Mechanical properties of medium density fiberboard reinforced with metal and woven synthetic nets

This research was planned to study the influence of reinforcement with metal and woven synthetic nets on the mechanical properties of medium density fiberboard (MDF). Sample boards were manufactured according to common practice. However, reinforcements were placed in the boards at one fourth of their thicknesses. Urea formaldehyde resin was used in the boards. However, some metal nets were embedded in an epoxy resin prior to board manufacture. Bending and tensile strengths were determined according to ASTM D 1037-99, impact load resistance according to ASTM D 256-04 and board’s creep according to ASTM D 6815-02. Results revealed that bending properties (MOE and MOR), tensile strength and impact load resistance were significantly increased due to the reinforcement. Boards reinforced with thin metal nets showed the highest MOR as 105% increase; while the highest MOE and impact load resistance were determined in the boards reinforced by thick metal nets, which were embedded primarily in the epoxy resin as 112% and 79%, respectively. The highest tensile strength was also determined in boards reinforced by thick metal nets. Boards reinforced by woven synthetic nets showed lower strengths than those of the metal nets.     

Chancen und Risiken des europäischen Spanplattenmarktes

The position for particleboard in the market will be determined by the common turn of the market and the development for competitive products. The consumption of particleboard for furniture, DIY-markets and for application in the building industry includes nearly 91% of the total consumption. In future for furniture production there will be a higher substitution of particleboard by MDF. In the DIY-markets the consumption of laminated wood (blockboard) will increase. In the building industry the gypsum fiberboard will get a better market position compared with particleboard, namely in the prefab-house production. In the past time particleboard has over-compensated all these losses. The situation for particleboard compared with competitive products (MDF, blockboard, gypsum fiberboard) in the future will be discussed.     

Development of selectively densified surface laminated wood based composites

An attempt was made to develop selectively densified surface laminated wood based composites. Two types of wood composites were produced (veneer laminated Medium Density Fiberboard, MDF and wafer overlaid particleboard, PB) in this study. Veneer or wafer plasticized by NaClO₂ treatment and PF resin impregnated were laminated on both sides of the MDF or PB and compressed at ordinary pressure. The main observation was that overlaying plasticized veneer on MDF before hot pressing is a promising method for improving mechanical properties and dimensional stability of commercial MDF. The MOR and MOE of surface laminated MDF attained 177 MPa and 18 GPa, respectively. The water absorption percentage of laminated MDF decreased from 160.7 to 7.2%. Furthermore, it is interesting to note that NaClO₂ treated and resin impregnated wafer or powder laminated particleboards showed excellent performance especially in stiffness. The MOR and MOE reached 40 MPa and 7 GPa which is more than two times higher compared to untreated wafer laminated board and three times higher than particleboard. This value is comparable to commercial lauan plywood having a density of 0.78 g/cm³. The processing technique of the composite is simple and can be easily applied by the industry.     

Korrelation zwischen Rohdichte und Harzgehalt sowie Qualitätskennwerten bei Homogenplatten aus Bagasse

The aim of the present publication is, to serve with experiences being available with production of boards from bagasse as far as they can be transferred to other renewable raw materials. In order to achieve good comparability, only one variable was changed in each series of trials. To demonstrate the correlations with the density, the resin content was kept constant. In turns, to show the correlations with the resin content, the density was kept constant. Defibering the bagasse was done after drying, since the project was aiming for a board quality comparable to particleboard, only. Defibering bagasse before drying would also be possible without problems. A finer fiber is then achieved bringing the structure of board even closer to MDF. The results show clearly, that with bagasse the minimum requirements of DIN 68761/68763 for V20 boards can be achieved either with a lower density or alternatively with a lower binder content as compared with wood mixes predominantly employed in Europe. The cross section of bagasse board is a prominent distinctive mark as compared with wood particleboard. The structure of cross section of bagasse board comes closer to that of MDF than to particleboard. These results cannot be fully transferred to other monocotyledones. Bagasse is not fully lignified and owns consequently a higher plasticity than fully lignified fibres. As consequence, with fibres from other monocotyledons than bagasse, the necessity of slightly higher density or higher resin content can be expected. The homogeneity may also be slightly less favourable as with bagasse.     

Mechanical and physical properties of agro-based fiberboard

In order to better utilize agricultural fibers as an alternative resource for composite panels, several variables were investigated to improve mechanical and physical properties of agro-based fiberboard. This study focused on the effect of fiber morphology, slenderness ratios (L/D), and fiber mixing combinations on panel properties. The panel construction types were also investigated such as hardboard (HB), medium density fiberboard (MDF), and bagasse core panel (BCP) made from bagasse/bamboo combinations with a combination of 1% pMDI/4% UF as a binder. Static bending properties and tensile strength increased as fiber L/D increased from 3 to 26. Fiber separation and morphology also influenced the mechanical property development of agro-based panels. Bagasse fiber bundles and particles smaller than L/D of 5.4 were responsible for the mechanical property loss of agro-based MDF. The BCP yielded promising results for modulus of elasticity (MOE) and modulus of rupture (MOR). However, HB appeared to be a better panel type for agro-based composites based on the property enhancement compared to wood-based panel products.     

Über die Eignung von thermo-mechanischem (TMP) und chemo-thermomechanischem (CTMP) Holzstoff aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

Medium density fibreboards (MDF) were made from thermomechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) derived from pine wood. As a binder a melamine reinforced urea formaldehyde resin (UF-resin) and diisocyanate polymers (PMDI) were applied. The mechanical-technical properties of the boards as well as some of their chemical properties were evaluated. The results of the investigation led to the following conclusions: MDF from CTMP showed in general higher mechanical properties (bending strength) compared to MDF from TMP. Moreover, the formaldehyde release of the CTMP-boards was lower. This may be due to the formaldehyde scavenging properties of the used pulping chemicals during the process of CTMP. MDF from CTMP showed much higher release of acetic acid compared to MDF from TMP. This is likely to higher deacetylation of the wood substance during CTMP process compared to the TMP technique.     

Optimierung des Eigenschaftsprofils von MDF

During the last years, medium density fibreboards (MDF) became firmly established on the European wood-based material market. The production figures indicate that this tendency is still growing, although in some areas a certain saturation of the market has been reached. MDF manufactured in a dry process offering the possibility of producing such boards in comparable variety and quantity to particleboard, represent a panel product which is a serious competitor for the latter. In Germany, the MDF-production was taken over mainly by particleboard manufacturers. Thus, MDF was no more a competing product but a completion and an enlargement of the existing board range, especially in areas where the particleboard was only suitable for certain purposes. Due to its manufacturing process MDF distinctly differs from particleboard and for this reason reveils a different property profile. The user has not to deal with a substitute product offering “better properties”, therefore, he has to prepare himself for the product. The properties of MDF will be presented in detail and hints for the development of this product will be given.     

Untersuchungen an Holzwerkstoffen für Möbel-Einlegeböden

The bending deflection of six different wood based materials used as shelves in the manufacture of furniture (unlaminated particleboard, melamine laminated particleboard, veneered particleboard, block-board, plywood and solid wood panel) of approximately equal thickness was investigated. Deflection data were obtained by applying loads to the board surfaces for a period of 28 days followed by a period of unloading of equal length. For all types of particleboards the deflections appeared to be greater than for the other wood based panels. The lowest bending deflection was found for the solid wood panel while plywood performed better than blockboard. Surface treatments improved the performance of particleboards but veneering appeared to be more advantagous than laminating with melamine. The bending deflection of the tested panels is strongly related to their bending strength and modulus of elasticity.     

Beitrag zur Kurzzeitfestigkeit und zum Dauerstandverhalten von MDF der ersten Generation

Characteristic features of MDF of the first generation are: manufacture of MDF from inferior wood assortments with bark, multilayer structure of the boards on fibrous materials of different fineness, gluing of the fibrous material in mixers, lower middle density. Typical properties of these MDF: density 700–730 kg/m³, internal bond 0.50–0.65 N/mm², bending strength 26–35 N/mm², modulusE _b 2700–3000 N/mm². Dealt with are results from former long-term tests in comparison with conventional particle boards for furniture (of lower bending strength). With constant load not graded according to the strength the deflection of these MDF was similar to, or higher than that of the particle boards, their creeping coefficient exceeded that of the particle boards.     

Short-term effect of the temperature on the bending strength of wood-based panels

Bending strength of different wood-based panels such as particleboard, MDF and OSB has been studied at temperatures between +20°C and +140°C. It was found that the temperature for all studied panels significantly affects bending strength. After one-hour effect of the temperature 140° the bending strength of panels is reduced (in comparison to the temperature of 20°C) by 40% for particleboard, by 37% for MDF and by 30% for OSB. The results of the present study indicate that it is important to consider the temperature effects in application of wood-based panels.     

Zusammenhänge zwischen Eigenschaften,Rohstoffkomponenten und dem Dichteprofil von Spanplatten

Modulus of elasticity (MOE) and bending strength (MOR) are particleboard properties which characterize their suitability for definite specifications. During pressing and curing of the binding agent a density distribution over the cross-section of the boards, typical of prevailing production conditions, is achieved. These density profiles have a decisive influence on board properties. Based on test results various mathematical profile evaluation methods and regression analyses are described, with which to improve the knowledge of how to influence board properties. This provides an extension, at reduced cost and material consumption, of ways and means to adapt several distinctive properties to certain specifications.     

Effect of surface modification of fibers on the medium density fiberboard properties

Surface modification of mixed hardwoods fibers by sodium hydroxide (NaOH) was conducted to investigate the effect of chemical treatment on the fiber properties along with physico-mechanical characteristics of the medium density fiberboard (MDF). The results indicated that the NaOH treatments can dissolve a portion of hemicelluloses and almost all amount of extractives from the fibers, but it was not strong enough to remove the lignin thoroughly. The FTIR results illustrated that chemical changes can occur during the various NaOH treatments of the fibers. X-ray diffraction analysis revealed that the crystallinity of the studied fibers increased after the alkaline treatment. Investigation of mechanical properties of the MDF showed that modulus of rupture and internal bond strength of the treated samples were decreased compared to the control ones. In addition, water absorption and thickness swelling of treated boards were higher than that of untreated samples. This study indicated that the physico-mechanical properties of the boards were negatively affected by the NaOH treatment.     

Einfluß der Lagerung von Industrierestholz der Klefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particle- and medium density fibreboards (MDF) were prepared from chips of spruce and pine, a byproduct of sawing wood in a saw mill with a profiling unti. The wood residues were stored in piles of 40 m³ volume for different time periods. The physical-technological properties of the particle- and fibrebroads prepared therefrom were evalutated and the formaldehyde release of the boards was assessed. The results reveal: In general, there is a positive influence of storage on the thickness swelling and internal bond strength of UF-bonded particleboards; the bending strength of UF-bonded particleboards showed no pronounced response to storage. The prositive influence of storage onthe thickness swelling and internal bond strength was much higher in case of boards made from pine chips than in case of spruce boards. On using PMDI as a binder for particleboards no significant influence of storage on the thickness swelling, internal bond strength and bending strength was detected. The influence of storage on the thickness swelling of UF-bonded MDF from pine fibres was much less pregnant than on that of UF-bonded particleboards. On UF-bonded MDF from spruce the influence of storage, if any, was negligible. On using PMDI as a binder for MDF there was no detectable change in the thickness swelling due to storage. The internal bond strength of UF-bonded MDF experiences only subtle positive change due to storage of pine wood chips. However, no notable change was detected in case of MDF from spruce. Storage has almost no influence on the chemical properties of boards.     

Gas pressure measurements during continuous hot pressing of particleboard

Knowledge about the development of the internal gas pressure during hot pressing of wood-based composites is important for the optimization of panel properties and production speed. The gas pressure heavily affects the thermodynamic conditions inside the wood furnish mat, and a too high maximum value at press opening might cause an impairment of the panel properties. In this paper, gas pressure and temperature measurements inside a particle mat while passing through a continuous hot press are presented for the first time. The measurements were performed with a transportable system, consisting of a steel tube attached to a miniature pressure transducer and a data logger. The particleboards had a target thickness of mainly 16 mm, but also of 28 mm and 38 mm, respectively. The measurements show a distinct horizontal gas pressure distribution in both directions, in production direction and across the mat’s width. In contrast, cross-sectional gas pressure gradients were only visible inside the panels after leaving the press. By comparing the gas pressure curves measured for particleboard with those for medium density fiberboard (MDF), characteristic differences became evident. Overall, the gas pressure is higher in MDF compared to particleboard. Finally, a comparison between the gas pressure levels measured for three different panel thicknesses showed a clear relation between panel thickness and gas pressure, with a decreasing panel thickness resulting in an increase in gas pressure. The results of this paper will contribute to our understanding about the events inside wood furnish mats during continuous hot pressing.     

Einfluß der Holzart und der Holzartenmischung auf die mechanischen Eigenschaften von Spanplatten bei Verwendung chilenischer Hölzer

The influence of Chilean wood species and mixtures of the same species on particleboard properties was studied. Species and mixture ratio had a great influence on board properties. It was also determined that bending strength and internal bond of particle board from wood mixtures can be calculated using the recorded strength of particle boards based on single wood species.     

Kriechverhalten UF-verleimter MDF

The object of investigation were MDF of 19 mm thickness bonded with UF-resin originating from different manufacturers. The boards distinetly differred from each other in their short-term properties as well as in their formaldehyde emission potential and their density profiles. The tests regarding the long-term behaviour were carried out according to the FESYP method. Despite the high short-term property values MDF proved to be very sensitive towards storage in changing climate. This phenomenon is likely to be caused by insufficient or wanting repartition of glue. Thus, after only 5 cycles one serie showed a decrease of the internal bond to only 1/3 of the initial strength. Also the bending strength values incurred a greater reduction than those of comparable particleboards. This is documented by the pronounced creep tendency of the tested MDF. It was varying to a large extent but was always clearly higher than the creep tendency of comparable particleboards.     

Creep behaviour of commercial wood based boards under long-term loading at room conditions in Taiwan

The purpose of this study was to investigate the creep behaviour of commercial wood based boards (sanded and laminated) under long-term loading at room conditions in Taiwan. Ten types of commercial wood based boards were used to test their physical and mechanical properties in this study. Four types of these boards were used for the same test after laminating with red oak (Quercus spp.) veneer or balanced paper. The bending creep was measured at room conditions with central concentrated loading. The values for creep deflection of commercial wood based boards 18 mm thick decreased from 1.06–1.19 mm ti 1.00–1.12 mm after laminating veneer or balanced paper. The relative creep (120 days) of those specimens decreased from 1.71–3.17 to 1.43–2.04 after laminating with veneer or balanced paper in four months’ loading. The creep deflections of specimens increased with increasing loading time. The linear regression function ist/y=a+bt, wheret is time,y is deflection. When theb value is larger, the boards displayed good creep resistance. The residual bending strength of wood based boards after creep test would be retained at about 80–95%, and the residual bending strength between particleboard proved more significant than between fiberboard.     

Untersuchungen über den Zusammenhang zwischen Schallgeschwindigkeit und Rohdichte,Querzug= sowie Biegefestigkeit von Holzspanplatten

Zusammenfassung Zehn verschiedene Holzspanplattenarten zweier Hersteller wurden zur Erprobung eines zerst?rungsfreien Prüfverfahrens hinsichtlich Schallgeschwindigkeit, Rohdichte, Querzugfestigkeit und Biegefestigkeit untersucht. Sieben Plattenarten wiesen eine straffe Korrelation zwischen Schallgeschwindigkeit und Rohdichte sowie Querzugfestigkeit auf. Die Korrelation zwischen Schallgeschwindigkeit und Biegefestigkeit war bei drei Plattenarten des einen Herstellers lose und bei fünf Plattenarten des anderen Erzeugers ziemlich straff; bei einer weiteren Platte bestand jedoch gar keine Korrelation. Durch die Ultraschallprüfung lassen sich bei Kenntnis der Regressionsgeraden und der Standardabweichung für die fraglichen Eigenschaften der betreffenden Plattenart Aussagen über Rohdichte, Querzugfestigkeit und Biegefestigkeit mit hinreichender Genauigkeit ableiten.

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On the correlation between sound velocity and density, tensile strength perpendicular to the surface and bending strength of particle board

Summary Ten different types of particle board from two different manufacturers were tested as to their sound velocity, density, tensile strength perpendicular to surface and bending strength to prove a non-destructive test procedure. Seven types of board showed a close correlation between sound velocity, density and tensile strength perpendicular to surface. The correlation between sound velocity and bending strength of the three types of board of one manufacturer was loose and of five types of boards of the other manufacturer rather close, however, in a further board it was null. By means of ultrasonic tests, knowing the regression straight line and the standard deviation of the properties in question of the respective type of board, statements may be deduced with sufficient accuracy concerning density, tensile strength perpendicular to surface and bending strength.

     

The development of the United States and Canada: Waferboard,oriented strand board,and medium density fiberboard The year 1984

A dramatic change is taking palce in the United States and Canadian structural panel and medium density fiberboard field. Changes in raw material supply, the increased shipping costs that have come about over the past 10 years, and technological improvements now favor the production of waterboard and oriented strand board, over that of softwood plywood. Medium density fiberboard probably will slowly supplant the conventional shavings-type particleboard as the supply of shavings dwindles. Most of the composition board products are moving as well into newer product lines such as siding and concrete form. This is in direct competition with plywood, hardboard, and other previously used materials. Research is also preparing the way for the possible production of lumber or lumber-type composition board products.     

Edge and face linear vibration welding of wood panels

Zusammenfassung Edge-to-edge linear vibration welding of particleboard, OSB, MDF and plywood gives better strength than face-to-face panel welding. In general, the edge-to-edge weldline is slightly weaker than the panels itself. The face-to-face weldline is stronger than the strength of the material in the same direction.