Table des matières
Feasibility of using two exotic larch species Larix gmelinii and Larix sibirica as raw material for medium density fiberboard (MDF) panel manufacturing was studied. Laboratory MDF panels were fabricated from fibers of two individual larch species Larix gmelinii and Larix sibirica mixed with an approximate proportion of 4:1, and the panels made from fibers of spruce, pine, and fir (S-P-F) were studied as a control. 10 % urea-formaldehyde (UF) resin and 0.5 % wax were blended with the fibers that were generated from larch and S-P-F wood. The schedule and temperature used for panel pressing were kept constant when making the two types of panels. According to American National Standard ANSI A 208.2-2002 for evaluation of MDF panels for interior application, modulus of rupture (MOR) of panels made from larch and S-P-F both met the requirement of Grade 120. MOE of panels made from larch did not meet the ANSI minimum requirement; MOE of panels made from S-P-F met the requirement of Grade 120. Larch panels produced favorable IB strength compared to those panels made from S-P-F. IB of larch panels was 0.78 MPa, and met the requirement of ANSI grade 140. MOR and MOE of panels made from larch wood were slightly lower than those of panels made from S-P-F. This difference can be compensated through optimizing hot-pressing parameters so as to acquire desirable panel density profile. According to ANSI/AHA A 135.4-1995 standard for basic hardboard, thickness swell and water absorption of the two types of panels were below the maximum specified values. It can be concluded that it is feasible to use the two exotic larch species as raw material for MDF panel manufacturing, although they are still inferior to S-P-F.
For a couple of decades, the shortfall of wood and fiber supply that has been experienced by papermaking and composites industries in North America has required extension and diversification in raw material. Recently, composite mills are paying attention to proper utilization of forest residues such as commercial thinnings, tops, branches, etc. as raw materials for composite panel manufacturing (Li et al. 1991). Even tree barks, although it is known that composite panel properties would be very adversely affected (Woodson 1976), have been often studied in recent years in order to develop new technologies for acquisition of qualified panel products.
There are ten species of larch ( Larix ) located mostly in colder climates in the northern hemisphere. Three larch species can be found in North America: the alpine larch ( Larix lyallii ) distributed primarily at high elevations in western Canada; the eastern larch ( Larix laricina ) distributed in boggy areas of the northern forests of eastern North America; and western larch ( Larix occidentalis ) distributed in the American West. The potential role of exotic larch in future sustainable fiber supply cannot be ignored since some introduced larch species such as Japanese larch ( Larix leptolepis ) and European larch ( Larix decidua ) often outperform Canadian native larch, pine, and spruce spieces and can produce two to three times more wood and fiber in the Lake States and southern parts of eastern Canada (Vallee and Stipanicic 1983; Fowler et al. 1988; Palmer 1991).
In this study, MDF panels were made from two individual exotic larch species Larix gmelinii and Larix sibirica . Species Larix sibirica is naturally distributed in west and central Siberia, Russia. Species Larix gmelinii has a larger natural distribution, dispersed from eastern Siberia to northeast China. These two species were introduced to northern Ontario, Canada in 1981. Seeding trials were established in six sites: Fort Frances, Kapuskasing, Ottawa, Espanola, Lindsay, and Huronia. A commercial thinning was carried out when the tree age was around 10-15 years, and the thinnings were collected and transported to Forintek Canada Corp. (Québec, Canada) for wood property characterization and panel manufacture. As a control, properties of MDF panels made from a mix of spruce, pine, and fir (S-P-F) were evaluated as well. S-P-F is a favorable material that is often utilized for MDF panel production in Québec, Canada. The aim of the study was to investigate the feasibility of using the two exotic larch species Larix gmelinii and Larix sibirica for MDF panel manufacturing.
There are ten species of larch ( Larix ) located mostly in colder climates in the northern hemisphere. Three larch species can be found in North America: the alpine larch ( Larix lyallii ) distributed primarily at high elevations in western Canada; the eastern larch ( Larix laricina ) distributed in boggy areas of the northern forests of eastern North America; and western larch ( Larix occidentalis ) distributed in the American West. The potential role of exotic larch in future sustainable fiber supply cannot be ignored since some introduced larch species such as Japanese larch ( Larix leptolepis ) and European larch ( Larix decidua ) often outperform Canadian native larch, pine, and spruce spieces and can produce two to three times more wood and fiber in the Lake States and southern parts of eastern Canada (Vallee and Stipanicic 1983; Fowler et al. 1988; Palmer 1991).
In this study, MDF panels were made from two individual exotic larch species Larix gmelinii and Larix sibirica . Species Larix sibirica is naturally distributed in west and central Siberia, Russia. Species Larix gmelinii has a larger natural distribution, dispersed from eastern Siberia to northeast China. These two species were introduced to northern Ontario, Canada in 1981. Seeding trials were established in six sites: Fort Frances, Kapuskasing, Ottawa, Espanola, Lindsay, and Huronia. A commercial thinning was carried out when the tree age was around 10-15 years, and the thinnings were collected and transported to Forintek Canada Corp. (Québec, Canada) for wood property characterization and panel manufacture. As a control, properties of MDF panels made from a mix of spruce, pine, and fir (S-P-F) were evaluated as well. S-P-F is a favorable material that is often utilized for MDF panel production in Québec, Canada. The aim of the study was to investigate the feasibility of using the two exotic larch species Larix gmelinii and Larix sibirica for MDF panel manufacturing.
Two larch species Larix gmelinii and Larix sibirica were introduced to Canada and seeded in northern Ontario in 1981. A commercial thinning was operated when the trees were at 10-15 years of age, and the thinnings were collected and transported to Forintek Canada Corp. Hence these larch thinings were mostly juvenile wood. It should be noted that they probably differ from mature larch material. The two individual species Larix gmelinii and Larix sibirica were mixed with an approximate proportion of 4:1. Larch trees were debarked, and a portable chipper was used to produce wood chips. Spruce, pine, and fir (S-P-F) wood chips were collected from a composite panel mill located in Québec, Canada.
Larch and S-P-F wood chips were fed into a pressurized refiner for fiber conversion. When refining, 30 minutes of transition time was retained to avoid mixing of the two different types of fibers. The refining speed was 2500 rpm, and kept constant for larch and S-P-F wood chips. The specific refining energy spent on larch and S-P-F wood was 125 KWh/t and 182 KWh/t. The clearance between the two plates was 0.038 mm and 0.020 mm for larch and S-P-F, respectively. Normally, the refining energy and clearance between the two plates determine the performance of the generated fibers (Maloney 1993). These two parameters were set differently for larch and S-P-F wood since we attempted to produce fibers with less fiber bundles and broken fibers. The produced fibers were visually checked for the performance at the beginning of refining, and the parameters were adjusted and then fixed accordingly. Larch and S-P-F wood were refined without resin and wax injection.
The two types of fibers were dried in a laboratory-scale dryer until the moisture content was 2-3 %. Before switching to another type of fiber, the walls of the dryer were cleaned up to prevent the two types of fibers from mixing. The dried fibers were passed through a hammer mill immediately to make the fibers fully separated from each other, so the resin and wax can be sprayed more uniformly onto the fibers. Resin and wax were injected to the fibers in a laboratory-scale blade blender. It is known that the properties of composites can be improved by applying more resin to panels (Maloney 1993). Therefore, a relatively low resin level was used in this study in order to avoid any concealment of difference in panel properties. Borden 302 urea formaldehyde (UF) resin with 65 % solid content was first diluted to 10 %. The diluted UF resin and 0.5 % wax were slowly sprayed onto the fibers. The fibers blended with UF resin and wax were passed through the hammer mill once again to disperse fiber balls that were formed during blending. The furnish moisture contents after resin and wax blending for larch and S-P-F were 11.1 % and 14.8 %. Panels were manufactured at a target density of 740 kg/m3, and panel size was 610×610×12 mm. Mats were hand formed in a frame without fiber orientation. Three panels were made for each type of fibers. MDF panels were hot-pressed using the same schedule at the pilot plant of Forintek Canada Corp. The platens were closed within 160 s. Panels were kept pressing for another 160 s and the platens were gradually opened in 40 s. The temperature of the two platens was set at 135 oC. The press settings were initiated based on realization of a flatter density profile, which can reduce the differences in panel properties resulted from different density gradient through panel thickness.
Before cutting the specimens from each panel, the panels were conditioned in a chamber at 22 oC and 65 % relative humidity (RH) for four weeks until the panels reached equilibrium moisture content. The size of the specimens for bending property testing was 338×75 mm, and three were cut from each panel; ten internal bond (IB) specimens with a size of 50×50 mm were cut from each panel, producing totally thirty for each type of panel. The dimension of the specimens for linear expansion (LE) was 305×76 mm, two were taken from each panel and totally six for each type of panel. The LE specimens were stored in a conditioning chamber at 22 oC and 50 % RH for four weeks until their weight remained constant; the length of the specimens was measured. Then, the specimens were conditioned in another chamber with 80 % RH at the same temperature for another four weeks until they reached equilibrium moisture content; and the length of the specimens was recorded. LE was determined using the change in length divided by the length measured from the specimens equilibrated at 22 oC and 50 % RH. Thickness swell (TS) and water absorption were tested on the specimens with a dimension of 152×152 mm; two specimens were cut from each panel and six were prepared for each type of panel. Before soaking the specimens in water, the thickness and weight were recorded. After 24 h water-soaking, the thickness and weight of the specimens were measured again. TS and water absorption were determined by the variations in thickness and weight divided by the thickness and weight measured from the specimens equilibrated at 22 oC and 65 % RH. The procedures and methods described in the standards ASTM D 1037-99 (2001) and ANSI A 208.2-2002 (2002) were followed for modulus of elasticity (MOE), modulus of rupture (MOR), IB, LE, TS, and water absorption testing. The surfaces of IB specimens were sanded for 1.5 mm before the specimens were glued with the blocks. Density profiles were measured from IB specimens before they were sanded.
Duncan’s multiple-range test was performed to compare the mean properties of MDF panels made from larch and S-P-F wood. The statistical software Statistical Analysis System (SAS) (1990) was used for the data analysis.
Fiber size distribution was determined using Bauer-McNett classifier while the procedures described in Tappi 233 cm-95 (1995) were followed. Size distribution of the fibers produced from larch and S-P-F wood chips is presented in Table 5-1.The percentages of fibers distributed in the mesh size ranges of 0.828-3.240 mm2 and 0.017-0.281 mm2 were comparable for larch and S-P-F. There were 15.4 % and 16.7 % fibers distributed in 0.828-3.240 mm2 size range, and 8.9 % and 7.3 % in 0.017-0.281 mm2 size range (Table 5-1). However, fibers distributed in >3.240 mm2, 0.281-0.828 mm2, and <0.017 mm2 mesh size ranges apparently differed for larch and S-P-F. Fibers refined from S-P-F wood contained more large particles than those produced from larch wood, which is shown in column ‘>3.240 mm2’ in Table 5-1. Meanwhile, the refining process produced more fines from larch wood than it did from S-P-F wood chips, which can be known from the percentages of fibers distributed in ‘<0.017 mm2’ range (Table 5-1). The more fines in the pulp can have a negative effect on panel properties (Barnes 2002; Woodson 1976). The percentage of larch fibers (26.3 %) distributed in 0.281-0.828 mesh range was higher than that of fibers refined from S-P-F wood (15.9 %) (Table 5-1). More fines weakens fiber to fiber bond, which is due to more resin consumption of the fine fibers (Barnes 2002; Woodson 1976). The higher fine fiber content of larch pulp may affect panel mechanical properties adversely. Nevertheless, higher content of large particles in S-P-F pulp may also have a negative impact on panel properties since it can destroy the overall uniformity of resin distribution on fiber surfaces.
Panel density profile influences panel properties significantly, especially panel mechanical properties (Wang and Winistorfer 2000; Wang et al. 2001; Wang et al. 2004). High peak density leads to superior bending properties, while high core density results in good IB strength (Woodson 1976). Figure 5-1 shows the average density profiles of larch and S-P-F panels. The peak density of S-P-F panels was slightly higher than that of larch panels and face layer of the former was thinner than the latter, which may slightly improve the bending properties of S-P-F panels. The core density of the two types of panels remained equal. Since the hot-pressing parameters were kept constant, the slight difference in panel density profile between the two types of panels may be mainly due to: 1) the difference in wood density and panel density, 2) different mat moisture content, 3) mat in-plane variation, etc. Low density of face layer can result in low bending properties for both types of panels.
The density of larch wood is higher than that of S-P-F wood (Table 5-2). Lower density of S-P-F wood can be advantageous when fabricating composite panels. Wood species with low density have the ability to yield higher compaction ratio. Compaction ratio is defined as the ratio of panel density to wood density (Maloney 1993). Normally, good panel mechanical properties were associated with higher compaction ratio (Shupe et al. 1999; Pugel et al. 1989). In Table 5-2, the lower wood density and higher average panel density gave higher compaction ratio to the panels made from S-P-F. The resulting higher compaction ratio of S-P-F panels can bring better mechanical properties to such panels when compared to the panels made from larch wood.
MOR and MOE of panels made from larch were significantly lower than those of panels made from S-P-F by Duncan’s multiple-range test (Table 5-2). As previously stated, lower compaction ratio and higher fine fiber content in the pulp can negatively influence the bending properties of larch panels. However, the larch panels yielded significantly higher IB than S-P-F panels did (Table 5-2). This could be attributed to other reasons such as fiber chemical properties. Fiber pH and buffering capacity are two important factors influencing the curing rate of UF resin when panels are pressed under heat. If UF resin is used for panel making, higher pH and lower base buffering capacity are always advisable (Maloney 1993; Johns and Niazi 1980). The pH and base buffering capacity of larch and S-P-F fibers were measured using Johns and Niazi’s method (1980). Results show that pH of larch fiber (4.39) was higher than that of S-P-F fiber (4.05), and the base buffering capacity of the two types of fibers were 1.92 ml and 1.83 ml, respectively. The lower pH of S-P-F fiber can result in pre-cure of the UF resin at the initial pressing stage, which weakens IB strength.
LE, TS, and WA are important panel properties reflecting panel stabilities in length with changing relative humidity and either in thickness or in weight when the panel is soaked in water. The LE and TS of larch panels were significantly higher than those of panels made from S-P-F at the 0.05 significance level (Table 5-2). But there was no significant difference in WA between the two types of panels. In the ANSI A 208.2-2002 standard, there are no performance requirements for LE, TS, and WA. According to the maximum TS and WA properties specified by ANSI/AHA A 135.4-1995 (1995) for basic hardboard, which are 25 % and 35 %, respectively, TS and WA of the panels made from larch and S-P-F were below the maximum levels.
According to American National Standard (2002), MOR of panels made from larch and S-P-F wood chips both met the requirement of Grade 120. MOE of panels made from larch did not meet the ANSI minimum requirement, while MOE of panels made from S-P-F wood chips met the requirement of Grade 120. IB of larch panels met the requirement of ANSI Grade 140, but S-P-F panels met the requirement of Grade 120. Although MOR and MOE values of larch panels were lower than those of panels made from S-P-F, this difference can be compensated through optimizing hot-pressing parameters so as to acquire desirable panel density profile. In addition, attention should be paid to the refining process in order to produce larch fibers with less fine content. LE of panels made from larch was higher that that of panels fabricated from S-P-F, which may be a problem when the larch panels are applied to a moist environment.
LE, TS, and WA are important panel properties reflecting panel stabilities in length with changing relative humidity and either in thickness or in weight when the panel is soaked in water. The LE and TS of larch panels were significantly higher than those of panels made from S-P-F at the 0.05 significance level (Table 5-2). But there was no significant difference in WA between the two types of panels. In the ANSI A 208.2-2002 standard, there are no performance requirements for LE, TS, and WA. According to the maximum TS and WA properties specified by ANSI/AHA A 135.4-1995 (1995) for basic hardboard, which are 25 % and 35 %, respectively, TS and WA of the panels made from larch and S-P-F were below the maximum levels.
According to American National Standard (2002), MOR of panels made from larch and S-P-F wood chips both met the requirement of Grade 120. MOE of panels made from larch did not meet the ANSI minimum requirement, while MOE of panels made from S-P-F wood chips met the requirement of Grade 120. IB of larch panels met the requirement of ANSI Grade 140, but S-P-F panels met the requirement of Grade 120. Although MOR and MOE values of larch panels were lower than those of panels made from S-P-F, this difference can be compensated through optimizing hot-pressing parameters so as to acquire desirable panel density profile. In addition, attention should be paid to the refining process in order to produce larch fibers with less fine content. LE of panels made from larch was higher that that of panels fabricated from S-P-F, which may be a problem when the larch panels are applied to a moist environment.
Using panels made from S-P-F wood chips as a comparison, it is found that it is feasible to use a mixture of two individual exotic larch species Larix gmelinii and Larix sibirica aged between 10 to 15 years as raw material for MDF panel manufacturing. Larch panels had favorable IB strength compared to those panels made from S-P-F. IB of larch panels was 0.78 MPa, and met the requirement of ANSI grade 140. MOR values for panels made from larch and SPF were 18.6 MPa and 23.1 MPa, respectively, and both met the requirement of ANSI Grade 120. MOE of larch panels was 1276 MPa, which did not meet the ANSI minimum requirement. MOE of panels made from S-P-F wood chips met the requirement of ANSI Grade 120. Bending properties of larch panels were lower than those of panels made from S-P-F, but those properties can be improved by adopting an optimal hot-pressing scheme. Compared to the panels made from S-P-F, the large LE of larch panels appears to be a problem. Modifications should be taken into consideration in order to enhance larch panels in linear stability. TS and WA of panels made from larch and S-P-F were below the maximum levels specified in the ANSI/AHA A 135.4-1995 standard for basic hardboard.
American Hardboard Association (AHA). Basic hardboard . ANSI/AHA A 135.4-1995. AHA, Palatine, IL. 1995.
American National Standards Institute (ANSI). Medium Density Fiberboard (MDF) for Interior Application . ANSI A 208.2-2002. Composite Panel Assoc., Gaithersburg. MD. 2002.
American Society of Testing and Materials (ASTM). Evaluating properties of wood-based fiber and particle panel materials . ASTM D 1037-99. Vol. 04.10. ASTM, Philadelphia. PA. Pp. 141-170; 2001.
Barnes, D. A. A model of the effect of fines content on the strength properties of oriented strand wood composites . Forest Prod. J. 52(5): 55-60; 2002.
Fowler, D. P., Simpson, J. D., Park, Y. S., and Schneider, M. H. Yield and wood properties of 25-year-old Japanese larch of difference provenance in eastern Canada . For. Chron. (12): 475-479; 1988.
Johns, W. E. and Niazi, K. A. Effect of pH and buffering capacity of wood on the gelation time of urea-formaldehyde resin . Wood Fiber Sci. 12(4): 255-263; 1980.
Li, M., Gertjejansen, R. O. and Ritter, D. C. Red pine thinnings as a raw material for waferboard . Forest Prod. J. 41(7/8): 41-43; 1991.
Maloney, T. M. Modern Particleboard & Dry-process fiberboard manufacturing . Updated edition. San Francisco. Miller Freeman Inc. 1993.
Palmer, C. L. Short-rotation culture of populus and larix: A literature review . Canada-Ontario For. Res. Dev. Agr. 65p; 1991.
Pugel, A. D., Price, E. W. and Hsu, C. Y. Composites from southern pine juvenile wood. Part 1: Panel fabrication and initial properties . Forest Prod. J. 40(1): 29-33; 1989.
SAS Institute, Inc. SAS/STAT User’s guide . Cary, N.C. 1990.
Shupe, T. F., Hsu, C. Y., Choong, E. T. and Groom, L. H. Effects of silvicultural practice and wood type on loblolly pine particleboard and medium density fiberboard properties . Holzforschung. 53(2): 215-222; 1999.
Tappi Standard. Fiber length of pulp by classification . T233cm-95. 1995.
Vallee, G. and Stipanicic, A. Growth and performance of larch plantations . Proceedings of a symposium sponsored by the Ontario Ministry of Natural Resources and the Faculty of Forestry, University of Toronto. Toronto, Ontario, Nov. 9, 1982. 1983.
Wang, S., Winistorfer, P. and Young, T. Fundamentals of vertical density profile formation in wood composites. Part III. MDF density formation during hot-pressing . Wood Fiber Sci. 36(1): 17-25; 2004.
Wang, S., Winistorfer, P. M., Young, T. M. and Helton, C. Step-closing pressing of medium density fiberboard. Part 1: Influences on the vertical density profile . Holz-als-Roh-und-Werkstoff. 59(1-2): 19-26; 2001.
Wang, S. and Winistorfer, P. M. Fundamentals of vertical density profile formation in wood composites . Part 2: Methodology of vertical density formation under dynamic conditions . Wood Fiber Sci. 32(2): 220-238; 2000.
Woodson, G. E. Effect of bark, density profile, and resin content on medium density fiberboards from Southern hardboards . Forest Prod. J. 26(2): 39-42; 1976.
American National Standards Institute (ANSI). Medium Density Fiberboard (MDF) for Interior Application . ANSI A 208.2-2002. Composite Panel Assoc., Gaithersburg. MD. 2002.
American Society of Testing and Materials (ASTM). Evaluating properties of wood-based fiber and particle panel materials . ASTM D 1037-99. Vol. 04.10. ASTM, Philadelphia. PA. Pp. 141-170; 2001.
Barnes, D. A. A model of the effect of fines content on the strength properties of oriented strand wood composites . Forest Prod. J. 52(5): 55-60; 2002.
Fowler, D. P., Simpson, J. D., Park, Y. S., and Schneider, M. H. Yield and wood properties of 25-year-old Japanese larch of difference provenance in eastern Canada . For. Chron. (12): 475-479; 1988.
Johns, W. E. and Niazi, K. A. Effect of pH and buffering capacity of wood on the gelation time of urea-formaldehyde resin . Wood Fiber Sci. 12(4): 255-263; 1980.
Li, M., Gertjejansen, R. O. and Ritter, D. C. Red pine thinnings as a raw material for waferboard . Forest Prod. J. 41(7/8): 41-43; 1991.
Maloney, T. M. Modern Particleboard & Dry-process fiberboard manufacturing . Updated edition. San Francisco. Miller Freeman Inc. 1993.
Palmer, C. L. Short-rotation culture of populus and larix: A literature review . Canada-Ontario For. Res. Dev. Agr. 65p; 1991.
Pugel, A. D., Price, E. W. and Hsu, C. Y. Composites from southern pine juvenile wood. Part 1: Panel fabrication and initial properties . Forest Prod. J. 40(1): 29-33; 1989.
SAS Institute, Inc. SAS/STAT User’s guide . Cary, N.C. 1990.
Shupe, T. F., Hsu, C. Y., Choong, E. T. and Groom, L. H. Effects of silvicultural practice and wood type on loblolly pine particleboard and medium density fiberboard properties . Holzforschung. 53(2): 215-222; 1999.
Tappi Standard. Fiber length of pulp by classification . T233cm-95. 1995.
Vallee, G. and Stipanicic, A. Growth and performance of larch plantations . Proceedings of a symposium sponsored by the Ontario Ministry of Natural Resources and the Faculty of Forestry, University of Toronto. Toronto, Ontario, Nov. 9, 1982. 1983.
Wang, S., Winistorfer, P. and Young, T. Fundamentals of vertical density profile formation in wood composites. Part III. MDF density formation during hot-pressing . Wood Fiber Sci. 36(1): 17-25; 2004.
Wang, S., Winistorfer, P. M., Young, T. M. and Helton, C. Step-closing pressing of medium density fiberboard. Part 1: Influences on the vertical density profile . Holz-als-Roh-und-Werkstoff. 59(1-2): 19-26; 2001.
Wang, S. and Winistorfer, P. M. Fundamentals of vertical density profile formation in wood composites . Part 2: Methodology of vertical density formation under dynamic conditions . Wood Fiber Sci. 32(2): 220-238; 2000.
Woodson, G. E. Effect of bark, density profile, and resin content on medium density fiberboards from Southern hardboards . Forest Prod. J. 26(2): 39-42; 1976.
Table 5-1 Size distribution of the fibers produced from larch and S-P-F wood chips.
Table 5-2 Density of larch and S-P-F wood chips, compaction ratio, average panel density, and properties of MDF panels. Numbers in columns ‘>3.240’, ‘0.828-3.240’, ‘0.281-0.828’, and ‘0.017-0.281’ were the percentages of fibers retained on the screens with mesh sizes of 3.240 mm2, 0.828 mm2, 0.281 mm2, and 0.017 mm2. Numbers in columns ‘<0.017’ were the percentages of fibers passed through the screen with mesh size of 0.017 mm2.
Methods described in Tappi 233 cm-95 were followed.
SD=standard deviation.
The means with the same letter were not significantly different by Duncan’s multiple range test at 0.05 of significance level.
Methods for panel density measurement were in accordance with ASTM D 1037-99.
Compaction ratios were based on density of panels equilibrated at 22 oC and 65 % RH and density of wood chips.
Table 5-2 Density of larch and S-P-F wood chips, compaction ratio, average panel density, and properties of MDF panels. Numbers in columns ‘>3.240’, ‘0.828-3.240’, ‘0.281-0.828’, and ‘0.017-0.281’ were the percentages of fibers retained on the screens with mesh sizes of 3.240 mm2, 0.828 mm2, 0.281 mm2, and 0.017 mm2. Numbers in columns ‘<0.017’ were the percentages of fibers passed through the screen with mesh size of 0.017 mm2.
Methods described in Tappi 233 cm-95 were followed.
Table 5-2 Density of larch and S-P-F wood chips, compaction ratio, average panel density, and properties of MDF panels.
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The means with the same letter were not significantly different by Duncan’s multiple range test at 0.05 of significance level.
Methods for panel density measurement were in accordance with ASTM D 1037-99.
Compaction ratios were based on density of panels equilibrated at 22 oC and 65 % RH and density of wood chips.
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