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Evaluation of surface roughness and mechanical properties of particleboard panels made from bagasse
Composites: Part B 42 (2011) 1330–1335
Contents lists available at ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Evaluation of surface roughness and mechanical properties of particleboard panels made from bagasse Taghi Tabarsa a, Alireza Ashori b,⇑, Maria Gholamzadeh a a b
Department of Wood and Paper Technology, Gorgan University of Agricultural Sciences & Natural Resources (GUASNR), Gorgan, Iran Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran
a r t i c l e
i n f o
Article history: Received 21 October 2010 Received in revised form 17 December 2010 Accepted 21 December 2010 Available online 30 December 2010 Keywords: A. Wood A. Resins B. Mechanical properties B. Surface properties
a b s t r a c t The main objective of this study is to investigate some of applied properties of experimental particleboard panels made with bagasse, as an alternative fibrous raw material. Modulus of elasticity (MOE), modulus of rupture (MOR), internal bond strength (IB) and thickness swelling (TS) of the specimens were evaluated. In addition, average roughness (Ra) and mean peak-to-valley height (Rz) were used to determine quantitatively surface characteristics of the panels. Three-layer mats with target density of 0.70 g/ cm3 were formed by using fine chips for the face layer (25 wt.%) and coarse chips for the core layer (50 wt.%). Variable factors were as wood species (bagasse, poplar and mixed hardwood species), moisture content of mat (face layer: 12%, 14% and core layer: 9%, 11%) and press time (6 and 8 min). Statistical analysis showed that all variable factors exerted a significant influence on MOR, MOE, IB, TS, Rz properties of the boards as a single factor. Panels made with bagasse particles had superior mechanical and physical properties compared to the poplar and mixed hardwoods particles. Bagasse boards exhibited better surface roughness, having lower Ra and Rz values, than those made with poplar and mixed hardwoods particles. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The demand for composite wood products, such as plywood, oriented strandboard (OSB), hardboard, particleboard, mediumdensity fiberboard, and veneer board products has recently increased substantially throughout the world [1]. Particleboard is 57% of total consumption of wood-based panels consumed and it is continuously growing at 2–5% annually [2]. The demand for particleboards in the sectors of housing construction, furniture manufacturing and interior decoration (wall and ceiling paneling) has continued to increase [3]. On the other hand, accelerated deforestation and forest degradation, in addition to a growing demand for wood-based boards, have raised an important issue regarding the sustained supply of raw material to the above sectors for a long time. As a result of these concerns, alternative fibers could play an important role in manufacture of composite panels such as particleboard [4]. There is a wide variety of non-wood plants (such as kenaf stalks [5], wheat straw and corn pith [6], cotton carpel [7] and cotton stalks and rice straw [8]) and agro-residues (such as coffee husk and hulls [9], kiwi prunings [10], waste grass clippings [11], branch wood and bark [12], waste tea leaves [13], almond shell [14], flax shiv [15] and durian peel and coconut coir [16]) that can be used as alternative fibers. ⇑ Corresponding author. Tel./fax: +98 21 88838337. E-mail address: [email protected] (A. Ashori). 1359-8368/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2010.12.018
Among many agro-residues, bagasse is one of the most promising and suitable raw material for both developing and developed countries [2]. Bagasse, an abundant agricultural lignocellulosic byproduct is a fibrous residue of sugarcane stalks left over after crushing and extraction process of the juice from sugarcane. About 54 million dry tons of bagasse is produced annually throughout the world [17]. Asia is the primary production region of sugar cane (45%), while South America is the second largest production region (35%) in the world. According to a report from Food and Agricultural Organization (FAO), Iran produces 5.3 million tons of bagasse annually [18] which is mainly centered in the southwestern province, namely Khuzestan. The utilization of this biomass for processing of novel wood-based composites has attracted growing interest because of ecological and renewable nature characteristic. The use of very thin overlays such as melamine impregnated papers, veneers, laminates, and vinyl films, on particleboard substrates has forced increasing attention to surface quality. When particleboard is used as substrate for surface coating, its particleboard surfaces must be capable of having resistance stresses to peeling. Fine irregularities on the board surface shows through overlays, affecting the product grade, quality, finishing, and gluing. Because films tend to be thin, they do not have good masking properties, and any imperfections in the board surface can telegraph through the film finish. The rough surfaces reduce the contact between the overlays and particleboard, resulting in a weak glue line and low bonding strength properties of the layers [19].
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Roughness is a measure of the fine irregularities on a surface. The degree of surface roughness is a function of both raw material properties and manufacturing variables [20]. Surface characteristics of particles are affected by the cutting tool geometry, crushing conditions during the cutting and anatomical structure of wood. The roughness of individual anatomical elements is also created by a variety of voids in tracheids and fibers. Hızırog˘lu and Suchsland [21] stated that high particle compaction and fine screen particles produced high surface quality. It was reported that board density had an effect on surface smoothness of hardboard samples. Boards with a densified face layer had smoother surfaces. It was found that wood species used in board manufacture affected the surface roughness [19]. The initial objective of this study is to evaluate the potential of bagasse as an alternative raw material for panel manufacture and to determine if the properties of such panels are similar to those made from other species. Moreover, the effects of wood species, press time and moisture content of the mat on the physical and mechanical properties of panels produced have been investigated. Currently, there is very little information about surface roughness of commercially produced particleboard in Iran. Therefore another objective of this work is to evaluate surface roughness of the boards. 2. Experimental 2.1. Materials The fibrous raw materials for this study were bagasse (B), poplar (P) and mixed hardwood (MH) species (such as oak, beech and hornbeam). The specimens were chipped and then classified into coarse and fine chips which passed through 20 and 40 meshes, respectively. The particles were dried at 103 ± 2 °C to certain moisture contents for the face (12% and 14%) and core (9% and 11%) layers. The adhesive was urea–formaldehyde (UF) which was produced by a local plant. The characteristics of the UF adhesive are given in Table 1.
Table 2 Treatment conditions for panel production. Board type
Mat MC (%)
Press time (min)
Species
Code
Face layer
Core layer
B
1 2 3 4
12 12 14 14
9 9 11 11
6 8 6 8
P
1 2 3 4
12 12 14 14
9 9 11 11
6 8 6 8
MH
4
14
11
8
constant. All panels were not sanded and no wax or any other hydrophobic substance was applied. Four panels were produced for each treatment. 2.3. Mechanical and physical testing After pressing, panels were conditioned to constant mass in an atmosphere of 65% relative humidity and at a temperature of 23 °C. Then, test samples were cut from the panels and the following mechanical properties were determined in accordance with appropriate European Union (EN) Standards: modulus of rupture (MOR) and modulus of elasticity (MOE) [22] and internal bond (IB) strength [23]. Physical properties, namely thickness swelling (TS) and surface roughness were also evaluated based on EN 317 [24]. The TS samples were submerged in distilled water for 2 h and 24 h period of time. A Rank Taylor Hobson Form Talysurf stylus instrument was employed for the surface roughness measurements. Two roughness parameters, average roughness (Ra) and mean peak-to-valley height (Rz) were used to evaluate surface roughness of the samples according to DIN 4768 [25]. Ten replicates were used for each treatment. 2.4. Statistical analysis
2.2. Production of panels Particleboard panels were manufactured in the Department of Wood and Paper Technology, GUASNR, Iran, using standardized procedures that simulated industrial production. The boards were formed using fine particles for the face layer and coarse particles for the core layer. The weight ratio of the face/core/face layers was set at 1:2:1. Dried particles were blended with UF resin in a rotating drum-type mixer fitted with a pneumatic spray gun. As can be shown in Table 2, three variable factors were wood species, mat moisture (face layer: 12%, 14% and core layer: 9%, 11%) and press time (6 and 8 min). Other parameters such as type of resin (UF), resin content (face layer: 11% and core layer: 9%), type of hardener (NH4Cl), hardener content (1%), press closing rate (5 mm/s), target density (0.7 g/cm3), press pressure (25 kg/cm2), panel thickness (16 mm) and press temperature (170 °C) were held
Table 1 Characteristics of UF adhesive used. Characteristics Formaldehyde/urea mole ratio Solid content, % Density, g/cm3 Viscosity, cps Gel time, s pH
1.2 63 1.27 60 40 7
Data for each test were statistically analyzed. Analysis of variance (ANOVA) and t-test were used to test the significant difference between factors and levels. 3. Results and discussion 3.1. Mechanical properties 3.1.1. MOR and MOE The data obtained in this research showed that the effects of all variables on mechanical properties in terms of MOR, MOE and IB were significant (Table 3). In addition, Fig. 1a illustrates improved MOR and MOE properties with increasing press time and moisture content of the mat. In general, boards made with bagasse exhibited superior mechanical properties compared to the poplar and mixed hardwood particles. For example, the maximum values of the MOR and MOE were 20.5 MPa and 2.12 GPa for bagasse, respectively, while the values for poplar were 13.2 MPa and 1.98 GPa, respectively. Salehi [26] mentioned that using of light species improve mechanical properties of wood composites due to high compaction ratio. Based on European Norms (EN), 11.5 MPa and 1.600 GPa are the minimum requirements for MOR and MOE of particleboard panels for general uses, respectively [27,28]. As it can be seen in Fig. 1a, all panels produced met the minimum MOR and MOE requirement of EN standards for general purposes. It is to be noted
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ior may be due to the high compaction of bagasse furnish which caused faster heat transfer to the core layer resulted more curing of resin. According to the statistical analysis results, moisture content of the mat negatively affected the internal bond strength of the panels. The moisture cannot be sufficiently evaporated from the mats at higher moisture content. This situation impedes the hardening of the adhesive in the core layer. For this reason, the contact between core layer particles decreases and water absorption to the pores between the particles increases. Similar results were reported by Nemli et al. [19] and Tabarsa and Movahedi [29]. The minimal requirement of IB strength for general purpose [27] and interior fitments [28] are 0.24 and 0.35 MPa, respectively. Based on the results, all boards produced in this work showed properties that are higher than the EN requirements. The IB and MOE values of the panels showed a similar tendency. According to the ANOVA test, all variable factors exerted a significant influence (p 6 0.01%) on TS, MOR and MOE properties of the boards as a single factor. While statistical analysis did not show an interaction between the variables factors.
Table 3 Statistical analysis of mechanical and physical properties of the boards produced with different variables. Parameters
MOR
MOE
IB
TS
Ra
1 2 3 12 13 23 123
Rz
NS
NS
NS NS NS
NS NS NS
NS NS NS
NS NS NS
NS NS
NS
Note: 1 = wood species, 2 = Mat MC, 3 = press time, TS 2 h. = Significant difference at the 1% level (p 6 0.01%). = Significant difference at the 5% level (p 6 0.05%), and NS = Not significant.
that, panels B and P which were made with treatment 4 had the highest values among the other types of treatments. In other words, all mechanical properties of the panels were improved when the press time was increased from 6 to 8 min, which clearly shows that at 6 min press time sufficient heat is not transferred to the core section of the mat. Besides, higher mat moisture gradient between face and core layer (treatment 4) improved heat transfer and resulted enhancing mechanical properties. This result supports the conclusions reached by Nemli et al. [19], that the fine particles and wood dust usages decrease the modulus of rupture, and modulus of elasticity due to the low amount of woody cells and short fibers.
3.2. Physical properties 3.2.1. TS The poor absorption resistance of the cellulosic material is mainly due to the presence of polar groups, which attract water molecules through hydrogen bonding. This phenomenon leads to a moisture build-up in the fiber cell wall (fiber swelling) and also in the fiber–adhesive interface. This is responsible for the changes in the dimension of wood-based panel composites; as a consequence, the outdoor applications will be greatly affected. Particleboard should have a maximum thickness swelling value of 8% and 15% for 2 h and 24 h immersion. The TS values of bagasse specimens for the 2 h water immersion vary from 15.1% to 18.1%, and these values are increased after 24 h immersion, varying from 22.6% to 24.5%. As shown clearly in Fig. 2, the TS values of boards
3.1.2. IB Statistical analysis of data showed that the effects of various treatments on IB of all experimental boards were significant (Table 3). Like MOR and MOE, boards made with bagasse particles showed higher IB than those made from poplar and mixed hardwood particles (Fig. 1b). The possible reason proposed for this kind of behav-
MOR (MPa)
20
2.5
(a)
MOR MOE
15
1.5
10
1.0
5
0.5
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
Board type 0.48 0.40
IB (MPa)
2.0
(b)
0.32 0.24 0.16 0.08 0.00
B1
B2
B3
B4
P1
P2
P3
P4
Board type Fig. 1. Effects of board types on the mechanical properties.
MH
0.0
MOE (GPa)
25
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36 2h
TS 2 h (%)
30
24 h
30
24
24
18
18
12
12
6
6
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
TS 24 h (%)
36
0
Board type Fig. 2. Effects of board types on the thickness swelling.
longer time, some particles in vertical position may return to horizontal position and surface layers were densified [19]. Panels showed a definitive relationship between the moisture content of the mat and surface roughness. With increasing the moisture of the mat from 12% to 14% improved the surface quality significantly. This is due to tight structure on the surfaces due to the close pressing of the particles at 14% moisture. Because high moisture causes steam bubbles on the surface layers, smoothness decreased with increasing the moisture content of the mat above 12%. Average surface roughness (Ra) and mean peak-to-valley height (Rz) are two most important parameters for evaluation of surface roughness. Both mentioned parameters (Ra and Rz) of bagasse boards are lower than those made with poplar and mixed hardwoods particles. Type B4 had an average Ra value of 12.3 lm with the smoothest surface while mixed hardwoods had the roughest one with an average Ra value of 91.4 lm among the nine types of panels (Fig. 3). A typical commercially manufactured particleboard could have Ra values ranging from 3 to 6 lm [31]. Therefore, roughness measurement of the samples suggest that surface quality of all the panels was found to be very rough and not ideal for overlaying applications as substrate without any sanding process. However, if the panels were sanded with a sequence of 150, 180, and 220 grit sandpaper, their surface roughness could have been improved and such panels would be used as substrate for these overlays without any problems [32]. Although Ra and Rz are considered the major roughness parameters to evaluate the characteristics of a surface, the irregularities profile should also be determined to have a better understand of a surface. The irregularities of the surface are visualized in Fig. 4. A comparison of the mean line profile curves illustrated that the irregularities of the board type B4 is much uniform than MH. It
increase with increase in water exposure time and all boards could not pass the required level of thickness swelling for general uses. The samples with codes 2 and 4 had the lowest TS compared to all boards. It was found that TS properties improved with increasing press time (p < 0.05). However, all treatments (wood species, moisture content of the mat and press time) affected TS properties, significantly. Nemli et al. [19] reported that fine particles fill the pores between the coarse particles in the core layer. Consequently contacts between the blended particles increase. In addition, fine particles have low amount of woody cells. For this reason, they absorb less water than thick particles. However, boards made with bagasse had lower TS values than those panels made with poplar and mixed hardwoods. 3.2.2. Surface roughness Results of the surface roughness measurements of the samples are presented in Table 3 and Figs. 3 and 4. In general, bagasse boards exhibited better surface roughness than those made with poplar and mixed hardwoods particles. Table 3 shows that the effects of wood species and press time on the surface quality of the particleboards were statistically significant. There was a largescale difference between the surface roughness values of the panels manufactured under different conditions. Increasing press time showed a positive effect on the surface roughness except for mixed hardwoods. This may be due to filling of the pores between the particles with fines. As shown in Fig. 3, particleboards pressed for 8 min had smoother surfaces than the panels pressed for 6 min. According to Philippou et al. [30], press time positively affected all properties of the particleboard. Improving the surface smoothness related to the increasing of the press time may be due to well hardening of the adhesive, and evaporating the moisture from the mat effectively. In addition, because the particles pressed for a
300 Ra
Ra (micro m)
75
250
Rz
200
60 45
150
30
100
15
50
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
Board type Fig. 3. Effects of board types on the surface roughness parameters (Ra and Rz).
0
Rz (micro m)
90
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Surface height
(a)
Measured length
Surface height
(b)
Measured length Fig. 4. Comparison of roughness profiles of the produced borads using (a) mixed hardwoods and (b) bagasse particles with treatment code 4.
means the board B4 has smoother surface than MH board, the same result was obtained from quantitative evaluation. 4. Conclusion 1. The boards made with bagasse improved both the mechanical and surface roughness properties. 2. Single variable factors affected the MOR, MOE, IB and TS properties, and surface roughness of the boards, significantly. However, statistical analysis did not show an interaction between the variables factors on the mechanical properties. 3. Panels made with bagasse particles had superior properties compared to the poplar and mixed hardwoods particles. 4. All types of strength characteristics of the samples manufactured from bagasse met the minimum strength requirements of the European standards for general uses. 5. Increasing press time and moisture content of the mat improved the surface quality in terms of Ra and Rz. 6. In general, bagasse boards exhibited better surface roughness, having lower Ra and Rz values, than those made with poplar and mixed hardwoods particles.
References [1] Sellers T. Growing markets for engineered products spurs research. Wood Technol 2000;127:40–3.
[2] Ashori A, Nourbakhsh A, Karegarfard A. Properties of medium density fiberboard based on bagasse fibers. Compos Mater 2009;43:1927–34. [3] Pan Z, Cathcart A, Wang D. Properties of particleboard bond with rice bran and polymeric methylene diphenyl diisocyanate adhesives. Ind Crops Prod 2006;23:40–5. [4] Tabarsa T, Jahanshahi S, Ashori A. Mechanical and physical properties of wheat straw boards bonded with a tannin modified phenol-formaldehyde adhesive. Composites Part B 2010. doi:4110.1016/j.compositesb.2010.09.01. [5] Kalaycıog˘lu H, Nemli G. Producing composite particleboard from kenaf (Hibiscus cannabinus L.) stalks. Ind Crops Prod 2006;24:177–80. [6] Wang D, Sun XS. Low density particleboard from wheat straw and corn pith. Ind Crops Prod 2002;15:3–50. [7] Alma MH, Kalaycıog˘lu H, Bektas I, Tutus A. Properties of cotton carpel-based particleboards. Ind Crops Prod 2005;22:141–9. [8] Heslop G. Compak: ten years of experience with commercial straw particleboard production. In: Proceedings of the 31st international symposium of Washington State University on particleboard/composite materials; 1997. p. 109–13. [9] Bekalo SA, Reinhardt H-W. Fibers of coffee husk and hulls for the production of particleboard. Mater Struct/Materiaux et Constructions 2010;43:1049–60. [10] Nemli G, Kırcı H, Serdar B, Ay N. Suitability of kiwi pruning for particleboard manufacturing. Ind Crops Prod 2003;17:39–46. [11] Nemli G, Demirel S, Gümüsßkaya E, Aslan M, Acar C. Feasibility of incorporating waste grass clippings (Lolium perenne L.) in particleboard composites. Waste Manage 2009;29:1129–31. [12] Nemli G, Kirci H, Temiz A. Influence of impregnating wood particles with mimosa bark extract on some properties of particleboard. Ind Crops Prod 2004;20:339–44. [13] Yalinkiliç MK, Imamura Y, Takahashi M, Kalaycioglu H, Nemli G, Demirci Z, et al. Biological, physical and mechanical properties of particleboard manufactured from waste tea leaves. Inter Biodeterior Biodegr 1998;41:75–84. [14] Gürü M, Tekeli S, Bilici I. Manufacturing of urea–formaldehyde-based composite particleboard from almond shell. Mater Des 2006;27:1148–51. [15] Papadopoulos AN, Hague JRB. The potential for using flax (Linum usitatissimum L.) shiv as a lignocellulosic raw material for particleboard. Ind Crops Prod 2003;17:143–7.
T. Tabarsa et al. / Composites: Part B 42 (2011) 1330–1335 [16] Khedari J, Charoenvai S, Hirunlabh J. New insulating particleboards from durian peel and coconut coir. Build Environ 2003;38:435–41. [17] Mulinari DR, Voorwald HJC, Cioffi MOH, da Silva MLCP, Luz SM. Preparation and properties of HDPE/sugarcane bagasse cellulose composites obtained for thermokinetic mixer. Carbohyd Polym 2009;75:317–21. [18] FAO, FAO Year books of Forest Products; 2008.. [19] Nemli G, Aydın I, Zekoviç E. Evaluation of some of the properties of particleboard as function of manufacturing parameters. Mater Des 2007;28:1169–76. [20] Hızırog˘lu S, Jarusombuti S, Fueangvivat V. Surface characteristics of wood composites manufactured in Thailand. J Build Environ 2004;39:1359–64. [21] Hızırog˘lu S, Suchsland O. Linear expansion and surface stability of particleboard. Forest Prod J 1993;43:31–4. [22] EN 310. Wood-based panels, determination of modulus of elasticity in bending and bending strength. European Committee for Standardization, Brussels, Belgium; 1993. [23] EN 317. Particleboards and fiberboards, determination of swelling in thickness after immersion. European Committee for Standardization, Brussels, Belgium; 1993. [24] EN 319. Particleboards and fiberboards, determination of tensile strength perpendicular to plane of the board. European Committee for Standardization, Brussels, Belgium; 1993.
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[25] DIN 4768. Determination of values of surface roughness parameters Ra, Rz, R max using electrical contact (stylus) instruments, concepts and measuring conditions. Berlin, Germany: Deutsches Institut für Norming; May 1990. [26] Salehi M. Investigation on effect of bagasse in particleboard production. M.Sc. thesis. Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran; 2005 [in Persian]. [27] EN 312-2. Particleboards-specifications-part 2: requirements for generalpurpose boards for use in dry conditions. European Standardization Committee, Brussels; 1996. [28] EN 312-3. Particleboards-specifications-part 3: requirements for boards for interior fitments (including furniture) for use in dry conditions. European Standardization Committee, Brussels; 1996. [29] Tabarsa T, Movahedi A. Investigation on feasibility of amigdalus branches in particleboard industry. J Agri Sci Nat Resour 2003;3:53–62. [30] Philippou JL, Zavarin E, Johns WE, Nguyen T. Bonding of particleboard using hydrogen peroxide, lignosulfonates, and furfural alcohol, the effect of process parameters. Forest Prod J 1982;32:27–32. [31] Hızırog˘lu S. Surface roughness analysis of wood composites: a stylus method. Forest Prod J 1996;46:67–72. [32] Hızırog˘lu S, Holcomb R. Some of the properties of the three-layer particleboard made of eastern red cedar. J Build Environ 2005;40:719–23.
Contents lists available at ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Evaluation of surface roughness and mechanical properties of particleboard panels made from bagasse Taghi Tabarsa a, Alireza Ashori b,⇑, Maria Gholamzadeh a a b
Department of Wood and Paper Technology, Gorgan University of Agricultural Sciences & Natural Resources (GUASNR), Gorgan, Iran Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran
a r t i c l e
i n f o
Article history: Received 21 October 2010 Received in revised form 17 December 2010 Accepted 21 December 2010 Available online 30 December 2010 Keywords: A. Wood A. Resins B. Mechanical properties B. Surface properties
a b s t r a c t The main objective of this study is to investigate some of applied properties of experimental particleboard panels made with bagasse, as an alternative fibrous raw material. Modulus of elasticity (MOE), modulus of rupture (MOR), internal bond strength (IB) and thickness swelling (TS) of the specimens were evaluated. In addition, average roughness (Ra) and mean peak-to-valley height (Rz) were used to determine quantitatively surface characteristics of the panels. Three-layer mats with target density of 0.70 g/ cm3 were formed by using fine chips for the face layer (25 wt.%) and coarse chips for the core layer (50 wt.%). Variable factors were as wood species (bagasse, poplar and mixed hardwood species), moisture content of mat (face layer: 12%, 14% and core layer: 9%, 11%) and press time (6 and 8 min). Statistical analysis showed that all variable factors exerted a significant influence on MOR, MOE, IB, TS, Rz properties of the boards as a single factor. Panels made with bagasse particles had superior mechanical and physical properties compared to the poplar and mixed hardwoods particles. Bagasse boards exhibited better surface roughness, having lower Ra and Rz values, than those made with poplar and mixed hardwoods particles. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The demand for composite wood products, such as plywood, oriented strandboard (OSB), hardboard, particleboard, mediumdensity fiberboard, and veneer board products has recently increased substantially throughout the world [1]. Particleboard is 57% of total consumption of wood-based panels consumed and it is continuously growing at 2–5% annually [2]. The demand for particleboards in the sectors of housing construction, furniture manufacturing and interior decoration (wall and ceiling paneling) has continued to increase [3]. On the other hand, accelerated deforestation and forest degradation, in addition to a growing demand for wood-based boards, have raised an important issue regarding the sustained supply of raw material to the above sectors for a long time. As a result of these concerns, alternative fibers could play an important role in manufacture of composite panels such as particleboard [4]. There is a wide variety of non-wood plants (such as kenaf stalks [5], wheat straw and corn pith [6], cotton carpel [7] and cotton stalks and rice straw [8]) and agro-residues (such as coffee husk and hulls [9], kiwi prunings [10], waste grass clippings [11], branch wood and bark [12], waste tea leaves [13], almond shell [14], flax shiv [15] and durian peel and coconut coir [16]) that can be used as alternative fibers. ⇑ Corresponding author. Tel./fax: +98 21 88838337. E-mail address: [email protected] (A. Ashori). 1359-8368/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2010.12.018
Among many agro-residues, bagasse is one of the most promising and suitable raw material for both developing and developed countries [2]. Bagasse, an abundant agricultural lignocellulosic byproduct is a fibrous residue of sugarcane stalks left over after crushing and extraction process of the juice from sugarcane. About 54 million dry tons of bagasse is produced annually throughout the world [17]. Asia is the primary production region of sugar cane (45%), while South America is the second largest production region (35%) in the world. According to a report from Food and Agricultural Organization (FAO), Iran produces 5.3 million tons of bagasse annually [18] which is mainly centered in the southwestern province, namely Khuzestan. The utilization of this biomass for processing of novel wood-based composites has attracted growing interest because of ecological and renewable nature characteristic. The use of very thin overlays such as melamine impregnated papers, veneers, laminates, and vinyl films, on particleboard substrates has forced increasing attention to surface quality. When particleboard is used as substrate for surface coating, its particleboard surfaces must be capable of having resistance stresses to peeling. Fine irregularities on the board surface shows through overlays, affecting the product grade, quality, finishing, and gluing. Because films tend to be thin, they do not have good masking properties, and any imperfections in the board surface can telegraph through the film finish. The rough surfaces reduce the contact between the overlays and particleboard, resulting in a weak glue line and low bonding strength properties of the layers [19].
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Roughness is a measure of the fine irregularities on a surface. The degree of surface roughness is a function of both raw material properties and manufacturing variables [20]. Surface characteristics of particles are affected by the cutting tool geometry, crushing conditions during the cutting and anatomical structure of wood. The roughness of individual anatomical elements is also created by a variety of voids in tracheids and fibers. Hızırog˘lu and Suchsland [21] stated that high particle compaction and fine screen particles produced high surface quality. It was reported that board density had an effect on surface smoothness of hardboard samples. Boards with a densified face layer had smoother surfaces. It was found that wood species used in board manufacture affected the surface roughness [19]. The initial objective of this study is to evaluate the potential of bagasse as an alternative raw material for panel manufacture and to determine if the properties of such panels are similar to those made from other species. Moreover, the effects of wood species, press time and moisture content of the mat on the physical and mechanical properties of panels produced have been investigated. Currently, there is very little information about surface roughness of commercially produced particleboard in Iran. Therefore another objective of this work is to evaluate surface roughness of the boards. 2. Experimental 2.1. Materials The fibrous raw materials for this study were bagasse (B), poplar (P) and mixed hardwood (MH) species (such as oak, beech and hornbeam). The specimens were chipped and then classified into coarse and fine chips which passed through 20 and 40 meshes, respectively. The particles were dried at 103 ± 2 °C to certain moisture contents for the face (12% and 14%) and core (9% and 11%) layers. The adhesive was urea–formaldehyde (UF) which was produced by a local plant. The characteristics of the UF adhesive are given in Table 1.
Table 2 Treatment conditions for panel production. Board type
Mat MC (%)
Press time (min)
Species
Code
Face layer
Core layer
B
1 2 3 4
12 12 14 14
9 9 11 11
6 8 6 8
P
1 2 3 4
12 12 14 14
9 9 11 11
6 8 6 8
MH
4
14
11
8
constant. All panels were not sanded and no wax or any other hydrophobic substance was applied. Four panels were produced for each treatment. 2.3. Mechanical and physical testing After pressing, panels were conditioned to constant mass in an atmosphere of 65% relative humidity and at a temperature of 23 °C. Then, test samples were cut from the panels and the following mechanical properties were determined in accordance with appropriate European Union (EN) Standards: modulus of rupture (MOR) and modulus of elasticity (MOE) [22] and internal bond (IB) strength [23]. Physical properties, namely thickness swelling (TS) and surface roughness were also evaluated based on EN 317 [24]. The TS samples were submerged in distilled water for 2 h and 24 h period of time. A Rank Taylor Hobson Form Talysurf stylus instrument was employed for the surface roughness measurements. Two roughness parameters, average roughness (Ra) and mean peak-to-valley height (Rz) were used to evaluate surface roughness of the samples according to DIN 4768 [25]. Ten replicates were used for each treatment. 2.4. Statistical analysis
2.2. Production of panels Particleboard panels were manufactured in the Department of Wood and Paper Technology, GUASNR, Iran, using standardized procedures that simulated industrial production. The boards were formed using fine particles for the face layer and coarse particles for the core layer. The weight ratio of the face/core/face layers was set at 1:2:1. Dried particles were blended with UF resin in a rotating drum-type mixer fitted with a pneumatic spray gun. As can be shown in Table 2, three variable factors were wood species, mat moisture (face layer: 12%, 14% and core layer: 9%, 11%) and press time (6 and 8 min). Other parameters such as type of resin (UF), resin content (face layer: 11% and core layer: 9%), type of hardener (NH4Cl), hardener content (1%), press closing rate (5 mm/s), target density (0.7 g/cm3), press pressure (25 kg/cm2), panel thickness (16 mm) and press temperature (170 °C) were held
Table 1 Characteristics of UF adhesive used. Characteristics Formaldehyde/urea mole ratio Solid content, % Density, g/cm3 Viscosity, cps Gel time, s pH
1.2 63 1.27 60 40 7
Data for each test were statistically analyzed. Analysis of variance (ANOVA) and t-test were used to test the significant difference between factors and levels. 3. Results and discussion 3.1. Mechanical properties 3.1.1. MOR and MOE The data obtained in this research showed that the effects of all variables on mechanical properties in terms of MOR, MOE and IB were significant (Table 3). In addition, Fig. 1a illustrates improved MOR and MOE properties with increasing press time and moisture content of the mat. In general, boards made with bagasse exhibited superior mechanical properties compared to the poplar and mixed hardwood particles. For example, the maximum values of the MOR and MOE were 20.5 MPa and 2.12 GPa for bagasse, respectively, while the values for poplar were 13.2 MPa and 1.98 GPa, respectively. Salehi [26] mentioned that using of light species improve mechanical properties of wood composites due to high compaction ratio. Based on European Norms (EN), 11.5 MPa and 1.600 GPa are the minimum requirements for MOR and MOE of particleboard panels for general uses, respectively [27,28]. As it can be seen in Fig. 1a, all panels produced met the minimum MOR and MOE requirement of EN standards for general purposes. It is to be noted
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ior may be due to the high compaction of bagasse furnish which caused faster heat transfer to the core layer resulted more curing of resin. According to the statistical analysis results, moisture content of the mat negatively affected the internal bond strength of the panels. The moisture cannot be sufficiently evaporated from the mats at higher moisture content. This situation impedes the hardening of the adhesive in the core layer. For this reason, the contact between core layer particles decreases and water absorption to the pores between the particles increases. Similar results were reported by Nemli et al. [19] and Tabarsa and Movahedi [29]. The minimal requirement of IB strength for general purpose [27] and interior fitments [28] are 0.24 and 0.35 MPa, respectively. Based on the results, all boards produced in this work showed properties that are higher than the EN requirements. The IB and MOE values of the panels showed a similar tendency. According to the ANOVA test, all variable factors exerted a significant influence (p 6 0.01%) on TS, MOR and MOE properties of the boards as a single factor. While statistical analysis did not show an interaction between the variables factors.
Table 3 Statistical analysis of mechanical and physical properties of the boards produced with different variables. Parameters
MOR
MOE
IB
TS
Ra
1 2 3 12 13 23 123
Rz
NS
NS
NS NS NS
NS NS NS
NS NS NS
NS NS NS
NS NS
NS
Note: 1 = wood species, 2 = Mat MC, 3 = press time, TS 2 h. = Significant difference at the 1% level (p 6 0.01%). = Significant difference at the 5% level (p 6 0.05%), and NS = Not significant.
that, panels B and P which were made with treatment 4 had the highest values among the other types of treatments. In other words, all mechanical properties of the panels were improved when the press time was increased from 6 to 8 min, which clearly shows that at 6 min press time sufficient heat is not transferred to the core section of the mat. Besides, higher mat moisture gradient between face and core layer (treatment 4) improved heat transfer and resulted enhancing mechanical properties. This result supports the conclusions reached by Nemli et al. [19], that the fine particles and wood dust usages decrease the modulus of rupture, and modulus of elasticity due to the low amount of woody cells and short fibers.
3.2. Physical properties 3.2.1. TS The poor absorption resistance of the cellulosic material is mainly due to the presence of polar groups, which attract water molecules through hydrogen bonding. This phenomenon leads to a moisture build-up in the fiber cell wall (fiber swelling) and also in the fiber–adhesive interface. This is responsible for the changes in the dimension of wood-based panel composites; as a consequence, the outdoor applications will be greatly affected. Particleboard should have a maximum thickness swelling value of 8% and 15% for 2 h and 24 h immersion. The TS values of bagasse specimens for the 2 h water immersion vary from 15.1% to 18.1%, and these values are increased after 24 h immersion, varying from 22.6% to 24.5%. As shown clearly in Fig. 2, the TS values of boards
3.1.2. IB Statistical analysis of data showed that the effects of various treatments on IB of all experimental boards were significant (Table 3). Like MOR and MOE, boards made with bagasse particles showed higher IB than those made from poplar and mixed hardwood particles (Fig. 1b). The possible reason proposed for this kind of behav-
MOR (MPa)
20
2.5
(a)
MOR MOE
15
1.5
10
1.0
5
0.5
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
Board type 0.48 0.40
IB (MPa)
2.0
(b)
0.32 0.24 0.16 0.08 0.00
B1
B2
B3
B4
P1
P2
P3
P4
Board type Fig. 1. Effects of board types on the mechanical properties.
MH
0.0
MOE (GPa)
25
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36 2h
TS 2 h (%)
30
24 h
30
24
24
18
18
12
12
6
6
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
TS 24 h (%)
36
0
Board type Fig. 2. Effects of board types on the thickness swelling.
longer time, some particles in vertical position may return to horizontal position and surface layers were densified [19]. Panels showed a definitive relationship between the moisture content of the mat and surface roughness. With increasing the moisture of the mat from 12% to 14% improved the surface quality significantly. This is due to tight structure on the surfaces due to the close pressing of the particles at 14% moisture. Because high moisture causes steam bubbles on the surface layers, smoothness decreased with increasing the moisture content of the mat above 12%. Average surface roughness (Ra) and mean peak-to-valley height (Rz) are two most important parameters for evaluation of surface roughness. Both mentioned parameters (Ra and Rz) of bagasse boards are lower than those made with poplar and mixed hardwoods particles. Type B4 had an average Ra value of 12.3 lm with the smoothest surface while mixed hardwoods had the roughest one with an average Ra value of 91.4 lm among the nine types of panels (Fig. 3). A typical commercially manufactured particleboard could have Ra values ranging from 3 to 6 lm [31]. Therefore, roughness measurement of the samples suggest that surface quality of all the panels was found to be very rough and not ideal for overlaying applications as substrate without any sanding process. However, if the panels were sanded with a sequence of 150, 180, and 220 grit sandpaper, their surface roughness could have been improved and such panels would be used as substrate for these overlays without any problems [32]. Although Ra and Rz are considered the major roughness parameters to evaluate the characteristics of a surface, the irregularities profile should also be determined to have a better understand of a surface. The irregularities of the surface are visualized in Fig. 4. A comparison of the mean line profile curves illustrated that the irregularities of the board type B4 is much uniform than MH. It
increase with increase in water exposure time and all boards could not pass the required level of thickness swelling for general uses. The samples with codes 2 and 4 had the lowest TS compared to all boards. It was found that TS properties improved with increasing press time (p < 0.05). However, all treatments (wood species, moisture content of the mat and press time) affected TS properties, significantly. Nemli et al. [19] reported that fine particles fill the pores between the coarse particles in the core layer. Consequently contacts between the blended particles increase. In addition, fine particles have low amount of woody cells. For this reason, they absorb less water than thick particles. However, boards made with bagasse had lower TS values than those panels made with poplar and mixed hardwoods. 3.2.2. Surface roughness Results of the surface roughness measurements of the samples are presented in Table 3 and Figs. 3 and 4. In general, bagasse boards exhibited better surface roughness than those made with poplar and mixed hardwoods particles. Table 3 shows that the effects of wood species and press time on the surface quality of the particleboards were statistically significant. There was a largescale difference between the surface roughness values of the panels manufactured under different conditions. Increasing press time showed a positive effect on the surface roughness except for mixed hardwoods. This may be due to filling of the pores between the particles with fines. As shown in Fig. 3, particleboards pressed for 8 min had smoother surfaces than the panels pressed for 6 min. According to Philippou et al. [30], press time positively affected all properties of the particleboard. Improving the surface smoothness related to the increasing of the press time may be due to well hardening of the adhesive, and evaporating the moisture from the mat effectively. In addition, because the particles pressed for a
300 Ra
Ra (micro m)
75
250
Rz
200
60 45
150
30
100
15
50
0
B1
B2
B3
B4
P1
P2
P3
P4
MH
Board type Fig. 3. Effects of board types on the surface roughness parameters (Ra and Rz).
0
Rz (micro m)
90
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Surface height
(a)
Measured length
Surface height
(b)
Measured length Fig. 4. Comparison of roughness profiles of the produced borads using (a) mixed hardwoods and (b) bagasse particles with treatment code 4.
means the board B4 has smoother surface than MH board, the same result was obtained from quantitative evaluation. 4. Conclusion 1. The boards made with bagasse improved both the mechanical and surface roughness properties. 2. Single variable factors affected the MOR, MOE, IB and TS properties, and surface roughness of the boards, significantly. However, statistical analysis did not show an interaction between the variables factors on the mechanical properties. 3. Panels made with bagasse particles had superior properties compared to the poplar and mixed hardwoods particles. 4. All types of strength characteristics of the samples manufactured from bagasse met the minimum strength requirements of the European standards for general uses. 5. Increasing press time and moisture content of the mat improved the surface quality in terms of Ra and Rz. 6. In general, bagasse boards exhibited better surface roughness, having lower Ra and Rz values, than those made with poplar and mixed hardwoods particles.
References [1] Sellers T. Growing markets for engineered products spurs research. Wood Technol 2000;127:40–3.
[2] Ashori A, Nourbakhsh A, Karegarfard A. Properties of medium density fiberboard based on bagasse fibers. Compos Mater 2009;43:1927–34. [3] Pan Z, Cathcart A, Wang D. Properties of particleboard bond with rice bran and polymeric methylene diphenyl diisocyanate adhesives. Ind Crops Prod 2006;23:40–5. [4] Tabarsa T, Jahanshahi S, Ashori A. Mechanical and physical properties of wheat straw boards bonded with a tannin modified phenol-formaldehyde adhesive. Composites Part B 2010. doi:4110.1016/j.compositesb.2010.09.01. [5] Kalaycıog˘lu H, Nemli G. Producing composite particleboard from kenaf (Hibiscus cannabinus L.) stalks. Ind Crops Prod 2006;24:177–80. [6] Wang D, Sun XS. Low density particleboard from wheat straw and corn pith. Ind Crops Prod 2002;15:3–50. [7] Alma MH, Kalaycıog˘lu H, Bektas I, Tutus A. Properties of cotton carpel-based particleboards. Ind Crops Prod 2005;22:141–9. [8] Heslop G. Compak: ten years of experience with commercial straw particleboard production. In: Proceedings of the 31st international symposium of Washington State University on particleboard/composite materials; 1997. p. 109–13. [9] Bekalo SA, Reinhardt H-W. Fibers of coffee husk and hulls for the production of particleboard. Mater Struct/Materiaux et Constructions 2010;43:1049–60. [10] Nemli G, Kırcı H, Serdar B, Ay N. Suitability of kiwi pruning for particleboard manufacturing. Ind Crops Prod 2003;17:39–46. [11] Nemli G, Demirel S, Gümüsßkaya E, Aslan M, Acar C. Feasibility of incorporating waste grass clippings (Lolium perenne L.) in particleboard composites. Waste Manage 2009;29:1129–31. [12] Nemli G, Kirci H, Temiz A. Influence of impregnating wood particles with mimosa bark extract on some properties of particleboard. Ind Crops Prod 2004;20:339–44. [13] Yalinkiliç MK, Imamura Y, Takahashi M, Kalaycioglu H, Nemli G, Demirci Z, et al. Biological, physical and mechanical properties of particleboard manufactured from waste tea leaves. Inter Biodeterior Biodegr 1998;41:75–84. [14] Gürü M, Tekeli S, Bilici I. Manufacturing of urea–formaldehyde-based composite particleboard from almond shell. Mater Des 2006;27:1148–51. [15] Papadopoulos AN, Hague JRB. The potential for using flax (Linum usitatissimum L.) shiv as a lignocellulosic raw material for particleboard. Ind Crops Prod 2003;17:143–7.
T. Tabarsa et al. / Composites: Part B 42 (2011) 1330–1335 [16] Khedari J, Charoenvai S, Hirunlabh J. New insulating particleboards from durian peel and coconut coir. Build Environ 2003;38:435–41. [17] Mulinari DR, Voorwald HJC, Cioffi MOH, da Silva MLCP, Luz SM. Preparation and properties of HDPE/sugarcane bagasse cellulose composites obtained for thermokinetic mixer. Carbohyd Polym 2009;75:317–21. [18] FAO, FAO Year books of Forest Products; 2008.
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[25] DIN 4768. Determination of values of surface roughness parameters Ra, Rz, R max using electrical contact (stylus) instruments, concepts and measuring conditions. Berlin, Germany: Deutsches Institut für Norming; May 1990. [26] Salehi M. Investigation on effect of bagasse in particleboard production. M.Sc. thesis. Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran; 2005 [in Persian]. [27] EN 312-2. Particleboards-specifications-part 2: requirements for generalpurpose boards for use in dry conditions. European Standardization Committee, Brussels; 1996. [28] EN 312-3. Particleboards-specifications-part 3: requirements for boards for interior fitments (including furniture) for use in dry conditions. European Standardization Committee, Brussels; 1996. [29] Tabarsa T, Movahedi A. Investigation on feasibility of amigdalus branches in particleboard industry. J Agri Sci Nat Resour 2003;3:53–62. [30] Philippou JL, Zavarin E, Johns WE, Nguyen T. Bonding of particleboard using hydrogen peroxide, lignosulfonates, and furfural alcohol, the effect of process parameters. Forest Prod J 1982;32:27–32. [31] Hızırog˘lu S. Surface roughness analysis of wood composites: a stylus method. Forest Prod J 1996;46:67–72. [32] Hızırog˘lu S, Holcomb R. Some of the properties of the three-layer particleboard made of eastern red cedar. J Build Environ 2005;40:719–23.