Open Journal of Composite Materials, 2013, 3, 127-131 Published Online October 2013 (
Copyright © 2013 SciRes. OJCM
Effect of Refining Parameters on Medium Density
Fibreboard (MDF) Properties from Oil Palm Trunk
(Elaeis guineensis)
Zawawi Ibrahim1*, Astimar Abdul Aziz1, Ridzuan Ramli1, Anis Mokhtar1, SiJoon Lee2
1Engineering & Processing Division, Malaysian Palm Oil Board, Selangor, Malaysia; 2Dongwha Chemical Malaysia Sdn Bhd,
Dongwha Malaysia Holdings Sdn Bhd, Kuala Lumpur, Malaysia.
Email: *
Received September 19th, 2013; revised October 5th, 2013; accepted October 9th, 2013
Copyright © 2013 Zawawi Ibrahim et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The properties of medium density fibreboard (MDF) made from oil palm trunk (OPT) as affected by refining pressure
and preheating time were investigated. The OPT chips were refined in the MDF pilot plant by using four refining pres-
sures (2, 4, 6 and 8 bar) and four different preheating time (100, 200, 300 and 400 seconds). The refined fibres were
blended with 10% of urea formaldehyde with a board target density of 720 kg/m3. MDF boards were evaluated based on
European Standard EN 622-5:2006 for thickness swelling (TS), internal bonding (IB), modulus of rupture (MOR) and
modulus of elasticity (MOE). Analysis of variance (ANOVA) was used to analyze the significance of the factors. The
results from this study indicated that refining pressure and preheating time are significant factors for all MDF properties.
Low refining pressure and preheating time produced higher TS, lower MOR and MOE with poor bonding than those
boards prepared from fibres refined at higher refining pressure and longer preheating time. OPT fibre treated with 8 bar
produced good swelling resistance but detrimental on mechanical properties of the finish board. 6 bar steam pressure
offered the highest value of mechanical properties (MOE, MOR and IB). Boards from intermediate refining condition
(6 bar and 300 seconds) were found the better board properties having 14.58%, 0.73 N/mm2, 38 N/mm2 and 3597
N/mm2 for TS, IB, MOR and MOE respectively.
Keywords: Oil Palm Trunk; Medium Density Fibreboard; Refining Pressure; Preheating Time
1. Introduction
The oil palm industry is one of the largest industries in
Malaysian crop and plantation area covering about 5.08
million ha planted area [1]. The main production is the
palm oil, but the oil produced only about 10% of the total
biomass from oil palm tree, meanwhile the remaining is
in the form of solid biomass. The residues include oil
palm trunks (OPT), oil palm fronds (OPF), oil palm em-
pty fruit bunch (EFB), mesocarp fibres and palm kernal
shells. The total biomass was estimated about 90 mil-
lion tonnes per year with 8.2 million tonnes of OPT, 12.9
million tonnes of OPF and 15.8 million tonnes of EFB
[2,3]. Some of these are being used as fuel, fertilizer,
animal feed and in composites [4,5].
Oil palm trunk (OPT) is available during replanting in
which the economic life span of oil palm tree is declining
at age about 25 - 30 years. With the implementation zero
burning policy by Malaysian Government, there are huge
amount of felled OPT available during the replanting.
The OPT can be utilized for many applications such as
plywood, laminated veneer lumber, particleboard, fibre-
board and chemical derivates. Due to the shortage of
wood in the wood based industry, such as the fibreboard
and the availability of this OPT, some interests have been
drowned towards using the OPT as a material for me-
dium density fibreboard (MDF) industry.
Refining is the process referring to the production of
refined fibres from chips and thermo-mechanical pulping
(TMP) is mainly the process used for refined fibres pro-
duction in pulp and fibreboard industries. In the MDF
manufacture, refining conditions play important function
to produce good quality of fibres and these conditions
affect the performance of final board properties. In com-
mon TMP process, refining pressure and preheating time
*Corresponding author.
Effect of Refining Parameters on Medium Density Fibreboard (MDF)
Properties from Oil Palm Trunk (Elaeis guineensis)
Copyright © 2013 SciRes. OJCM
are the two main manufacturing parameters that influ-
ence these properties. The refining stage, refining pres-
sure is the dominant factor that leads to the quality of the
fibres [6]. Many researchers have indicated that refining
conditions have obvious effects on the final MDF proper-
ties. The increasing of refining pressure results in low
MOR and MOE values, with better dimensional proper-
ties [7]. High refining pressure reduced the thickness
swelling (TS) of the boards [8]. MDF manufactured at
higher refining pressure resulted in lower MOR, MOE
and IB strength due to the reduction in fibre length and
having poor fibre contact [9]. The fibreboard from oil
palm produced under higher pressure resulted in high IB
but low MOR value [10]. They also reported that high
pressure and preheating time resulted in better dimen-
sional stability as the fibres lost its elasticity. In addition,
the fibre refined under higher refining pressure and pre-
heating time had better IB value because these conditions
leaded to better self-bonding ability [11].
The objective of this investigation is to evaluate the
effects of refining pressure and preheating time during
the refining process in the production of MDF from oil
palm trunk.
2. Material and Method
2.1. Material Preparation
The raw material for this study was the trunk collected
from oil palm plantation located at FELDA Keratong,
Pahang. The trunks were manually cut and were chipped
using a chipper. The chips were refined using the Sprout-
Bauer (ANDRITZ) refiner at the MDF pilot plant located
in MPOB/UKM Research Station, following the parame-
ters as stated in Table 1 . After refining, the refined fibres
were dried in the oven until the moisture content (MC) is
about 4% - 5%.
2.2. MDF Boards Preparation and Properties
The OPT refined fibres were blended with emulsion wax
and urea formaldehyde (UF) as the adhesive in the glue
blender machine. A wooden former with the dimension
of 300 × 300 mm was used in this study. The fibres were
manually formed into a single layer mat followed by
pre-press and finally hot-pressed. The parameters for the
MDF production are presented in Table 2.
The boards were kept conditioned at temperature of
22˚C and relative humidity of 65% until it reached equi-
librium moisture content before testing. The boards were
cut into specific sizes before testing. The mechanical
properties for IB (50 × 50 mm) and static bending
strength (290 × 50 mm) were tested using Zwick 10 kN
Universal Testing Machine. The TS (50 × 50 mm) were
Table 1. Refining parameters used with four different re-
fining pressure and time.
Refining Pressure (Bar) Preheating Time (Seconds)
2 100
4 200
6 300
8 400
Table 2. The MDF of OPT manufacturing parameters.
Processing Parameter Value
Target MC of fibres after oven dry (%) 4 - 5
Urea formaldehyde (UF) content (%) 10
Solid content of UF resin (%) 64
Emulsion wax content (%) 0.5
Hardener (g) -
Target MC after blending (%) 8 - 10
Board density (kg·m3) 720
Board dimension (mm) 300 × 300
Board thickness (mm) 12
Pressing temperature (˚C) 200
Pressing time (min) 5
carried out by 24 h immersed in the water. All the prop-
erties were tested according to European Standard EN
622-5:2006 [12].
2.3. Data Analysis
The Analysis of Variance (ANOVA) was conducted, and
T-test was used by using Least Significant Difference
(LSD) method (Statistical Analysis System (SAS) soft-
ware) to compare the mean values of TS, IB, MOR and
MOE of the boards under various refining condition at
the 95% confident level.
3. Results and Discussion
3.1. Analysis of Variance (ANOVA) of the
Refining Parameters
The results of analysis of variance (ANOVA) for all pa-
rameters are listed in Table 3 . It shows that the effects of
refining pressure and preheating time have significant
effects (p 0.01) towards the TS, IB, MOR and MOE.
The interaction between refining pressure and preheating
time factors also significantly affected the TS, IB and
MOR at p 0.01, and MOR at p 0.05.
The mean value according to least significant differ-
ence (LSD) of TS, IB, MOR and MOE are given in Ta-
ble 4.
Effect of Refining Parameters on Medium Density Fibreboard (MDF)
Properties from Oil Palm Trunk (Elaeis guineensis)
Copyright © 2013 SciRes. OJCM
Table 3. Table of analysis of variance (ANOVA) on the board properties.
Pr > F
Parameter TS IB MOR MOE
Refining pressure (RP) <0.0001*** 0.0002*** <0.0001*** <0.0001***
Preheating time (PT) 0.0008*** <0.0001*** <0.0001*** <0.0001***
Interaction between RP × PT <0.0001*** <0.0001*** 0.0115** <0.0001***
Note: ***Significantly different at p 0.01; **Significantly different at p 0.05.
Table 4. The mean value of board properties: TS, IB, MOR and MOE.
Refining pressure (bar) Preheating time (seconds) TS (%) IB (N/mm2) MOR (N/mm2) MOE (N/mm2)
100 20.50a 0.59c 29.80e 2829d
200 19.02b 0.64b 30.07e 2935d
300 19.18b 0.61c 31.77d 2918d
400 18.11c 0.66b 32.07d 2809d
100 16.83c 0.64b 37.63b 3418b
200 17.39d 0.62b 37.14b 3355b
300 16.42d 0.70a 36.52b 3349b
400 17.19d 0.71a 36.80b 3192c
100 15.69e 0.68b 38.31a 3444a
200 14.63f 0.72a 39.89a 3538a
300 14.58f 0.73a 38.33a 3597a
400 14.37f 0.73a 35.14b 3421a
100 13.38g 0.64b 37.59b 3361b
200 13.05g 0.62b 37.39b 3312b
300 12.82g 0.64b 35.07c 3309b
400 12.81g 0.54c 33.74c 3287b
Minimum Requirement EN 622-5:2006 1 5.00 0.60 22.00 2500
Note: Means followed by same letters in each column are not significantly different at p 0.05 according to least significant difference (LSD) method.
3.2. The Effects of Refining Pressure and
Preheating Time on the Thickness Swelling
of the Boards
The boards from higher and longer refining pressure and
preheating time showed low TS. The TS value decreased
with the increasing of refining pressure and preheating
time. This may be due to the removal of hemicelluloses
that is hydrophilic component resulted from refining pro-
cess [13].
Higher refining pressure generated more individual
and short fibres, thus increased the effective surface area
and absorbs less water [14]. The higher the proportion of
shorter fibre, the higher the bulk density of the board [15].
This is due to the fact that shorter fibres make denser
structures between fibres and resulted in larger contact of
fibre-to-fibre area during hot pressing, and finally pro-
duced larger bonding area and lower porosity. These con-
ditions produced board with better dimensional proper-
Except for the boards prepared from the fibres refined
at 2 and 4 bar at all preheating time, and also at 6 bar for
100 seconds of preheating time, boards made with other
refining conditions showed TS below 15% and meet the
minimum requirements of EN 622-5:2006.
3.3. The Effect of Refining Pressure and
Preheating on the Internal Bonding of
the Boards
The value of IB increased with the increasing of refining
pressure and preheating time from 2 bar (at all preheating
time) to 6 bar (at all preheating time), but decreased with
a further increased in refining pressure of 8 bar and
Effect of Refining Parameters on Medium Density Fibreboard (MDF)
Properties from Oil Palm Trunk (Elaeis guineensis)
Copyright © 2013 SciRes. OJCM
longer preheating time. Refining at 2 bar at 100 seconds,
the IB value was 0.59 N/mm2, but the value increased to
0.66 N/mm2 when the preheating time was increased to
400 seconds. The board from 6 bar of refining pressure
showed highest IB value.
The value of IB increase due to the fact that short fibre
(resulted from severe refining conditions) increased the
bonding area, thus improve the bonding by developing
more interlocking fibre-to-fibre bonding. Using higher
steam pressure during the refining process has increased
the IB value of fibreboard prepared from miscanthus
sinensis [16].
Furthermore, during refining, the hemicellulose were
hydrolyzed, thus increase the amount of by product ma-
terials. Refining causes decomposition of the hemicellu-
lose and convert it into water-soluble carbohydrates,
which could act as a binding agent for the fibres [17,18].
Using steam pressure of 0.6 - 1.0 MPa for 5 minutes for
the refining of sugarcane, the hemicellulose content was
decreased as the steam pressure and time increased [19].
Refining pressure of 8 bar, the IB values decreased pos-
sibly due to the severe refining condition resulted in ex-
cess of fine fibres [20]. More short and fine fibres re-
sulted in higher fibre surface area that expose to bonding
with other fibres. The 10% UF is not distributed well into
the fibres surface area, created fibres with less UF pene-
tration, and influences the bonding properties. Except for
the boards from fibres refined at 2 bar for 100 seconds,
the IB of all boards exceeded the requirements.
3.4. The Effect of Refining Pressure and
Preheating on the Bending Strength of
the Boards
The MOR and MOE value increased significantly when
the refining pressure and preheating time increased from
2 to 8 bar, and from 100 - 400 seconds respectively. At
the refining condition of 2 bar for 100 seconds, the MOR
and MOE value were 29.8 N/mm2 and 2829 N/mm2, re-
spectively. And at 6 bar for 100 seconds, the MOR and
MOE value were increased to 35.14 and 3421 N/mm2.
This trend of MOR and MOE are similar to the IB trend,
where the value decreased at severe refining pressure (8
bar) and longer the preheating time.
Higher refining condition significantly increased both
MOR and MOE value. This could be due to the more
individual fibres were generated, thus higher percentage
of overlap between two fibres resulted in better fibre-to-
fibre orientation and arrangement. The fibre geometry,
fibre orientation, fibre arrangement and fibre volume
factors controls many mechanical properties [21]. The
bending strength (MOR and MOE) improved when re-
fining steam pressure increases [22].
At 8 bar of refining pressure, however, increasing the
preheating time results in lower MOR and MOE value.
This could be attributed to the damage fibre cell walls.
Higher refining pressure destroyed lumen and S3 layer
due to the explosion caused by the higher pressure inside
the lumen during refining [23]. The nano-cracks in fibres
also generated by higher refining pressure, and influence
the strength of the fibres.
4. Conclusion
The refining pressure and preheating time process of
OPT chips play significant factors toward determining
the MDF board properties. Low refining conditions give
poor dimensional stability and bonding, and low bending
strength. OPT fibre refined with 8 bar produces better
swelling properties but detrimental in mechanical proper-
ties. The optimum refining parameters in producing
MDF from OPT are 6 bar of refining pressure and 300
seconds of preheating time.
5. Acknowledgements
The author wish to thank the Director General of MPOB
for permission to publish this paper.
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