Sini Metsä-Kortelainen

Decay resistance of sapwood and heartwood of untreated and thermally modified Scots pine and Norway spruce compared with some other wood species.

Abstract Thermal modification has been developed for an industrial method to increase the biological durability and dimensional stability of wood. In this study the effects of thermal modification on resistance against soft- and brown-rot fungi of sapwood and heartwood of Scots pine and Norway spruce were investigated using laboratory test methods. Natural durability against soft-rot microfungi was determined according to CEN/TS 15083-2 (2005) by measuring the mass loss and modulus of elasticity (MOE) loss after an incubation period of 32 weeks. An agar block test was used to determine the resistance to two brown-rot fungi using two exposure periods. In particular, the effect of the temperature of the thermal modification was studied, and the results were compared with results from untreated pine and spruce samples. The decay resistance of reference untreated wood species (Siberian larch, bangkirai, merbau and western red cedar) was also studied in the soft-rot test. On average, the soft-rot and brown-rot tests gave quite similar results. In general, the untreated heartwood of pine was more resistant to decay than the sapwood of pine and the sapwood and heartwood of spruce. Thermal modification increased the biological durability of all samples. The effect of thermal modification seemed to be most effective within pine heartwood. However, very high thermal modification temperature over 230°C was needed to reach resistance against decay comparable with the durability classes of “durable” or “very durable” in the soft-rot test. The brown-rot test gave slightly better durability classes than the soft-rot test. The most durable untreated wood species was merbau, the durability of which could be evaluated as equal to the durability class “moderately durable”.

Wettability of sapwood and heartwood of thermally modified Norway spruce and Scots pine

In this research, the effect of thermal modifications at 170°C, 190°C, 210°C and 230°C on the wettability of sapwood and heartwood of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) was studied by measuring the static contact angles of distilled water on the surfaces as a function of time. The results were compared to industrially kiln-dried reference samples. The thermal modification at the lower temperatures of 170°C and 190°C increased the wettability of all wood materials with the exception of the heartwood of pine that had been thermally modified at 170°C, which was the most water-repellent material in the whole study. Thermal modification at the very high temperature of 230°C was needed to decrease the wettability of wood. The differences in water repellency between sapwood and heartwood were greater for pine than for spruce.ZusammenfassungIn dieser Studie wird der Einfluss einer thermischen Behandlung bei 170°C, 190°C, 210°C und 230°C auf die Benetzbarkeit von Splint- und Kernholz der Kiefer (Pinus sylvestris) und der Fichte (Picea abies) untersucht. Dazu wurde der statische Kontaktwinkel von destilliertem Wasser auf der Oberfläche in Abhängigkeit der Zeit bestimmt und die Ergebnisse wurden mit technisch getrockneten Kontrollproben verglichen. Bei allen untersuchten Prüfkörpern führte eine thermische Behandlung bei den niedrigeren Temperaturen von 170°C und 190°C zu einem Anstieg der Benetzbarkeit, mit Ausnahme von Kiefernkernholz bei 170°C, dem am meisten hydrophoben Holz der gesamten Untersuchung. Erst bei der höchsten Behandlungstemperatur von 230°C konnte die Benetzbarkeit von Holz reduziert werden. Bei Kiefernholz war der Unterschied in der Wasserabweisung zwischen Splint- und Kernholz größer als bei Fichte.

Effect of fungal exposure on the strength of thermally modified Norway spruce and Scots pine

Abstract Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself.

Durability of thermally modified Norway spruce and Scots pine in above-ground conditions

Abstract One of the main objectives of thermal modification is to increase the biological durability of wood. In this study the fungal resistance of Norway spruce and Scots pine, thermally modified at 195°C and 210°C, was studied with a lap-joint field test. Untreated pine and spruce and pine impregnated with tributyl tin oxide (TBTO) and copper, chromium and arsenic (CCA) were selected as reference materials. The evaluations were carried out after 1, 2 and 9 years of exposure. After 1 and 2 years of exposure mainly discoloration was detected. Only the untreated pine was slightly affected by decay fungi. There were significant differences in the decay ratings of untreated and thermally modified wood materials after 9 years in the field. While the untreated wood materials were severely attacked by decay fungi or reached failure rating, only small areas of incipient decay were detected in the thermally modified samples. Thermally modified pine was slightly more decayed than thermally modified spruce. The only wood material without any signs of decay was CCA-treated pine, since some of the TBTO-treated pine samples were also moderately attacked by fungal decay. The results of the lap-joint test had a good correlation with mass losses in a laboratory test with brown-rot fungi.

Durability of thermally modified sapwood and heartwood of Scots pine and Norway spruce in the modified double layer test

Abstract In the present study, durability of untreated and thermally modified sapwood and heartwood of Scots pine and Norway spruce was examined using a modified double layer test. Base layer samples were partly on contact with ground where exposure conditions were harder than that in a double layer test above the ground. The base layer on ground contact gave results already after one year of exposure in Finnish climate, but the top layer of a double layer test element simulated more the situation of decking exposure. Significant differences in durability and moisture content (MC) between the wood materials were detected after six years of exposure in the field. Thermally modified pine heartwood performed very well in all layers of the test element and only minor signs of decay were found in some of the base samples. Both sapwood and heartwood of thermally modified spruce were suffering only slight amounts of decay while thermally modified pine sapwood was slightly or moderately decayed. Untreated sapwood samples of pine and spruce were severely decayed or reached failure rating after six years in the field. Untreated heartwood samples performed clearly better. The highest MCs were measured from untreated and thermally modified pine samples. Thermal modification increased significantly the durability and decreased the MC values of all wood materials.

Material Challenges in the Manufacturing of Tailored Structures with Direct Write Technologies

Two different direct write technologies, Direct Write Paste (DWP) and Direct Write Thermal Spray (DWTS), and the general material challenges related to these technologies are described in this paper. These new technologies open new routes to produce highly functional products that can be tailored and customised according to the demands of the applications. The DWP process is based on dispensing paste-like materials through a tip onto a substrate. Depending on the paste material, either 2 or 3 dimensional structures can be printed. The DWTS technique is based on thermal spraying, which is a spray process where the powder material is accelerated in molten form and impinged onto a surface. Products made using DWTS are especially targeted at harsh environment solutions. Results related to development of printable materials and printed products are presented.