Some chemical properties of hazelnut husk and its suitability for particleboard production

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1 Building and Environment 42 (2007) Some chemical properties of hazelnut husk and its suitability for particleboard production Y. C- o pu r,c.gu ler, M. Akgu l, C. Tas-c-ıog lu Faculty of Forestry, Department of Forest Products Engineering, Abant Izzet Baysal University, Duzce, Turkey Received 5 May 2006; received in revised form 22 June 2006; accepted 6 July 2006 Abstract Hazelnut husk is a renewable natural resource that has not industrial utilization yet. The objective of this study was to examine some chemical properties (holocellulose, cellulose, lignin and ash contents, alcohol benzene, hot and cold water solubility and solubility in dilute alkali (1% NaOH)) of hazelnut husk and to evaluate its suitability to produce composite panels. For this study, particleboards were produced using hazelnut husk as an alternative raw material for the forest products industry. Two panel density levels (0.6 and 0.7 g/cm 3 ) and three types of resins (urea-formaldehyde (UF), phenol formaldehyde (PF), melamine-formaldehyde (MUF)) were selected as treatments. The findings indicated that hazelnut husk waste is a valuable renewable natural resource for particleboard production and could be utilized as a substitute for wood in board production. Its shortcomings, such as higher water absorption and thickness swelling could easily be controlled by adding water repellent chemicals in production. The bending and the internal bond strength properties of the hazelnut husk boards produced met the requirement for the general purpose product standards (TS-EN 312-2) at 0.70 g/cm 3 density. r 2006 Elsevier Ltd. All rights reserved. Keywords: Chemical properties; Hazelnut husk; Mechanical properties; Particleboard; Physical properties; Renewable natural resources 1. Introduction The demand for wood in the forest industry has been growing, but the production of industrial wood from the natural forests continues to decline. The decline in forest resources in developing countries is due to the depletion of the resources and in developed countries due to the withdrawal of forest areas from industrial production for other uses such as recreational areas. Also, there is a significant pressure on standing forest resources as a result of higher demand for wood in forest industry due to the increasing population and new application areas. Consequently, there is a need for alternative resources to substitute wood raw material. Agricultural residues are excellent alternative materials to substitute wood because they are plentiful, widespread, and easily accessible. Aside from their abundance and renewability, utilization of agricultural residues has advantages for economy, environment, and technology. Corresponding author. Tel.: ; fax: address: copur_y@ibu.edu.tr (Y. C- o pu r). Traditionally, farmers harvest grain and burn or otherwise dispose the residues (stalks, husk, etc.), but the heightened interest in industrial utilization of agricultural wastes can mean for farmers second income from grain plantings. Burning agricultural residues also causes environmental problems such as air pollution, soil erosion, and a decrease in soil biological activity. Therefore, utilizing agricultural residues not only prevents air pollution due to residual burn which adversely affect air quality and human and environmental health, but also economically profitable for farmers. The use of agricultural residues as a raw material in the forest industry is not new and it dates back to 1900s for pulp and panel industry. Today chemical pulp and panel products using wheat straw and other crop residues are being commercially manufactured in a number of countries including Turkey. The observed problems with industrial usage of agricultural residues in the forest industry are the high cost of collecting, transporting, and storing the residue material. Some of these problems could be overcome by building local, small scale mills close to the rural areas /$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi: /j.buildenv

2 Y. C- öpür et al. / Building and Environment 42 (2007) To meet the future demand and to overcome the wood shortage, studies have been conducted to utilize agricultural residues in the forest industry as raw material components for composite production in several countries. Youngquist et al. [1] cites research reports worldwide on the use of non-wood plants for the forest industry. Overall studies pointed to the viability of utilizing agricultural residues in forest industry. Turkey has been a forest poor country for decades and the shortage of wood and inadequate timber resources results in higher dependency to foreign countries. Consequently, several studies in Turkey examined the practicability of substituting wood-based materials and studied the cotton carpel [2], cotton stalks [3], sunflower stalks [4] and kiwi prunings [5] to produce composite panels. One of the agricultural residues, hazelnut husk, abundant in Turkey, on the other hand, has not drawn much attention as an agricultural residue that can be used in forest industry. Turkey is the biggest hazelnut producer and exporter in the world producing 73% of the world hazelnut production (400, ,000 tons/year) [6]. Therefore, approximately 400, ,000 tons/year of husk residue is estimated to be burned or left in the field after harvest and any possible usage of which will yield economic as well as environmental dividends. Therefore, the aim of this study is to investigate the potential utilization of hazelnut husk in tree-layer particleboard production as supplement and to alleviate the shortage of raw material in forest industry. 2. Materials and methods Hazelnut husk residues used to produce particleboard collected from the field right after hazelnut harvest in Du zce, Turkey. The residues were cleaned from impurities, chipped and then screened to obtain appropriate particle size for particleboard production. Particles collected on the 1.5 and 0.8 mm sieves were used in middle-layer and surface-layer on panel production, respectively. Density determination of the hazelnut husk was carried out according to the water displacement method. For chemical tests, specimens were sampled and prepared according to Tappi T 257 om-85. Hollocellulose and a- cellulose contents were determined according to the chloride [7] and Tappi T 203 om-71 methods, respectively. The following tests were performed to determine the lignin (Tappi T 222 om-98) and ash (Tappi T 211 om-93) contents. The solubility properties were also determined based on alcohol benzene (Tappi T 204 cm-97), cold and hot water (Tappi T 207 om-93) and 1% NaOH (Tappi T 212 om-98) methods. Screened husk material to produce particleboards was dried to 3% moisture content at C. Ureaformaldehyde (UF), phenol formaldehyde (PF) and melamine-urea formaldehyde (MUF) adhesives were utilized in particleboard production. The properties of the adhesives were given in Table 1. Thirty three percent of Table 1 Properties of the adhesives Properties UF a PF b MUF c Solid (%) Density (g/cm 3 ) PH Viscosity (cps) Ratio of water tolerance 10/27 10/28 Reactivity Free formaldehyde (%) % NH 4 Cl content (max, %) 1 1 Gel point (100 1C, s) Storage time (25 1C, max day) Flowing point (25 1C, s) a Urea formaldehyde. b Phenol formaldehyde. c 5% Melamine+95% urea formaldehyde. ammonium chloride (NH 4 Cl) solution was used as a hardener. No water repellent chemicals were utilized during the particleboard production. Experiments were conducted for the hazelnut husk particleboards to evaluate the effects of panel density (0.6 and 0.7 g/cm 3 ) and the resin types (UF, PF and MUF). Thus the experimental design for three-layer particleboards is summarized in Table 2. The particleboards prepared were pressed at a max pressure of 25 kg/cm 2 and 150 1C for 6 min. Two experimental particleboards having dimension of cm were produced for each design and then the produced particleboards were conditioned at C and 6575% of relative humidity to the moisture content of about 12%. Edges of the boards were trimmed to the final dimension of cm. Some physical properties: density (TS-EN 323, 1999), water absorption and thickness swelling (TS-EN 312, 1999) of the particleboards were determined according to standard method. Some mechanical properties: static bending strength (TS-EN 310, 1999) and internal bond (TS-EN 312, 1998), strength of the particleboards were determined on a universal tester (Instron). All the data were statistically analyzed by using the analysis of variance (ANOVA) and Duncan s mean separation tests. 3. Results and discussion The density of the hazelnut husk is found to be 0.23 g/ cm 3 (70.21). This finding shows that the density of hazelnut husk is much lower compared to the wood raw material ( g/cm 3 ) [8] and kiwi stalks (0.50 g/cm 3 ) but close to the cotton stalks (0.28 g/cm 3 ). Certain chemical properties of the hazelnut husk were listed in Table 3. A comparison between husk and other crop residues and wood species (Table 3) indicated that hazelnut husk had the lowest holocellulose and a-cellulose content. In terms of lignin, hazelnut husk had a higher content (35.1%) compared to the other crop residues, close to the hardwoods. Regarding cold and hot water solubility,

3 2570 ARTICLE IN PRESS Y. C- öpür et al. / Building and Environment 42 (2007) Table 2 Experimental design Board type Pressure time (min) Density (g/cm 3 ) Adhesive type Adhesive (%) Proportion (%) Surface Middle Surface Middle A UF B MUF C PF D UF E MUF F PF Table 3 Chemical composition of hazelnut husk, cereal straw [11], cotton carpel [2] and soft/hardwoods [12] Raw material Holocellulose (%) a-cellulose (%) Lignin (%) Ash (%) Solubility (%) Alcohol benzene (2/1) 1% NaOH Hot water Cold water Husk (std. deviation) 55.1 (0.10) a 34.5 (0.28) 35.1 (0.23) 8.22 (0.21) 1.63 (0.18) 50.4 (0.27) 20.9 (0.15) 18.2 (0.11) Cereal Straw Cotton carpel Hardwoods Softwoods a Values are the standard deviations for the triplicate tests. hazelnut husk was found to be much higher than the others. The 1% NaOH solubility value for hazelnut husk was the highest, close to the cotton carpel. On the other hand, alcohol benzene solubility for the hazelnut husk was the lowest, almost similar to the wood species. The results of ANOVA and Duncan mean separation tests for the thickness swelling and water absorption of the produced particleboards using hazelnut husk were given in Table 4. The mean thickness swelling percent of particleboards produced using hazelnut husk significantly differed in terms of water immersion time (po0:001), and it increased with soaking time from 2 to 24 h for all board types. The density of the particleboards had an effect on the mean thickness swelling percents of the particleboards (po0:05). One of the dense (0.7 g/cm 3 ) particleboards which was produced using UF adhesive had higher mean thickness swelling for 2 h and had lower mean thickness swelling for 24 h soaking time. The other dense particleboard produced using MUF adhesive gave lower mean thickness swelling for both 2 and 24 h soaking time. The third dense particleboard produced using PF adhesive, on the other hand, resulted in insignificant thickness swelling for 2 h, however, at 24 h soaking time the thickness swelling was relatively lower. High mean thickness swelling percents observed for denser particleboards could be explained by the higher number of water attractive OH groups in the material. Also, the types of adhesives used might have had a varied effect on the thickness swelling of the produced particleboards depending on the soaking times. Similar results had also been observed for 2 h water immersion time for cotton stalks [3] and kiwi prunings [5] and for 24 h immersion time for cotton stalks [3]. The adhesive type had an effect on thickness swelling of the materials (po0:001), and the highest means thickness swelling percents were observed with MUF-bonded particleboards and the lowest with the PF-bonded particleboards. The thickness swelling percents for 24 h was higher than the TS-EN 312 requirement (14%) for all boards produced in this study. This could be due to lack of using water repellent chemicals during the board production. Higher thickness swelling percents for crop particleboards were therefore typical and as follows: for flax [9] 20%,, for tobacco straw [10] 22%, for cotton stalks [3] 24%, for hemp [9] 25%, for sunflower stalks [4] 25%, for cotton carpel [2] 26% and for tea plant waste [10] 27%. The water absorption values of particleboards produced using hazelnut husk are significantly different depending on the density (po0:001), adhesive type (po0:001) and water immersion time (po0:001). Increase in soaking time from 2 to 24 h and increase in density from 0.6 to 0.7 g/cm 3 resulted in higher water absorption values for the particleboards. MUF-bonded particleboards had the highest water absorption value for both 2 and 24 h soaking times. Denser particleboards, having lower void spaces in the structure, were expected to absorb less water. This observation is parallel to previous finding in literature [3]. The results of ANOVA and Duncan mean separation tests for the bending strength and internal bond strength test results of the produced particleboards were given in Table 5. The mean bending strengths of the particleboards obtained vary from 7.70 to 12.0 N/mm 2. The boards produced, except for UF and PF-bonded particleboards,

4 Y. C- öpür et al. / Building and Environment 42 (2007) Table 4 Thickness swelling (TS) test results of ANOVA and Duncan s mean separation tests of particleboards produced from Hazelnut husks Physical properties Board type Soaking time (min) Mean (%) a Std. deviation Std. Error X Min b X Max c p d Thickness swelling (TS) A u * B u,v * C p * D p,s * E s * F p,s * A w * B z * C v D x * E y * F w * Water absorption (WA) A p * B s,u * C p,s * D u,v * E u,w * F u,v * A u,w * B w * C u,w * D y * E z * F x * a Mean values are the average of 20 specimens. b Maximum value. c Minimum value. d Significance level of (for ANOVA). p,s,u,v,w,x,y,z Values having the same letter are not significantly different (Duncan test). Table 5 The mechanical properties of particleboards made from Hazelnut husks and the test results of ANOVA and Duncan s mean separation tests Mechanical properties Board type Mean (%) a Std. deviation Std. error X Min b X Max c p d MOR (N/mm 2 ) A 11.9 z * B 10.1 y * C 12.0 z * D 8.18 x * E 7.70 x * F 8.49 x * IB (N/mm 2 ) A z * B x,y * C y,z * D x * E x * F x * a Mean values are the average of 10 specimens. b Maximum value. c Minimum value. d Significance level of (for ANOVA). x,y,z Values having the same letter are not significantly different (Duncan test). having density of 0.70 g/cm 3 did not meet the minimum bending strength (11.5 N/mm 2 ) required in TS-EN standard for general purpose particleboards. Results indicated that increasing board density had a positive effect on the bending strength of the particleboards (po0:001). Similar results were also reported by other researchers for cotton carpel [2] and kiwi prunings [5]. The adhesive used in this study had an effect on bending strength, and UF and PF-bonded particleboards gave higher bending strengths (po0:01).

5 2572 ARTICLE IN PRESS Y. C- öpür et al. / Building and Environment 42 (2007) The internal bond (IB) strengths of the produced particleboards varied from to N/mm 2. The minimum requirements in the standards are 0.24 N/mm 2 for general purpose (EN 312-2, 1996), 0.35 N/mm 2 for interior fitments (EN 312-3, 1996) and for load-bearing boards (EN 312-4, 1996) and 0.50 N/mm 2 for heavy-duty load bearing boards (EN 312-6, 1996). Results indicated that UF-bonded particleboard having density of 0.70 g/cm 3 was the only one meeting the requirement for the heavyduty load bearing boards. MUF and PF-bonded particleboards with density of 0.70 g/cm 3 met the minimum requirements for the interior fitments and for load-bearing boards. Particleboards with density of 0.60 g/cm 3, on the other hand, met only the minimum requirement for the general-purpose boards. It should be mentioned that the UF-bonded particleboard (D) was on the margin for the interior fitments and for load-bearing boards. Increasing board density led to an increase on the IB properties (po0:001). On the other hand, adhesive type was found to have no significant effect on the IB properties at 95% confidence level. 4. Conclusions The results indicated that the manufacture of particleboards from hazelnut husk wastes alone by using UF, MUF, and PF adhesives is technically feasible. It was shown that hazelnut husks could be used as a valuable material for the production of particleboards. Hazelnut husk gave the lowest holocellulose and a-cellulose contents, but the lignin content in hazelnut husk was higher compared to other crop residues and wood species. In terms of solubility, hazelnut husk had the highest cold and hot water solubility. Solubility of 1% NaOH was comparable to cotton carpel, and alcohol benzene solubility was close to the wood species. The observed results indicated that particleboards produced utilizing hazelnut husks gave relatively high thickness swelling and water absorption values compared to the boards made from wood materials. Adding water repellent chemicals such as paraffin during the board production could easily reduce the rate of thickness swelling and water absorption. Mechanical tests indicated that UF and PF-bonded particleboards produced at 0.70 g/cm 3 density with 8 10% resin addition complied with the minimum requirements in the standards for general grade particleboards. MUF-bonded particleboards resulted in lower bending and internal bond strength values. References [1] Youngquist J, English B, Scharmer S, Chow P, Shook S. Literature review on use of non-wood plant fibers for building materials and panels. Gen. technical report FPL-GTR-80, USDA Forest Serv., Forest Products Lab., Madison, WI, [2] Alma MH, Kalaycıoğlu H, Bektas- İ, Tutus- A. Properties of cotton carpel-based particleboards. Industrial Crops and Products 2005;22(8): [3] Gu ler C, Özen R. Some properties of particleboards made from cotton stalks (Gossypium hirsitum L.). Holz Als Roh-und Werkstoff 2004;62(9):40 3. [4] Bektas- İ,Gu ler C, Kalaycıoğlu H. The manufacture of particleboards using sunflower stalks (Helianhus annuus I.) and poplar wood (Populus alba L.). Journal of Composite Materials 2005;39(5): [5] Nemli G, Kırcı H, Sedar B, Alp H. Suitability of kiwi (Actinidia siensis P.) prunings for particleboard manufacturing. Industrial Crops and Products 2003;17(2): [6] Anonymous. Hazelnut economical report, Fiskobirlik Giresun, Turkey, [7] Wise LE, Karl HL. Cellulose and hemicellulose in pulp and paper science and technology. In: Earl LC, editor, vol. 1. New York: McGraw Hill Book Co.; [8] Gencer A, Eroğlu H, Özen R. Medium density fiberboard manufacturing from cotton stalks. Inpaper International 2001;5(2):26 8. [9] Kozlowski R, Piotrowski R. Produkc-a Plyt Pazdzıezowo-Trocinowych (Flax Shives saw dust production) Prace Instytutu Krajowych Wlokien Naturalnych (Works of the Institute of Natural Fibers) vol. XXXI p [10] Kalaycıoğlu H. Utilization of annual plant residues in production of particleboard. ORENKO-92. First national forest product congress, Trabzon, Turkey; p [11] Eroglu H. Fiberboard industry, vol Trabzon, Turkey: Karadeniz Technical University Publication. [12] Fengel D, Wegener G. Ultrastructure, reactions. In: Wood chemistry. Berlin: Walter de Gruyter & Co.; 1989.