula pubescens Ehrh.) wood. According to the results, the strength of wood is strongly dependent on the relative share of tracheids, and length of the libriform cells. The strength of the wood increases when the share of tracheids decreases and the length of libriform cells increases. The specific gravity can be used as an indication of the strength of wood, especially if it is possible to analyze the structure of the wood.
The PDF includes a summary in German.
The paper presents preliminary results on the relationships of the longitudinal modulus of elasticity (E) in bending, based on ISO Standard 3349 tests on small, clear specimens, and some basic characteristics of Finnish Scots pine (Pinus sylvestris L.) wood. A manual image analysis method – quantitative stereological counting – was introduced and applied for the investigations of wood structure.
The main results were consistent with those from the prior research. The range of E was 9.7 to 19.1 GPa. Increase in especially fibre density index (R2 = 0.95), weight density and specific gravity (R2 = 0.90), Runkel’s ratio, coefficient of cell rigidity and number of growth rings per cross-sectional unit area, but also in latewood percentage (R2 = 0.58) resulted in an increase in E. Increase in growth ring width, particularly in the width of the late wood section within a ring (R2 = 0.63 to 0.90) had a reverse effect. Cell wall thickness did not show any clear effect. Except for tracheid diameter, the relationships were stronger for the variables determined in the tangential than in the radial wood direction.
Quantitative stereological counting has been used to some degree in the Finnish wood research. The procedure is technically feasible and easy to use. A large sample of counting areas is frequently needed to obtain accurate mean results for the size and distribution of the features. Because the actual analysis points are located at a fixed distance from each other, the method is not in principle well suited for wood with a regular and simple structure, as Scots pine. However, the good correlations between E and some characteristics obtained with stereological counting did not support this misgiving.
The PDF includes an abstract in Finnish.
Properties of fibres in pulpwood, especially length, width and the thickness of walls in tracheids, are essential for strength properties of pulp and paper. Length and width of tracheids increase from pith to surface in radial direction. Young and small-sized stems have also smaller fibres. Small-sized Pinus sylvestris L. test trees had tracheids that were shorter both in stems and knot wood than those in normal sized trees. However, cell walls in test trees were as thick as in normal sized trees. It seems that especially the L/T -ratio (length/thickness) in small stems is worse than in normal sized pulp wood.
The PDF includes an abstract in English.
Variation in tracheid morphology were examined for the bole wood of lodgepole pine (Pinus contorta Douglas ex Loudon) grown in Southern and Central Finland. Tracheid lengths were examined in a fast-grown and in slow-grown trees from three stands. Tracheid length increased with increasing height to 4–8 metres and decreased after that, and increased also with increasing age from the pith. The variation between stems was high. The shortest tracheids were about 1.11 mm near the piths and the longest about 4.10 mm near the bark.
Tracheid diameter and cell wall thickness were measured for the total number of 16 stems from Southern and Central Finland. Tracheid diameter increased with increasing distance from pith and the largest tracheids were at a height of 4–8 metres. Cell wall thickness varied independently of height in the stem. Summerwood cell wall thickness was twice that of springwood. There was a difference of 0.6 μm in springwood and 1.0 μm in summerwood double cell wall thickness between the two stands. Cell wall percentage was 29±4.7 in springwood and 69±7.3 in summerwood.
The PDF includes a summary in English.