Partial replacement of urea-formaldehyde with modified oil palm starch based adhesive to fabricate particleboard

Author’s Accepted Manuscript PARTIAL REPLACEMENT OF UREAFORMALDEHYDE WITH MODIFIED OIL PALM STARCH BASED ADHESIVE TO FABRICATE PARTICLEBOARD Nurul Syuhada Sulaiman, Rokiah Hashim, Othman Sulaiman, Mohammed Nasir, Mohd Hazim Mohamad Amini, Salim Hiziroglu

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S0143-7496(18)30024-1 https://doi.org/10.1016/j.ijadhadh.2018.02.002 JAAD2127

To appear in: International Journal of Adhesion and Adhesives Received date: 28 July 2017 Accepted date: 28 January 2018 Cite this article as: Nurul Syuhada Sulaiman, Rokiah Hashim, Othman Sulaiman, Mohammed Nasir, Mohd Hazim Mohamad Amini and Salim Hiziroglu, PARTIAL REPLACEMENT OF UREA-FORMALDEHYDE WITH MODIFIED OIL PALM STARCH BASED ADHESIVE TO FABRICATE PARTICLEBOARD, International Journal of Adhesion and Adhesives, https://doi.org/10.1016/j.ijadhadh.2018.02.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

PARTIAL REPLACEMENT OF UREA-FORMALDEHYDE WITH MODIFIED OIL PALM STARCH BASED ADHESIVE TO FABRICATE PARTICLEBOARD

Nurul Syuhada Sulaimana, Rokiah Hashima,*, Othman Sulaimana, Mohammed Nasira, Mohd Hazim Mohamad Aminib, Salim Hizirogluc a

Division of Bioresource, Paper and Coatings Technology, School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia b Faculty of Bio Engineering and Technology, Universiti Malaysia Kelantan, 17600 Jeli, Kelantan, Malaysia c Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma 74078-6013, USA

ABSTRACT This study investigated the efficacy of epichlorohydrin-modified oil palm starch as an adhesive in addition to urea formaldehyde, to minimise the use of urea formaldehyde adhesive in particleboard manufacturing. A single-layer particleboard was fabricated from rubberwood particles and urea formaldehyde resin supplemented with modified oil palm starch adhesive. The adhesive performance was analysed by studying the physical properties (actual density, moisture content, thickness swelling and water absorption) and mechanical properties (bending strength and internal bond strength) of the prepared panels. The panels of two target densities were manufactured (600 and 800 kg/m3) at two different pressing times (15 min and 20 min). The performance of manufactured panels were analysed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis and differential scanning calorimetry. The panels manufactured in this study met the minimum required strength as stated in Japanese Industrial Standards (JIS) but a lower water resistant property. Furthermore, a panel with a density of 800kg/m3 had

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improved mechanical properties in comparison to a panel exhibiting a density of 600kg/m 3 when manufactured with a 15 min pressing time.

Keywords: Epichlorohydrin; Oil palm starch; Urea formaldehyde resin. *Corresponding author, [email protected], Tel. +60 4 6535217 Fax: +60 46536375

1.

INTRODUCTION Natural raw materials such as starch, protein and tannin have been utilised as

adhesives for centuries. However, the use of such natural based adhesives has been discouraged due to poor bonding quality. Over the last few decades, synthetic adhesives such as those based on formaldehyde-based resins have replaced natural adhesives due to their superior bonding, and greater water resistance properties (Vick, 1999). The particleboard industry is one of the largest wood-based composite industries around the world which has fully relied on formaldehyde-based adhesives. Although formaldehyde-based adhesives have many advantages over natural based adhesives, they emit formaldehyde which is carcinogenic in nature (Moubarik et al., 2010). Due to this carcinogenic nature, alternative, non-formaldehyde based adhesives, have been under intensive investigation to mitigate the emission problem. Therefore, the study of natural adhesives has regained the interest of researchers (Moubarik et al., 2013; Nasir et al., 2013; Norström et al., 2014; Qi et al., 2013) and starch modified adhesive is one of the most attractive examples of it (Salleh et al., 2015; Sulaiman et al., 2013). Oil palm tree (Elaeis guineensis), a major cash crop of south-east Asian countries, is grown for the vegetable oils it contains, but, following processing to remove the oil, the remaining plant trunk is treated as waste and left to decay or is burned. Noor et al. (1999) have reported that the oil palm trunk contains 7.15% starch and that most of this is found in the parenchyma of the oil palm trunk which was reported to be 55.5% by Tomimura (1992). 2

The high starch content in the oil palm trunk makes the extraction process possible and economical. Cheng et al. (2004), has modified soybean flour with chemicals and have prepared a wheat straw particleboard in order to improve the mechanical properties and water resistance of the resulting particleboard panels. The results showed that panels manufactured using soybean flour modified with urea and N-(n-butyl) thiophosphoric triamide had better mechanical properties while the panel bonded by boric acid treated soybean flour had better water resistance. Moubarik et al. (2010), investigated corn starch-tannin adhesives and observed improved shear strength values at lower viscosities. According to their study, the resulting particleboard had mechanical properties comparable to panels manufactured using urea formaldehyde (UF) resin. Much research has been carried out on modified starch, obtained from various sources and characterised for use as an adhesive, but its application in particleboard manufacturing has been minor (Chen et al., 2013; Moubarik et al., 2013). Research based on the utilization of oil palm starch as a raw material to produce natural based adhesive in particleboard manufacturing is still very limited (Sulaiman et al., 2013). Thus, this study was carried out with the aim to reduce the amount of UF resin by supplementing with natural starch adhesive obtained from oil palm trunk. The physical and mechanical properties of manufactured particleboards were investigated in order to determine the performance of the adhesive.

2.

MATERIALS AND METHODS

2.1.

Adhesive preparation Urea formaldehyde resin was supplied by Momentive Specialty Chemicals Sdn. Bhd

located in Kawasan Perindustrian Perai, Perai, Malaysia. The starch adhesive preparation started with the extraction of oil palm starch followed by its modification. Starch from oil

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palm trunk was extracted according to the methodology practiced by Noor et al. (1999) with modification on soaking time. Approximately 1000 mL aliquots of a 0.5% (w/v) aqueous solution of sodium metabisulphite were prepared. Fresh oil palm trunk slabs were reduced into smaller size particles and were soaked in the aqueous solution of sodium metabisulphite prepared beforehand for 48 hr. Then, the solution was cleared by removing the oil palm trunk particles and filtering the residues using a sieve with a mesh aperture of 250 µm. The starch was then obtained as a precipitate from the solution by applying centrifuge machine (Beckman Coulter Allegra X-15R) at 4750 rpms for 15 min. Precipitated starch was carefully removed from the centrifuge bottle and dried immediately in an oven at 50 ± 2 °C for 3 days. Dried oil palm starch was ground using a blender and chemically modified in accordance with the preceding work by Jyothi et al. (2006). The starch modification was carried out using epichlorohydrin. Oil palm starch solution was prepared by the addition of distilled water to the starch powder. The mixture was mechanically stirred until the starch powder was completely dissolved. Then, the starch solution was placed in a water bath previously pre-heated to 90 °C. The solution was continuously stirred using an overhead stirrer. Epichlorohydrin was added to the starch solution at a ratio of 1:4 (w/w) once the temperature of the solution had reached 55 °C (Zhou et al., 2014). The solution was continuously stirred until a temperature of 90 °C was attained. Finally, the solution was left to cool to room temperature before it was used in the manufacturing of particleboard.

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2.2.

Adhesive characterization The solid content of starch adhesive was determined by drying 2 g of adhesive in an

oven at a temperature of 105 ±2 °C. The solid content of the starch adhesive was calculated based on the percentage weight loss after drying. The viscosity of the starch was determined using a rotary rheometer (AR1000-N) (Jyothi et al. 2006; Moubarik et al. 2010) at a shear rate of 150 s-1. The pot life was determined as the time taken for the starch adhesive sample to become unsuitable for further use. The starch adhesive sample was prepared and left at room temperature to dry.

2.3.

Particleboard manufacture A total of 20 particleboard panels were manufactured from rubberwood (Hevea

brasiliensis) particles which were obtained from Hevea Board Sdn Bhd, Seremban, Negeri Sembilan, Malaysia. The panels were manufactured based on two target densities, namely 600 kg/m3 and 800 kg/m3 and two pressing times (15 min and 20 min) with 5 replicates for each set. Particles were dried in an oven beforehand to obtain a constant weight of particles prior to application of starch adhesive and UF resin. The adhesive was prepared by mixing 13 % starch (oven dried weight of wood) and 2% of UF resin (oven dried weight of the wood). The adhesive mixture was then mixed manually with the rubberwood particles. Then, the mixture of particles and adhesive was placed in a mould with dimensions of 20.1 cm x 20.1 cm x 0.5 cm. A mat was formed by pre-pressing the mixture with a cold press machine. Finally, the mixture was passed through a hot press machine at a temperature of 165 °C and a pressure of 5 MPa for 15 and 20 min to form a particleboard panel. The resulting panel was conditioned at 25 ± 2 ºC and 65 ± 2 % relative humidity for several days prior to testing.

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2.4.

Particleboard evaluation Particleboard panels were evaluated for their physical and mechanical properties. The

physical properties determined were density, moisture content, thickness swelling (TS) and water absorption (WA), whereas the mechanical properties determined were modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond (IB) strength. Both physical and mechanical properties were evaluated in accordance with the appropriate JIS-A-5908 (2003) specification. 15 samples with a size of 5 cm x 5 cm were used to determine density, TS and WA respectively, while 5 samples with the same dimensions were used for the measurement of moisture content (MC). Density test was carried out to determine the actual density of panel manufactured by taking the measurement of length, width, thickness, and mass for each sample. The actual density was calculated by dividing the mass over the volume of the sample. The TS and WA tests were done by taking the first reading of thickness and mass of the sample before the sample was immersed in distilled water. A second reading was taken after 2 h and 24 h immersion to record the increase in thickness and weight of the sample. The MC of the panel was assessed by determining the mass of the sample prior to drying in an oven followed by drying until a constant weight was achieved. The MOR and MOE results were obtained by taking the average reading of MOR and MOE from 10 samples with dimensions of 20 cm x 5 cm. While, for the IB test, 15 samples with dimensions of 5 cm x 5 cm were used. An Instron tensile testing machine model 5582 with crosshead speeds of 10 mm/min and 2 mm/min was used for the bending and internal bond strength tests respectively. The urea formaldehyde release test was carried out according to the procedure described in British Standard (1996). Particleboard samples with dimensions of 25 mm x 25 mm x 5 mm were hanged 40 mm over the surface of distilled water in a closed polyethylene 6

bottle. The distilled water was then subjected to test to determine formaldehyde emission from the sample as per the standard. 2.5.

Particleboard characterizations

2.5.1. X-ray diffractometry analysis X-ray diffractometry (XRD) analysis was carried out to determine the crystallinity index of the manufactured panels. The analysis was conducted using a Kristalloflex D-5000 X-ray diffraction system (Siemens, Germany) with the powdered panel material placed in a sample holder. The finished surface of the sample was then smoothed using air blow. The Xrays (Cu-Kα), generated at an opening voltage and current of 40 kV and 30 mA, respectively, were used to complete the step scan measurement. Scans were made from a diffraction angle 2θ ranging from 10° to 40°, corresponding to a scanning speed of 0.02° and 2°/min. The crystallinity index was calculated using equation 1, CrI (%) = [(I200-Iam)/ I200] x 100

(Eq. 1)

where I200 is the peak intensity of the crystalline fraction and Iam is the peak intensity of the amorphous fraction. 2.5.2. Thermogravimetric analysis (TGA) Thermogravimetric analysis was carried out to determine the change in weight of a sample when subjected to a steadily increasing temperature. The analysis was carried out using a Metler Toledo TGA/SDTA851e thermogravimeter (Mettler Toledo Corp., Switzerland) with STARe software (version 9.20). Approximately 10 mg of a powdered sample of the panel was weighed into an aluminium pan. The sample was then heated at a heating rate of 20 °C/min between 30 °C and 800 °C. The analysis was conducted under a nitrogen atmosphere.

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2.5.3. Differential scanning calorimetry (DSC) analysis The melting temperature (Tm) of manufactured panels was determined using differential scanning calorimetry analysis. The analysis was carried out using a Perkin Elmer differential scanning calorimeter (Model DSC 8000). Approximately 5 mg of powdered panel material was placed in an aluminium pan. This was then transferred to a heating pan followed by heating, at a heating rate of 10 °C/min, between -15 °C and 280 °C with an empty pan being used as the reference. This analysis was run under a nitrogen atmosphere. 2.5.4. Fourier transform-infrared spectroscopy (FTIR) analysis Approximately 95 mg of potassium bromide was ground and then mixed with 5 mg of powdered panel material. The mixture was pressed into pellet form with a thickness of approximately 1 mm. The FTIR spectrum of the pellet was then taken in a Nicolet Avatar 360 ESP FTIR. The pellet was scanned 64 times over a region of 4000-400 cm-1 at a resolution of 4 cm-1. 2.5.5. Scanning electron microscopy (SEM) analysis Small cubes of particleboard panel were cut for a cross cut view. Samples were glued onto a stub using tape followed by coating the samples with a thin layer of gold using the Polaron SC515 SEM coating system (Fisons Instruments) so as to minimise charging effects. Samples were examined using a scanning electron microscope (Model Supra 50 VP) with an acceleration voltage of 15 kV (Amini et al., 2013).

3.

RESULTS AND DISCUSSIONS

3.1.

Adhesive characterization Analysis found that the solid content of epichlorohydrin modified oil palm starch was

measured as 29.97% compared to 27.43% for natural oil palm starch. Viscosity was found to

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be 1.96 Pa.s and 0.65 Pa.s for epichlorohydrin modified oil palm starch and natural oil palm starch, respectively. The higher viscosity of the epichlorohydrin modified oil palm starch was due to crosslinking by epichlorohydrin. Gel time was recorded as 19.13 min and 22.30 min for the epichlorohydrin modified oil palm starch and natural oil palm starch, respectively. The pot life of epichlorohydrin modified oil palm starch was lower, recorded as 3 days compared to natural oil palm starch which showed 5 days of pot life. Crosslinking action by epichlorohydrin also reduced the pot life of the starch by accelerating the curing process. 3.2.

Physical properties The physical properties of epichlorohydrin modified oil palm starch with urea

formaldehyde manufactured panels are presented in Table 1. As indicated, the panel with a target density of 600 kg/m3 was observed to be 620 kg/m3 while the panel with a target density of 800 kg/m3 was observed to be 790 kg/m3 and 780 kg/m3 as average actual density manufactured at 15 and 20 min pressing times, respectively. The results show that only a small difference exists between target density and actual density for panels manufactured with different pressing times. This same trend was also observed in the case of moisture content. Panels with a target density of 600 kg/m3 manufactured with 15 and 20 min had moisture contents of 8.57 and 7.71 %, respectively. While, for panels with a target density of 800 kg/m3 manufactured with 15 and 20 min pressing times, the corresponding values were 6.81 and 6.48 %, respectively. Density results for control samples which were the epichlorohydrin modified oil palm starch particleboard and urea formaldehyde particleboard also showed the same trend with density ranges from 610 kg/m3 to 630 kg/m3 and 790 kg/m3 to 810 kg/m3 for target densities of 600 kg/m3 and 800 kg/m3, respectively. All moisture content values of the manufactured panels in this study met the requirements stated in JIS-A5908 (2003), which were in the range of 5-13 %.

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Table 2 shows water absorption (WA) and thickness swelling (TA) values of samples manufactured at 15 min and 20 min pressing times with target densities of 600 kg/m3 and 800 kg/m3, respectively. As indicated, the results reveal similar trends for both target densities and pressing times i.e. increasing water absorption and thickness swelling values as epichlorohydrin is incorporated into the formulation at the expense of urea formaldehyde. The higher thickness swelling values were found on panels with the highest density levels which can be attributed to the amount of particles they contained. Particles in the panels are the main component responsible for the water uptake of the panel. The absorption of water by particles caused the particles to be pushed apart. Since the arrangement of particles were parallel to the surface of the panel, increases in panel thickness were observed following water immersion (Cheng et al., 2004). However, an increase in density also resulted in a decreased value of water absorption. This can be explained by greater contact between the particles and binder during the panel manufacture. The greater quantity of particles present in the high density panels resulted in the particles being compressed tightly. As a result, the starch adhesive present in the voids between the particles was cured more efficiently (Gokay Nemli et al., 2007). Thus, lower water absorption was obtained with high density level panels as there will exist a relatively small number of voids within these panels responsible for water uptake (Loh et al., 2010). The UF resin is a formaldehyde-based resin which has poor water resistance (Conner, 1996). However, the hydrolytic stability of a UF resin can be enhanced by curing at high temperature which can help to lower the water uptake experienced by a manufactured panel (Park & Jeong, 2011). In addition, it has been shown that the compact structures of modified starch which form through crosslinking reactions (Hamdi & Ponchel, 1999) decrease the capability of starch to absorb water compared to their native form (Kartha & Srivastava, 1985; Yook et al., 1993). However, all values of thickness swelling and water absorption

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obtained in this study did not meet the JIS-A-5908 (2003) requirement of 12 % for 2 h soaking time. Thus, additional treatment needs to be carried out such as the use of a surface coating on particleboard as suggested by Yalinkilic et al. (1998). The addition of wax during the mixing of starch and particles (Nourbakhsh, 2010) also is one of the ideas which can be accomplished in order to improve the thickness swelling and water absorption of the panel that could meet the requirement as stated in the JIS standard. 3.3.

Mechanical properties Table 3 presents the mechanical properties of panels manufactured in this study. The

data shows that increasing the density of a panel results in significant improvements in its mechanical properties. This improvement can be ascribed to the existence of a high concentration of particles in high density panels which results in the particles being compressed more tightly (Cheng et al., 2004). Hence, the starch adhesive as well as the UF resin was cured more efficiently resulting in stronger bonding between adhesive and particles (Yimsamerjit et al., 2007). Additionally, panels manufactured comprising high particle contents were able to resist greater levels of mechanical loading in comparison to those panels manufactured with lower particle densities (Yalinkilic et al., 1998). The results also revealed that panels manufactured with a 15 min pressing time had higher mechanical strength compared to those manufactured with a 20 min pressing time. This observation was found with panels manufactured with both 600 and 800 kg/m3 target densities. The use of modified starch with the addition of UF resin also contributes to the mechanical strength of the panel. The crosslinking of starch with epichlorohydrin resulted in the formation of starch highly resistant to mechanical shear and with improved bonding between the starch granules and particles (Jyothi et al., 2006). The addition of UF into the modified starch helps to increase the mechanical strength of a panel through interactions between the UF resin and modified starch due to the UF resin providing good cohesion 11

between the materials it glued (Dunky, 2003). All manufactured panels were shown to have mechanical properties higher than the minimum requirement stated in JIS-A-5908 (2003) which requires 8 N/mm2 and 0.15 N/mm2 for MOR and IB strength, respectively.

3.4.

Formaldehyde release Results for formaldehyde release tests conducted on epichlorohydrin-modified oil

palm starch with urea formaldehyde particleboard and an unmodified urea formaldehyde particleboard are shown in Table 4. At 15 min press time, the epichlorohydrin-modified oil palm starch with urea formaldehyde particleboard and the unmodified urea formaldehyde particleboard showed 1.57 mg and 3.05 mg of formaldehyde release per 100 g board, respectively. At 20 min press time, their formaldehyde release is 1.35 mg and 1.97 mg per 100 g board, respectively. It was observed that a longer press time lowered formaldehyde release by a reduction of free, unreacted formaldehyde inside the particleboard as shown between 15 min press time and 20 min press time particleboard. Experimental results showed a decrement of 48.52 % and 31.47 % of formaldehyde release for particleboard press times of 15 min and 20 min, respectively.

3.5.

Particleboard characterization

3.5.1. X-ray diffraction (XRD) analysis X-ray diffraction analysis was performed on panels manufactured with 15 and 20 min pressing times. The crystallinity index, which was computed based on Eq. 1, is listed in Table 5. The panels manufactured with modified oil palm starch with the addition of UF resin for both 15 and 20 min pressing times had major intensity lines close to 22 degree of 2θ angle. The crystallinity index values for panels manufactured with 15 and 20 min pressing

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times were 44.05 % and 46.77 %, respectively. These results revealed that manufactured panels with 20 min pressing time had a higher crystallinity index compared to the ones manufactured with a 15 min pressing time. In addition, it was observed that panels with high crystallinity index values had low physical and mechanical properties. In this study, the crystallinity index obtained maybe considerably low with the presence of UF resin which was known to have crystalline structure when cured. This may be explained by the fact that the structure of UF resin will change from microcrystalline to amorphous when it cured on wood (Levendis et al., 1992). Overall, the results show that, with the systems studied, crystallinity index varies as follows: epichlorohydrin modified oil palm starch > epichlorohydrin modified oil palm starch with urea formaldehyde > urea formaldehyde.

3.5.2. Thermogravimetric analysis (TGA) Results from thermogravimetric analysis experiments conducted on the various panels have been expressed as weight loss curves (TG) and derivative thermogravimetric curves (DTG) as shown in Figure 1. The TG curves showed that all the investigated samples in this study exhibited weight loss in three stages. The first stage of all samples was revealed by a minor decrease in weight with an initial temperature around 29 °C. This stage involves the evaporation of water and easily volatile materials (El-Wakil et al., 2007). The initial degradation temperatures for the second and third stages of all samples are shown in Figure 3. The second and third stages indicate degradation of the polymer chains and complete decomposition of the sample residue, respectively (Wang et al., 2011). The TG curves showed that panels manufactured with a 15 min pressing time had a low initial degradation temperature for all stages in comparison to those manufactured with a 20 min pressing time. The amount of residue at the end of the analysis was found to be highest for panels

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manufactured with a 20 min pressing time. Similarly DTG curve observations revealed higher rates of decomposition on panels manufactured with the 20 min pressing time.

3.5.3. Differential scanning calorimetry (DSC) The melting temperatures (Tm) for panels manufactured with 15 and 20 min pressing times were shown on DSC thermograms as illustrated in Figure 2. As shown in Figure 2, the melting temperatures for panels manufactured with 15 and 20 min pressing times were 78.08 °C and 80.15 °C, respectively. The results indicated that panels manufactured with a 20 min pressing time had a higher melting temperature than those manufactured with a 15 min pressing time. This showed that panels manufactured with a 20 min pressing time had a high thermal stability and that this observation corresponded with the result obtained in the TGA analysis. According to this study, it was found that panels with high thermal stability had a high crystallinity index but low physical and mechanical strength.

3.5.4. Fourier transform infrared spectroscopy (FTIR) The FTIR spectra of panels manufactured with 15 and 20 min pressing times are illustrated in Figure 3. Differences in spectra for panels manufactured with different pressing times were difficult to determine due to transmittance peaks being similar. Both spectra showed the O-H stretching band peak in the region of 3600-3000 cm-1 which indicates the presence of the starch backbone (Jyothi et al., 2006). The FTIR analysis in this study can be used as a tool to confirm the successful modification of starch as well. The crosslinking of epichlorohydrin with starch resulted in the formation of ether groups as a new linkage between particles and starch and also within starch granules (Hamerstrand et al., 1960). The identification of ether groups can be revealed by the presence of peaks relating to C-O bonds at wavenumbers of approximately 1050 cm-1 (Bruice, 2010). The existence of a C-O bond

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peak in the spectra of a manufactured panel proves the successful modification of starch in this study. The existence of both O-H stretching bands and those relating to the C-O bond are labelled in Figure 3.

3.5.5. Scanning electron microscopy (SEM) SEM micrographs at two magnifications of a panel manufactured with a target density of 800 kg/m3 and a pressing time of 20 min are shown in Figures 4a and b. The micrographs show that the starch adhesive was dispersed evenly within the rubberwood particles. The compact structure of the cell wall and fiber of rubberwood particles can be seen as a result of the pressure to which the panels were subjected during the manufacturing process. These two factors lead to the existence of better bonding between the rubberwood particles and modified starch molecules. The compatibility between UF resin and modified starch will also be an additional factor which will result in better bonding between the particles and starch molecules. Therefore, the physical properties and mechanical strength of the panels manufactured also will be improved.

4.

CONCLUSIONS The particleboard panels manufactured in this study met the minimum modulus of

rupture, modulus of elasticity and internal bond strength as quoted in the JIS standard. However, the panels did not meet the minimum criteria of thickness swelling and water absorption. Thus; additional treatment would be necessary in order to achieve those minimum requirements. Based on the characterization conducted on the manufactured panels, it was found that panels manufactured with 20 min pressing time had a higher crystallinity index and a higher thermal stability than those manufactured with 15 min pressing time. According to the observations in this study, a panel with a high crystallinity index and high thermal stability was found to have relatively low physical and mechanical properties. FTIR analysis 15

showed that the modification of starch was successful and there were no clear differences which can be observed to differentiate the spectra for the manufactured panels with different pressing times. The morphological analysis showed that the manufactured panels were compact in structure and the starch adhesive was distributed evenly between the particles. This resulted in better bonding between the particles and starch adhesive. In the light of this study, it can be concluded that starch modification with the addition of UF resin did give better properties to the starch granules which thus contributed to the strength of the manufactured panels.

5.

ACKNOWLEDGEMENTS The authors acknowledged Universiti Sains Malaysia for the research university grant

(1001/PTEKIND/815066), PRGS Grant (1001/PTEKIND/844104), Hevea board Sdn Bhd and Momentive Specialty Chemicals Sdn Bhd for providing raw materials to be used in this study. The authors are thankful to Universiti Sains Malaysia for awarding Postdoc fellowship to Dr. Mohammed Nasir.

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List of Figures

eight

1/℃

,%

Temperature, ℃

A B Temperature, ℃

1/℃

eight ,%

Temperature, ℃

C D

Temperature, ℃

eight

1/℃

,%

Temperature, ℃

E F Temperature, ℃

20

Figure 1 TG (left) and DTG (right) curves of; A: Epichlorohydrin-modified oil palm starch (15 min press time), B: Epichlorohydrin-modified oil palm starch (20 min press time), C: Epichlorohydrin-modified oil palm starch with addition of UF resin (15 min press time), D: Epichlorohydrin-modified oil palm starch with addition of UF resin (20 min press time), E: Urea formaldehyde (15 min press time) and F: Urea formaldehyde (20 min press time). A B C D E F

Figure 2 DSC thermograms of A: Epichlorohydrin-modified oil palm starch (15 min press time), B: Epichlorohydrin-modified oil palm starch (20 min press time), C: Epichlorohydrin-modified oil palm starch with addition of UF resin (15 min press time), D: Epichlorohydrin-modified oil palm starch with addition of UF resin (20 min press time), E: Urea formaldehyde (15 min press time) and F: Urea formaldehyde (20 min press time).

21

A B

C D E F

Figure 3 FTIR spectra of A: Epichlorohydrin-modified oil palm starch (15 min press time), B: Epichlorohydrin-modified oil palm starch (20 min press time), C: Epichlorohydrin-modified oil palm starch with addition of UF resin (15 min press time), D: Epichlorohydrin-modified oil palm starch with addition of UF resin (20 min press time), E: Urea formaldehyde (15 min press time) and F: Urea formaldehyde (20 min press time).

(b)

(a)

Figure 4 SEM micrographs showing cross section view of epichlorohydrin-modified oil palm starch and UF resin based panel with target density of 800 kg/m3 and 20 min pressing time at magnification of (a) 100x, (b) 200x.

List of Tables 22

Table 1. Physical properties of particleboard bonded with epichlorohydrin-modified oil palm starch supplemented with urea formaldehyde resin. Target density

Pressing time

(kg/m3)

(min)

15 600

20

15

Sample

Actual density

Moisture content

(kg/m3)

(%)

EMOPSUF

620 (0.03)

8.57 (0.73)

EMOPS

610 (0.04)

5.64 (0.55)

UF

620 (0.03)

5.00 (0.57)

EMOPSUF

620 (0.04)

7.71 (1.30)

EMOPS

620 (0.01)

5.7 (0.98)

UF

630 (0.03)

5.07 (0.78)

EMOPSUF

790 (0.04)

6.81 (0.21)

EMOPS

810 (0.01)

5.75 (0.51)

UF

790 (0.03)

5.51 (0.55)

EMOPSUF

780 (0.02)

6.48 (0.39)

EMOPS

780 (0.03)

6.34 (0.40)

UF

790 (0.02)

5.11 (0.42)

800

20

a

Data is average of 20 panels and standard deviation is indicated in parentheses. EMOPSUF: epichlorohydrin-modified oil palm starch with addition of UF resin, EMOPS: epichlorohydrin-modified oil palm starch and UF: urea formaldehyde Table 2. Physical properties of manufactured particleboards

b

Press

Thickness swelling (%)

Water absorption (%)

binder

2 hours

24 hours

2 hours

EMOPS

43.15 (5.87)

54.81 (7.94)

114.02 (3.99)

Type of

Density, time, kg/m3

24 hours

min 123.84 15

(11.92) 115.63

600 15

EMOPSUF

35.86 (7.01)

44.43 (7.91)

86.52 (4.67) (15.62)

15

UF

23.22 (3.28)

29.22 (5.17)

23

63.2 (3.05)

83.07 (2.65)

154.66 20

EMOPS

46.08 (6.51)

64.45 (5.81)

122.63 (6.12) (17.09) 119.41

20

EMOPSUF

45.08 (10.81)

57.47 (7.77)

89.08 (7.35) (16.42)

20

UF

24.71 (4.35)

29.36 (3.89)

67.56 (3.88)

15

EMOPS

54.35 (7.66)

71.50 (10.05)

106.57 (6.78)

89.47 (2.79) 126.46 (5.98) 102.97

15

EMOPSUF

48.96 (7.09)

67.61 (10.89)

82.41 (6.54) (12.46)

15

UF

26.24 (5.03)

30.31 (2.20)

69.05 (4.66)

20

EMOPS

50.07 (14.91)

69.62 (8.46)

104.23 (3.47)

90.09 (4.43)

800 120.32 (7.31) 101.66 20

EMOPSUF

47.97 (7.97)

58.92 (4.63)

80.25 (6.54) (13.94)

20

UF

27.41 (3.41)

32.04 (3.38)

73.25 (9.58)

91.43 (5.17)

a

Data is average of 20 panels and standard deviation is indicated in parentheses. EMOPSUF: epichlorohydrin-modified oil palm starch with addition of UF resin, EMOPS: epichlorohydrin-modified oil palm starch and UF: urea formaldehyde

b

Table 3. Mechanical properties of particleboard Bending strength (N/mm2)

Density,

Press time,

Type of

kg/m3

min

binder

MOR

EMOPS

10.59 (1.51)

MOE

IB (N/mm2)

1975.96 0.35 (0.06) (370.49) 2511.98 15

EMOPSUF

12.12 (0.98)

0.58 (0.06) (313.06)

600

UF

15.64 (2.92)

24

2216.80

0.76 (0.11)

(323.05) 2124.28 20

EMOPS

9.61 (1.17)

0.32 (0.10) (482.52) 2197.09

EMOPSUF

10.79 (1.07)

0.51 (0.04) (274.37) 1988.60

UF

15.05 (2.37)

0.87 (0.24) (223.71) 3471.64

EMOPS

19.09 (1.62)

0.49 (0.15) (460.52) 3855.20

15

EMOPSUF

24.56 (1.83)

0.68 (0.08) (599.33) 3499.07

800

UF

25.63 (2.07)

0.95 (0.21) (345.23) 3703.16

EMOPS

15.92 (1.90)

0.45 (0.06) (474.54) 3364.31

20

EMOPSUF

22.42 (1.89)

0.59 (0.11) (690.24) 4284.04

UF

25.22 (4.48)

1.17 (0.33) (602.29)

a

Data is average of 20 panels and standard deviation is indicated in parentheses. EMOPSUF: epichlorohydrin-modified oil palm starch with addition of UF resin, EMOPS: epichlorohydrin-modified oil palm starch and UF: urea formaldehyde

b

25

Table 4 Formaldehyde release for each type of particleboard Type of particleboard

EMOPSUF

UF

Density (Press time)

Formaldehyde release (mg/ 100 g board)

600 kg/m3 (15 minutes)

1.98 (0.95)

600 kg/m3 (20 minutes)

1.65 (0.22)

800 kg/m3 (15 minutes)

1.57 (0.17)

800 kg/m3 (20 minutes)

1.35 (0.15)

600 kg/m3 (15 minutes)

2.40 (0.16)

600 kg/m3 (20 minutes)

2.14 (0.07)

800 kg/m3 (15 minutes)

3.05 (0.90)

800 kg/m3 (20 minutes)

1.97 (0.27)

*Data is expressed as average *Values in parenthesis indicate Standard Deviation *EMOPSUF, epichlorohydrin-modified oil palm starch with UF resin; UF, urea formaldehyde resin

26

Table 5. Crystallinity index for particleboard panel with target density of 800 kg/m3 Type of particleboard EMOPSUF EMOPS UF

Pressing time, min 15 20 15 20 15 20

Crystallinity index, % 44.05 46.77 47.33 47.41 34.78 32.15

a

EMOPSUF: epichlorohydrin-modified oil palm starch with addition of UF resin, EMOPS: epichlorohydrin-modified oil palm starch and UF: urea formaldehyde

27