Medium Density Fiberboard from Quercus robur
The objective of this study was to investigate the suitability
of oak (Ouercus robur L.) wood fibers from Turkey as a raw material
for medium density fiberboard. In this study, some of the oak wood parts
that are especially not suitable for other forest industries was utilized
to produce fiberboards in laboratory environment. Test panels of varying
densities (0.6, 0.7 and 0.8 g cm-3) were produced at 18 mm
thickness using urea-formaldehyde adhesive. Mechanical, water resistance
and dimensional stability properties of the test panels were determined
according to Turkish standards. The results indicated that laboratory
MDF panels produced using oak fibers resulted in mechanical properties
that exceed (except panel type A) levels specified in the appropriate
existing standards for the general propose fiberboards.
Oak, a rare forest tree has survived for approximately 80-100 million
years since its first appearance in geological ages to today. There are
over 200 oak species, subspecies, varieties and natural hybrids in the
mild zones of the northern hemisphere. Turkey consisting 18 native oak
species, some subspecies and varieties, has a quite important oak stock
in the world (Yaltirik, 1998). One or more oak taxons could be observed
in all regions of Turkey including steppes. Compared to the past years,
oak distributions are quite limited due to destructions. Now, the total
distribution is of oak is 5.8 million hectares (http://www.ogm.gov.tr/agaclarimiz/agac12.htm
2006). Oak still is the most widespread leaved tree in Turkey. Therefore,
oak wood is extensively utilized in timber, furniture and parquet industries.
There is a significant pressure on standing forest resources as a result
of higher wood demand in forest industry due to increasing population
and new application areas. On the other hand, collecting industrial wood
from the natural forests continues to decline. The decline in forest resources
is due to the depletion of the resources and the withdrawal of forest
areas from industrial production for other uses like recreational area.
The shortage of raw material in medium density fiberboard industry as
well as other forest industries tends to utilize different forest resources
as raw material.
Birch (Betula), ash (Fraxinus), lime (Tilia), douglas-fir
(Pseudotsuga), spruce (Picea) and larch (Larix) fibers
has been recognized as high quality raw material to produce MDF (Chow
and Zhao, 1992). Fibers produced from low quality oak, beech and pine
are used either lonely or in a mixture in MDF production in Turkey (Akbulut
et al., 2000). In addition, the study (Akgül et al.,
2007) with rhododendron (R. ponticum) biomass showed that the production
of MDF from this biomass is technically feasible and it could be utilized
in a mixture at varying ratios with pine and oak fibers.
MDF production in Turkey tends to increase and the demand shows that
the increase will continue in coming years. The expected increase could
be around 15% for 2007 (Çöpür et al., 2005). On
the other hand, the shortage of the raw material for the forest industry
is the main problem. To overcome the shortage of the raw material, this
study aimed to examine the feasibility of using some of oak wood parts
that are especially not suitable for other forest industries to produce
medium density fiberboard.
MATERIALS AND METHODS
Oak wood except steam obtained from the Duzce region in 2006 was used
as a raw material in this study. Fibers were generated with pressurized
disc refiners at feed pressure of 10 and 40 psi in Divapan A.Ş.,
Duzce-Turkey. Before further processing, the fibers were dried at 100-110°C
to reach the target moisture content (3-4%). Fibers were used to produce
18 mm thick MDF panels in three selected densities (A: 0.6 g cm-3,
B: 0.7 g cm-3 and C: 0.8 g cm-3). The produced fiberboards
had 8% resin and 1% wax content based on solid content and oven-dry fiber
weight. Each panel density was considered a replicated set and 2 individual
panels were produced for each density. Urea formaldehyde resin and hardener,
1% of ammonium chloride (solid content 33%) were mixed together using
a high speed laboratory mixer.
||The properties of urea-formaldehyde adhesive
||Production parameters of fiberboards
The mixture was sprayed onto wood fibers in a drum type blender. The
properties of the urea-formaldehyde used in this study are given in Table
1. All panels were consolidated using steam heated press in the laboratory
of Duzce University. Panels were pressed to 25 kg cm-2 at 150°C
for 6 min. Test panels having dimensions of 50x50x1.8 cm was conditioned
at 20±2°C and 65±5% of relative humidity to reach
the moisture content of 12%. Finally, edges of the boards were trimmed
to the final dimension of 48x48x1.8 cm. Fiberboard production parameters
were summarized in Table 2.
Mechanical and physical properties were tested according to TS-EN 326-1
(1999). Prior to mechanical testing all test specimens were conditioned
at 65% relative humidity and 20°C in a conditioning room. The water
absorption and thickness swelling of the specimens were measured according
to TS-EN 317 (1999). The specimens were also tested for bending (TS-EN
310, 1999), internal bond strengths (TS-EN 319, 1999) and hardness (ASTM
D 1037-78, 1994). The obtained data were statistically analyzed by using
the analysis of variance (ANOVA) and Duncan mean separation tests.
RESULTS AND DISCUSSION
The results of ANOVA and Duncans mean separation tests for water
absorption and thickness swelling of the fiberboards made from Oak wood
fibers are shown in Table 3 for the produced fiberboards.
Statistical analyses showed that water absorption and thickness swelling
of fiberboards were significantly affected by panel density.
Higher thickness swelling was observed when the densities of the boards
were increased from 0.6-0.8 g cm-3 for both 2 and 24 h soaking
times. This result was expected because denser boards have more fibers
holding higher moisture which results in more swelling. The measured thickness
swelling met the minimum required value according to TS 64-5 EN 622-5
(1999). Standard for the 24 h water immersion time.
||Thickness Swelling (TS) and Water Absorption (WA) test
results of ANOVA and Duncans mean separation tests
|aMean values are the average of 20 specimens.
bMinimum value; cMaximum value; dSignificance
level of 0.001 (for ANOVA); p,s,u,t,v,yValues having the
same letter are not significantly different (Duncan test)
||The mechanical properties of fiberboards and the test
results of ANOVA and Duncans mean separation tests
|aMean values are the average of 10 specimens.
bMinimum value; cMaximum value; dSignificance
level; * Significant at 0.001, **Significant at 0.01, *** significant
at 0.05 for ANOVA; p,sValues having the same letter are
not significantly different (Duncan test)
On the other hand, increase in panel density resulted in lower water
absorption for the produced panels. This could be due to the intra- and
intermolecular hydrogen bonds that may restrain water acceptability (Sjostrom,
1993) in denser panels. Thickness swelling and water absorption of fiberboards
produced in this study was higher compared to the industrially produced
fiberboards (Ayrilmis, 2003).
The mechanical properties of the produced fiberboards (modulus of rupture,
modulus of elasticity, internal bond and janka hardness) were shown in
Table 4. Results indicated that panel density significantly
affected Modulus Of Rupture (MOR), Modulus Of Elasticity (MOE), Internal
Bond (IB) and janka hardness. The measured mechanical properties increased
as the panel density increased. This could be explained by the compression
ratio, which affects both physical and mechanical properties of fiberboards.
Panels with higher density gave higher compression ratios.
The standard method (TS64-5 EN622-5, 1999) recommends a minimum MOR (22
N mm-2), MOE (2500 N mm-2) and IB (0.50 N mm-2)
values for the fiberboards manufactured for general propose use. The findings
in this study indicated that all produced fiberboards met the minimum
requirement except panel type A (density at 0.6 g cm-3) for
MOR and MOE. The measured janka hardness values ranged from 58.1-66.5
N mm-2. Results indicated that increase in panel density
resulted in harder panels. The mechanical properties measured in this
study were almost similar to the properties measured for industrially
manufactured fiberboards (Ayrilmis, 2002).
In this study, this study examined certain physical and mechanical properties
of fiberboards produced using oak wood fibers for varying panel densities.
Results indicated that panel density significantly has a significant effect
on physical and mechanical properties of fiberboards. Panel density resulted
in an increase in thickness swelling and a decrease in water absorption.
Higher mechanical properties were obtained for denser panels. The results
from this experiment indicated that laboratory MDF panels made from oak
fibers could be manufactured with panel mechanical properties that exceed
(except panel type A) levels specified in the appropriate existing standards
for general purpose fiberboards.
ASTM D-1037-78, 1994. Standard Methods of Evaluating the Properties of Wood-Base Fiber and Particle Panel Materials. The American Society For Testing and Materials, USA.
Akbulut, T., S. Hiziroglu and N. Ayrilmis, 2000. Surface absorption, surface roughness and formaldehyde emission of Turkish medium density grainboard. Forest Prod. J., 50: 45-45.
Ayrilmis, N., 2002. Effect on tree species on some mechanical properties of MDF. Review of the Faculty of Forestry, University of Istanbul. Series A., 52: 125-146.
Ayrilmis, N., 2003. Effects of species on some physical properties of MDF. Review of the Faculty of Forestry, University of Istanbul. Series A., 53: 57-73.
Chow, P. and L. Zhao, 1992. Medium density fiberboard made from phenolic resin and wood residues of mixed species. For. Prod. J., 42: 65-67.
Direct Link |
Copur, Y., A. Tozluolu and O. Çamlibel, 2005. The production of medium density fiberboard in global scale. Ahap Teknik, 10: 23-26.
Sjostrom, E., 1993. Wood Polysaccharides, Lignin and Pulping Chemistry. In: Wood Chemistry: Fundamentals and Applications. Academic Press, New York, pp: 51-146.
TS 64-5, EN622-5, 1999. Fiberboards-Specifications-Part 5. Requirements for Dry Process Boards (MDF). TSE, Ankara.
TS EN 326-1, 1999. Wood-Based Panels-Sampling, Cutting and Inspection-Part 1: Sampling Test Pieces and Expression of Test Results. TSE, Ankara.
TS-EN 310, 1999. Wood Based Panels, Determination of Modulus of Elasticity in Bending and Bending Strength. European Standardization Committee, Brussell.
TS-EN 317, 1999. Particleboards and Fiberboards, Determination of Swelling in Thickness after Immersion. European Standardization Committee, Brussell.
TS-EN 319, 1999. Particleboards and Fiberboards, Determination of Tensile Strength Perpendicular to Plane of the Board. European Standardization Committee, Brussell.
Yaltirik, F., 1998. Dendrology Book II. Publisher Istanbul University, Faculty of Forestry, Istanbul, pp: 256.