Henrik Heräjärvi

Influence of felling season, drying method and within-tree location on the brinell hardness and equilibrium moisture content of wood from 27–35-year-old Betula pendula

The Brinell hardness and equilibrium moisture content (EMC) were measured from thinning-aged silver birch wood. Wood material both from the trees harvested in the first commercial thinning and from trees remaining on site after the thinning was included. The average Brinell hardness was 19.40 MPa. It correlated significantly with the basic density of wood. With respect to the distance from the pith, the Brinell hardness of air-dried wood was higher than that of artificially dried wood. The average EMC of the conditioned (20°C, 65% relative humidity) wood was 12.0%. The EMC of the wood also varied, with the EMC being higher for air-dried wood than for kiln-dried wood. EMC was the highest at a distance of 30–40 mm from the pith, decreasing towards both pith and log surface. Seasonal variation in both the Brinell hardness and the EMC of the wood was found. It was presumed to be a consequence of season-dependent physiological changes in trees.

Small-Diameter Scots Pine and Birch Timber as Raw Materials for Engineered Wood Products

Abstract In the future, the building industries will need predictable, homogeneous and cost-competitive wood products with structural safety in increasing quantity and quality. This can be provided by, e.g., breaking solid wood and reconstructing the structure in a way that the degrading influence of knots, cracks, decay and other natural irregularities in wood will be eliminated. Beams, panels or boards made by this principle are called the engineered wood products (EWP). The purpose of this study was to investigate the possibilities to utilize small-diameter Scots pine and birch timber for production of EWPs that are reconstituted of strands. The wood technological characteristics of the tree species used in these products worldwide were studied based on the literature, and the findings were compared to the characteristics of domestic woods. In addition, test specimens were manufactured from domestic raw materials of Scots pine and birch species, and tested in order to examine the differences between woods from young trees from the first commercial thinnings and top sections of mature trees from final cuttings as a raw material. According to the literature review, the average basic density and, consequently, many mechanical properties of pine and birch grown in Finland do not markedly differ from those of the numerous foreign species used for EWPs. The empirical tests indicated that beams (air-dry density ca. 620–800 kgm-3) with relatively auspicious static stiffness (ca. 6000–8500 MPa) and bending strength (ca. 32–42 MPa) could be manufactured from timber equal to or smaller than pulpwood in diameter.

Detection of the effective refractive index of thermally modified Scots pine by immersion liquid method

The purpose of this study was to determine the effective refractive index of thermally modified Scots pine (Pinus sylvestris L.) wood specimens as a quantitative measure regarding the change of wood density which is due to the thermal modification. The refractive index of thermally modified Scots pine wood was obtained by introducing pine wood powder into an immersion liquid and measuring light backscattering with a homebuilt multifunction spectrophotometer. The present method provides useful information that in principle can be applied, for example, in the optimization of the thermal modification process and inspection of the quality of thermally modified wood.

Relation of arabinogalactans to density, growth rate and shear strength in wood of cultivated Siberian larch

Present in high concentrations in the heartwood of Larix species, water-soluble arabinogalactans affect the density, moisture content and processing properties of larch wood. The aim of this study was to chart arabinogalactan concentration (AC) and to define the relations between arabinogalactans, and density and shear strength at different axial and radial locations in Larix sibirica Ledeb. trunks. In addition, growth rate (ring width, fibre dimensions) was compared with AC to determine the link between them. Although quite low AC levels were observed, values differed significantly between sapwood and heartwood, with a slight increasing trend from pith to mature heartwood. Variation in growth rate affected AC levels in juvenile wood only. In conclusion, AC levels were clearly lower in the studied cultivated, fast-grown Siberian larches than those measured earlier in trees of natural origin. AC had a weak correlation with growth rate and shear strength.ZusammenfassungWasserlösliche Arabinogalactane, die in hohen Konzentrationen im Kernholz von Lärchen vorhanden sind, haben einen Einfluss auf die Dichte, die Holzfeuchte und die Verarbeitungseigenschaften dieses Holzes. Ziel dieser Studie war es, die Arabinogalactankonzentration (AC) zu ermitteln und die Beziehung zwischen Arabinogalactanen und der Dichte sowie der Scherfestigkeit in verschiedenen axialen und radialen Lagen im Stamm von Larix sibirica Ledeb. zu bestimmen. Darüber hinaus wurde die Wuchsleistung (Jahrringbreite, Faserabmessungen) mit der Arabinogalactankonzentration verglichen, um einen möglichen Zusammenhang aufzuzeigen. Trotz relativ niedriger Arabinogalactankonzentrationen unterschieden sich die Werte von Splint- und Kernholz signifikant, wobei eine leichte Zunahme vom Mark hin zum adulten Kernholz festzustellen war. Unterschiedliche Wachstumsgeschwindigkeiten hatten nur einen Einfluss auf die Arabinogalactankonzentration in juvenilem Holz. Zusammenfassend ist zu sagen, dass die Arabinogalactankonzentration der hier untersuchten, angebauten, schnellwachsenden sibirischen Lärchen eindeutig niedriger war als die der früher untersuchten Lärchen aus natürlichen Beständen. Die Arabinogalactankonzentration korrelierte schwach mit der Wuchsleistung und der Scherfestigkeit.

Dependence of shear strength on wood properties in cultivated Larix sibirica

Abstract Mechanical properties are very important in structural uses of wood. In the case of larch wood, shear strength (SS) may be a limiting property, because the wood is brittle and it splinters easily. In this study, SS of Siberian larch (Larix sibirica) wood was studied in relation to its axial and radial location and to some other wood properties in the part of the trunk that produces logs of good carpentry quality. SS increased by 21–23% from the pith to the outer heartwood at each studied height (butt, 4.5 and 9 m), and it was at its most approximately 7% higher at the butt than at the other studied heights. The main reason for the radial increase in SS was the increase in density caused by wood maturation, but other factors also affected SS, depending on the grouping mode (combined material, radial/axial location). An exception was sapwood, for which no factors affecting SS could be identified. Thus, sapwood may behave differently from heartwood regarding use, even unexpectedly. The results suggest that mature heartwood, but not juvenile wood and sapwood, of Larix sibirica should primarily be used in products that require high SS.

Combined production of sawn timber and firewood billets at a birch sawmill in Finland: a simulation approach.

Abstract Growing markets for chopped firewood have created alternative uses for the by-products of sawmills. Based on empirical data and simulated results, the potential of birch (Betula pendula Roth, Betula pubescens Ehrh.) from commercial thinnings for combined industrial production of sawn timber and firewood billets was investigated. In the simulations, different sawing patterns were used for logs intended to combine production of sawn timber and billets for chopped firewood (‘sawlogs’), and for logs intended only to firewood production (‘firewood logs’). Finally, economical feasibility analysis was done concerning the differences between the sawmills’ traditional business concept and the novel concept combining sawn wood and firewood production. The bucking results for the volume yield of different timber assortments varied only slightly between the different bucking options, i.e. the combinations of timber assortments. The main differences in the volumes of timber assortments were due to the stand type where the birch trees were sampled (planted, naturally regenerated, mixed birch–spruce). In the sawing procedure, the output of sawn timber varied between 24% and 42% of the log volume in the sawlogs, depending on the log diameter class. As the volume yield of sawn timber and firewood billets was counted together in the case of sawlogs, the log consumption was c. 1.75 m3 of roundwood per 1 m3 of sawn timber and firewood billets. In the case of the firewood logs, the log consumption rate was considerably lower, only c. 1.35. The economic calculations showed that using the firewood approach in sawing may increase the net added value of products by €1.9–5.4 m−3 of logs, depending on their diameter class. As a conclusion, parallel production of sawn timber and firewood from logs from the first and second commercial thinning of birch-dominated stands is a concept that could work as an alliance between a sawmiller and a firewood entrepreneur. The concept could be competitive compared with both traditional sawmilling and production of chopped firewood.