Development of an air-injection press for preventing blowout of particleboard II: improvement of board properties using small-diameter holes for air injection

An air-injection press, which has holes punched in the heating plates, injects high-pressure air through the holes of one plate into boards during press heating. The air-injection press can manufacture boards from high-moisture-content particles by controlling blowouts of the boards. In this study, boards were manufactured from particles that had a moisture content of 25% by using the air-injection press, which reduced the required pressing time. Boards manufactured by injecting air through holes of 5 mm in diameter were of poor quality with a low internal bond strength of only 0.31 MPa. When the hole diameter was reduced to 1 mm, the internal bond strength increased to 0.44 MPa. A high air-injection pressure of 0.55 MPa also resulted in improved board properties over those for boards manufactured at lower pressures. This was probably because a large amount of binder was released from boards through the 5-mm holes, together with water vapor, during air injection; the small-diameter holes reduced the release of binder, resulting in better board properties.     

Performance of particleboard manufactured using air-injection press I: effects of air-injection press on preventing blowout of board manufactured from low-moisture particles

An air-injection press (AIP) was developed to prevent accidental blowouts of boards during production. In this study, the effects of the AIP on preventing blowouts were investigated by artificially creating a blowout-prone condition, and the press was shown to be effective in preventing blowouts. The modulus of rupture of the boards was almost constant irrespective of pressing time. Longer pressing time resulted in higher internal bond strength when pressed at 170 °C. The thickness swelling of the boards pressed at 170 or 190 °C was almost uniform irrespective of pressing time, and the manufactured boards showed performance similar to those manufactured with an ordinary press. The AIP prevented blowouts sufficiently even when the pressure of the injected air was reduced, and this reduction did not adversely decrease the performance of the boards. Air injection reduced formaldehyde emissions from the board.     

Performance of particleboard manufactured using air-injection press II: effects of board density and thickness on the performance of board manufactured from low-moisture particles

Particleboards of different densities (0.6, 0.7 and 0.8 g/cm³) and thicknesses (10 and 20 mm) were manufactured from low-moisture particles using an air-injection press. The effects of the air injection on preventing blowout of the boards of different densities and thicknesses were investigated by artificially creating blowout-prone conditions using metal frames. The effects of the air-injection pressure on the board performance were also investigated. 10-mm-thick boards of 0.8 g/cm³ pressed at 170 °C blew out when air was not injected, but were successfully manufactured by injecting air. 10-mm-thick boards at 150 °C showed constant internal bond (IB), regardless of density, but at 170 °C, IB was higher in boards of higher densities. This was likely due to accelerated hardening of the urea–formaldehyde resin at 170 than 150 °C. At both pressing temperatures, low air-injection pressure did not cause blowout and a reduction in board performance. Air injection also prevented the blowout of thick boards of 20 mm and enabled successful manufacture, showing its effectiveness. The IB of the 20-mm-thick board manufactured using the air-injection press exceeded that of 20-mm-thick board manufactured using an ordinary hot press.     

The effects of chemical components and particle size on the mechanical properties of binderless boards made from oak (<Emphasis Type="Italic">Quercus</Emphasis> spp.) logs degraded by shiitake fungi <Emphasis Type="Italic">(Lentinula edodes</Emphasis>)

Binderless boards are composite boards that rely on self-bonding mechanisms for inter-fibre bonding. Quercus acutissima and Quercus serrata logs degraded by Lentinula edodes (shiitake fungi) were used in this study to investigate whether physical and chemical changes induced by shiitake fungi can enhance board mechanical properties. Binderless boards were manufactured with 0.8 g/cm³ target density, 220 °C pressing temperature, 5 MPa pressure, and pressing duration of 10 min. Boards made from logs degraded for ≥?26 months were stronger than control boards and met modulus of rupture (MOR) and internal bonding (IB) requirements for fibreboards. Chemical composition and particle size distribution of the wood powder used to make the boards were determined to elucidate the drivers of board mechanical properties. The proportion of small particles (<?150 µm) showed a strong positive correlation with MOR for both species and hot water extractives showed a strong positive correlation with IB for Q. acutissima boards. Introduction of shiitake fungi pre-treatment to the production process may enhance the mechanical strength of binderless boards.     

Effects of air injection on properties of particleboard manufactured using a radio-frequency hot press

The effectiveness of air injection for preventing the blowout of particleboards manufactured using a radio-frequency hot press was investigated by evaluating the board properties under artificially created conditions that were conducive to blowout. For evaluation, 10-mm-thick boards with densities of 0.7 and 0.8 g/cm³ and 20-mm-thick boards with a density of 0.7 g/cm³ were manufactured. Pressing times for the 10-mm-thick boards were 2, 4, 6, and 8 min, and those for the 20-mm-thick boards were 4, 6, 8, and 10 min. Without air injection, blowout occurred in all manufactured boards. With air injection, however, blowout did not occur in the 10-mm-thick boards with a density of 0.7 g/cm³. Moreover, air injection prevented blowout even when the board density and board thickness were increased to 0.8 g/cm³ (for 10-mm-thick boards) and 20 mm (the density was kept at 0.7 g/cm³), respectively. Air-injection radio-frequency pressing reduced the pressing time from 4 to 2 min for 10-mm-thick boards, and from 6 to 4 min for 20-mm-thick boards. Moreover, this reduction in the pressing time was achieved without a large reduction in the internal bond strength of the boards.     

Development of an air-injection press for preventing blowout of particleboard V: effects of board density and thickness on property of board manufactured from high-moisture particles

Particleboards with thickness of 10 mm and densities of 0.6, 0.7 and 0.8 g/cm³ were manufactured from high-moisture particles using urea–formaldehyde resin and the effectiveness of air injection was examined. The temperature in the 0.6 and 0.7 g/cm³ boards was lower with air injection than without during the initial to middle stages of pressing, while the temperature in the 0.8 g/cm³ board remained lower with air injection than without throughout the entire pressing process. Air injection reduced the pressing time required to manufacture the 0.6 and 0.7 g/cm³ boards and also increased the internal bond strength of boards of all densities. In the 0.6 and 0.7 g/cm³ boards, air injection reduced the modulus of rupture (MOR), while in the 0.8 g/cm³ boards, the MOR was similar between those manufactured by injecting and not injecting air. Air injection was also found to be effective for boards of high densities. The effectiveness of the air injection on thick boards was investigated by manufacturing 20-mm-thick boards of 0.7 g/cm³. Without air injection, it was not possible to manufacture the 20-mm-thick boards, even by extended hot pressing, but air injection allowed the boards to be manufactured by pressing for 16 min. Air injection was also shown to be effective for manufacturing thick boards.     

Properties of particleboard manufactured using an air-injection radio-frequency hot press

A hot press was used to manufacture particleboards (H boards). A radio-frequency hot press (for RH boards) and an air-injection radio-frequency hot press (for ARH board) were also used, and the effects of air injection on preventing blowout and board properties were analyzed. The thicknesses and densities of manufactured boards were 10 and 30 mm, and 0.6, 0.7, and 0.8 g/cm³, respectively. The investigation ascertained the effects of air injection in preventing blowout when a radio-frequency hot press is used. The increasing order of temperature was ARH board > RH board > H board during the final pressing stage. For the 30-mm-thick boards, the temperature of H board increased to 100 °C and remained constant at 100 °C even when the pressing time was extended. The temperature of the RH board increased to 100 °C more quickly than in the case of the H board and remained constant at 110–118 °C. The temperature of the ARH board increased linearly to 130–142 °C. For both the 10- and 30-mm-thick boards, the internal bond strength of the RH board was almost the same as that of the ARH board at densities of 0.6 and 0.7 g/cm³. In contrast, the internal bond strength of the RH board was lower than that of the ARH board at a density of 0.8 g/cm³. For the 10-mm-thick boards, the thickness swelling in the RH board was almost the same as that in the ARH board irrespective of the density. However, for the 30-mm-thick boards, the thickness swelling in the RH board was higher than that in the ARH board. The low plasticization of particles due to air injection presumably results in a high degree of thickness swelling.     

Characterization of bagasse binderless particleboard manufactured in high-temperature range

This paper describes the features of binderless particleboard manufactured from sugarcane bagasse, under a high pressing temperature of 200–280 °C. Mechanical properties [i.e., modulus of rupture (MOR) and elasticity (MOE) in dry and wet conditions, internal bonding strength (IB)] and dimensional stability [i.e., thickness swelling (TS)] of the board were evaluated to investigate the effect of high pressing temperature. Recycled chip binderless particleboards were manufactured under the same conditions for comparison, and particleboards bonded with polymeric methylene diphenyl diisocyanate (PMDI) resin were manufactured as reference material. The target density was 0.8 g/cm³ for all of the boards. The results showed that the mechanical properties and dimensional stability of both types of binderless boards were improved by increasing the pressing temperature. Bagasse showed better performance than that of recycled chip as a raw material in all evaluations. Bagasse binderless particleboard manufactured at 260 °C had an MOE value of 3.5 GPa, which was equivalent to the PMDI particleboard, and a lower TS value of 3.7 % than that of PMDI particleboard. The MOR retention ratio under the dry and wet conditions was 87.0 %, while the ratio for the PMDI particleboard was only 54.6 %. The obtained results showed the possibility of manufacturing high-durability binderless particleboard, with good dimensional stability and water resistance, which previously were points of weakness for binderless boards. Manufacturing binderless boards under high temperature was effective even when using particles with poor contact area, and it was possible to express acceptable properties to allow the manufacture of particleboards. Further chemical analysis indicated a contribution of a saccharide in the bagasse to the improvement of the board properties.     

Effects of sealed press on improving the properties of particleboard

To improve the properties of particleboard, boards were produced using a sealed press. With the sealed press, boards were processed under high-temperature and high-pressure steam. This increased the saturation temperature, causing a dramatic rise in temperature inside the board, faster curing of the binder, and a shorter pressing time. The boards were bonded with urea formaldehyde resin, melamine urea formaldehyde resin, or poly(methylene diphenyl diisocyanate) (PMDI). The sealed press improved the internal bond strength and thickness swelling of boards regardless of the binder used during the reduced pressing time. The increased bonding strength improved the board properties, allowing PMDI with a lower resin content to be used for bonding the boards.     

Manufacture and properties of ultra-low-density fiberboard

Low-density fiberboards with densities ranging from 0.05 to 0.50g/cm³ were manufactured with steam injection pressing. Bond-type and foam-type isocyanate compound resin adhesives were used separately at 10% and 30% resin content levels. Two types of different-size fibers from softwood were used. Mechanical, dimensional, thermal, and sound insulation properties of the fiberboards were tested. The results are as follows: (1) Bond-type isocyanate adhesive showed higher mechanical and dimensional properties of low-density fiberboards than the foam-type adhesive. (2) Fiberboards produced from small fibers have better mechanical and dimensional properties than those made from large fibers. (3) Thermal conductivity of fiberboards depends more on the board density than on the type of resin or fiber dimension. At a board density lower than 0.2 g/cm³, the thermal conductivity is almost equivalent to those of thermal insulation materials such as polystyrene foam and rock wool, (4) Generally, the sound absorption coefficient of low-density fiberboards tends to increase at higher sound frequency. As the board thickness increases, low-frequency sounds are more readily absorbed by boards.Part of this report was presented at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Development of an air-injection press for preventing blowout of particleboard I: effects of an air-injection press on board properties

An air-injection press was developed to prevent particleboard from blowing out during the manufacturing process. The air-injection press, which has holes punched in the heating plates, injects high-pressure air into the board through the holes of one plate and releases the air through the holes of the other plate. The high-pressure air forces out vapor trapped within the board, thus preventing blowout. The newly developed press reduced the pressing time required for manufacturing board from high-moisture-content particles. However, the manufactured boards exhibited mechanical properties and dimensional stability inferior to conventionally manufactured boards.     

Effects of water soaking and outdoor exposure on modulus of rupture and internal bond strength of particleboard

Phenol–formaldehyde resin-bonded particleboard (PF board) and isocyanate resin-bonded particleboard (MDI board) were soaked in water at 40, 70 and 100 °C, and the relationships between soaking conditions and board properties were analyzed. The relationships between the deterioration of board properties resulting from water soaking and those arising from outdoor exposure were also analyzed. At 100 °C, the modulus of rupture (MOR) and internal bond strength (IB) of the PF board decreased significantly within the first hour, and subsequently constant values were shown with increasing soaking time. This low constant value was defined as the lower limit. At 70 °C, both the MOR and IB decreased with increasing soaking time, and reached the lower limit. At 40 °C, however, neither decreased significantly with increasing soaking time and neither reached the lower limit. The MOR of the MDI board showed the same trend as the PF board. However, the IB of the MDI board showed a different trend to the PF board, that is, the lower limit of IB required extensive soaking, even at 100 °C. The MOR and IB of both the PF and MDI boards reached the lower limit when thickness change peaked. On the other hand, the MOR and IB for outdoor exposure were lower than those for water soaking, even at the same thickness change. The MOR and IB of water soaking decreased owing to the collapse of the bonding points caused by board swelling. On the other hand, the board properties of outdoor exposure decreased owing to the collapse of the bonding points, and biodegradation also added to the decrease.     

Preparation of composite board using foil-laminated and plastic-laminated liquid packaging paperboard as raw materials

We investigated the properties of composite board formed using base sheets of aluminum foil-laminated and polyethylene (PE) plastic-laminated liquid packaging paperboard (LP) as an alternative to recycling these items in wastepaper stream. Boards of different specific gravities ranging from 0.55 to 0.75 were made by pressing shredded LP blended with urea resin having resin content of 6%–10% at 180°C. Subsequently, we also prepared mixed particleboard [wood (WD) particles and LP mixed], three-layered particleboard (LP as the middle layer, WD in the upper and lower layers), and wood particleboard all having resin content of 10% and various specific gravities. Static bending and internal bonding strengths and thickness swelling of the specimens were determined to examine their properties. At the same specific gravity, the properties of LP particleboards were affected by their resin content. The modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond strength of the LP particleboards increased with increasing specific gravity of the boards at the same resin content, but thickness swelling of the LP particleboards showed the reverse trend. The average MOR of the LP particleboards approximated that of the mixed particleboards and was greater than those of the three-layered particleboards and wood particleboards. Internal bond strength and thickness swelling of the LP particleboards were smaller than those of the other particleboards. Based on the above observations, we deemed that LP can be made into composite boards with adequate properties either alone or mixed with wood particles.     

广宁县竹香骨下脚料制备竹碎料刨花板及其复合改性研究

采用竹香骨下脚料为原料,以脲醛树脂和三聚氰胺改性脲醛树脂胶粘剂制备竹碎料刨花板,并与木纤维复合改性,检测并分析了内结合强度、静曲强度、弹性模量和吸水性。结果表明,在热压温度为160℃时,竹碎料板和竹木复合碎料板的物理力学性能均满足国标规定在干燥状态下使用的普通用板要求。当木纤维与竹碎料复合后,复合板材的静曲强度和弹性模量有一定程度提高,但内结合强度降低。     

Development of an air-injection press for preventing blowout of particleboard (III): effects of pressing temperature on board performance

An air-injection press, which has holes punched in the heating plates, injects high-pressure air through the holes of one plate into particleboards and discharges the air and vapor through the other plate during press heating. The press can manufacture particleboards from high-moisture particles by preventing blowouts of the boards. In this study, the effects of pressing temperature were investigated by pressing boards at 190, 210, and 230°C. The internal bond strength increased from 0.43 to 0.60?MPa by raising the temperature from 190 to 210°C, but did not increase further when the temperature was raised to 230°C. Raising the temperature from 190 to 210°C also helped improve the thickness swelling. No relationship was found between the modulus of rupture and pressing temperature.     

Effects of water soaking and outdoor exposure on nail joint properties of particleboard

Phenol-formaldehyde resin-bonded particleboard (PF board) and isocyanate resin-bonded particleboard (MDI board) were soaked in water at 40, 70 and 100 °C, and the relationships between soaking conditions and nail joint properties were analyzed. The soaking time to reach the lower limit of nail-head pull-through (NHPT) of the PF board was 2 h at 100 °C, while it took 168 h at 70 °C. The soaking time to reach the lower limit of lateral nail resistance (LNR) of the PF board was 24 h at 100 °C, but it did not take 168 h at 70 °C to reach it. The lower limits of NHPT and LNR for the MDI board were higher than those for the PF board. For the PF board, there was a high correlation between modulus of rupture, internal bond strength and nail joint properties. Based on the results of water soaking and outdoor exposure, it was shown that thickness change has a significant effect on NHPT and LNR, and that the reduction in NHPT and LNR results from the collapse of bonding points owing to swelling of the board.     

Effect of furnish type and high-density raw material from mill residues on properties of particleboard panels

The purposes of this study were to examine the use of furniture mill residues containing high-density raw materials in particleboard production and to evaluate the effect of mixing several types of furnish on board performance. Wood wastes collected from the furniture industry in Japan containing matoa (Pometia pinnata), Douglas-fir (Pseudotsuga menziesii), and sugi (Cryptomeria japonica) with different particle shapes were prepared as raw materials for use in the manufacture of experimental particleboards. Seven board types and three mixed boards were manufactured with three replications. Methylene diphenyl diisocyanate (MDI) resin was applied at 6 % content in mat preparation. The pressing conditions were temperature of 180 °C, initial pressure of 3 MPa, and pressing time of 5 min. The target density was 0.72 g/cm³. This study showed that matoa particleboard had properties suitable for use in interior applications, although its properties were considered inferior compared with other particleboards. Improvement of matoa particleboard could be achieved by mixing with higher quality wood particles such as those from sugi or Douglas-fir. The furnish type used in this study affected board performance. All residues from furniture mills have the potential to be used for particleboard production, even when they contain different furnish types and wood species.     

Phenol-formaldehyde resin curing and bonding under dynamic conditions

Summary To better understand the curing and bonding behavior of phenol-formaldehyde (PF) resin under dynamic conditions, flakeboards were manufactured either by conventional pressing at 7% or 12% mat moisture content or by steam injection pressing with 10 or 20 seconds steaming duration. Resin-impregnated glass-cloth samples and lap-shear tension specimens were embedded in the core of each flakeboard. After the flakeboards were pressed for various periods of times, the samples and specimens were quickly retrieved. The degree of resin cure was determined on the resin-impregnated glass-cloth samples by dynamic mechanical analysis. The bond strengths were measured from the lap-shear tension specimens on a mechanical testing machine. The results of resin curing and bonding were then correlated to the performance of the resin-bonded boards, which were evaluated by internal bond, modulus of rupture, modulus of elasticity, and thickness swelling. Resin curing and lap-shear bonding did not proceed simultaneously. In conventional pressing, the mat moisture content (MC) at 12% favored resin curing, but slightly retarded lap-shear bonding, as compared to 7%MC. In steam injection pressing, the rates of resin curing and lap-shear bond strength development were much faster for 20 seconds than for 10 seconds of steaming duration. Longer press times were needed to obtain boards with maximum strength in the 12%MC conventional pressing and the 20-s steam duration steam injection pressing than in those conditions where moisture content was lower or steam time was less. The need for longer press times must be attributed to higher internal vapor pressures and/or lower wood and resin component strengths, rather than to incomplete cure or bonding.This material is based on work supported by the Ministry of International Affairs, Quebec Government, the Natural Sciences and Engineering Research Council of Canada, and Laval University (Quebec City). The work was also supported by the U.S. Department of Agriculture under research joint venture agreement FP-92-1835     

Influence of pressing parameters on mechanical and physical properties of self-bonded laminated beech boards

Abstract

Five-ply self-bonded boards were obtained by pressing beech veneers parallel to the grain without additional adhesives, steam or pre-treatment. Fifteen different combinations of pressing parameters were tested, including temperature (200°C, 225°C and 250°C), pressure (4, 5 and 6 MPa) and pressing time (240, 300 and 360 seconds). Due to severe pressing conditions, the new product showed a higher density and different properties compared to a conventionally glued laminated wooden board. The self-bonding quality was assessed through dry shear strength tests, through a three-point bending test and a water-soaking test at 20°C. The dimensions in the cross section of the boards were measured after soaking in water. Results show that the choice of pressing parameters affects all the mechanical and physical properties tested. A statistical analysis revealed that the pressing temperature is the most influential parameter. Boards pressed at 200°C delaminated rapidly in water, whereas boards pressed at 225°C delaminated only at core-positioned layers after 48 hours and boards pressed at 250°C did not delaminate at all in water. Compared to panels pressed at lower temperatures, boards pressed at 250°C had the highest density, a higher shear and bending strength and a lower water absorption.     

Plywood made from plasma-treated veneers: melamine uptake,dimensional stability,and mechanical properties

This study investigates the dimensional stability and mechanical properties of plywood boards made of thermally modified and unmodified beech veneers that have undergone plasma pre-treatment before melamine resin impregnation. The water and melamine resin uptake and resulting weight percent gain of the veneers were investigated, whereby the air plasma pre-treated veneers showed improved liquid uptake. Five-layer plywood boards were then manufactured and tested for their dimensional stability, compressive strength, bending strength, and tensile strength. Plywood boards made of thermally modified and plasma pre-treated veneers showed a significantly improved dimensional stability, along with small influences on their mechanical properties.