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Properties of Medium Density Fiberboard Based on Bagasse Fibers
Article in Journal of Composite Materials · August 2009
DOI: 10.1177/0021998309341099
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Properties of Medium Density
Fiberboard Based on Bagasse Fibers
ALIREZA ASHORI*
Department of Chemical Industries, Iranian Research Organization for
Science and Technology (IROST), P.O. Box 15815-3538, Tehran, Iran
AMIR NOURBAKHSH
AND
ABOLFAZL KAREGARFARD
Department of Wood and Paper Science, Research Institute of Forests
and Rangelands (RIFR), P.O. Box 13185-116, Tehran, Iran
ABSTRACT: In this study, sugarcane bagasse fiber was used for medium density
fiberboard (MDF) manufacturing. The purpose of this study was to determine
the effects of maleic anhydride (MA) and press temperature on the mechanical
(static bending, modulus of elasticity, and internal bond) and physical properties
(thickness swelling, water and steam absorption) of the boards. This study showed
that all the MDF panels made from bagasse fibers treated with MA at 190 C press
temperature had the highest values among the other types of panels for general
purpose boards. In addition, treated fibers at 190 C showed minimum steam absorption. The absorption of steam increased with increase in time from 12 to 120 h in all
the treatments. Beyond 120 h no additional absorption of steam was found in any of
the six MDF boards. Overall results showed that MDF panels made from bagasse
exceed the EN standards for internal bond, modulus of elasticity, and static bending.
However, thickness swelling values were higher (poor) than requirements. For this
reason, additional work needs to be done on improving the physical properties of
particleboard produced from bagasse.
KEY WORDS: static bending, modulus of elasticity, internal bond, swelling
behavior, wood-based panel.
INTRODUCTION
(MDF) is one of the most widely used wood-based
panels to manufacture building and housing components such as furniture units for
interior applications. In recent years, production of MDF has significantly increased and
has a major market share in the wood composites industry [1,2]. MDF has many
M
EDIUM DENSITY FIBERBOARD
*Author to whom correspondence should be addressed. E-mail: ashori@irost.ir
Figures 1 and 2 appear in color online: http://jcm.sagepub.com
Journal of COMPOSITE MATERIALS, Vol. 43, No. 18/2009
0021-9983/09/18 1927—8 $10.00/0
DOI: 10.1177/0021998309341099
ß SAGE Publications 2009
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A. ASHORI
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advantages such as smoother surface, easier machinability, and is an ideal panel material
as substrate for thin overlays used in indoor conditions [3]. MDF can be produced from
variety of natural fibers; but wood, because of its relative abundance and year-round
availability, is still the most important raw material. However, increasing demand of
forest resources for different uses has led to the shortage of wood supply. Therefore,
there is a need to find alternative raw materials or complete use of wood resources including harvesting residues, annual plants, lumber and furniture plant residues, residues of
pulp plants, and recycled paper, etc. [4—7].
One of the most promising annual plant residue materials for manufacturing MDF is
sugarcane bagasse, which can play a major role in providing the balance between supply
and demand. Bagasse, an abundant agricultural lignocellulosic byproduct is a fibrous
residue of cane stalks left over after the crushing and extraction process of the juice
from sugarcane. About 54 million dry tons of bagasse is produced annually throughout
the world. The utilization of this biomass for processing of novel composites has attracted
growing interest because of its ecological and renewable nature characteristic. Indeed
enormous interest in the development of new composite materials filled with natural
fibers has been shown by important industries such as automotive, construction, or packaging industry [8,9].
Natural fibers compared to inorganic fibers, present some disadvantages such as tendency to form aggregates during processing and low resistance to moisture. Natural fibers
consist primarily of cellulose, hemicellulose, and lignin. The elementary unit of cellulose
macromolecule is a D-anhydroglucose, which contains three hydroxyl (—OH) groups.
These hydroxyl groups are responsible for moisture absorption [10]. Fiber modification
can be used to improve properties in composites made of both natural and synthetic
resources used for geotextiles, filters, sorbents, packaging, and nonstructural composites.
Many chemical reaction systems have been utilized for the modification of agro-fibers.
These chemicals include anhydrides, such as, phthalic, succinic, maleic, propionic, and
butyric anhydride. Utilization of maleic anhydride (MA) is of interest in production of
environmentally friendly MDF and particleboard produced [11]. MA groups react chemically with the —OH groups of the wood fiber and improve interfacial adhesion considerably. However, such a modification usually does not solve all the problems mentioned
above, like aggregation, appearance, and water adsorption [12].
Present work was carried out on the effects of some manufacturing factors on the
properties of MDF panels made from bagasse fibers. One of the main issues in reducing
the cost of the final product is to reduce the press cycle time. Hence, the influences of press
temperature on the mechanical (static bending, modulus of elasticity, and internal bond)
and physical (thickness swelling, water and steam absorption) properties of panels were
determined. Another objective of this study was to investigate the mechanical and physical
properties of panels, which were treated with or without MA.
MATERIALS AND METHODS
Materials
Bagasse was supplied by a local sugarcane mill, after the extraction of cane juice. Fiber
morphology and chemical components of bagasse fibers are given in Table 1. These
parameters are important as they may influence the resulting mechanical and physical
1929
Properties of MDF Based on Bagasse Fibers
Table 1. Fiber morphology and chemical
component of bagasse.
Chemical components:
Cellulose (%)
Lignin (%)
Extractive (%)
Ash (%)
Fiber morphology:
Length (mm)
Diameter (mm)
Aspect ratio (L/D)
52.70 3.1
20.63 0.91
0.89 0.06
1.35 0.4
1.24 0.63
22.90 1.07
54 3
properties of MDF composite. The dried bagasse was cut and screened into 0.4—0.8 mm
particle size, and dried again at 50 C. The bagasse fibers were produced by refiner mechanical pulping process.
MA (C4H2O3) was used as a grafting monomer to functionalize fibers because of the
higher reactivity of the anhydride group. The 10% of MA (based on weight of oven-dried
fiber) was dissolved in the least possible amount of acetone, typically, for 1 g of MA,
4—5 mL of acetone was required. The MA solution was mixed thoroughly with the
fibers to get even distribution of the MA on the fibers. The mixture was left inside a
fume hood to allow acetone evaporation and then heated at 110 C for 180 min.
Urea—formaldehyde (UF) resin at 62% solid content and pH of 8 was supplied from
Sobran Co. No wax or any other additives were utilized during the MDF production.
MDF Panel Fabrication
MDF panels were manufactured in the Department of Wood and Paper Science, RIFR,
Iran, using standardized procedures that simulated industrial production. Bagasse fibers
were dried to 2—3% (based on oven-dry weight) using a traditional oven before resin
blending to avoid excess moisture of the MDF mat. The fibers were first hand-mixed
and then placed in a laboratory drum blender. Commercial liquid UF resin was applied
to the fibers at 10% (dry basis) and then air-formed using a forming box. After mat
formation, the material was compacted in a pre-press without heat transfer. The prepressing procedure was following by pressing in a hydraulic press heated electrically to
a maximum pressure of 30 kg/m2 for 4 min. Then, the panels were pressed by a single hotpress under 30 kg/cm2 pressure for 5 min. Three levels of press temperature were applied;
180, 190 and 200 C. After pressing, all panels were trimmed to a final size of
400 400 10 mm3 with a target density of 700 0.01 kg/m3. Table 2 shows the experimental design of the study.
Mechanical and Dimensional Stability
European standards were used to measure modulus of rupture (MOR), modulus of
elasticity (MOE) (EN 310), internal bond strength (IB) (EN 319), and dimensional stability
(EN 317). For the determination of the mechanical and dimensional stability properties,
nine specimens (three specimens from three individual panels) for each level and combination of MA treatment and press temperature were used. Prior to the mechanical tests,
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A. ASHORI
ET AL.
Table 2. Experiments design.
Panel type
A
B
C
D
E
F
MA (%)
Press
temperature (8C)
10
10
10
0
0
0
180
190
200
180
190
200
the panels were conditioned at 65% relative humidity (RH) and 20 C. Mechanical properties were determined using an Instron Universal testing machine (model 1186).
The dimensional stability of square test specimens with a nominal side length of 50 mm
(conditioned at 65% RH and 20 C) was determined by measuring the increase in thickness
of the specimens after immersion in water (20 C, pH 7) at 2 and 24 h. The specimens were
placed in the water bath with their faces in the vertical position. For steam absorption
study, the samples were hung in a closed water bath provided with a heater system to boil
the water continuously for 216 h. The samples were surface dried using blotting paper after
water and steam absorption.
Data Analysis
Data for each test were statistically analyzed. The effects of MA treatment and press
temperature on the MDF panels properties were evaluated by analysis of variance
(ANOVA) and t-test to test for significant difference between factors and levels. When
the ANOVA indicated a significant difference among factors and levels, a comparison of
the means was done employing Duncan’s multiple range test (DMRT) to identify which
groups were significantly different from other groups at a 95% and 99% confidence level.
RESULTS AND DISCUSSION
Statistical analyses of physical and mechanical properties of MDF panels made from
bagasse fiber are summarized in Tables 3 and 4. As can be seen from Figures 1 and 2, both
physical and mechanical properties of panels were influenced by the addition of MA and
press temperature.
Mechanical Properties
The statistical analysis showed a significant effect of MA treatment and press temperature on the MOR, MOE, and IB at a probability level of 0.01 and 0.05, respectively
(Table 3). In fact, an increase in the MOR, MOE, and IB were observed following fiber
treated with MA and 190 C press temperature.
Based on EN standard (312-3) 13 and 1600 N mm 2 are the minimum requirements for
MOR and MOE of panels for general purpose and interior fitments, respectively. As can
be seen from Table 4, all of the panels had much higher MOE and MOR than the general
purpose requirements. The results of t-test and DMRT for the bending strength of the
1931
Properties of MDF Based on Bagasse Fibers
Table 3. Statistical analysis of physical and mechanical properties
of MDF produced with different variables.
Property
(C.V.%)
MA
Press temperature. ( C)
MA and press
temperature
MOR
(N mm 2)
MOE
(N mm 2)
IB
(N mm 2)
TS 2 h
(%)
TS 24 h
(%)
WA 2 h
(%)
WA 24 h
(%)
5
NS
NS
**
3.70
**
NS
**
23.1
NS
NS
*
13.34
*
NS
*
7.44
**
NS
*
13.99
**
7.28
*
*
*
**Significant difference at the 1% level (p 0.01%), *Significant difference at the 5% level (p 0.05%).
NS,Not significant.
Table 4. Duncan’s Multiple range test of the MA treatment and press temperature.
Panel type
Property
2
MOR (N mm )
MOE (N mm 2)
IB (N mm 2)
TS 2 h (%)
TS 24 h (%)
WA 2 h (%)
WA 24 h (%)
A
B
C
D
E
F
27.2(B)
2197(B)
0.32(A)
9.7(A)
17.9(A)
43.3(B)
79.5(B)
28.6(A)
2582(A)
0.23(C)
9.8(A)
18.4(A)
38.8(A)
73.7(A)
27.2(B)
2243(B)
0.18(C)
11.7(B)
21.7(B)
45.9(B)
83.6(C)
25.2(A)
2111(B)
0.17(C)
11.8(B)
21.9(B)
51.5(C)
85.1(C)
24.3(C)
1903(C)
0.20(B)
14.2(C)
23.5(C)
62.2(D)
92.7(D)
27.7(B)
2157(B)
0.20(B)
11.7(B)
21.0(B)
49.6(C)
84.0(C)
Values (A,B,C,D) having the same letter are not significantly different.
105
Dimension stability (%)
Untreated
90
Treated
75
60
45
30
15
0
180 190 200
180 190 200
180 190 200
180 190 200
TS (2 h)
TS (24 h)
WA (2 h)
WA (24 h)
Temperature (°C)
Figure 1. Dimension stability as a function of press temperature and MA treatment.
produced particleboards are given in Tables 3 and 4. The MOR values for samples in
groups A—F met the standard value of EN 312-6 (20 N mm 2). In general, the modification treatment had a positive effect on the MOR and MOE of the panels. The increase in
the mechanical properties of the MDF due to chemical modification is an indication of
improved interaction and stress transfer between the components.
The maximum MOR and MOE strength values were obtained by pressing the
MA treated fibers at 190 C; increasing the press temperature to 200 C caused a decrease
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A. ASHORI
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8
7
Steam absorption (%)
6
5
4
3
2
180°C Untreated
190°C Untreated
200°C Untreated
180°C Treated
190°C Treated
200°C Treated
1
0
12
24
48
72
96
120
144
168
216
Time (h)
Figure 2. Comparison of absorption of steam in MDF panels.
in strength properties. Concerning the lower strength value of the MDF panels at temperature higher than 190 C it should be noted that, thermal degradation of the fibers is
possible. At 200 C, the bagasse fiber components such as hemicellulose begin to depredate
[13]. The thermal degradation of the fibers also resulted in production of volatile compounds at processing temperatures above 200 C. This phenomenon will produce porous
products with lower densities and inferior mechanical properties [14]. On the other hand,
this degradation could be macroscopically detected through poor organoleptic properties
(such as color, smell, etc.). For the improvement of thermal stability, attempts have been
made to coat and/or graft the fibers with monomers [15,16].
IB data ranged from 0.17 to 0.32 N mm 2. The minimal requirement of IB strength for
general purpose (EN 312-2) is 0.24 N mm 2. According to the test results, all of the MDF
produced did not meet the IB requirement of EN, except panel type A which had the
highest values among the other types of specimens for general purpose boards. The significant negative influence of press temperature on internal bond strength can be explained
by the thermal degradation of the fibers. On the contrary, MA treatment could improve
the IB properties in the MDF panels.
Dimensional Stability
Figure 1 shows thickness swelling (TS) and water absorption (WA) of the MDF
panels produced from treated with and without MA at three different press temperatures.
Based on EN standard, MDF panel should have a maximum TS value of 8% and 15% for
2 and 24 h immersion, respectively. Average TS of the samples ranged from 17.90 to
23.55% for 24-h immersion. However, the Ts value 17.90% for panel A was close to
the required level of TS of panels for general use.
Average WA of the samples ranged from 73.7 to 92.7% for 24-h immersion (Figure 1).
However, the water absorption of panel B was much lower than other MDF panels.
Properties of MDF Based on Bagasse Fibers
1933
MA treatment is known to form ester and hydrogen bonds with —OH groups of wood
components. By reducing free —OH groups in wood, susceptibility of the wood material to
water and thereby to swelling is reduced.
Steam Swelling Behavior
Figure 2 illustrates the effect of steam absorption of MA treated and untreated panels at
three levels of press temperature for 216 h. It shows that the absorption of steam increases
with an increase in time from 12 to 120 h in all the six treatments. Beyond 120 h no
considerable additional absorption of steam is found in any of the six MDF panels.
Among the samples after 24-h exposure to steam, untreated bagasse fibers at 200 C
showed a maximum steam absorption and treated panel at 190 C show a minimum
steam absorption. From these results, it is found that the MA-treated fiber MDF shows
lesser steam absorption of water than the untreated bagasse fibers. The steady increase in
absorption of steam in untreated panels is due to the availability of free —OH groups.
However, the esterification of the —OH group by maleic anhydride minimizes the capability of the cellulose fibers to absorb steam.
CONCLUSIONS
The main goal of the present work was to investigate the potential utilization of bagasse
fibers in MDF production to alleviate raw material shortages. Based on the results of the
mechanical and dimensional stability tests of the MDF, the following results were
obtained:
– All panels treated with MA had higher values than those untreated and exceeded the
EN standards for MOR and MOE for interior fitments including furniture manufacturing application.
– The MA treatment had a positive effect on the MOR and MOE of the panels. However,
increasing press temperature had a significant negative influence on IB strength causing thermal degradation of the fibers. In general, MA treatment and press temperature
had a significant effect on the mechanical and dimensional stability of MDF panels.
– The WA of the panels was relatively high, ranging from 73.7 to 92.7% for 24-h immersion. Since no hydrophobic substance was used during the panel manufacturing, lowdimensional stability of the panels can be related to this fact.
– MA-treated fibers showed less absorption of steam and water than the respective
untreated fibers. The trend of absorption of steam becomes constant after 120 h in
treated and untreated samples.
– Based on the findings of this study, it can be stated that bagasse fiber has potential as
a supplement fibrous material for MDF manufacturing.
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