Oil palm trunk is a kind of biomass rich in starch content. Oil palm trunk waste was available throughout the year in Malaysia and Indonesia due to continuous felling of nonproductive, over 25-year-old trees. Even though some manufacturers were using it in plywood and veneer production, they are hard to handle which later becomes less favorable raw materials due to a high moisture content where combination with a high starch content quickly attracts fungus and wood-decaying agents. The objective of this work was to evaluate properties of experimental wood composite panels, manufactured using oil palm-extracted starch modified with glutardialdehyde (OPSMG) as a binder. Different analyses were employed to characterize the properties of the samples besides evaluation of bending, internal bonding strength, and dimensional stability of the panels. Characterization on the functional group using the FT-IR analysis showed presence of aldehyde groups and ketone stretching vibrations at 1736.05 cm−1 and 1596.25 cm−1, which proves the presence of glutardialdehyde besides formation of bonding between the OPSMG and the woody materials. The XRD analysis showed the starch modification had lowered the crystallinity index which in turn increased the strength of the manufactured wood composites. The OPSMG wood composites were also found to have lower thermal stability, as evaluated using the TGA analysis. It was recorded that the maximum modulus of rupture for OPSMG wood composites was achieved at the 0.80 g/cm3 density level with an average value of 15.446 N/mm2 which showed 38.00% increment in strength between those two types of wood composites. Thickness swelling after immersion in water can still be improved by incorporating the moisture-repellent material later. After analyzing the results, it was concluded that modified oil palm starch has the potential to be used as an environment friendly binder for wood composite making.
Wood composite is one of the most commonly used interior composite panel products manufactured from sawmill waste and fast grown species in many countries for the last 60 years. It is fact that more sustainable use of forest resources triggered development of research projects related to biomass as the raw material for such panels. Trend toward using the forest logging residue and different types of agricultural waste as the raw materials in the wood composite manufacture has been great in the last decades [
Starch is a carbohydrate polymer consisting of glucose units by
Without modification, starch was used as a binder in their native form by Ozemoya et al. [
The source of starch, the oil palm tree, initially originated from West Africa [
Considering the potential of the huge amount of oil palm biomass available, this work investigates the suitability of oil palm starch modified using glutardialdehyde as a binder for wood composite manufacturing. Glutardialdehyde (GDA) was obtained in colorless organic compound with the formula CH2(CH2CHO)2. It is commonly used as the chemosterilizing agent for different medical equipment [
Rubberwood particles for wood composite making were obtained from Heveaboard Sdn Bhd, in Negeri Sembilan, Malaysia, for panel manufacture. Raw material was dried at a temperature of 50°C in an oven until the moisture content of the particles reaches 2%. Oil palm trunks were obtained from Kuala Lumpur Kepong oil palm plantation in Kedah, Malaysia. Freshly cut oil palm trunks were stored in large freezers to keep their freshness before further use. The glutardialdehyde 25% used for starch modification was purchased from Merck chemical company.
Fresh oil palm trunks were chipped into smaller pieces with an approximate dimension of 2 cm × 2 cm × 4 cm. Sodium metabisulphite of 0.5% concentration was prepared for the extraction process. Chipped oil palm trunks of 100 g were soaked in 1000 mL of 0.5% sodium metabisulphite for 24 h [
The oil palm starch powder was dissolved in distilled water at a temperature of 30 ± 5°C and stirred. The temperature was increased slowly up to 50°C. After addition of glutardialdehyde solution 25%, the temperature was further increased up to 90°C [
Based on the literatures, the suitable target densities of the manufactured wood composites will be set between 0.60 g/cm3 and 0.90 g/cm3. Most works choose one to three different density levels to study its effect on the performance of the wood composites [
A total of 30 panels were produced with 5 replicates for each density levels. Fifteen percent of modified oil palm starch was weighed and mixed manually as homogeneous as possible with rubberwood particles. The formed mat was cold pressed for 5 seconds before being hot pressed using Carver hot press using 5 MPa pressure at a temperature of 165°C for 20 min. Manufactured wood composites were conditioned in a climate room with a temperature of 20°C and a relative humidity of 65% for 2 weeks before they were cut into test samples according to the required dimension for each test. Replicates of 30 were prepared for density measurement, and 15 replicates were used for other tests including moisture content, thickness swelling, water absorption, bending strength, and internal bond strength evaluations [
The solubility and swelling power determination were carried out following the` method by Builders et al. [
Scanning electron microscopy (SEM) analysis was done to determine the distribution of the binder between the wood particles. The infrared spectra of the wood composite were measured using the FT-IR spectrophotometer (Nicolet, AVATAR FT-IR-360) equipped with Omnic software. Wood composite ground particles were mixed with KBr fine powder to produce the pellets. The samples were scanned in the range of 4000–470 cm−1 to characterize the functional group inside the wood composite.
The X-ray diffraction analysis was carried out using Diffractometer D5000 Kristalloflex, Siemens. Powdered wood composites samples were evaluated for their crystallinity by step scan measurements using X-rays (Cu-Ka) set at 40 kV and 40 mA. Scanning of 2
The thermal decomposition of the manufactured wood composites was evaluated using Mettler Toledo TGA/SDTA 851 thermogravimetric analyzer. Approximately about 5–10 mg was placed in an aluminum pan with a heating rate of 20°C min−1 under a nitrogen atmosphere. The weight changes of the samples were recorded by heating samples from a temperature of 30 to 800°C [
The differential scanning calorimeter (DSC) Pyris 1 PerkinElmer was used to evaluate the behavior of the samples towards temperature at a heating rate of 10°C/min. About 7 mg of the grounded wood composite sample was added to an aluminum pan and sealed entirely, and an empty sealed aluminum pan was used as a reference. The aluminum pan with the sample was heated from −10°C to 280°C at the respective heating rate.
The flexural strength and internal bond strength of the samples were tested using Instron Machine Model 5582 equipped with a load cell having 1,000 kg each. The crosshead speeds were set at 10 mm/min and 2 mm/min for bending and internal bonding strength test, respectively. Thickness swelling and water absorption of the samples were also evaluated to determine dimensional stability of the samples. They were carried out by soaking 50 mm × 50 mm × 5 mm samples in distilled water for 2 hours and 24 hours. Increment of thickness and weight of the specimens were measured at each time period and expressed in percentage. All tests were done based on Japanese Industrial Standard [
Table
Solubility and swelling power of OPS and OPSMG.
Starch | Temperature (°C) | Solubility (%) | Swelling power (g/g) |
---|---|---|---|
OPS | 50 | 5.60 | 7.80 |
60 | 9.51 | 19.32 | |
70 | 16.35 | 19.51 | |
80 | 24.26 | 25.57 | |
90 | 28.50 | 33.83 | |
|
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OPSMG | 50 | 4.93 | 5.21 |
60 | 5.98 | 7.56 | |
70 | 13.04 | 8.65 | |
80 | 16.97 | 19.38 | |
90 | 21.77 | 23.68 |
Micrographs taken from the samples on SEM are illustrated in Figures
SEM image of wood composite made using oil palm starch modified with glutardialdehyde at 1000x (a) and 3000x (b) magnification.
Fourier transform infrared (FT-IR) spectroscopy of powdered samples from wood composite made using OPSMG and OPS as the binder is shown in Figure
FT-IR spectra of powdered samples from wood composite made using OPSMG and OPS.
Figure
X-ray diffraction pattern of powdered samples from wood composite made using OPSMG and OPS.
The thermal gravimetry analysis was done to determine the effect of temperature towards decomposition of wood composite. Figure
Thermal gravimetric analysis (A) and derivative thermal gravimetric analysis (B) curve for OPS wood composite powder and OPSMG wood composite powder.
Initial weight reduction of both samples at low temperature could be due to the evaporation of moisture, breaking of water linkage, while the second step may correspond to the degradation of the whole wood composite polymer [
Figure
Differential scanning calorimetry curves of the OPS wood composite powder and OPSMG wood composite powder.
Table
Statistical analysis for wood composites made using OPS and OPSMG as a binder.
Panel type | Target density (g/cm3) | Measured density (g/cm3) | Moisture content (%) | Thickness swelling (%) | Water absorption (%) | Bending test (N/mm2) | Internal bonding strength (N/mm2) | |||
---|---|---|---|---|---|---|---|---|---|---|
2 h | 24 h | 2 h | 24 h | Modulus of elasticity | Modulus of rupture | |||||
OPS | 0.60 | 0.56 (0.07)a | 5.72 (0.02)a | 70.20 (17.32)a | 78.93 (21.61)a | 140.17 (15.92)a | 213.26 (47.68)a | 661.20 (192.73)a | 2.80 (0.75)a | 0.08 (0.02)a |
0.70 | 0.67 (0.07)b | 5.54 (0.07)b | 83.98 (20.74)ab | 89.44 (24.03)a | 145.51 (10.15)a | 177.32 (6.23)b | 1860.06 (450.77)b | 8.15 (2.86)b | 0.10 (0.01)b | |
0.80 | 0.76 (0.12)c | 6.10 (0.14)c | 100.69 (19.07)b | 109.07 (13.53)b | 146.02 (28.29)a | 178.79 (32.36)b | 2569.77 (409.38)b | 9.58 (1.25)c | 0.22 (0.01)c | |
|
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OPSMG | 0.60 | 0.57 (0.10)a | 6.40 (0.44)a | 57.38 (19.84)a | 67.95 (24.78)a | 130.38 (7.26)a | 165.47 (8.28)a | 2057.54 (345.90)a | 7.15 (2.15)a | 0.43 (0.05)a |
0.70 | 0.67 (0.10)b | 5.27 (0.20)b | 60.88 (14.67)a | 72.46 (17.84)ab | 121.84 (11.96)b | 162.18 (15.88)a | 2354.23 (175.51)a | 7.78 (1.66)a | 0.45 (0.06)a | |
0.80 | 0.75 (0.10)c | 5.56 (0.06)b | 80.89 (13.99)b | 97.60 (10.08)b | 128.79 (4.40)b | 163.49 (9.99)a | 3944.62 (957.70)b | 15.45 (5.56)b | 0.59 (0.06)b |
Thickness swelling and water absorption of wood composites after immersion in water were carried out for the 2 h and 24 h period. Table
The results also showed increments of thickness swelling as the density level were increased from 0.60 g/cm3 to 0.80 g/cm3. This happened because of a higher amount of wood particles in higher density wood composites. More wood will absorb more moisture, so the panel will expand more in the water because of hygroscopicity of wood and breakage of the binder system. Water absorption showed a different trend, except for 2 h thickness swelling for wood composites made using OPS as a binder. The results of water absorption properties did not follow the trend because the amount of water that penetrates into the test pieces is not uniform throughout the surface and small particles may be disintegrated from the test piece. The results also revealed that the thickness swelling and water absorption for 24 h are always higher than the thickness swelling and water absorption for 2 h. This could occur because a longer exposure to water gives more time for the moisture to penetrate into the test piece and a higher binder breakage and leads to more expansion of the dimensions of test pieces. The more crucial finding from the test results were the thickness swelling and water absorption of wood composites made using OPSMG are always lower than wood composites made using OPS. Figure
Normalized chart of thickness swelling and water absorption when using OPSMG as a binder compared to wood composites made using OPS as a binder.
Flexural strength testing of the wood composites yielded two beneficial results which are the modulus of elasticity and modulus of rupture, expressed in N/mm2. Flexural strength is an essential characteristic of a wood panel as it reflects the ability of the composite material to withstand a certain amount of load before it breaks. This is crucial for wood panels involved in application for furniture and wall paneling industries.
The first result is the modulus of rupture which reflects the maximum load or capacity of a material could withstand before failure. It is well accepted to use modulus of rupture as an evaluation of strength of wood panels. From the results in Table
Elasticity could be defined as the recoverability of a material from a low stress deformation under the proportional limit to its original state after load is removed. Flexural modulus of elasticity is a measure of the resistance of a material to bending deflection, which is in contrast to the stiffness. The modulus of elasticity can be obtained from the slope of the stress-strain curve of the wood composite flexural strength result [
Another evaluation is the internal bonding strength which reflects the strength of binder to hold woody materials together when load is applied towards two different directions. The results in Table
Wood composites had been fabricated using OPS and OPSMG as the binder at three density levels. Characterization of the functional group using the FT-IR analysis showed presence of aldehyde groups and ketone stretching vibrations at 1736.05 cm−1 and 1596.25 cm−1 which proves the presence of glutardialdehyde in the powdered sample, while the ketone group detection showed formation of bonding between the oil palm starches modified using glutardialdehyde and the woody materials. The XRD analysis showed the starch modification had lowered the crystallinity index which in turn increased the strength of the manufactured wood composites. The OPSMG wood composites were also found to have a lower thermal stability as evaluated using the TGA analysis. From the test results, the highest and lowest modulus of rupture values were determined from the OPSMG wood composite recorded at 15.45 N/mm2 and achieved by the 0.80 g/cm3 density level, while the highest value of modulus of rupture for wood composite made using OPS was 9.58 N/mm2 at the same density level. Internal bonding strength showed a higher value for the OPSMG wood composite which was 0.59 N/mm2 for 0.80 g/cm3, compared to 0.22 N/mm2 for wood composite made using OPS as the binder. Both types of wood composite satisfy requirements of Japanese Industrial Standard for the mechanical strength properties at the 0.80 N/mm2 density level. The thickness swelling, however, for both types of wood composites, did not meet the requirement in Japanese Industrial Standard. However, this drawback could be improved by incorporating water-repellent materials such as wax into the formulation or applying surface coating to protect it from moisture. To the very less extent, it could be limited for usage in dry conditions.
Oil palm starch
Oil palm starch modified with gluardialdehyde
Crystallinity index
Scanning electron microscopy
Fourier transform infrared
Thermal gravimetry analysis
Differential scanning calorimetry analysis.
The characterisation data used to support the findings of this study are available from the corresponding author at
The authors declare that they have no conflicts of interest.
The authors acknowledge the Universiti Sains Malaysia for the Research University Grant (1001/PTEKIND/815066) to Rokiah Hashim and Ministry of Higher Education Malaysia for Research Acculturation Grant Scheme (R/RAGS/A08.00/01046A/002/2015/000302) for Mohd Hazim Mohamad Amini. Appreciation was also given to the Heveaboard Sdn Bhd, Malaysia, for providing the raw materials for the manufacture of wood composites.