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Properties of particleboard made from rubberwood using modified starch as binder
Composites: Part B 50 (2013) 259–264
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Properties of particleboard made from rubberwood using modified starch as binder Mohd Hazim Mohamad Amini a, Rokiah Hashim a,⇑, Salim Hiziroglu b, Nurul Syuhada Sulaiman a, Othman Sulaiman a a b
Division of Bio-resource, Paper and Coatings Technology, School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia Department of Natural Resource Ecology & Management, 303G Agricultural Hall, Okhahoma State University, Stillwater, OK 74078-6013, USA
a r t i c l e
i n f o
Article history: Received 11 April 2012 Received in revised form 8 November 2012 Accepted 24 February 2013 Available online 4 March 2013 Keywords: A. Wood D. Mechanical testing D. Surface analysis
a b s t r a c t The objective of the study was to evaluate physical and mechanical properties of experimental particleboard panels made from rubberwood (Hevea brasiliensis) using modified starch as binder. Panels were manufactured using 15% corn starch modified with glutardialdehyde and tested for their properties based on Japanese Standard. The modulus of rupture and the internal bond strength of the panels met the requirement of the specified standard. Based on the findings in this work modified corn starch can have a potential to be used as binder to produce particleboard panels with acceptable properties. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Rubberwood (Hevea brasiliensis) is one of the most commonly used raw materials to manufacture composite panels such as fibreboard and particleboard in Malaysia. Rubberwood originated as indigeneous species to the Amazon forest in Brazil was first introduced to South East Asia in mid 1800s [1]. In early 1990s Malaysia had a great success using rubberwood in manufacture of valueadded products and became leader in South East Asia. The rubberwood sawn timber industry in Malaysia is well developed and used such resource as efficiently as possible. Currently waste materials from furniture and lumber manufacture and low quality small logs are the main raw material for composite panel producers in Malaysia. Similar to wood composite industry in many other countries, formaldehyde based adhesives are also widely used in Malaysia. In the case of particleboard, urea formaldehyde is the most commonly used binder due to its fast curing time, clear color and low cost [2]. However one important disadvantage of such adhesive is its formaldehyde emission. The fundamental mechanism in formaldehyde emission from urea formaldehyde bonded particleboard is simply related to unreached free formaldehyde from the binder and hydrolysis of partially and completely cured adhesive. Several conditions of formaldehyde could be present such as monomeric formaldehyde entrapped between wood particles, as monomeric by hydrogen bonding of formaldehyde to the wood or as polymeric (solid) formaldehyde as well as loosely bound ⇑ Corresponding author. Fax: +60 46573678. E-mail address: [email protected] (R. Hashim). 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2013.02.020
formaldehyde which could be easily released by hydrolytic reactions [3]. Formaldehyde emission from urea formaldehyde bonded panels gained attention as a public health concern last 30 years. It is well known fact that formaldehyde causes a significant health problems as well as environmental pollution. Of course very low concentration of formaldehyde in the atmosphere does not create any problems. For example, typical formaldehyde concentration in atmosphere is generally less than 0.1 ppm [4]. In one of the preview works, free formaldehyde percentage in urea formaldehyde bonded particleboard made from different European species were found less than 0.3 ppm. Also experimental particleboards panels manufactured from pine and spruce resulted in lower formaldehyde emission than those samples made from beech [5]. Wood composite industries in many countries try to control and reduce formaldehyde emission from the wood composite panels. There maybe two approaches to achieve that, namely to modify the chemical structure of the adhesive and reduce the amount of resin in board manufacture. However, even very little reduction of adhesive in the panels can significantly influence both physical and mechanical properties of the final product. Therefore some manufacturers are also interested in development and using nonformaldehyde base adhesive in their product line to eliminate such problem. Green and environmentally friendly materials including soybean and various types of starches would have potential to produce composite panels without having problems stated above. Starch is carbohydrate materials that consist of amylase and amylopectin which could be differentiated by its chemical structure. The linear a-(1 ? 4) linked glucan is called amylase while an a-(1 ? 4) linked glucan with 4.2–5.9% a-(1 ? 6) branch linkages is amylopectin [6]. It can be obtained from various plant
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materials such as corn, potato, rice, wheat, sago and many more and widely available throughout the world commonly used in food industries. Therefore, modification of starches were well documented by many researchers [7]. Various modifications of starch were evaluated, including through oxidation, esterification, etherification and crosslinking of starch. These processes yield, for example carboxymethyl starch, dialdehyde starch, hydroyethyl starch and starch xanthate [8]. Besides for food industries application, utilization of starch in non-food industries was also investigated by researchers, especially in the biodegradable thermoplastic field [9]. Although properties of rubberwood particleboard have been investigated in various works, currently there is no information on characteristics of composite panels made from rubberwood manufatured by modified starch as binder [1,10]. Therefore the objective of the work was to manufacture experimental panels from rubberwood and modified starch, and to evaluate both physical and mechanical properties of the samples to determine if they were similar to those of commercially manufactured particleboard panels.
2. Materials and methods Commercially produced rubberwood ( H. brasiliensis) particles supplied by a local particleboard company in Negeri Sembilan, Malaysia were used to make experimental panels. The particles were dried to 2% moisture content in a laboratory type oven. Corn starch in powder form modified with glutaraldehyde in liquid form in a ratio of 1:2 (w/w) was used as binder in a ratio of 15% based oven dry particle weight. Initially corn starch powder was dissolved in distilled water with a temperature of 30 °C before it was stirred and added 25% glutardialdehyde solution. Glutardialdehyde (GDA) is a colorless oily liquid organic compound with the formula of CH2 (CH2CHO)2. It is widely used as disinfector agent for medical equipment. It has specific density ranging from 1.06 to 1.12 at 20 °C [11]. A total of 15 panels, five for each density level with dimension of 20.1 cm by 20. 1 cm by 0.5 cm was manufactured for the experiments, as shown in Table 1. Panels were made for target density levels of 0.60 g/cm3, 0.70 g/cm3 and 0.80 g/cm3. Fifteen percent modified corn starch was manually mixed with rubberwood particles before they were processed in a computer control press using a pressure of 5 MPa at a temperature of 165 °C for 20 min. Panels were conditioned in a climate chamber with a temperature of 20 °C and a relative humidity of 65% for 2 weeks. After the samples were conditioned, their modulus of elasticity (MOE), modulus of rupture (MOR), internal bond strength (IB), thickness swelling, water absorption and surface roughness were evaluated based on Japanese Industrial Standard [12]. Both bending and internal bond strength test were carried out on using Tensile Strength Tester Machine Model 5582 (INSTRON) equipped with a load cell having 1000 kg each. Crosshead speeds of 10 mm/min and 2 mm/min were used for bending strength and internal bond strength, respectively. Thickness swelling and water absorption test were carried out by soaking 50 mm 50 mm 5 mm samples in water for 2 h and 24 h. Surface roughness profile were done
on 15 samples with 3 readings taken for each samples using the Hommel Tester T500, which consists of the main unit and the pick up model TkE. The pick up has a skid type diamond stylus with 5 lm tip radius and a 90° tip angle. The stylus moves over the surface at constant speed of 1 mm/s over 15.2 mm tracing length. Vertical displacement of the stylus was converted into an electrical signal. Three roughness parameters, i.e., average roughness (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) were used for surface roughness evaluation of the samples. Specifications of these parameters were discussed in previous studies [5,13,14]. Determination of surface roughness is important as some coating materials really depend on the surface of the panels to work. Scanning electron microscopy (SEM) analysis was also carried out to see the interaction and distribution of the adhesive between the wood particles. Characterizations of chemical and thermal properties of the manufactured particleboard were done. Infra-red spectra in the range of 4000–470 cm1 of the particleboard were measured with FTIR spectrophotometer, (Nicolet, AVATAR FTIR-360), running Omnic software, to characterize the functional group inside the particleboard. To evaluate the crytallinity of the materials inside the particleboard, finely powdered samples were prepared from the IB test specimen, examined by XRD analysis using Diffraktometer D5000 Kristalloflex, Siemens. Step scan measurements were done using X-rays (Cu–Ka) at 40 kV and 40 mA. Scanning of 2h was ranging from 10.0° to 40.0° corresponding to scanning speeds of 0.02°/ min and 2°/min [15]. The crystallinity index (C Ir) was calculated using the formula:
C Irð%Þ ¼ ðI200 Iam Þ=I200 100 L¼
ð1Þ
K k b cos h
ð2Þ
where I200 is the peak intensity corresponding to crystalline and Iam is the peak intensity of the amorphous fraction. Thermal decomposition of the manufactured particleboards was done using a Metler Toledo TGA/SDTA 851 thermogravimetric analyzer, recorded from 30 °C to 800 °C for samples of 5–10 mg placed in an aluminum pan with a heating rate of 20 °C min1 under a nitrogen atmosphere [16]. Differential scanning calorimetry, (DSC) Pyris 1, Perkin Elmer was used to evaluate the thermal behaviors of the manufactured particleboards, with heating rate of 10 °C/min. About 7 mg of powdered particleboard was added to an aluminum pan and sealed. An empty, sealed aluminum pan was used as reference. Then it was heated from 10 °C to 280 °C at the respective heating rate. Melting temperature of particleboard was determined from the obtained DSC curve. 3. Results and discussion Table 2 displays test results of the samples. The highest average values of 3541 N/mm2 and 20.38 N/mm2 were found for MOE and MOR of the panels with density of 0.80 g/cm3, respectively. These values were 59.41% and 58.35% higher than those of the specimens made with 0.70 g/cm3 target density. The samples produced with 0.60 g/cm3 density level resulted in the lowest bending properties
Table 1 Experimental design. Particleboard density (g/cm3)
0.60 0.70 0.80
Number of sample Density
Thickness swelling
Water absorption
Surface roughness
Bending
Internal bond strength
30 30 30
15 15 15
15 15 15
15 15 15
15 15 15
15 15 15
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Table 2 Test results with statistical analysis of the samples. Target density (g/cm3)
Measured density (g/cm3)
Bending test (N/mm2) MOE
MOR
0.60
0.58 (0.03)a
0.70
0.69 (0.04)b
0.80
0.78 (0.07)c
1967.07 (349.50)a 2221.28 (336.44)a 3540.97 (475.22)b
9.85 (2.43)a 12.87 (2.44)b 20.38 (3.55)c
Internal bonding (N/mm2)
Thickness swelling, %
Water absorption, %
Surface roughness, lm
2h
24 h
2h
24 h
Ra
Rz
Rmax
0.62 (0.11)a
28.76 (6.75)a 34.81 (7.38)b 45.77 (7.32)b
39.087 (5.92)a 47.53 (10.64)b 60.80 (8.13)b
87.35 (8.55)a 90.02 (11.26)a 91.09 (6.37)a
106.01 (3.9)a 107.42 (8.31)a 107.58 (6.89)a
3.62 (0.97)a 3.64 (1.23)a 2.86 (1.13)b
41.69 (8.28)a 37.51 (8.63)ab 35.15 (9.13)b
50.65 (13.15)a 52.92 (11.1)a 50.3 (9.07)a
0.88 (0.21)b 1.02 (0.26)b
Values in parentheses shows standard deviation. Different letter shows significant difference between groups within the same column at a = 0.05.
Fig. 1. SEM cross sectional view of particleboard made using glutardialdehyde modified corn starch as a binder at 500 magnification with the presence of modified corn starch granules shown with arrows.
having average values of 1967 N/mm2 and 9.85 N/mm2 for MOE and MOR tests. It is well known fact that density of almost any wood composites is a major parameter influencing their bending characteristics [17]. All density levels of the panels made 15% was modified starch met JIS standard in term of their bending properties which prescribed to be at least 8.0 N/mm2. In a previous study, particleboard made from oil palm trunk particles without using any binders had 13.37 N/mm2 for their MOR [18]. It seems that using starch as binders enhanced overall bending properties of the panels as compared to those made without using any adhesive. Effect of density was also main factor on IB strength values of the samples. The panels made with 0.80 g/cm3 density had the highest IB strength value of 1.02 N/mm2 while the lowest IB value of 0.62 N/mm2 was determined from those manufactured with 0.60 g/cm3 target density. Table 2 shows statistical analysis of all tests. The MOE values from board made of 0.60 g/cm3 target density were determined was not significantly different from board made with target density of 0.70 g/cm3 panels. However, the MOE value of panels made at 0.80 g/cm3 target density were significantly different from MOE values from panels made with target density of 0.60 g/cm3 and 0.70 g/cm3. For MOR, panels from each density group were significantly different from each other. This observation support the theory of density increment will increase the bending properties of wood panels. Satisfactory bending and IB strength properties of the panels suggested that starch was mixed uniformly with particle and developed a well bonding line. Based on micrograph taken from the surface of samples it is clear that starch particles were attached to the surface of particles and resulted in a complete contact
between particles during pressing and cured as function of temperature. Fig. 1 illustrates modified corn starch granules located on the particles. Statistical analysis shown in Table 2 indicated that IB strength values of panels from 0.60 g/cm3 target density were significantly different from the panels made from other two densities group. This analysis showed the maximum IB strength could be obtained in a range of densities between 0.70 g/cm3 and 0.80 g/cm3 where higher density of panel could only slightly increased the IB strength. Starch is hydrophobic material and even if it is modified by using GDA, it still keeps such characteristic, influencing dimensional stability of the panels adversely. Both thickness swelling and water absorption of the panels were found unsatisfactorily and did not meet minimum requirement stated in the JIS standard. Thickness swelling of the samples ranged from 28.76% to 60.80% as a result of 2 and 24 h water soaking test. Substantial amount of water also ranged from 87.35% to 107.58% for the same exposure time periods. Results in Table 2 showed poor dimensional stability of the panels made in this work. For water absorption, all the density groups were not significantly different from each other. This could be explained because panels from each density absorbed almost same amount of water, in ratio to their original sample weight. The thickness swelling follows the same trend as IB strength of panels with 0.60 g/cm3 target density was significantly different from the other two densities group. Dimensional stability of the experimental particleboards and fibers is a main concern when the panels were made with starch or without any binders [19]. Such problem became more prominent in the case of starch used due to its hygroscopicity as mentioned above. However, certain treatments including heat treatment and chemical treatments could be considered to enhance thickness swelling and water absorption of the samples. Also in typical commercial panel manufacturer, around 1% wax is used to have better dimensional properties of the products. In this study, if very little amount of wax was added into the samples, particularly their poor thickness swelling and water absorption could have been improved. Panels with density levels of 0.60 g/cm3 and 0.70 g/cm3 had average roughness values of 3.62 lm and 3.64 lm, respectively. Based on statistical analysis, no significant difference was found between surface roughness values of these two types of samples. However, once their density was increased to 0.80 g/cm3 surface quality of the panels significantly improved, having 2.86 lm average value, 26.57% lower than those panels made with 0.60 g/cm3 density. It is well known fact that surface quality of particleboard increases with its increasing density due to higher densification and compaction ratios of the face layer. In another study, particleboard made with higher density also resulted in better surface quality [20]. Characterization of grounded particleboard powder using FT-IR shows presence of O–H group at wavenumber of 2928.69 cm1, that was detected from wood and starch structure. Carbonyl chromophores were detected at wavelength 1736.41 cm1 and
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A
1736.41 1646.46 2928.69
B I002 Secondary peak
Secondary peak
Iam
Fig. 2. FT-IR spectra (A) and XRD spectra (B) of glutardialdehyde modified starch particleboard sample made using glutardialdehyde modified corn starch as a binder.
1646.46 cm1, in aldehyde and ester form, respectively, as shown in Fig. 2A. These chromophores shows the presence of glutardialdehyde modified corn starch as the binder in the particleboard [21]. An XRD spectrum in Fig. 2B. shows that the powder of glutardialdehyde modified corn starch was highly amorphous. Major intensity peaks at 2h was observed near 23° related to their crystalline structure. Secondary peaks were also observed at 2h = 15° and 2h = 20.5°. The crystallinity index was calculated to quantify the crystallinity of the sample, yielded as 70.59%. Fig. 3A and B illustrate the weight loss curves (TG) and derivative thermogravimetric (DTG) profiles of the modified corn starch particleboard. A slight 6% weight loss between the 30 °C and 100 °C was due to loss of moisture from the sample. There was a
sharp decrease of weight as the sample was heated from 250 °C to 425 °C which is from 91.7% to 25.69%, a 66.01% weight decrement. This large weight loss was probably due to the thermal decomposition of hemicellulose, carbon dioxide and water [16]. The TG profile also showed that the ash content of the particleboard is lower than 18.43% as longer heating and higher temperature could increase decomposition of sample. The DTG profile showed a detail view of the analysis. The DTG shows rate of decomposition or mass loss at certain temperature [22]. Water loss is highest at 43 °C while thermal degradation of sample was at the highest rate at 360 °C, determined as 0.15 %/min. From differential scanning calorimetry analysis of manufactured particleboard samples, two exothermic peaks were found at 32 °C and 172 °C. There
M.H.M. Amini et al. / Composites: Part B 50 (2013) 259–264
A
263
4. Conclusions 100
91.7%
Weight (%)
80
60
40
25.69% 20
50 100 150 200 250 300 350 400 450 500 550 600 650 700
From the results, the highest and lowest modulus of elasticity values were determined as 3540 MPa and 1967 MPa for the panels with 0.80 g/cm3 and 0.60 g/cm3 density levels, respectively. Internal bonding strength showed the same trend, highest at 1.02 N/ mm2 for 0.80 g/cm3 panels and lowest at 0.62 N/mm2, measured from 0.6 g/cm3 panels. Thus, it can be concluded that these panels satisfied the Japanese Industrial Standard. The dimensional stability of the panels towards moisture needs to be improved by addition of water repellent materials or the manufactured particleboards should be restricted to only dry condition usage. Considering all the parameters above, glutardialdehyde modified corn starch has the possibility to be commercialized as wood binder in particleboard industry.
Temperature (°C)
B
Acknowledgement
Derivative weight (1/min)
0.00
The authors were thankful for the Ministry of Higher Education of Malaysia for the MyPhd funding to Mohd Hazim Mohamad Amini. The authors also acknowledged Universiti Sains Malaysia for the Research University Grant (1001/PTEKIND/815066) to Rokiah Hashim and Postgraduate Research Grant Scheme (1001/PTEKIND/ 844104) for Mohd Hazim Mohamad Amini. Appreciation was also given to the Heveaboard Sdn Bhd for providing the raw materials for particleboard making.
-0.05
-0.10
References
-0.15
50 100 150 200 250 300 350 400 450 500 550 600 650 700
Temperature (°C) Fig. 3. TG curve (A) and DTG curve (B) of the manufactured particleboard sample made using glutardialdehyde modified corn starch as a binder.
Heat Flow Endo Up (mW)
10
8
6
4
2
0
20
40
60
80 100 120 140 160 180 200 220 240 260 280
Temperature (°C) Fig. 4. DSC curve of glutardialdehyde modified corn starch particleboard sample made using glutardialdehyde modified corn starch as a binder.
is no specific explanation on these peaks but loss of moisture or reaction of unreacted glutardialdehyde or chemical compound could be the reason. Highest endothermic peak was found as 8.63 mW, at temperature of 92 °C, which is the melting temperature of the particleboard, as shown in Fig. 4.
[1] Teoh Y, Don M, Ujang S. Assessment of the properties, utilization, and preservation of rubberwood (Hevea brasiliensis): a case study in Malaysia. J Wood Sci 2011;57(4):255–66. [2] Pizzi A. Urea-formaldehyde adhesives. In: Pizzi A, Mittal KL, editors. Handbook of adhesive technology. New York: Taylor & Francis Group, LLC; 2003 [Revised and expanded]. [3] Que Z, Furuno T, Katoh S, Nishino Y. Effects of urea-formaldehyde resin mole ratio on the properties of particleboard. Build Environ 2007;42(3):1257–63. [4] Markessini E. Formaldehyde emission from wood-based panels and ways to reduce them. Monument Environ 2004;2:57–64. [5] Akbulut T, Hiziroglu S, Ayrilmis N. Surface absorption, surface roughness, and formaldehyde emission of Turkish MDF. Forest Prod J 2000;50(6):45–8. [6] Robyt JF. Starch: structure, properties, chemistry and enzymology. In: FraserReid OB, Tatsuta K, Thiem J, editors. Glycoscience chemistry and chemical biology. Berlin (Heidelberg, New York): Springer-Verlag; 2008. p. 2866. [7] Verwimp T, Vandeputte GE, Marrant K, Delcour JA. Isolation and characterisation of rye starch. J Cereal Sci 2004;39(1):85–90. [8] Tharanathan RN. Starch—value addition by modification. Crit Rev Food Sci Nutr 2005;45(5):371–84. [9] Thiré RMSM. Starch-based plastics. In: Bertolini AC, editor. Starches : characterization, properties, and applications. Boca Raton, FL: CRC; 2010. [10] Hong LT, Sim HC, Institute FR, Rubberwood processing and utilisation1999: Forest Research Institute of Malaysia. [11] Lenga RE. The sigma-aldrich library of chemical safety data. vol. 2. United Kingdom: Sigma-Aldrich Corporation; 1988. p. 2175. [12] JIS A 5908. Particleboards, Japanese standards association: Tokyo, Japan; 2003. [13] American National Standards Institute. Surface texture: surface roughness, waviness, and lay : ASME B46.1-1995 (revision of ANSI/ASME B46.1-1985). New York. American Society of Mechanical Engineers; 1995. p. 43. [14] American National Standards Institute. Medium density fiberboard (MDF) for interior applications. Premiere Ct. Gaithersburg, MD: Composite Panel Association; 2009. [15] Hermawan D, Hata T, Kawai S, Nagadomi W, Kuroki Y. Manufacturing oil palm fronds cement-bonded board cured by gaseous or supercritical carbon dioxide. J Wood Sci 2002;48(1):20–4. [16] Baskaran M, Hashim R, Said N, Raffi SM, Balakrishnan K, Sudesh K, et al. Properties of binderless particleboard from oil palm trunk with addition of polyhydroxyalkanoates. Compos Part B: Eng 2011. [17] Wong ED, Zhang M, Wang Q, Kawai S. Formation of the density profile and its effects on the properties of particleboard. Wood Sci Technol 1999;33(4): 327–40. [18] Hashim R, Nadhari WNAW, Sulaiman O, Kawamura F, Hiziroglu S, Sato M, et al. Characterization of raw materials and manufactured binderless particleboard from oil palm biomass. Mater Des 2011;32(1):246–54. [19] Ayoub AS, Rizvi SSH. An overview on the technology of cross-linking of starch for nonfood applications. J Plast Film Sheet 2009;25(1):25–45.
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[20] Hiziroglu S, Kosonkorn P. Evaluation of surface roughness of Thai medium density fiberboard (MDF). Build Environ 2006;41(4):527–33. [21] Wade LG. Organic chemistry. 6th ed. New Jersey: Pearson Education Inc.; 2006. p. 1330.
[22] Hermawan D, Hata T, Umemura K, Kawai S, Nagadomi W, Kuroki Y. Rapid production of high-strength cement-bonded particleboard using gaseous or supercritical carbon dioxide. J Wood Sci 2001;47(4):294–300.
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Properties of particleboard made from rubberwood using modified starch as binder Mohd Hazim Mohamad Amini a, Rokiah Hashim a,⇑, Salim Hiziroglu b, Nurul Syuhada Sulaiman a, Othman Sulaiman a a b
Division of Bio-resource, Paper and Coatings Technology, School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia Department of Natural Resource Ecology & Management, 303G Agricultural Hall, Okhahoma State University, Stillwater, OK 74078-6013, USA
a r t i c l e
i n f o
Article history: Received 11 April 2012 Received in revised form 8 November 2012 Accepted 24 February 2013 Available online 4 March 2013 Keywords: A. Wood D. Mechanical testing D. Surface analysis
a b s t r a c t The objective of the study was to evaluate physical and mechanical properties of experimental particleboard panels made from rubberwood (Hevea brasiliensis) using modified starch as binder. Panels were manufactured using 15% corn starch modified with glutardialdehyde and tested for their properties based on Japanese Standard. The modulus of rupture and the internal bond strength of the panels met the requirement of the specified standard. Based on the findings in this work modified corn starch can have a potential to be used as binder to produce particleboard panels with acceptable properties. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Rubberwood (Hevea brasiliensis) is one of the most commonly used raw materials to manufacture composite panels such as fibreboard and particleboard in Malaysia. Rubberwood originated as indigeneous species to the Amazon forest in Brazil was first introduced to South East Asia in mid 1800s [1]. In early 1990s Malaysia had a great success using rubberwood in manufacture of valueadded products and became leader in South East Asia. The rubberwood sawn timber industry in Malaysia is well developed and used such resource as efficiently as possible. Currently waste materials from furniture and lumber manufacture and low quality small logs are the main raw material for composite panel producers in Malaysia. Similar to wood composite industry in many other countries, formaldehyde based adhesives are also widely used in Malaysia. In the case of particleboard, urea formaldehyde is the most commonly used binder due to its fast curing time, clear color and low cost [2]. However one important disadvantage of such adhesive is its formaldehyde emission. The fundamental mechanism in formaldehyde emission from urea formaldehyde bonded particleboard is simply related to unreached free formaldehyde from the binder and hydrolysis of partially and completely cured adhesive. Several conditions of formaldehyde could be present such as monomeric formaldehyde entrapped between wood particles, as monomeric by hydrogen bonding of formaldehyde to the wood or as polymeric (solid) formaldehyde as well as loosely bound ⇑ Corresponding author. Fax: +60 46573678. E-mail address: [email protected] (R. Hashim). 1359-8368/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2013.02.020
formaldehyde which could be easily released by hydrolytic reactions [3]. Formaldehyde emission from urea formaldehyde bonded panels gained attention as a public health concern last 30 years. It is well known fact that formaldehyde causes a significant health problems as well as environmental pollution. Of course very low concentration of formaldehyde in the atmosphere does not create any problems. For example, typical formaldehyde concentration in atmosphere is generally less than 0.1 ppm [4]. In one of the preview works, free formaldehyde percentage in urea formaldehyde bonded particleboard made from different European species were found less than 0.3 ppm. Also experimental particleboards panels manufactured from pine and spruce resulted in lower formaldehyde emission than those samples made from beech [5]. Wood composite industries in many countries try to control and reduce formaldehyde emission from the wood composite panels. There maybe two approaches to achieve that, namely to modify the chemical structure of the adhesive and reduce the amount of resin in board manufacture. However, even very little reduction of adhesive in the panels can significantly influence both physical and mechanical properties of the final product. Therefore some manufacturers are also interested in development and using nonformaldehyde base adhesive in their product line to eliminate such problem. Green and environmentally friendly materials including soybean and various types of starches would have potential to produce composite panels without having problems stated above. Starch is carbohydrate materials that consist of amylase and amylopectin which could be differentiated by its chemical structure. The linear a-(1 ? 4) linked glucan is called amylase while an a-(1 ? 4) linked glucan with 4.2–5.9% a-(1 ? 6) branch linkages is amylopectin [6]. It can be obtained from various plant
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M.H.M. Amini et al. / Composites: Part B 50 (2013) 259–264
materials such as corn, potato, rice, wheat, sago and many more and widely available throughout the world commonly used in food industries. Therefore, modification of starches were well documented by many researchers [7]. Various modifications of starch were evaluated, including through oxidation, esterification, etherification and crosslinking of starch. These processes yield, for example carboxymethyl starch, dialdehyde starch, hydroyethyl starch and starch xanthate [8]. Besides for food industries application, utilization of starch in non-food industries was also investigated by researchers, especially in the biodegradable thermoplastic field [9]. Although properties of rubberwood particleboard have been investigated in various works, currently there is no information on characteristics of composite panels made from rubberwood manufatured by modified starch as binder [1,10]. Therefore the objective of the work was to manufacture experimental panels from rubberwood and modified starch, and to evaluate both physical and mechanical properties of the samples to determine if they were similar to those of commercially manufactured particleboard panels.
2. Materials and methods Commercially produced rubberwood ( H. brasiliensis) particles supplied by a local particleboard company in Negeri Sembilan, Malaysia were used to make experimental panels. The particles were dried to 2% moisture content in a laboratory type oven. Corn starch in powder form modified with glutaraldehyde in liquid form in a ratio of 1:2 (w/w) was used as binder in a ratio of 15% based oven dry particle weight. Initially corn starch powder was dissolved in distilled water with a temperature of 30 °C before it was stirred and added 25% glutardialdehyde solution. Glutardialdehyde (GDA) is a colorless oily liquid organic compound with the formula of CH2 (CH2CHO)2. It is widely used as disinfector agent for medical equipment. It has specific density ranging from 1.06 to 1.12 at 20 °C [11]. A total of 15 panels, five for each density level with dimension of 20.1 cm by 20. 1 cm by 0.5 cm was manufactured for the experiments, as shown in Table 1. Panels were made for target density levels of 0.60 g/cm3, 0.70 g/cm3 and 0.80 g/cm3. Fifteen percent modified corn starch was manually mixed with rubberwood particles before they were processed in a computer control press using a pressure of 5 MPa at a temperature of 165 °C for 20 min. Panels were conditioned in a climate chamber with a temperature of 20 °C and a relative humidity of 65% for 2 weeks. After the samples were conditioned, their modulus of elasticity (MOE), modulus of rupture (MOR), internal bond strength (IB), thickness swelling, water absorption and surface roughness were evaluated based on Japanese Industrial Standard [12]. Both bending and internal bond strength test were carried out on using Tensile Strength Tester Machine Model 5582 (INSTRON) equipped with a load cell having 1000 kg each. Crosshead speeds of 10 mm/min and 2 mm/min were used for bending strength and internal bond strength, respectively. Thickness swelling and water absorption test were carried out by soaking 50 mm 50 mm 5 mm samples in water for 2 h and 24 h. Surface roughness profile were done
on 15 samples with 3 readings taken for each samples using the Hommel Tester T500, which consists of the main unit and the pick up model TkE. The pick up has a skid type diamond stylus with 5 lm tip radius and a 90° tip angle. The stylus moves over the surface at constant speed of 1 mm/s over 15.2 mm tracing length. Vertical displacement of the stylus was converted into an electrical signal. Three roughness parameters, i.e., average roughness (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) were used for surface roughness evaluation of the samples. Specifications of these parameters were discussed in previous studies [5,13,14]. Determination of surface roughness is important as some coating materials really depend on the surface of the panels to work. Scanning electron microscopy (SEM) analysis was also carried out to see the interaction and distribution of the adhesive between the wood particles. Characterizations of chemical and thermal properties of the manufactured particleboard were done. Infra-red spectra in the range of 4000–470 cm1 of the particleboard were measured with FTIR spectrophotometer, (Nicolet, AVATAR FTIR-360), running Omnic software, to characterize the functional group inside the particleboard. To evaluate the crytallinity of the materials inside the particleboard, finely powdered samples were prepared from the IB test specimen, examined by XRD analysis using Diffraktometer D5000 Kristalloflex, Siemens. Step scan measurements were done using X-rays (Cu–Ka) at 40 kV and 40 mA. Scanning of 2h was ranging from 10.0° to 40.0° corresponding to scanning speeds of 0.02°/ min and 2°/min [15]. The crystallinity index (C Ir) was calculated using the formula:
C Irð%Þ ¼ ðI200 Iam Þ=I200 100 L¼
ð1Þ
K k b cos h
ð2Þ
where I200 is the peak intensity corresponding to crystalline and Iam is the peak intensity of the amorphous fraction. Thermal decomposition of the manufactured particleboards was done using a Metler Toledo TGA/SDTA 851 thermogravimetric analyzer, recorded from 30 °C to 800 °C for samples of 5–10 mg placed in an aluminum pan with a heating rate of 20 °C min1 under a nitrogen atmosphere [16]. Differential scanning calorimetry, (DSC) Pyris 1, Perkin Elmer was used to evaluate the thermal behaviors of the manufactured particleboards, with heating rate of 10 °C/min. About 7 mg of powdered particleboard was added to an aluminum pan and sealed. An empty, sealed aluminum pan was used as reference. Then it was heated from 10 °C to 280 °C at the respective heating rate. Melting temperature of particleboard was determined from the obtained DSC curve. 3. Results and discussion Table 2 displays test results of the samples. The highest average values of 3541 N/mm2 and 20.38 N/mm2 were found for MOE and MOR of the panels with density of 0.80 g/cm3, respectively. These values were 59.41% and 58.35% higher than those of the specimens made with 0.70 g/cm3 target density. The samples produced with 0.60 g/cm3 density level resulted in the lowest bending properties
Table 1 Experimental design. Particleboard density (g/cm3)
0.60 0.70 0.80
Number of sample Density
Thickness swelling
Water absorption
Surface roughness
Bending
Internal bond strength
30 30 30
15 15 15
15 15 15
15 15 15
15 15 15
15 15 15
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Table 2 Test results with statistical analysis of the samples. Target density (g/cm3)
Measured density (g/cm3)
Bending test (N/mm2) MOE
MOR
0.60
0.58 (0.03)a
0.70
0.69 (0.04)b
0.80
0.78 (0.07)c
1967.07 (349.50)a 2221.28 (336.44)a 3540.97 (475.22)b
9.85 (2.43)a 12.87 (2.44)b 20.38 (3.55)c
Internal bonding (N/mm2)
Thickness swelling, %
Water absorption, %
Surface roughness, lm
2h
24 h
2h
24 h
Ra
Rz
Rmax
0.62 (0.11)a
28.76 (6.75)a 34.81 (7.38)b 45.77 (7.32)b
39.087 (5.92)a 47.53 (10.64)b 60.80 (8.13)b
87.35 (8.55)a 90.02 (11.26)a 91.09 (6.37)a
106.01 (3.9)a 107.42 (8.31)a 107.58 (6.89)a
3.62 (0.97)a 3.64 (1.23)a 2.86 (1.13)b
41.69 (8.28)a 37.51 (8.63)ab 35.15 (9.13)b
50.65 (13.15)a 52.92 (11.1)a 50.3 (9.07)a
0.88 (0.21)b 1.02 (0.26)b
Values in parentheses shows standard deviation. Different letter shows significant difference between groups within the same column at a = 0.05.
Fig. 1. SEM cross sectional view of particleboard made using glutardialdehyde modified corn starch as a binder at 500 magnification with the presence of modified corn starch granules shown with arrows.
having average values of 1967 N/mm2 and 9.85 N/mm2 for MOE and MOR tests. It is well known fact that density of almost any wood composites is a major parameter influencing their bending characteristics [17]. All density levels of the panels made 15% was modified starch met JIS standard in term of their bending properties which prescribed to be at least 8.0 N/mm2. In a previous study, particleboard made from oil palm trunk particles without using any binders had 13.37 N/mm2 for their MOR [18]. It seems that using starch as binders enhanced overall bending properties of the panels as compared to those made without using any adhesive. Effect of density was also main factor on IB strength values of the samples. The panels made with 0.80 g/cm3 density had the highest IB strength value of 1.02 N/mm2 while the lowest IB value of 0.62 N/mm2 was determined from those manufactured with 0.60 g/cm3 target density. Table 2 shows statistical analysis of all tests. The MOE values from board made of 0.60 g/cm3 target density were determined was not significantly different from board made with target density of 0.70 g/cm3 panels. However, the MOE value of panels made at 0.80 g/cm3 target density were significantly different from MOE values from panels made with target density of 0.60 g/cm3 and 0.70 g/cm3. For MOR, panels from each density group were significantly different from each other. This observation support the theory of density increment will increase the bending properties of wood panels. Satisfactory bending and IB strength properties of the panels suggested that starch was mixed uniformly with particle and developed a well bonding line. Based on micrograph taken from the surface of samples it is clear that starch particles were attached to the surface of particles and resulted in a complete contact
between particles during pressing and cured as function of temperature. Fig. 1 illustrates modified corn starch granules located on the particles. Statistical analysis shown in Table 2 indicated that IB strength values of panels from 0.60 g/cm3 target density were significantly different from the panels made from other two densities group. This analysis showed the maximum IB strength could be obtained in a range of densities between 0.70 g/cm3 and 0.80 g/cm3 where higher density of panel could only slightly increased the IB strength. Starch is hydrophobic material and even if it is modified by using GDA, it still keeps such characteristic, influencing dimensional stability of the panels adversely. Both thickness swelling and water absorption of the panels were found unsatisfactorily and did not meet minimum requirement stated in the JIS standard. Thickness swelling of the samples ranged from 28.76% to 60.80% as a result of 2 and 24 h water soaking test. Substantial amount of water also ranged from 87.35% to 107.58% for the same exposure time periods. Results in Table 2 showed poor dimensional stability of the panels made in this work. For water absorption, all the density groups were not significantly different from each other. This could be explained because panels from each density absorbed almost same amount of water, in ratio to their original sample weight. The thickness swelling follows the same trend as IB strength of panels with 0.60 g/cm3 target density was significantly different from the other two densities group. Dimensional stability of the experimental particleboards and fibers is a main concern when the panels were made with starch or without any binders [19]. Such problem became more prominent in the case of starch used due to its hygroscopicity as mentioned above. However, certain treatments including heat treatment and chemical treatments could be considered to enhance thickness swelling and water absorption of the samples. Also in typical commercial panel manufacturer, around 1% wax is used to have better dimensional properties of the products. In this study, if very little amount of wax was added into the samples, particularly their poor thickness swelling and water absorption could have been improved. Panels with density levels of 0.60 g/cm3 and 0.70 g/cm3 had average roughness values of 3.62 lm and 3.64 lm, respectively. Based on statistical analysis, no significant difference was found between surface roughness values of these two types of samples. However, once their density was increased to 0.80 g/cm3 surface quality of the panels significantly improved, having 2.86 lm average value, 26.57% lower than those panels made with 0.60 g/cm3 density. It is well known fact that surface quality of particleboard increases with its increasing density due to higher densification and compaction ratios of the face layer. In another study, particleboard made with higher density also resulted in better surface quality [20]. Characterization of grounded particleboard powder using FT-IR shows presence of O–H group at wavenumber of 2928.69 cm1, that was detected from wood and starch structure. Carbonyl chromophores were detected at wavelength 1736.41 cm1 and
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A
1736.41 1646.46 2928.69
B I002 Secondary peak
Secondary peak
Iam
Fig. 2. FT-IR spectra (A) and XRD spectra (B) of glutardialdehyde modified starch particleboard sample made using glutardialdehyde modified corn starch as a binder.
1646.46 cm1, in aldehyde and ester form, respectively, as shown in Fig. 2A. These chromophores shows the presence of glutardialdehyde modified corn starch as the binder in the particleboard [21]. An XRD spectrum in Fig. 2B. shows that the powder of glutardialdehyde modified corn starch was highly amorphous. Major intensity peaks at 2h was observed near 23° related to their crystalline structure. Secondary peaks were also observed at 2h = 15° and 2h = 20.5°. The crystallinity index was calculated to quantify the crystallinity of the sample, yielded as 70.59%. Fig. 3A and B illustrate the weight loss curves (TG) and derivative thermogravimetric (DTG) profiles of the modified corn starch particleboard. A slight 6% weight loss between the 30 °C and 100 °C was due to loss of moisture from the sample. There was a
sharp decrease of weight as the sample was heated from 250 °C to 425 °C which is from 91.7% to 25.69%, a 66.01% weight decrement. This large weight loss was probably due to the thermal decomposition of hemicellulose, carbon dioxide and water [16]. The TG profile also showed that the ash content of the particleboard is lower than 18.43% as longer heating and higher temperature could increase decomposition of sample. The DTG profile showed a detail view of the analysis. The DTG shows rate of decomposition or mass loss at certain temperature [22]. Water loss is highest at 43 °C while thermal degradation of sample was at the highest rate at 360 °C, determined as 0.15 %/min. From differential scanning calorimetry analysis of manufactured particleboard samples, two exothermic peaks were found at 32 °C and 172 °C. There
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A
263
4. Conclusions 100
91.7%
Weight (%)
80
60
40
25.69% 20
50 100 150 200 250 300 350 400 450 500 550 600 650 700
From the results, the highest and lowest modulus of elasticity values were determined as 3540 MPa and 1967 MPa for the panels with 0.80 g/cm3 and 0.60 g/cm3 density levels, respectively. Internal bonding strength showed the same trend, highest at 1.02 N/ mm2 for 0.80 g/cm3 panels and lowest at 0.62 N/mm2, measured from 0.6 g/cm3 panels. Thus, it can be concluded that these panels satisfied the Japanese Industrial Standard. The dimensional stability of the panels towards moisture needs to be improved by addition of water repellent materials or the manufactured particleboards should be restricted to only dry condition usage. Considering all the parameters above, glutardialdehyde modified corn starch has the possibility to be commercialized as wood binder in particleboard industry.
Temperature (°C)
B
Acknowledgement
Derivative weight (1/min)
0.00
The authors were thankful for the Ministry of Higher Education of Malaysia for the MyPhd funding to Mohd Hazim Mohamad Amini. The authors also acknowledged Universiti Sains Malaysia for the Research University Grant (1001/PTEKIND/815066) to Rokiah Hashim and Postgraduate Research Grant Scheme (1001/PTEKIND/ 844104) for Mohd Hazim Mohamad Amini. Appreciation was also given to the Heveaboard Sdn Bhd for providing the raw materials for particleboard making.
-0.05
-0.10
References
-0.15
50 100 150 200 250 300 350 400 450 500 550 600 650 700
Temperature (°C) Fig. 3. TG curve (A) and DTG curve (B) of the manufactured particleboard sample made using glutardialdehyde modified corn starch as a binder.
Heat Flow Endo Up (mW)
10
8
6
4
2
0
20
40
60
80 100 120 140 160 180 200 220 240 260 280
Temperature (°C) Fig. 4. DSC curve of glutardialdehyde modified corn starch particleboard sample made using glutardialdehyde modified corn starch as a binder.
is no specific explanation on these peaks but loss of moisture or reaction of unreacted glutardialdehyde or chemical compound could be the reason. Highest endothermic peak was found as 8.63 mW, at temperature of 92 °C, which is the melting temperature of the particleboard, as shown in Fig. 4.
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