Investigation of the interrelations between defibration conditions,fiber size and medium-density fiberboard (MDF) properties

Defibration conditions and raw material properties affect wood fiber characteristics, and thereby the properties of fiber-based panels such as high-density fiberboard (HDF), medium-density fiberboard (MDF) and wood fiber insulation board. This study investigates the influence of steaming conditions (time and temperature), grinding disc distance, wood species (pine, beech, birch and poplar), method of refiner discharging (radial and tangential stock outlet) and wood chip size on fiber length and fiber length distribution, and further the influence of fiber size on MDF properties. Fiber lengths were determined applying the recently developed image analysis-based fiber size measuring system FibreCube. This system enables an automated and nearly complete mechanical separation of woolly-felted fiber samples prior to image acquisition, software-supported post-separation of overlapped-lying fibers at the beginning of image analysis, and flow line tracing-based length measurement. It was found that grinding disc distance and wood species are the most influential parameters on fiber length characteristics. Especially the content of undefibrated fiber bundles (shives) was found to strongly correlate with the grinding disc distance. Wood anatomical differences between hardwood and softwood were reflected clearly by the fiber length characteristics. Fiber size was found to be one of the parameters influencing panel properties. However, other fiber characteristics—in particular the chemical nature of the fiber, which is responsible for its wettability with water (thickness swelling) and glue (mechanical properties)—have to be considered as important influencing parameters on panel properties.     

Estimation of physical and mechanical properties of agro-based particleboards by near infrared spectroscopy

Partial least square regression (PLS-R) calibrations based on near infrared (NIR) spectroscopic data were developed in order to predict mechanical and physical properties of agro-based particleboards. The panels were manufactured using Eucalyptus and Pinus wood particles and sugar cane bagasse. The following panel properties were evaluated according to standard methods: modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) strength, water absorption (WA24H), and thickness swelling (TS24H) after 24 hours of immersion. NIR spectra information was measured on samples cut from each particleboard and correlated with their physical and mechanical properties by PLS-R to build predictive NIR models. The NIR models for IB, WA24H and TS24H presented satisfactory coefficient of determination (0.73; 0.72 and 0.75, respectively.) The key role of resins (adhesives), cellulose, and lignin for NIRS calibrations of mechanical and physical properties of the particleboards is shown. These models can be useful to quickly verify such properties in unknown agro-based particleboards.     

Pilot study for MDF manufacture from sugarcane bagasse and eucalyptus fibers

As an innovation in scientific research and development of a new product and with the objective of adding value to sugarcane bagasse, laboratory panels were made with 0%, 25%, 50%, 75% and 100% particles from Saccharum spp bagasse mixed with Eucalyptus grandis fibers, a?raw material traditionally used for MDF panels in Brazil. The physical and mechanical properties of the panels were evaluated according to EN 622-5 (1997). The results indicated that panels with up to 75% bagasse showed average physical and mechanical property values that meet the current specification, thus opening up the prospect of using this abundant agricultural fiber resource.     

Effects of recycled fiber content on the properties of medium density fiberboard

The large global production quantity of medium-density fiberboard (MDF) creates equal quantities of waste MDF, which consequently requires research on the recycling of MDF. This work was conducted to study the effect of recycled fiber (RF) content on the recycling properties of MDF. After pretreating waste MDF, a refiner and hammer were used to isolate refiner RFs (RRFs) and hammer mill RFs (HRFs) from two softwood species. This work also characterized the physical, chemical, and morphological features of RFs and virgin fibers (VFs). RRF and HRF contents of 0, 5, 10, 20, 30, 50, and 100% were used to fabricate recycled MDF (rMDF) panels. All RFs had shorter fiber lengths and higher fines contents than VFs had. The presence of N from urea–formaldehyde resins was confirmed by multiple analyses; more N was distributed in RFs than in VFs. The highest internal bonding (IB) strength of the rMDF occurred at 10% RF, regardless of isolation method and wood species; IB strength decreased afterward. The mechanical properties, including modulus of rupture, modulus of elasticity, and screw withdrawal resistance of rMDF, showed behaviors similar to the IB strength with increasing RF content. However, the thickness swelling, water absorption, and formaldehyde emission of rMDF samples decreased with increasing RF content. Statistical analysis indicates that the minimum of 10% RFs can be used to replace VFs without diminishing the properties of rMDF. The improved properties of rMDF were ascribed to the reinforcing effects of RFs covered with cured resins.     

Dimensional stability and creep behavior of heat-treated exterior medium density fiberboard

A series of commercial phenol-formaldehyde bonded MDF panels were exposed to a post-manufacture heat-treatment at various temperatures and durations using a hot press and just enough pressure to ensure firm contact between the panel and the press platens. Physical properties and static flexural strengths of the post heat-treated MDF panels were evaluated according to ASTM D 1037 (2002). The results indicated that the post-manufacture heat-treatment of the exterior MDF panels resulted in improvement of thickness swelling. Water absorption and linear expansion properties were adversely affected by the heat-treatment. Modulus of rupture and modulus of elasticity values of the heat-treated panels decreased with increasing treatment temperature. A series of three 12-week creep tests were performed in climatic chambers conditioned at 65% RH, 90% RH, and cyclic 65–90% RH, all at a steady temperature of 20 °C. The creep tests generally followed procedures as specified in ASTM D 6815-02a (2002). Creep deflections of the panels increased with increasing temperature of the post heat-treatment.     

Properties of MDF from black spruce tops as affected by thermomechanical refining conditions

Wood composite industry has focused on traditional wood fibre resources such as logs, wood chips and sawmill-residues for panel manufacturing. It is becoming necessary now for the wood composite panel industry to look for ways to utilize non-traditional forest resources such as forest residuals for panel manufacturing. A full factorial experimental design with two factors: retention time of preheating and steam pressure of thermal mechanical refining and three levels with 3, 5, 7 minutes of retention time and 6, 9, 12 bar of steam pressure was carried out in the MDF pilot plant of Forintek Canada Corp. in Quebec City of Canada to evaluate the effect of refining conditions on the properties of MDF panels made from the tops of black spruce (Picea mariana). The results from this study indicate that black spruce tops could be a good raw material for MDF manufacture. The effects of steam pressure of thermomechanical refining on modulus of elasticity (MOE), thickness swelling (TS), water absorption (WA) and linear expansion (LE) were considerable. The effect of retention time of preheating on internal bond strength (IB) was significant. The effects of retention time as well as the interaction between retention time and steam pressure were also significant for modulus of rupture (MOR).     

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.     

Optimization of processing parameters of medium density fiberboard using response surface methodology for multiwalled carbon nanotubes as a nanofiller

In the present work, medium density fiberboard (MDF) panels were produced using multiwalled carbon nanotubes (MWCNT) reinforced urea formaldehyde resin. Response surface methodology was employed to optimize the relationship between the three variables, viz. pressing time, percentage of UF resin and percentage of MWCNT, used in the fabrication of MDF, and the influence of variables on the internal bonding (IB) and modulus of rupture (MOR) was studied. The optimum conditions based on the IB strength were determined as 8.18 % of UF resin, pressing time of 232 s, and MWCNT of 3.5 %. Similarly, the optimized conditions for MOR are also reported in this paper.     

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.     

纤维增强对镁基复合板物理力学性能的影响

以玻璃纤维为增强材料,以镁基无机矿物质为基体材料,制备了新型纤维增强镁基无机复合板.研究了短切纤维、纤维网格布以及短切纤维结合纤维网格布3种增强方式对镁基复合板的物理力学性能和耐湿热性能的影响.结果表明,纤维增强方式对镁基无机复合板的密度、含水率、吸水率等性能影响较小,对复合板的力学性能和耐湿热尺寸稳定性影响较大,采用...     

Microstructural Study,Tensile Properties,and Scanning Electron Microscopy Fractography Failure Analysis of Various Agricultural Residue Fibers

This paper presents an approach to examine the microstructural properties and mechanical behavior of coconut husks, banana pseudo-stem, pineapple leaf, and sugarcane bagasse fibers by scanning electron microscope and mini-tensile tester, respectively. Single fiber bundles were examined by using scanning electron microscope. Tensile tests were performed at different diameters (0.15–0.55 mm) and gauge lengths (10, 15, 20, and 30 mm/min) to assess the effects of diameter and gauge length on tensile properties. It was found that fibers consisted of different types of regularly arranged cells. The tensile strength (310 MPa) and Young’s modulus (7.4 GPa) of pineapple leaf fiber bundles showed the highest value compared to the other fibers. The tensile strength and Young’s modulus decreased with the increase of diameter and gauge length of fiber bundles. Scanning electron microscopic fractography analysis showed comparatively heterogeneous ruptures associated with more participants of microfibrils for pineapple leaf and banana pseudo-stem fibers compared to coconut husk and sugarcane bagasse fibers. These fractographic observations were discussed in the light of current knowledge of the microstructure of each fiber and the corresponding mechanical properties.     

Natural Fiber Improvement by Laccase; Optimization,Characterization and Application in Medium Density Fiberboard

Crystallinity of cellulosic fiber directly affects the physical and chemical behavior of the individual fiber and ultimately the product made from. In a controlled condition, if the natural fiber is exposed to enzymatic hydrolysis, its crystallinity improves without affecting the cellulose component of the fiber. In this work, four basic factors for enzymatic reaction, i.e., temperature, time, pH, and enzyme amount, were optimized using response surface methodology (RSM). The response was taken as the fiber crystallinity index, measured by X-ray diffraction method. The optimum treated fiber was further analyzed for the field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and results were compared with untreated fiber. Medium density fiberboards (MDF) were manufactured from optimum treated fiber and its tensile properties and water resistance properties were compared with MDF made from untreated fiber. The observation revealed a maximum of up to 14% increment in fiber crystallinity index (CrI) as compared to untreated fiber. The MDF prepared from optimum treated fiber exhibits improved tensile property and lower water absorption property as compared to MDF prepared from untreated fibers.     

Empirical correlations between test methods of measuring formaldehyde emission of plywood, particleboard and medium density fiberboard

Since different test methods of measuring the formaldehyde emission (FE) from wood-based composite panels have been used for different countries and regions, this study attempted to establish empirical correlations between three test methods (i.e., 24-hour desiccator, 1 m³ chamber, and perforator) for plywood (PLW), particleboard (PB), and medium density fiberboard (MDF), particularly emphasizing on correlations between the 24-hour desiccator and the 1 m³ chamber method. The desiccator method found statistically high correlations with other two methods, resulting in regression coefficient values ranging from 0.96 to 0.88 for PLW, PB, and MDF samples. In particular, the desiccator method had an empirically high correlation with the 1 m³ chamber method that had been adopted as the reference method of comparing regionally different test methods of measuring the FE of wood-based composite panels by the ISO/TC89.     

Vergleichende Untersuchungen an mittelharten Faserplatten (MDF) und Spanplatten

Mechanical and physical properties of commercial medium density fiberboard (MDF) and particleboard were determined and compared. The investigation showed that bending strength and face strength for MDF were considerably higher than corresponding particleboard properties. Concerning internal bond strength and screw holding ability no remarkable differences were found between the two board types. Medium density fiberboard showed lower hygroscopicity and thickness swelling but higher linear expansion than particleboard. Both board types were found to have higher bending strength and lower linear expansion parallel rather than perpendicular to feeding direction. Furthermore MDF showed lower surface roughness than particleboard.     

Virtual characterization of MDF fiber network

A virtual design method for medium density fiberboards (MDF) is proposed with the aim to optimize the fiber orientation and lay-up of MDF. The new method estimates the stiffness and strength by using microstructure models of the MDF fiber network. The virtual design is used to improve the manufacturing technology of MDF plates with multilayer oriented fiber structure. Experimental investigations of the mechanical behavior of MDF microstructure for various fiber geometries, glue content and distribution are complicated, time consuming and expensive. On the other side, virtual microstructure design allows to develop a new wood fiber based material with less experimental work. Microstructure models help to better understand the non-linear damage mechanical behavior of a wood fiber network depending on fiber geometrical parameters. Such parameters as crack distribution and fiber deformation on micro-scale level are complicated to experimentally measure, but possible to model using computer simulations. The virtual design tool requires less empirical data. The model takes into account information on average wood fiber orientation, fiber diameter, fiber length and mechanical properties of wood fiber cell wall and glue. The numerical method for strength and stiffness analysis of MDF microstructure was calibrated using standard MDF with non-oriented fibers. It turned out that this method gives precise results for MDF with oriented fibers and even with multilayer structure. The proposed virtual microstructure design tool can significantly improve and speed-up the optimization manufacturing technology of MDF and other wood fiber based composites.     

防潮中纤板用改性脲醛胶新工艺的开发

通过添加自制助剂和三聚氰胺对脲醛胶进行改性。用改性脲醛胶制备的中纤板性能达到GB/T 11718—2009《中密度纤维板》中普通型及家具型中密度纤维板在潮湿状态下的使用要求;用改性脲醛胶工业化生产地板基材用纤维板,其性能达到LY/T 1611—2003《地板基材用纤维板》的要求。     

The effect of Na+ montmorillonite (NaMMT) nanoclay on thermal properties of medium density fiberboard (MDF)

In this study, the potential use of nanotechnology was evaluated to improve the thermal properties of medium density fiberboard (MDF). For this, Na⁺ montmorillonite (NaMMT) nanoclay was added to urea formaldehyde resin to produce MDF. In order to characterize the structure of the MDF, X-ray diffraction (XRD) and SEM observation were performed, and the thermal properties were examined using thermogravimetric analysis (TGA), differential thermal analysis (DTA), thermal conductivity test and fire test. Characterization of the MDFs shows that dispersed and exfoliated structures were generated by the hot press. The X-ray diffraction confirmed the suitable exfoliation of NaMMT in the MDFs containing NaMMT. The SEM images of NaMMT-added boards showed a suitable dispersion of NaMMT through the MDF. The results of thermal tests indicated a desirable effect of NaMMT on thermal-oxidative stability and thermal conductivity of MDF.     

Utilization of bark flours as additive in plywood manufacturing

Increasing demand for wood based panel products and shortage of wood as raw material have triggered many efforts to utilize residues generated annually by the forest industries including a large portion of bark in panel production. In this study, the effects of using bark flours as additives obtained from different wood species (walnut, chestnut, fir and spruce), having much polyphenol content, on some physical and mechanical properties and formaldehyde emission of plywood panels were examined. Wheat flour, which has been used widely as additive in plywood manufacturing, served as control. Plane tree (Platanus orientalis) logs were obtained for veneer manufacturing. Urea formaldehyde (UF) resin with 55 % solids content was used as adhesive. The bonding shear strength, bending strength, modulus of elasticity (MOE), density, equilibrium moisture content and formaldehyde emission of plywood panels were determined according to related standards. It was found that the use of flours obtained from the barks of chestnut and fir trees in the glue mixture decreased the formaldehyde emission of panels. The bonding strength values of the test panels made using the glue mixture including the flour of walnut and spruce barks as additive were lower than those of the panels with adhesive containing the flour of fir and chestnut barks. The panels manufactured with adhesives including the flour of fir bark gave the highest bending strength and modulus of elasticity values.     

Effect of panel properties on the concentrated static load (CSL) performance of oriented strand board (OSB)

The relationship between concentrated static load (CSL) performance of oriented strand board (OSB) and panel thickness, local density, and some mechanical properties (including modulus of elasticity (MOE), modulus of rupture (MOR), and interlaminar shear strength in both major and minor directions) was investigated using both a simple linear regression method and a stepwise multi-linear regression technique. The sample boards were laboratory manufactured OSB panels consisting of eighteen combinations of different strand geometries (length, width, and thickness), strand orientations, and fines contents. Simple linear regression analysis showed that MOE (major direction), MOR (major direction), shear strength (major direction), local thickness, average board density and local density were all significantly and negatively correlated with the CSL deflection; however, in the stepwise multi-linear regression analysis only MOE (major) and local thickness were retained as significant factors possibly due to inter-correlation amongst the variables. Shear strength (major direction), MOR (major direction), average board density, MOE (major direction), MOR (minor direction), local thickness, average board thickness, local density, and shear strength (minor direction) were all found to be significantly and positively correlated with the CSL ultimate load in the simple regression analyses, but only shear strength (major) and local panel thickness were retained in the stepwise multi-linear regression model for the CSL ultimate load.     

Effect of Filler Content of Chemically Treated Short Bagasse Fiber-Reinforced Cardanol Polymer Composites

In this work, the sugarcane bagasse fiber was used as a filler to make a new type of biodegradable composite, using the cardanol resin, as a fully biodegradable thermosetting polymer matrix. Biocomposite performance was improved by chemically modified bagasse fiber using alkaline treatment. Two sets of composites were prepared with a fiber length of 10 and 20 mm with various weight percentages viz., 0, 5, 10, 15, and 20 of cardanol resin using a compression molding machine. The mechanical properties were studied using some tests and the morphological study in flexural fractured specimens was carried out using SEM. The thermal properties of biodegradable polymer composites were evaluated using TGA. The chemical formation of the new biocomposites was also examined by the FT-IR spectroscopy technique. The result proved that the morphology of the composites has improved the bonding between the fiber and resin, thus leading to enhancement of the mechanical properties. The result had shown the tensile and flexural strength with an increase in the range of bagasse fiber up to 15 wt% in both the sets. The TGA results showed that biocomposites of 15 wt% in both sets had the highest thermal stability. This investigation recommended the possibility of introducing bio-fiber obtained from waste agricultural residues in polymer matrix composites.