Improvement of Technological Quality of Eucalypt Wood By Heat Treatment in Air at 170-200C

Abstract

Eucalypt wood is a low-value wood considered a nondurable species with low dimensional stability, used almost exclusively for pulp and paper or as firewood. The heat treatment was made in an oven in the presence of oxygen during 2 to 24 hours and temperatures of 170 to 200C. Mass loss with treatment, equilibrium MC, dimensional stability measured as ASE in radial and tangential directions and at 35 percent, 65 percent and 85 percent relative humidity, MOE, bending strength and wettability were determined. Mass loss increased with treatment time and temperature reaching 9.5 percent for wood treated at 190C for 24h. Equilibrium MC decreased more than 50 percent (at 35 percent relative humidity) reaching a maximum of 61 percent reduction. At higher air relative humidity the reduction was smaller, 49 percent and 38 percent at the most for 65 percent and 85 percent relative humidity. Dimensional stability (ASE) increased with maximum values of 88 percent and 96 percent in radial and tangential direction, respectively. The improvement was higher for lower relative humidity. There was a reduction on mechanical resistance with heat treatment especially for bending strength that decreased about 20 percent for 3 percent mass loss, reaching 60 percent for mass losses higher than 10 percent. MOE decreased with heat treatment the reduction was under 10 percent until 8 percent mass loss. The contact angle increased until 5 percent mass loss, decreasing slightly afterward. Heat treatment was shown to be a useful method to improve the technological quality of eucalypt wood as regards dimensional stability, allowing it to compete with higher- cost woods for some applications.

(ProQuest-CSA LLC: ... denotes formulae omitted.)

In the last years several heat treatments of wood appeared in Europe with the publication of quite a few patents.

The Thermowood process developed in Finland (Viitanen et al. 1994) is probably the most evolved with more than a dozen factories producing heat-treated wood. The treatment is made with vapour, with less than 3 to 5 percent of oxygen, at ambient pressure and with an air speed of at least 10 m/s (Syrjnen and Kangas 2000). The process starts with a fast increase in the oven temperature with heat and vapour until 100C, followed by a gradual increase up to 130C until wood moisture is almost zero; after that, the thermal treatment is done between 185C and 230C during 2 to 3 hours (Militz 2002), and at the end the temperature decreases to about 80 to 90C. The species used are mainly pine (Pinus sylvestris), spruce (Picea abies), aspen (Populus tremula) and birch (Betula pendula), and the treated wood is applied for exterior uses like decks, fences, garden furniture, doors and windows and for interior uses like kitchen furniture, parquet and panels.

Plato Wood, in Holland, is a four-step process that uses green or air-dried wood (Tjeerdsma et al. 1998). The first step, named hydrothermolysis, is carried out between 160 to 190C in wet conditions and above atmospheric pressure during about 4 to 5 hours (Boonstra et al. 1998); in the second step, wood dries until about 10 percent moisture by conventional processes during 3 to 5 days, and in the third step, wood is heated up until 170 to 190C during 14- 16 hours in dry conditions (Militz 2002); the last step is used to raise the wood equilibrium moisture to normal functioning conditions. Wood treated by this method is already commercialised with a plant in Arnhem (Holland) with a capacity of 35,000 m^sup 3^/ year.

In France two processes were developed: the Rectification process (Dirol and Guyonnet 1993) treats wood with 12 percent moisture in an oven with nitrogen in one step at 200 to 240C; the process Boisperdure uses green wood and consists of a fast drying with vapour at 200 to 240C.

The process used in Germany, OHT, is quite different because it uses oil at high temperatures (Rapp and Sailer 2001). The wood is enclosed in a container where hot oil is introduced at high temperatures and remains for 18 to 24 hours. The oil promotes a good heating and limits the oxygen but wood absorbs a great amount of oil corresponding to a mass increase of 50 to 70 percent which can be a disadvantage (Sailer et al. 2000).

The heat treatment of wood reduces its equilibrium moisture (Jamsa and Viitaniemi 2001) and increases the dimensional stability (Kollmann and Schneider 1963, Viitaniemi et al. 1997, Bekhta and Niemz 2003) and rot resistance {Kirn et al. 1998, Kamdemet al. 2002). Moreover the treatment darkens the wood (Mitsui et al. 2001, Bekhta and Niemz 2003), which might be an advantage for less- attractive woods. The largest disadvantage of heat-treated wood is the decrease in some mechanical properties, namely in bending strength (Kirn et al. 1998, Kubojima et al. 2000. Bengtsson et al. 2002). Surface wettability decreases (Ptrissans et al. 2003, Hakkou et al. 2005), but gluing can be easily adapted for treated wood (Militz 2002).

Eucalypt wood (Eucalyptus glohulus) is one of the cheapest woods on the market. The possibility to transform this wood into a durable material capable of competing for some applications with tropical woods of much higher cost opens a window of new opportunities. The low dimensional stability and durability are the main reasons for the low value of eucalypt wood, together with the difficulty to use preservative treatments. Impregnation is almost impossible and only feasible for sapwood and small diameters. Even when treated, eucalypt wood is still vulnerable to soft-rot fungus (Reimo and Nunes 1989), and there is substantial preservative leaching because of the large diameter of vessels. Nowadays eucalypts are cut down at about 10 to 14 years of age for pulp and paper, but older eucalypts with larger dimensions and very high extractives content are not adequate for pulping and are sold as firewood.

In this paper we report the results on the technological improvement of eucalypt wood by using a heat treatment in air in the range 170 to 200C regarding dimensional stability, equilibrium moisture and wettability, and on its effects on the mechanical resistance of treated wood. It is the objective to contribute to increase the timber value of mature eucalypt (Eucalyptus globulus) trees and to reduce the use of tropical woods in some applications.

Material and methods

Material

Eucalypt wood (Eucalyptus globulus Labill.) was tested for heat treatment in the presence of air using a radial board from a tree with a 100-cm diameter. The samples were cut with clear radial, tangential and transversal faces from the heartwood region in the board (sapwood width was less than 10 cm). The samples for determination of equilibrium moisture and dimensional stability were cubic with 40 mm of edge. The samples for measurement of mechanical properties had 360 by 20 by 20, in mm, respectively in transverse, radial and tangential directions, 4 replicates of each kind were used for each time/temperature of treatment. All the samples were kept for 3 weeks in a room with 50 percent relative humidity and 20C. After this period samples were weighed and the wood equilibrium MC was determined.

Heat treatment

The heat treatment was made in an oven during 2 to 24 hours and temperatures from 170C to 200C. The oven heating was made by electric coils located in the walls without forced convection, but with exhaustion of the heated gases by natural convection through an opening on the oven wall. The period to reach the treatment temperature was about 1 hour, which was kept approximately constant at 5C. The samples were put in the oven in the beginning of the heating process at ambient temperature. At the end of the treatment the samples were cooled in a desiccator and weighed.

Equilibrium MC, dimensional stability and wettability

The heat-treated and untreated samples were kept in an oven at 20C and 35 percent relative humidity until stabilization. Afterward, samples were weighed and measured with a digital gauge with an error of 0.01 mm in radial, tangential and transversal directions. The same procedure was done on separate samples kept at 65 percent and 85 percent relative humidity.

Dimensional stability in radial and tangential directions was determined at 35 percent, 65 percent and 85 percent air relative humidity by the ASE (Anti Shrinking Efficiency) method. ASE gives the difference between the swelling coefficient of treated and untreated samples, from oven-dry to 35 percent (ASE^sub 35^), 65 percent (ASE^sub 65^) and 85 percent (ASE^sub 85^) relative humidity. Total ASE corresponding to volume difference was also determined. A higher ASE value means that the effect of the treatment on wood dimensional stabilization was higher.

Wettability of wood was determined in tangential and radial sections, by the contact angle method, measured 10 seconds after the contact of the water drop with the wood surface. A high contact angle means the surface wettability is low.

Mechanical properties

Bending strength and apparent modulus of elasticity were determined by a three-point bending device. Measurements for MOE were made using a constant velocity of 0.3 mm/min. For ben\ding strength the velocity was set to cause rupture in 3 minutes. MOE and bending strength were determined according to (NP-619 1973):

...

where F is the load on rupture measured in kgf/mm, ΔF/ Δχ is the slope of the elastic zone in kgf/mm, L is the arm length, h the height and b the width, all expressed in mm.

Results

Mass loss with treatment

The mass loss of eucalypt wood with heating in air at 170C, 180C, 190C and 200C during 2 to 24 hours is shown in Figure 1. Mass loss increased with treatment time and temperature. At 170C mass loss was very small in the first 2 hours, and increased with time until reaching 4 percent for a 24-hour treatment. Mass loss also increased with temperature of treatment. For instance, a 3 percent mass loss was obtained between 6 and 8 hours of treatment at 180C and between 4 and 6 hours at 190C. The maximum mass loss was 4 percent, 7 percent and 9.5 percent for a 24-hour treatment at 170C, 180C and 190C, respectively. For 200C mass loss was 1.8 percent with 2 hours of treatment and reached 10.3 percent with 12 hours.

The rate of mass loss was higher in the beginning of the treatment and decreased for longer exposure times. The rate of mass loss increased with temperature.

Equilibrium moisture

The equilibrium MC of the heat-treated samples decreased in relation to the untreated wood. Even for the less severe 2-hour treatment at 170C, the wood equilibrium MC at 35 percent relative humidity was reduced by more than 50 percent, from 8.4 percent to 4.1 percent.

The decrease of the wood equilibrium MC depended to some extent on treatment temperature and duration. It decreased with temperature (3.3% for 170C and 3.0 percent for 200C) and at the same temperature, with treatment time, e.g., at 170C it varied between 4.1 percent (2 h) and 3.3 percent (24 h). However, the difference in the wood equilibrium moisture between the treatments was irrelevant when compared with the difference between treated and untreated wood.

Figure 2 presents the equilibrium MC, for 35 percent air relative humidity, of heat-treated wood vs. the corresponding mass loss with the treatment. The wood equilibrium MC decreased steadily until a mass loss of 4 to 6 percent, and remained approximately constant for higher mass losses at a value of approximately 3 percent.

The treatment was less effective at higher air relative humidities. For example, the decrease of the equilibrium moisture for wood samples treated at 170C in relation to the untreated samples was 61 percent, 49 percent and 38 percent respectively for 35 percent, 65 percent and 85 percent air relative humidity. Higher treatment temperatures narrowed the differences, e.g., 64 percent, 57 percent and 48 percent, respectively, for 200C treated samples.

Dimensional stability

The dimensional variations of eucalypt wood between oven dry and 35 percent, 65 percent and 85 percent air humidity are presented in Table 1. The dimensional changes in tangential direction (from 3.3% to 5.6%) were higher than in radial direction, (from 1.8% to 3.5%). The volume variation was between 5.1 to 9.2 percent. The tangential/ radial ratio was between 1.8 to 1.6 for untreated wood.

The dimensional stability improvement given by the heat treatment was evaluated by the ASE (Anti Shrinking Efficiency) in 35 percent, 65 percent and 85 percent air relative humidity.

Dimensional stability improved with heat treatment even for short durations. For example a treatment of 2 hours at 170C lead to a 60 percent ASE in radial direction. There was an increase in ASE with treatment time until the maximum value was achieved. For 170C the maximum ASE35 in radial direction of 76 percent was obtained with a 12-hour treatment, and a further increase in treatment time did not lead to an increase in dimensional stability.

Dimensional stability increased with treatment temperature, with ASE reaching 76 percent for 170C and 88 percent for 200C.

The dimensional stability improvements were generally higher in the tangential direction than in the radial direction, e.g., ASE35 of wood treated at 180C ranged 63 to 85 percent for radial and 69 to 95 percent for tangential directions. The maximum value obtained at each temperature was also higher in the tangential direction, ranging from 84 to 96 percent against 76 to 88 percent in the radial direction at 170 to 200C. Despite the higher reduction of tangential swelling with heat treatment, the absolute swelling value is still higher than in radial direction but the anisotropy is smaller than in untreated wood.

The air relative humidity influenced the dimensional stability improvement. Although the general trends for ASE65 and ASE^sub 65^ were similar to ASE^sub 35^, the values were smaller. For example, in the radial direction of wood treated at 170C, ASE^sub 65^ ranged 45 to 59 percent and ASE^sub 85^ 17 to 45 percent, while maximum ASE values were between 59 to 71 percent and 45 to 57 percent for 65 percent and 85 percent air relative humidity respectively.

Figure 3 presents the radial ASE in function of mass loss with heat treatment in 35 percent, 65 percent and 85 percent air relative humidity. The rate of dimensional stability increase was higher until 4 percent mass loss but for higher mass losses ASE increased only slightly, having reached maximum values between 4 to 6 percent mass loss. These values of mass loss correspond to the mass loss at which the minimum equilibrium moisture was obtained.

Wettability

Figure 4 presents the contact angle of eucalypt wood measured in radial and tangential sections as a function of mass loss with heat treatment. The contact angle increased until about 5 percent mass loss, reaching approximately 70 in radial section and 75 in tangential section, corresponding to a decrease of surface wettability. The increase was very high even for small mass losses of about I percent, e.g., contact angle changed from 25 to about 55 in radial section and from 52 to about 72 in tangential section. For mass losses higher than 6 percent the contact angle seemed to decrease.

Mechanical resistance

Figure 5 presents a stress-strain curve for eucalypt wood untreated and treated at 200C for 2h, 6h and 12h. The initial zone where deformation is elastic is similar for treated and untreated wood, while the plastic deformation zone where deformation is definitive was shortened in the heat treated samples and almost did not exit for wood treated for 12 hours. With the increase of treatment severity the stress-strain curve changed, and rupture occurred for smaller tensions. In some samples, the rupture was preceded by some failure as, for example, the sample treated at 200C during 6 hours (Fig, 5).

The apparent modulus of elasticity (MOE) of eucalypt wood without treatment was on average 14,197 MPa, varying between 9289 to 17782 MPa. MOE decreased with heattreatment temperature and time, but for the less-severe heat treatments the difference was very small. For example, with 2 hours, the reduction of MOE was 0 percent (180C), 3 percent (190C) and -1% (200C) and with 12 hours, 6 percent (180C), 6 percent (190C) and 25 percent (200C).

Figure 6 shows the variation of MOE and bending strength of eucalypt wood with mass loss by heat treatment. The decrease in MOE was of small magnitude (under 10%) until 8 percent mass loss but reached 25 percent for about 10 percent mass loss. The treatment effect on MOE was much smaller than in bending strength. The reduction of bending strength was considerable even for short treatments and increased with temperature: with 2 hours 11 percent (180C), 47 percent (190C) and 34 percent (200C) and with 12 hours 27 percent (180C), 48 percent (190C) and 61 percent (200C).

The mechanical resistance of heat-treated eucalypt wood decreased with mass loss (Fig. 6), and bending strength decreased about 20 percent at 3 percent mass loss and reached 60 percent for mass losses higher than 10 percent.

Discussion

The mass loss with heat treatment increased with treatment time and temperature (Fig. 1), which is in agreement with earlier studies reported for species like beech, spruce or birch (Viitaniemi et al. 1997, Aln et al. 2002). The kinetic behavior of mass loss showed a higher rate in the beginning of the treatment for all the temperatures studied. Similar results were reported by Gonzlez-Pena et al. (2004) with Western red cedar treated at temperatures 190 to 230C. This higher rate of mass loss in the first phase of the heating process and at higher temperatures should be due to the rapid removal of more volatile extractives from wood. In eucalypt wood extractives amount to 4.9 percent for 11-to 14-year-old eucalypts (Pereira 1988). The disappearance of some extractives from wood with the increase in treatment temperature was also reported (Nuopponen et al. 2003).

The equilibrium MC of eucalypt wood decreased significantly with the heat treatment (Fig. 2). Identical results were reported by Jmsa and Viitaniemi (2001) using a steam heat treatment, by Rapp and Sailer (2001) using hot oil, and by Militz and Tjeerdsma (2001) for the Plato treatment with steam and pressure.

The differences in equilibrium moisture between heattreated and untreated wood decreased for higher air relative humidities. This is in accordance with Kamdem et al. (2002) with beech wood treated by the Boisperdure method at temperatures between 200 to 260C and conditioned at 66 percent and 86 percent air relative humidity, but Militz and Tjeerdsma (2001) reported that the effect of the heat treatment was more pronounced at relative humidities higher than 70 percent.

The reduction in the wood equilibrium MC was improved only until 4 to 6 percent mass loss and remained approximately constant for higher mass losses (Fig. 2).

Wood dimensions vary with air relative humidity, mainly in tangential and radial directions, resulting into wood shrinking and swelling. T\he volumetric variation is mainly due to the dimensional changes that occur in tangential and radial directions since the axial variation is very small. Wood swelling is anisotropic with the tangential swelling of untreated wood higher than radial swelling (Table 1). Despite the more substantial dimensional stability improvement in the tangential direction, the anisotropy of swelling still remains for the heat treated wood.

The heat treatment was more efficient at lower air relative humidities (Fig. 3). For example at 35 percent air relative humidity ASE was always higher than 60 percent, while it was 40 percent and 20 percent for 65 percent and 85 percent air relative humidity (Fig. 3). The dimensional stability increased even for small mass losses with heat treatment and until 4 to 6 percent mass loss (Fig. 3). These values correspond to the mass loss at which the minimum equilibrium moisture was obtained (Fig. 2), showing the close relation between equilibrium moisture and dimensional stability.

Surface wettability decreased sharply even for small mass losses until 3 to 4 percent (Fig. 4). These results are in accordance with earlier studies (Pecina and Paprzycki 1988, Petrissans et al. 2003, Hakkou et al. 2005). At higher mass losses (above 6%) there was an increase in wettability, which should be due to the occurrence of thermal degradation compounds (Pecina and Paprzycki 1988).

The mechanical resistance of eucalypt wood decreased with the heat treatment. The reduction on MOE was of small magnitude until 8 percent mass loss and at the mass losses necessary to attain maximum stability (4% to 6%) it was only about 5 percent. The MOE reduction reached 25 percent for a 10 percent mass loss (Fig. 6). Yildiz et al. (2002) reported for beech wood treated at temperatures 130 to 200C for 2 to 10 hours a higher decrease in MOE, exceeding 45 percent, although the corresponding mass loss was not mentioned. Santos (2000) referred a surprising increase in MOE of eucalypt wood with heat treatment but no information was given on treatment conditions.

The decrease in bending strength was higher, attaining 20 percent and 60 percent respectively for 3 percent and 10 percent mass loss. At 4 to 6 percent mass loss, corresponding to the highest improvement on dimensional stability, the reduction on bending strength was between 25 to 40 percent. A similar decrease was reported by Bengtsson et al. (2002) with spruce wood and Scots pine.

In conclusion, it was shown that the heat treatment of eucalypt wood decreased its hygroscopicity and improved substantially its associated properties: the wood equilibrium MC decreased, the dimensional stability improved and the tangential/radial anisotropy decreased. Maximum gains in these properties could be attained with relatively mild treatment conditions, e.g., 5 hours at 190C, corresponding to a mass loss of about 4 percent. In these conditions the effect on MOE was negligible and the bending strength was reduced by only about 20 percent. Stronger treatment conditions leading to higher mass losses will reduce significantly the bending strength and this effect must be considered when envisaging the heat- treated wood applications.

Literature cited

Aln, R., R. Kotilainen. and A. Zaman. 2002. Thermochemical behavior of Norway spruce (Picea abies) at 180-225 C. Wood Sci. and Tech. 36:163-171.

Bekhta, P. and P. Niemz. 2003. Effect of high temperature on the change in eolour, dimensional Stability and mechanical properties of spruce wood. Holzforschung 57:539-546,

Bengtsson, C., J. Jermer, and F. Brem. 2002. Bending strength of heattreated spruce and pine timber Inter. Res. Group on Wood Preservation. Section 4-Proccsses. No. IRG/WP 02-40242. Stockholm. Sweden.

Boonstra, M., B. Tjecrdsma. and H. Groeneveld. 1998. Thermal Modification of Non-Durable Wood Species 1. The Plato technology: Thermal modification of wood. In: The Inter. Res. Group On Wood Preservation, section 4 Processes. 29 Annual Meeting, Maastricht, June 14-19. Stockholm, Sweden. 13 pp,

Dirol. D. and R. Guyonnet. 1993. Durability by rectification process. Inter. Res. Group on Wood Preservation, section 4- Processes. No. IRG/WP 93-40015. Stockholm, Sweden.

Gonzlez-Pea, M., M. Brecse. and C. Hill. 2004. Hygroscopicity in heat-treated wood: Effect of extractives. In: ICHCFOP - Inter. Conf. on Environmentally Compatible Forest Products. 22-24 September 2004. pp. 105-119.

Hakkou, M., M. Petrissans. A. Zoulalian, and P. Gerardin. 2005. Investigation of wood wettability changes during heat treatment on the basis of chemical analysis. Polym. Degrad. Stabil. 89:1-5.

Jms, S. and P. Viitaniemi. 2001. Heat treatment of wood - Better durability without chemicals. COST ACTION E22-Knvironmental optimisation of wood protection. Proc. of special seminar held in Antibes, France.

Kamdem, D., A. Pizzi, and A. Jermannaud. 2002. Durability of heat treated wood. Holz als Roh- und Werkstoff 60:1-6.

Kim, G., K. Yun, and J. Kirn. 1998. Effect of heat treatment on the decay resistance and the bending properties of radiala pine sapwood. Mat. und Org.32(2):101-108.

Kollmann, F. and A. Schneider. 1963. On the sorption behaviour of heat stabilized wood. Holz als Roh-und Werkstoff 21(3):77-85.

Kubojima. Y., T. Okano, and M. Ohta. 2000. Bending strength of heattreated wood. J. of Wood Sci. 46:8-15.

Militz, H. 2002. Thermal treatment of wood: European processes and their background. Inter. Res. Group on Wood Preservation, section 4-Processcs. No. IRG/WP 02-40241. Stockholm. Sweden.

______ and B. Tjeerdsma. 2001. Heat treatment of wood by the PLATO-process, COST ACTION E22-Environmental optimisation of wood protection. Proc. of Special Seminar in Antibes, France.

Mitsui, K., H. Takada. M. Sugiyuma, und R. Hasegawa. 2001. Changes in the properties of light-irradiated wood with heat treatment: Part I Effect of treatment conditions on the change in colour. Holzforschung 55:601-605.

Nuopponen, M., T. Vuorinen, S. Jamsa, and P. Viilaniemi. 2003. The effects of heat treatment on the behaviour of extractives in softwood studied by FTIR spectroscopic methods. Wood Sci. and Tech. 37:109115.

Pecina, H. and O. Paprzycki. 1988. Interrelations between the treatment temperature of wood and its wettability. Holzforschung Holzvcrwcrtung 40(1):5-X.

Percira, H. 1988. Variability in the chemical composition of plantation eucalypts(Eucalyptus globulus Labill). Wood and Fiber Sci. 20(1):8290.

Ptrissans, M, G. Philippe, 1. El Bakali. and M. Serraj. 2003. Wettability of heat-treated Wood. Holzforschung 57:301-307.

NP 619 Portuguese Standard. 1973. Static bending test of wood. Portuguese Inst. of Quality.

Rapp, A. and M. Sailer. 2001. Heat treatment of wood in Germany- state of the art, COST ACTION E22-Environmental optimisation of wood protection. Proc. of Special Seminar in Antibcs, France.

Reimao. D. and L. Nunes. 1989. A study about impregnability of round eucalypt wood. National Lab. of Civil Engineering. Lisbon.

Sailer, M., A. Rapp. and H. Leithoff. 2000. Improved resistance of Scots pine and spruce by application of an oil-heat treatment. Inter. Res. Group on Wood Preservation, section 4-Processes. No. IRG/ WP 0040162. Stockholm, Sweden.

Santos. J. 2000. Mechanical behaviour of Eucalyptus wood modified by heat. Wood Sci. and Tech. 34:39-43.

Syrjnen, T. and E. Kangas. 2000. Heat treated timber in Finland. Inter. Res. Group on Wood Preservation, section 4-Processes. No. IRG/ WP 00-40158. Stockholm, Sweden.

Tjeerdsma, B., M. Boonstra, and H. Militz. 1998. Thermal modification of nondurable wood species: Improved properties of thermally treated wood. Inter. Res. Group on Wood Preservation. No. IRG/WP 9840124. Stockholm, Sweden.

Viitanen. H., S. Jamsa, L. Paajanen, A. Nurmi. and P. Viitaniemi. 1994. The effect of heat treatment on the properties of spruce. No. IRG/WP 94-40032. Stockholm, Sweden.

Viitaniemi, P., S. Jamsa, and H. Viitanen. 1997. Method for improving biodgradation resistance and dimensional stability of cellulosic products. United Stales Patent N" 5678324 (US005678324). Washington, DC.

Yildiz, S.. G. Colakoglu, U. Yildiz. E. Gezcr, and A. Tcmiz. 2002. Effects of heal treatment on modulus of elasticity of beech wood. Inter. Res. Group on Wood Preservation, Section 4-Processes. No. IRG/WP 02-40222. Stockholm. Sweden.

The authors are, respectively. Assistant Professor and Coordinator Professor, Depart. Wood Engineering, Superior School of Technology of Viseu, Polytechnical Inst. of Viseu, 3504-010 Viseu, Portugal (bruno@demad.estv.ipv.pt; ijd@dmad.estv.ipv.pt) and Cathedratic Professor, Center of Forest Studies, Superior Inst. of Agronomy, Tapada da ajuda, 1349-017 Lisbon, Portugal (hpereira@isa.utl.pt). This paper was received for publication in February 2006. Article No. 10170.

Forest Products Society 2007.

Forest Prod. J. 57(1/2):47-52.

Copyright Forest Products Society Jan/Feb 2007

(c) 2007 Forest Products Journal. Provided by ProQuest Information and Learning. All rights Reserved.