Wood Properties and Drying Characteristics of Korean Sawtooth
Oak (Quercus acutissima Carruth.) Wood
Yeonjung Han
1* and Yoon-Seong Chang
1
* Corresponding author: Yeonjung Han; E-mail: yeonjungh@korea.kr
1Department of Forest Products National Institute of Forest Science
Seoul, 02455, Republic of Korea
ABSTRACT
The objective of this study was to present the wood properties and drying characteristics of sawtooth oak (Quercus acutissima Carruth.) for the spread of its utilization in South Korea. The annual ring, latewood ratio, dimension of vessels, density, and shrinkage of specimens manufactured from five sawtooth oak trees were measured and compared by age class. And drying rate and drying defects of sawtooth oak boards were measured during kiln-drying. In order to present the processing performance of surface on sawtooth oak wood, the roughness on radial and tangential sections after sawing and planing process was measured by roughness tester and the texture of surface on each section was observed by stereoscopic microscope. It is expected that the fundamental properties of Korean sawtooth oak wood presented in this study will contribute to the extension of utilization of Korean oak species.
1.INTRODUCTION
The forest area (6,383,441 ha) in South Korea occupies is 64% of total land area (10,036,372 ha) and the growing stock is 971,599,553 m3 on the basis of 2017 (Korea Forest Service 2018). The proportion of broad-leaved and mixed forest is 49% and 12%, respectively. Of that, forest area and growing stock of Quercus species are 975,181 ha and 133,606,365 m3, respectively.
Quercus species are widespread across Asia, Europe, North America and Africa (Fang et al. 2011). Quercus species
have been used for different purposes such as timber, charcoal, bed logs for the cultivation of mushrooms, raw material for tannin extract, and bioenergy (Lee et al. 2008, Okamura et al. 2001, Oshima et al. 1997). The sawtooth oak (Quercus acutissima Carruth.) broadly inhabits the deciduous broad-leaved forest zone of eastern Asia, as a frontier species of deforest areas (Jung and Tamai 2012). The sawtooth oak is one of the domestic hardwood species (Kim 2002) that manly inhabits at altitudes below 600 m and grows straightly up to 20 – 30 m height.
As mentioned above, Quercus species, which can be used for various purposes, is used in low-grade applications such as bed log for mushroom, handle of tools, and charcoal in Korea. Quercus species for use as timber and lumber is being imported. As of 2011, oak wood was imported 8,000 m3 and 4,400 m3 in the form of lumber and log, respectively. Because Quercus species were no continuous supply of high quality wood required by the lumber industry, it was not treated as wood in Korea. Also, forest policy in Korea was focused on forest greenification, which put emphasis on the cultivation of rapid grown species. From now on, a national policy is needed to raise oak trees which have great potential value as timber resource.
It was commonly accepted that wood from trees grown in certain locations under certain conditions was stronger, more durable, more easily worked with tools, or finer grained than wood from trees in other locations (Wiemann 2010). In the present study, anatomical and physical properties of domestic sawtooth oak wood were measured and presented. The specimens were taken from five sawtooth oak trees. The age class of sawtooth oak trees was IV, V, and VI, respectively. The ring width, proportion of latewood, length and diameter of vessel elements, density, and shrinkage were measured by each age class of sawtooth oak wood. The drying rate and drying defects of sawtooth oak wood during kiln-drying were measured. To analyze the surface processability of sawtooth oak wood, the roughness of radial and tangential section after cutting specimens was measured by roughness tester and the surface texture was observed
by stereoscopic microscope. It is expected that the domestic sawtooth oak wood will be utilized in various ways through the results in this study.
2.MATERIALS AND METHODS
2.1.MATERIALS
The domestic sawtooth oak (Quercus acutissima Carruth.) were felled in the area of Andong-si, Gyeongsangbuk-do, Korea to measure the wood properties and drying characteristics. The disks with 50-mm thickness were collected from five sawtooth oak wood and the strips (radial direction) with 30-mm width were prepared from each disk. After planing the cross section of each strip, the cross section images were obtained using scanner (Epson, Japan). The width of earlywood and latewood in obtained images was measured using WinDENDROTM (Régent Instrument Inc. Canada). The IV, V, and VI age class in five sawtooth oak wood were two, two, and one, respectively. The mean, earlywood, latewood, juvenilewood, and maturewood ring width of each age class of sawtooth oak wood were described in Table 1.
Table 1: Annual ring width of sawtooth oak
Age class IV V VI
Ring width (mm) Mean 5.005 ±2.011 3.930 ±1.998 2.760 ±0.774 Earlywood 0.873 ±0.342 0.790 ±0.253 0.706 ±0.104 Latewood 4.182 ±2.007 3.140 ±1.859 2.054 ±0.750 Juvenile wood 5.880 ±2.213 5.369 ±2.175 2.642 ±1.062 Mature wood 3.851 ±0.636 2.742 ±0.530 2.826 ±0.563
2.2.METHODS
Two strips of 30-mm and 20-mm thickness were manufactured from the strip (30-mm width × 50-mm thickness) in the sawtooth oak disks. The strips of 30-mm and 20-mm thickness were used for measurement of density and vessel elements size, respectively. The strips were cut with five annual rings intervals from pith to bark in order to measure the length and diameter of vessel elements. The length and diameter of vessel elements were measured using the image analysis program (DeltaFix, Netherlands), after the preparats of vessel elements were made by the Schultz method (Seo et al. 2014).
The specimens with 20-mm (width) × 20-mm (thickness) × 20-mm (length) prepared for measuring the density and shrinkage. The basic density, oven-dry density, and shrinkage from green to oven-dry of sawtooth oak wood were calculated by measuring the weight and dimension of green and oven-dry conditions.
Table 2: Kiln schedule for sawtooth oak wood
Step Moisture content
(%) Dry-bulb temperature (℃) Wet-bulb temperature (℃) Equilibrium moisture content (%) 1 Above 40 43.3 41.1 17.7 2 40 to 35 43.3 40.6 16.6 3 35 to 30 43.3 38.9 13.6 4 30 to 25 48.9 41.1 10.0 5 25 to 20 54.0 37.8 5.7 6 20 to 15 60.0 32.2 2.9 7 15 to final 82.2 54.4 3.5
The eighty eight sawtooth oak boards were dried in a laboratory-scale kiln (Drying Eng., Korea) according to the FPL (Forest Products Laboratory, US Forest Service) kiln-drying schedule (T4-C2; Table 2; Boone et al. 1988). The initial moisture content (MC) of the boards ranged from 34.7 to 64.9%. Drying was continued until a final target MC of 12% in the board was reached. The boards (130-mm width × 25-mm thickness × 2.7-m length) were stacked eight wide and 11 high. The internal dimensions of the kiln were 1.5 × 1.5 × 4.0 m3, and the walls were insulated using 100 mm of urethane form. The air velocity was 2 m/s, and the airflow was parallel to the longitudinal axis of the boards. Drying defects such as cup, bow, crook, and twist were measured after drying. The cup was measured by selecting the farthest point from the plane after the widthwise edges of the board contacted the plane. The bow and crook were measured by selecting the farthest point from the plane after the longitudinal edges of the board contacted the plane. The twist was measured taking into consideration the height of the remaining vertex away from the plane after the rest of the vertices were in contact with plane.
After circular sawing, band sawing, and planing of sawtooth oak boards, the roughness of radial and tangential sections were measured by roughness tester (Time HighTech, China) and the surface texture was observed by stereoscopic microscope. And the roughness of sawtooth oak was compared with the Japanese larch wood that was widely used in Korea. Although the profiles representing surface roughness were various (International Organization for Standard 1997), in present study, three parameters (Ra, Rt, and Rp) were presented that express the roughness of entire surface. The average of ordinates (Ra), maximum peak to vally roughness height (Rt), and maximum profile peak height (Rp) were shown in Figure. 1 and the average of ordinates can be calculated as shown in equation 1.
01
l aR
Z x dx
l
(1)where, l = sample length and Z(x) = ordinate values.
Figure 1: Digitized representation of a 3A Common red oak board.
3.RESULTS AND DISCUSSION
3.1.ANATOMICAL AND PHYSICAL PROPERTIES OF SAWTOOTH OAK
The length and diameter of vessels dissociated from sawtooth oak were measured to 0.01 μm length unit (Figrue 2). The length and diameter of vessels was 376.8 μm (60.2 SD) and 280.7 μm (43.1 SD) in IV age class, 379.6 μm (55.6 SD) and 266.4 μm (38.9 SD) in V age class, and 373.6 μm (61.7 SD) and 268.7 μm (39.9 SD) in VI age class, respectively. The dimension of the vessels was measured relatively large, as a result of collecting the vessels mainly distributed in earlywood. A typical ring-porous wood has very large earlywood vessels with diameters from 200 to 350 μm (Siau 1995). It was similar to the result in this study.
Density (or specific gravity) is one of the most important physical properties of wood (Desch and Dinwoodie 1996, Bowyer et al. 2003). Base on the oven-dry weight, the average basic density and oven-dry density was 688.4 kg/m3 (37.1 SD) and 781.8 kg/m3 (37.8 SD), respectively. In hardwood, density is dependent not only fiber wall thickness, but also on the amount of void space occupied by vessels and parenchyma (Wood Handbook Ch.3, Wiedenhoeft). The reason for the high density of sawtooth oak wood was that the ring width of latewood was larger than those of earlywood. The shrinkage of sawtooth oak specimens from initial MC (32.5-48.0%) to oven dry condition were 0.269% (0.189 SD) in longitudinal, 3.985% (0.892 SD) in radial, and 7.980% (1.357 SD) in tangential direction. Because of the high density and shrinkage of sawtooth oak wood, it is necessary to analyze the lumbering, planning, and drying process.
Figure 2: The length and diameter of vessel in sawtooth oak.
3.3.DRYING CHARACTERISTICS OF SAWTOOTH OAK
The average changes in MC for 130 mm (width) × 25 mm (thickness) × 2.7 m (length) sawtooth oak boards in accordance with the drying schedule (T4-C2) is shown in figure 3. Drying was conducted for 262 h, and 10 specimens among the dried sawtooth oak boards among the in kiln were used to measure the average changes in MC. The initial MCs of 10 specimens ranged from 34.7 to 64.9%, and the final MC of the specimens was 5.5% (2.1 SD), the average drying rate was 0.166%/h (0.029 SD) which ranged from 0.115%/h to 0.250%/h due to the wide variation of initial MCs within the specimens.
Figure 3: The MC change of sawtooth oak wood during kiln drying.
The cup, bow, crook, and twist of sawtooth oak boards were 1.409 (0-4.59), 3.474 (0-11.19), 7.038 (1.34-10.73), and 5.030 (1.74-7.97) mm, respectively. These values are similar to the results obtained from a previous study of the drying defects of larch wood (Han et al. 2016). In this study, cup and twist were suppressed by applying an upper load to the stacked boards during kiln drying. However, crook was measured relatively large, so other ways are required to solve this problem.
Warp1 (mm) and its rate (%)
Cup Bow Crook Twist
1.409 3.474 7.038 5.030
(1.084)2 (0.174)3 (0.352)3 (0.252)3 1 Distance between surface of board and surface of plate 2 The rate in the case of cup : warp / width × 100
3 The rate in the case of bow, crook, and twist : warp / length × 100
3.3.SURFACE CHARACTERISTICS AFTER SAWING AND PLANING
After circular sawing, band sawing, and planing of sawtooth oak and Japanese larch wood, the roughness of radial and tangential sections were presented in Table 3 as three roughness parameters Ra, Rt, and Rp. The roughness of radial and tangential section found to have no significant difference in both sawtooth oak and Japanese larch wood. Also, it can be seen that the roughness parameters decrease after planing. However, the roughness after band sawing was not measured out of range in roughness tester. The roughness of sawtooth oak wood after wood processing was smaller than coniferous Japanese larch wood. To identify these causes, each surface of sawtooth oak and Japanese larch wood was observed through the stereoscopic microscope.
Table 4: Surface roughness of sawtooth oak wood and Japanese larch wood after wood processing
Sawtooth oak Japanese larch
Circular
sawing Band sawing Planing Circular sawing Band sawing Planing Radial
section Ra 2.580 (0.576 SD) Out of range1 1.767 (0.428 SD) 4.250 (1.086 SD) Out of range1 2.608 (0.824 SD) Rt 22.806 (7.788 SD) 15.418 (6.020 SD) 32.978 (6.960 SD) 19.988 (5.914 SD) Rp 5.798 (1.106 SD) 4.675 (1.370 SD) 9.817 (2.462 SD) 5.972 (1.739 SD) Tangential section Ra 2.444 (0.485 SD) 1.723 (0.688 SD) 3.558 (1.803 SD) 3.042 (0.602 SD) Rt 23.238 (4.350 SD) 17.700 (8.956 SD) 26.732 (9.573 SD) 23.064 (4.096 SD) Rp 6.065 (1.259 SD) 4.280 (1.974 SD) 8.758 (2.938 SD) 8.178 (1.576 SD) 1 The range of roughness tester : ±40 μm
Microscopic photographs of 150 times on radial and tangential section of sawtooth oak wood after circular sawing, band sawing, and planing were shown in figure 4 and 5. Compared to the circular sawing, there were many tissue destruction and saw mark left on the surface after band sawing.
Figure 5: Tangential section image of sawtooth oak after wood processing (a: circular sawing, b: band sawing, c: planing). In figure 6 and 7, the radial and tangential section of Japanese larch wood after wood processing were presented for comparison of sawtooth oak wood. Many trace of broken fibers after circular and band sawing were observed on the surface of Japanese larch with relative long tracheids. Therefore, it was considered that the surface of Japanese larch wood was measured roughly compared to the sawtooth oak wood.
Figure 6: Radial section image of Japanese larch after wood processing (a: circular sawing, b: band sawing, c: planing).
Figure 7: Tangential section image of Japanese larch after wood processing (a: circular sawing, b: band sawing, c: planing).
4.SUMMARY
The objective of this study was to present the wood properties and drying characteristics of sawtooth oak for the spread of its utilization in South Korea. The annual ring width of sawtooth oak showed a tendency to decrease with increasing age class. The dimension of vessels was similar to typical ring–pourous species. As a result of kiln-drying experiment on sawtooth oak with high basic density (688.4 kg/m3) and shrinkage (3.985% in radial and 7.980% in tangential direction), the drying rate was 0.166%/h. Drying defects except for crook, was not significant. The surface on sawtooth oak wood after band sawing was rougher than circular sawing.
REFERENCES
Boone, R. S., C. J. Kozlik, P. J. Bois, and E. M. Wengert. 1988. Dry Kiln Schedules for Commercial Woods: Temperate and Tropical. USDA Forest Products Laboratory GTR-57. DOI: 10.2737/FPL-GTR-57.
Bowyer, J., R. Shmulsky, and J. G. Haygreen. 2003. Forest Products and Wood Science: An Introduction. Iowa State Press, Iowa City. 554 pp.
Desch, H. E. and J. M. Dinwoodie. 1996. Timber structure, properties, conversion and use. Macmillan Press, UK. 306 pp. Fang, S., Z. Liu, Y. Cao, D. Liu, M. Yu, and L. Tang. 2011. Sprout development, biomass accumulation and fuelwood
characteristics from coppiced plantations of Quercus acutissima. Biomass Bioenergy 35(7):3104-3114.
distortion of laminas on the productions yield of cross-laminated timber (CLT) using Larix kaempferi wood. Eur. J. Wood Prod. 74(4):519-526.
International Organization for Standard. 1997. Geometrical product Specifications (GPS) – Surface texture: Profile method – Terms, definitions and surface texture parameters. ISO-4287.
Jung, N. C. and Y. Tamai. 2012. Anatomical observation of polyphenol changes in epidermal cells during the development of Quercus acutissima-Scleroderma verrucosum ectomycorrhize. Trees 26(2):301-310.
Kim, C. 2002. Mass loss rates and nutrient dynamics of decomposing fine roots in a sawtooth oak and a Korean pine stands. Korean J. Ecol. Sci. 1(2):101-105.
Korea Forest Service. 2018. Statistical Yearbook of Forestry. Korea Forest Service, Daejeon, Korea. 444 pp.
Lee, S. H., M. S. Eom, K. S. Yoo, N. C. Kim, J. K. Jeon, Y. K. Park, B. H. Song, and S. H. Lee. 2008. The yields and composition of bio-oil produced from Quercus acutissima in a bubbling fluidzed bed pyrolyzer. J. Analytical Appl. Pyrolysis 83(1):110-114. Okamura, M., T. Taniguchi, and T. Kondo. 2001. Efficient embryogenic callus induction and plant regeneration from embryonic
axis explants in Quercus acutissima. J. Forest Res. 6(2):63-66.
Oshima, K., Y. Tang,and L. Washitani. 1997. Spatial and seasonal patterns of microsite light availability in remnant fragment of deciduous riparian forest and their implication in the conservation of Arissaema heterophyllum, a threatened plant species. J. Plant Res. 110(3):321-327.
Seo, J. W., C. D. Eom, S. Y. Park. 2014. Study on the variation of inter-annual tracheid length for Korean red pine from Sokwang-ri in Uljin. J. Korean Wood Sci. Technol. 42(6):646-652.
Wiedenhoeft, A. 2010. “Chapter 3-Structure and Function of Wood”, in Wood Handbook–Wood as an Engineering Material. USDA Forest Products Laboratory GTR-190. DOI: 10.2737/FPL-GTR-190.
Wiemann, M. C. 2010. “Chapter 2-Characteristics and Availability of Commercially Important Woods”, In Wood Handbook–Wood as an Engineering Material. USDA Forest Products Laboratory GTR-190. DOI: 10.2737/FPL-GTR-190.
