Eur. J. Wood Prod. (2011) 69:3–10 DOI 10.1007/s00107-009-0390-5

ORIGINALS · ORIGINALARBEITEN

The effect of acetylated particle distribution and type of resin on physical and mechanical properties of poplar particleboard Hamideh Abdolzadeh · Kazem Doosthoseini · Ali Naghi Karimi · Ali Akbar Enayati

Received: 18 January 2009 / Published online: 6 January 2010 © Springer-Verlag 2010

Abstract This paper presents the results of a study on using acetylated particles for particleboard production. A three-layer board with distributed acetylated particles on the surface layers and a single-layer board with a uniform distribution of acetylated particles were fabricated. Three levels of acetylation of 0, 8.4 and 17.3% weight percentage gain (WPG), i.e., zero, medium and high levels of acetylation, were applied. The boards were fabricated with 4 wt% methylene diphenyl diisocyanate (MDI) and 10 wt% urea formaldehyde (UF) adhesive. The results indicated that the mechanical properties of the boards were negatively affected by acetylated particles. Overall, MDI-bonded particleboards gave superior mechanical performance, water resistance, and thickness swell to UF-bonded particleboards. The strength of UF-bonded boards decreased much more than that of MDI-bonded boards as acetylation level increased. The MDI-bonded single-layer boards made using medium-level acetylation were recognized to have suitable mechanical properties, and the MDI-bonded three-layer boards made from high level acetylation showed suitable dimensional stability.

Einfluss der Verteilung acetylierter Späne im Plattenquerschnitt und der Harzart auf die physikalischen und mechanischen Eigenschaften von Pappelspanplatten

Additional corresponding author e-mail address: [email protected]

1 Introduction

H. Abdolzadeh (u) · K. Doosthoseini · A. N. Karimi · A. A. Enayati University of Tehran, Wood Science and Technology Department, Natural Resources Faculty, Chamran Boulevard, P.O. Box 4314, 3158777878 Karaj, Iran e-mail: [email protected]

Dimensional instability and susceptibility to biodegradation are critical limitations of wood-based composite materials exposed to weather. The properties of particleboards currently greatly depend on the type of bonding agent used in

Zusammenfassung Vorgestellt werden die Ergebnisse einer Studie über die Verwendung von acetylierten Spänen zur Herstellung von Spanplatten. Es wurden eine dreischichtige Platte mit acetylierten Spänen in den Deckschichten und eine einschichtige Platte mit 50% acetylierten Spänen hergestellt. Dabei wurden drei Acetylierungsgrade angewandt 0, 8,4 und 17,3% Gewichtszunahme (WPG), d. h. null, mittlerer und hoher Grad an Acetylierung. Die Platten wurden mit 4 Gew.% Methylendiphenyldiisocyanat (MDI) und 10 Gew.% Harnstoff-Formaldehydharz (UF) hergestellt. Die Ergebnisse zeigten, dass die acetylierten Späne einen negativen Einfluss auf die mechanischen Eigenschaften der Platten hatten. Im Allgemeinen zeigten die MDI-verklebten Spanplatten bessere mechanische Eigenschaften, Wasserresistenz und Dickenquellung als die UF-verklebten Spanplatten. Mit zunehmendem Acetylierungsgrad nahm die Festigkeit der UF-verklebten Platten stärker ab als die der MDI-verklebten Platten. Die MDI-verklebten einschichtigen Platten mit mittlerem Acetylierungsgrad wiesen brauchbare mechanische Eigenschaften auf und die MDI-verklebten dreischichtigen Platten mit hohem Acetylierungsgrad ergaben eine brauchbare Dimensionsstabilität.

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their production; about 90% of the world production of particleboard is manufactured with the use of urea formaldehyde (UF) resins (Sellers 1992), mainly because of its relatively low price, good technological properties, absence of colors in cured polymers and easy adaptability to a variety of curing conditions. However, among the disadvantages of this type of board is free formaldehyde content and low resistance to changeable environmental conditions. These factors considerably limit the range of UF resin uses (Pizzi 1994). Although the results of contemporary studies on the environmental properties of particleboards enable the reduction of formaldehyde emission by 80–90% (Dziurka et al. 2003), researchers to date have not succeeded in increasing the water resistance or improving the mechanical properties of the boards. The need for expanding the usable range of the boards, as well as increasing demand for further reduction of formaldehyde emission, has led to intensification in research aiming at improving properties of particleboards by means of modifying the UF resin. However, compounds introduced into UF resins may cause a disturbance of the polymer condensation process due to the reaction of hydroxymethylene groups, resulting in the deterioration of the properties of particleboards. Therefore, the methods of modification of the wood surface designed for the production of particleboards are becoming increasingly important (Pizzi 1989). Acetylation is the most investigated of all chemical modification treatments and is widely acknowledged as a candidate for chemical treatment methods. Stamm and Tarkow (1947) were among the first to acetylate whole wood with acetic anhydride. A number of researchers have subsequently explored the applicability of acetylation (e.g., Rowell et al. 1986, Sheen 1992). Because the properties of wood depend on the chemistry of the cell wall components, the basic properties of wood can be changed by modifying the basic chemistry of the cell wall polymers. There are several approaches to cell wall modification, depending on what property is to be modified. For example, if the objective is water repellency, then the approach might be to reduce the hydrophilic nature of the cell wall by bonding to hydrophobic groups. If dimensional stability is to be improved, the cell wall can be bulked with bonded chemicals or a cell wall polymer. Acetylation of both solid wood and wood composites has the generally advantageous effect of decreasing the hygroscopicity of wood cell-wall material (Rowell 1982). Acetylation of wood using acetic anhydride has been done mainly as a liquid-phase reaction. The reaction with acetic anhydride results in esterification of the accessible hydroxyl groups in the cell wall, with the formation of by-product acetic acid (Rowell et al. 1994). wood–OH + CH3 –CO–O–CO–CH3 −→ wood–O–CO–CH3 + CH3 –CO–OH Acetic anhydride

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Acetylated wood

Acetic acid

Acetylation may consequently, however, decrease the number of hydrogen bonds formed between wood and the adhesive and thereby interfere with the adhesive process, which is all-important in the manufacturing of wood-based composites. It is reasonable to expect that reduced availability of hydroxyl groups may decrease bond strength development rates, as well as final bond strength. Acetylation may impair the hydrophilic nature of the wood substrate, reduce its wettability, and thus lead to poor adhesive penetration and bonding (Rowell and Banks 1987). The strength of fully cured panel products made with resol PF or isocyanate adhesive is already known to be somewhat reduced by acetylation (Youngquist and Rowell 1986, Rowell et al. 1989, Chow et al. 1996). Methylene diphenyl diisocyanate (MDI) and polymeric diphenyl methane diisocyanate (PMDI) are important adhesives for the manufacture of particleboard (Das et al. 2007). These wood binders polymerize into a polyurea/poly (biuret) network through rapid reaction with adsorbed wood moisture (Frazier and Ni 1998). The adhesives are also capable of forming covalent urethane bonds with wood (Zhou et al. 2001), which enhance bond line durability. Isocyanate resins, unlike urea formaldehyde (UF) resins, which are normally soluble in water, are used either as a 100 percent solid content or in an emulsion form to which water and/or other additives may be added. Since they were first introduced to the German particleboard market in the early 1970s, the use of MDI binders in composite panels has grown significantly (Papadopoulos 2006). However, the effect of acetylation on the mechanical properties of the produced particleboard is still a serious concern. The objective of this research was to improve the dimensional stability of particleboards by acetylation of poplar particles and to assess the bond quality of methylene diphenyl diisocyanate (MDI) as well as urea formaldehyde resin with acetylated particles. In addition, as an improving alternative, the effect of distribution and location of acetylated particles on the properties of the particleboard were studied.

2 Material and methods 2.1 Raw materials Poplar particles were used as raw material. Since the moisture content has a detrimental influence on acetylation of wood particles, they were dried in an oven at 103 ± 2°C for 24 h. Two types of synthetic resin were used, namely, urea formaldehyde (UF) at a level of 10 wt% and methylene diphenyl diisocyanate (MDI) at a level of 4 wt% for manufacturing of single-layer and three-layer particleboards with acetylated particles.

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Table 1 Characteristics of the adhesives Tabelle 1 Klebstoffeigenschaften

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Resin type

Density (g.cm−3 )

Gel time (s)

Viscosity (CP)

Solid content (%)

UF MDI

1.26 1.27

60 –

350 300

63 100

Fig. 1 Distribution of the acetylated and untreated particles in three-layer and single-layer manufactured boards Abb. 1 Verteilung der acetylierten und unbehandelten Sp¨ane in den dreischichtigen und einschichtigen Platten

Characteristics of the adhesive used are given in Table 1. Ammonium chloride (NH4 Cl) was added as a hardener to urea formaldehyde adhesive at a level of 2% (dry resin basis weight). 2.2 Acetylation The acetylation of the particles was conducted according to Rowell et al. (1986) and Rowell and Ellis (1981) by reaction with acetic anhydride for 2 or 4 h to reach the desired level of acetylation, i.e., medium (8.4) and high (17.3) weight percentage gain (WPG). The untreated particles were considered as blank (0 WPG). This reaction does not require catalysis and is carried out at reaction temperatures of 150°C. After the acetylation, the particles were placed in cold water to stop the reaction; subsequently they were leached in running water to remove the unreacted acetic anhydride and the by-product acetic acid until the smell of these chemicals disappeared. After leaching, the acetylated particles were air dried for 5 days and then oven dried at 105°C for 12 h. To determine the WPG, about five weighed samples (4 ± 0.1 g, equivalent to oven dry weight) placed into permeable rag bags were acetylated with each treatment at the same time. After treatment the samples were oven dried and weighted out to nearest 0.1 g. The WPG was then calculated as follows: WPG, % = 100(Wat − Wbt )/Wbt . Where, W bt : sample oven dry weight before treatment, W at : sample oven dry weight after treatment. The calculated WPG will be quite representative for average WPG of the acetylated particles.

2.3 Mat fabrication Two types of mats were manufactured by mixing each level of acetylated particles with untreated particles at a 1:1 ratio following the depicted distribution patterns in Fig. 1. According to the following method, the desired amounts of adhesive were blended with acetylated and untreated particles separately for preparation of three-layer boards using a laboratory blender with a rotor speed of 20 rpm. On the other hand, for single-layer particleboards, adhesives were blended simultaneously with acetylated and untreated particles within the same batch. The suitable moisture contents of the MDI-mat and the UF-mat for particleboard manufacturing were adjusted at 8 and 12%, respectively. Since MDI adhesive contains no water, prior to mat fabrication, some water was added to the wood particles to obtain the necessary MDI-mat moisture content. The mats were formed using a laboratory mold with dimensions of 400 × 400 mm2 . 2.4 Board manufacture To fabricate the single-layer board, a mixture of acetylated and untreated particles was distributed uniformly on the surface and through the core of the board. The three-layer boards were made by distributing the acetylated particles on the surface layers and untreated particles in the core. Aluminum foil was applied on the MDI-mat to avoid the MDI adhesive sticking to the hot press plates. The UF-mat was pressed for 6 min in a hot press with the temperature and pressure controlled at 160°C and 4.41 N mm–2 , respectively. For the MDI-mat, the time, temperature and pressure were 4 min, 180°C and 4.41 N mm–2 , respectively (Table 2). The dimensions of the boards were 400 × 400 × 25 mm3 .

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Table 2 Wood based panels manufacture conditions Tabelle 2 Herstellungsbedingungen der Spanplatten

Type of resin

Press temperature (◦ C)

Press time (min)

Press pressure (N/mm)

UF MDI

160 180

6 4

4.41 4.41

All of the boards were manufactured with an average target density of 0.75 g cm–3 . Three replicate sample boards were fabricated for each treatment. After fabrication, the boards were conditioned at 65 ± 1% relative humidity and 20 ± 3°C for about 3 weeks. Before being cut into test specimens, the conditioned particleboards were trimmed about 2 cm around the edges to avoid edge effects.

2.5 Particleboard properties evaluation The boards were cut into test specimens according to standard. Three specimens were prepared from each sample board to determine the physical and mechanical properties. The dimensions of the samples were 250 × 50 mm for bending strength and 50 × 50 mm for shear strength, water absorption and thickness swelling. Bending and shear strength were measured according to DIN 52362 (1965) and ASTM D 1037 (1999) standards, respectively. Water absorption and thickness swelling after 24-h immersion were measured according to the ISO 16983 (2003) standard.

2.6 Statistical analysis The experimental design was CRD (Completely Randomized Design) and the data were analyzed using analysis of variance. The standard deviations were also computed from the data and are shown as error bars in each corresponding figure.

3 Results and discussion The measurements of the physical and mechanical properties of all boards are summarized in Table 3. 3.1 Bending strength Bending strength of particleboards varied from 17.92 to 34.12 MPa, and the standard deviations from 1.26 to 6.91 (Fig. 2). It can be seen from Fig. 2 that the bending strength of the board differs significantly with the acetylation level; the bending strength of the board decreased as the acetylation levels increased. The obtained results are similar to those described by others (Rowell et al. 1989, Rowell 2006). The reason for this behavior is attributed to the weak adhesion and decreased surface wetting by the resin between the acetylated particles. Substitution of hydroxyl groups was shown to decrease adhesion between chemically modified particles due to the loss of hydroxyl functionality (Rudkin 1950). The results also showed that the bending strength of the UF-bonded boards decreases more sharply than that of MDI-bonded boards. This is assumed to be due to the high reactivity of isocyanate with the modified materials as acetylated particles (Xiaoqun 2003, Taramian et al. 2007). The bending strengths of the MDI-bonded boards containing a medium level of acetylated particles (WPG: 8.4%) were higher than those of UF-bonded boards. In general, single-layer boards had a higher bending strength in comparison with three-layer boards. In threelayer boards, acetylated particles, the cause of bending strength loss, were used in the surface layer that had

Table 3 Average values of physical and mechanical properties of the studied particleboards Tabelle 3 Mittelwerte der mechanischen und physikalischen Eigenschaften der untersuchten Spanplatten Type of resin Type of board Acetylation levels

Blank

MDI Single-layer board Medium High

Three-layer board Medium High

Blank

UF Single-layer board Medium High

Three-layer board Medium High

Bending strength∗∗ Shear strength∗ Water absorptionns Thickness swellingns

33.81 6.42 31.36 13.79

34.12 5.57 30.49 10.32

27.92 4.61 38.39 11.16

30.21 4.02 62.75 29.15

29.82 2.61 59.58 26.69

18.5 2.97 58.98 22.27

∗∗ Significant

at 1% level at 5% level ns Not significant ∗ Significant

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28.31 4.56 29.74 9.39

24.28 4.63 37.04 8.3

17.92 1.89 58.76 21.95

20.15 2.87 49.77 14.68

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Fig. 2 Effect of acetylation on bending strength of the poplar particleboards (Medium: 8.4 WPG, High: 17.3 WPG, and Blank: 0 WPG) Abb. 2 Einfluss der Acetylierung auf die Biegefestigkeit der Pappelspanplatten (Null: 0 WPG, Medium: 8,4 WPG und Hoch: 17,3 WPG)

Fig. 3 Effect of acetylation on shear strength of the poplar particleboards (Medium: 8.4 WPG, High: 17.3 WPG, and Blank: 0 WPG) Abb. 3 Einfluss der Acetylierung auf die Scherfestigkeit der Pappelspanplatten (Null: 0 WPG, Medium: 8,4 WPG und Hoch: 17,3 WPG)

the greatest effect on bending strength. Based on the American National Standard and the European Standard for particleboard (EN 312-2 1996, ANSI A208.1 1998), the minimum requirements for bending strength of particleboard panels for general uses are 11.0 MPa and 11.5 MPa, respectively. All obtained values for bending strength of the panels were higher than those specified in the standards. The bending strength of the UF-bonded particleboard containing a high level of acetylated particles (WPG: 17.3%) in a three-layer board was the lowest.

3.2 Shear strength As shown in Fig. 3, the shear strength of the boards decreased significantly with an increase in the acetylation levels. As discussed previously, this is attributed to acetylated particles and increasing acetylation level of particles that interfere with adhesion. The obtained results are similar to those described by others (Dreher et al. 1964). Similarly to the bending strength, as the acetylation level increased, the shear strength of the UF-bonded board decreased much more than that of the MDI-bonded board.

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The shear strength of the MDI-bonded three-layer board was lower than that of the single-layer board, but the opposite was true for UF-bonded boards. However, it was observed that the MDI-bonded board had higher shear strength than UF-bonded boards due to the higher reaction of MDI with cell wall hydroxyl groups (Papadopoulos 2006). For particleboards, the shear strength is closely related to the internal bond strength (IB) (Wang et al. 1999). Based on the ANSI A 208.1 (1998) standard for generalpurpose particleboard, the IB strength requirement is 0.4 MPa. From the linear regression formula suggested by Wang et al. (1999), the minimum requirement for shear strength of particleboard for general uses is in the range of 1.22–2 MPa. As shown in Fig. 2, all shear strength values of the produced boards were comparable to those required by EN 312-2 (1996). All values obtained for shear strength of the boards were higher than those required by ANSI except single-layer boards containing a high level of acetylation and UF-bonded boards. 3.3 Water absorption Water absorption of produced particleboards varied from 29.8 to 62.8% (Fig. 4). The result indicated that the water absorption of the MDI-bonded single-layer boards was lower than that of corresponding three-layer boards. The UF-bonded boards had higher water absorption than MDI-bonded boards. The water absorption of the boards decreased with an increase of acetylation level. There are three different methods to improve the water resistance and thickness swell in the particleboard manufacturing industry. The first method is to add wax (0.5–1%) to the

Fig. 4 Effect of acetylation on water absorption of the poplar particleboards (Medium: 8.4 WPG, High: 17.3 WPG, and Blank: 0 WPG) Abb. 4 Einfluss der Acetylierung auf die Wasseraufnahme der Pappelspanplatten (Null: 0 WPG, Medium: 8,4 WPG und Hoch: 17,3 WPG)

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mixture of adhesive and particles during the manufacturing process. The second method is to decrease the “springback” effect by reducing the density of particleboards (Zheng et al. 2006). If reducing particleboard density is not desirable for certain applications, adding wax should be used even though the mechanical properties may be lowered to some degree (Grigoriou 2003, Okino et al. 2004). The third method, which was also considered in this work here, is to acetylate the particles. Acetylation decreases the hygroscopicity of wood cell wall material and consequently increases the dimensional stability of the particleboards. These findings also confirm the results presented by other authors (Krzysik et al. 1992, Rowell 2005). Water absorption of boards was decreased using MDI adhesive. MDI can react with remaining cell wall hydroxyl groups. It has been suggested that furniture particleboard requires less than 60% long-term water absorption (ASTM D 1037-99 1999). Almost all the treatments satisfied the water absorption for furniture manufacturing according to ASTM D 1037-99 (1999) standard except the blank comprising unmodified wood particles with UF. 3.4 Thickness swelling Thickness swelling measurements indicated that MDIbonded boards have high water resistance and greater dimensional stability compared to UF-bonded boards (Fig. 5). The results indicated that the thickness swelling of the three-layer boards decreased with increasing acetylation level. Acetylated particles in the surface of the three-layer board act as a constraint that prevents thickness swelling.

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Fig. 5 Effect of acetylation on thickness swelling of the poplar particleboards (Medium: 8.4 WPG, High: 17.3 WPG, and Blank: 0 WPG) Abb. 5 Einfluss der Acetylierung auf die Dickenquellung der Pappelspanplatten (Null: 0 WPG, Medium: 8,4 WPG und Hoch: 17,3 WPG)

The thickness swelling values of the UF-bonded particleboards and the MDI-bonded particleboards were in the ranges of 14.7–28.3% and 8.3–13.1%, respectively. In addition to chemical modification like acetylation, the thickness swell is also affected by bond quality (Sauter 1996), adhesive properties (Boquillon et al. 2004) and compaction ratio (Halligan 1970) of the boards. Since MDI has significantly superior water resistance and forms stronger bonds than UF resin does, less water could penetrate into the particleboard, resulting in less thickness swelling. Particleboard based on the ASTM D 1037-99 (1999) standard should have a maximum thickness swelling value of 25% for general uses. All of the treatments were within the ASTM limit except the blank and single-layer board with medium-level acetylation containing UF. According to ANSI A 208.1 (1998) and EN 317 (1993) standards, the thickness swelling norms for home decking and bearing particleboards are 8 and 14%, respectively. The UF-bonded panels had higher thickness swelling values than those allowed by the standard. All types of the panels bonded with MDI resin satisfied the maximum thickness swelling allowed by ASTM D 1037-99 (1999) and EN 317 (1993) standards. Based on the ANSI A208.1 (1993) standard, only the three-layer boards made with a high level of acetylation and containing MDI resin are suitable for home decking in this study.

4 Conclusion The results of this study indicate that the mechanical properties of the produced particleboards are negatively

affected by the use of acetylated particles. The strength of the UF-bonded board decreased much more than that of the MDI-bonded board as acetylation level increased. The three-layer boards with a distribution of acetylated particles on the surface layers had lower bending strength than single-layer boards with a uniform distribution of acetylated and untreated particles. Resin type had a significant effect on the mechanical and physical properties of particleboards; however, MDI resin utilization resulted in better application properties. Dimensional stability of the particleboards with high levels of acetylation increased. All three-layer boards bonded with MDI satisfied the ASTM D 1037-99 (1999) and EN 317 (1993) standards for thickness swelling for general uses. Overall, MDI-bonded particleboards gave superior mechanical performance, water resistance, and thickness swell than did UF-bonded particleboards. MDI-bonded particleboards fully satisfied the minimum requirements set by EN, ASTM D 1037-99 (1999) and ANSI A208.1 (1998) for general uses. The strength of the UF-bonded board decreased much more than that of the MDI-bonded board as acetylation level increased. The MDI-bonded boards made using both medium and high level acetylation had suitable mechanical properties, and the MDI-bonded three-layer boards made using high-level acetylation had suitable dimensional stability. Acknowledgements This research was supported by the Center of Excellence of Applied Management of Fast Growing Wood. The authors would like to thank Dr. M. Azadfallah for helping to correct this paper.

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References ANSI A208.1 (1998) Particleboard. American National Standard. Composite Panel Association ASTM D 1037-99 Standard (1999) Standard test method for evaluating properties of wood-based fiber and particle panel materials. Designation, West Conshohocken, pp 142–171 Boquillon N, Elbez G, Schonfeld U (2004) Properties of wheat straw particleboards bonded with different types of resin. J Wood Sci 50:230–235 Chow P, Bao Z, Youngquist JA, Rowell RM, Muehl JH, Krzysik AM (1996) Properties of hardboard made from acetylated aspen and southern pine. Wood Fiber Sci 28:252–258 Das S, Malmberg MJ, Frazier CE (2007) Care chemistry of wood polymeric isocyanate (PMDI) bonds: effect of wood species. Int J Adhes Adhes 27:250–257 DIN 52362 (1965) Testing of wood chipboards; bending test, determination of bending strength. DIN German Institute for Standardization. Beuth Verlag GmbH, Berlin, Köln Dreher WA, Goldstein IS, Gramer GR (1964) Mechanical properties of acetylated wood. For Prod J 14:66–68 Dziurka D, Te¸cka J, Mirski R (2003) The effect of grafting particles with acetoactyl groups on the properties of particleboards. EJPAU 6(2), #02 http://www.ejpau.media.pl/volume6/issue2/wood/art02.html EN 317 (1993) Particleboards and fiberboards, determination of swelling in thickness after immersion. European Standardization Committee, Brussels EN 312-2 (1996) Particleboards – specifications – part 2: requirements for general-purpose boards for use in dry conditions. European Standardization Committee, Brussels Frazier CE, Ni J (1998) On the occurrence of network interpenetration in the wood-isocyanate adhesive interphase. Int J Adhes Adhes 18:81–87 Grigoriou AH (2003) Waste paper-wood composites bonded with isocyanate. Wood Sci Technol 37:79–89 Halligan AF (1970) A review of thickness swelling in particleboard. Wood Sci Technol 4:301–319 ISO 16893 (2003) Wood-based panels – determination of swelling in thickness after immersion in water. ISO International Organization for Standardization Krzysik AM, Yonugquist JA, Muehl JM, Rowell RM, Chow P, Shook SR (1992) Dry-process hardboard from recycled newsprint paper fibers. In: Rowell RM, Laufenberg TL, Rowell JK (eds) Materials interactions relevant to recycling of wood-based materials. Materials Research Society, Pittsburgh, pp 73–79 Okino EYA, Teixeira DE, Souza MR, Santana MAE, Sousa ME (2004) Properties of oriented strand board made of wood species from Brazilian planted forests: part 1. 80 mm-long strands of Pinus taeda L. Holz Roh- Werkst 62:221–224 Papadopoulos AN (2006) Property comparisons and bonding efficiency of UF and PMDI bonded particleboards as affected by key process variables. Bioresources 1:201–208 Pizzi A (1989) Wood adhesive, chemical and technology. Marcel Dekker Inc., New York

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Eur. J. Wood Prod. (2011) 69:3–10

Pizzi A (1994) Advanced wood adhesives technology. Marcel Dekker Inc., New York Rowell RM (1982) Distribution of acetyl groups in southern pine reacted with acetic anhydride. J Wood Sci 15:172–182 Rowell RM (2005) Handbook of wood chemistry and wood composites. CRC Press, Boca Raton Rowell RM (2006) Acetylation of wood. For Prod J 56:1–12 Rowell RM, Banks WB (1987) Tensile strength and work to failure of acetylated pine and lime flakes. Br Polym J 19:479–482 Rowell RM, Ellis WD (1981) Bonding of isocyanates to wood. In: Edwards KN (ed) American Chemical Society Symposium Series 172. Washington DC, pp 263–284 Rowell RM, Imamura Y, Kawai S, Noimoto M (1989) Dimensional stability, decay resistance and mechanical properties of veneerfaced low density particleboards made from acetylated wood. Wood Fiber Sci 21:67–79 Rowell RM, Simonson R, Tillman A (1986) A simplified procedure for the acetylation of chips for dimensionally stable particleboard products. Paperi ja Puu 68:740–744 Rowell RM, Simonson R, Hess S, Plackett DV, Cronshaw D, Dunningham E (1994) Acetyl distribution in acetylated whole wood and reactivity of isolated wood cell wall components to acetic anhydride. Wood Fiber Sci 26:11–18 Rudkin AW (1950) The role of the hydroxyl group in the gluing of wood. Aust J Appl Sci 1:270–283 Sauter SL (1996) Developing composites from wheat straw. In: Proceeding of the 30th international symposium of Washington State University on particleboard/composite materials, pp 197–214 Sellers Jr T (1992) Wood adhesives market builds a promising future on a profitable past. Adhes Age 35:22–25 Sheen AD (1992) The preparation of the acetylated wood fiber on a commercial scale. In: Plackett DV, Dunningham EA (eds) Chemical modification of lignocellulosics. FRI Bulletin 176. New Zealand Forest Research Institute, Rotorua, New Zealand, pp 1–8 Stamm AJ, Tarkow H (1947) Dimensional stabilization of wood. J Phys Colloid Chem 51:493–505 Taramian A, Doosthoseini K, Mirshokraii SA, Faezipour M (2007) Particleboard manufacturing: An innovative way to recycle paper sludge. Waste Manage 27:1739–1746 Wang SY, Chen TY, Fann JD (1999) Comparison of internal bond strength and compression shear strength of wood-based materials. J Wood Sci 45:396–401 Xiaoqun MO (2003) Physical properties of medium density wheat straw particleboard using different adhesives. Dissertation, Kansas State University Youngquist JA, Rowell RM (1986) Mechanical properties and dimensional stability of acetylated aspen flack board. Holz Roh- Werkst 44:453–457 Zheng Y, Pan Z, Zhang R, Jenkins BM, Blank S (2006) Properties of medium-density particleboard from saline Athel wood. Ind Crop Prod 23:318–320 Zhou X, Frazier CE, Ni J (2001) Double labeled isocyanate resins for the solid-state NMR detection of urethane linkages to wood. Int J Adhes Adhes 21:259–264