Fracture energy vs. internal bond strength – mechanical characterization of wood-based panels

Abstract

A new testing method measuring the specific fracture energy of wood-based panels in Mode I is proposed. Three types of wood-based panels, i.e. oriented strand board (OSB), particleboard (PB) and medium density fibreboard (MDF) are investigated, using fracture energy and the industrial European standard method of internal bond strength according to EN 319. Double cantilever beam specimens are notched in the middle layer to introduce an initial crack. To apply tensile load perpendicular to the surface of the panels to open the crack in Mode I specimens were adhesively bonded to steel braces. Besides the calculation of the total fracture energy an advanced analysis of the load–displacement curve was also performed. Results of the fracture energy method were compared to internal bond strength (IB). Specimen shape is optimized for industrial purposes using double cantilever beams, while the determination of the fracture energy is performed by simple integration of the load–displacement curve. While IB showed a large scattering of data, the fracture energy test yielded statistically significant differences between the board types.     

Effect of element type on the internal bond quality of wood-based panels determined by three methods

Three mechanical tests with different loading modes were conducted to evaluate the effect of element type on the internal bond quality of wood-based panels. In addition to the internal bond test, which is commonly used for mat-formed panels, interlaminar and edgewise shear tests were used to test oriented strandboard (OSB), particleboard, medium-density fiberboard (MDF) of two thicknesses, and plywood. The following results were obtained. Epoxy resin proved to be suitable for determining the interlaminar shear modulus instead of hot-melt glue. There was a linear relation between panel density and interlaminar shear modulus and a linear correlation between the interlaminar shear strength and internal bond (IB) strength for the mat-formed panels tested. OSB had the highest edgewise shear modulus, and MDFs had the highest edgewise shear strength in this study. The modulus/strength ratio also depended on both panel type and loading mode. The relation between the shear moduli determined from the edgewise and interlaminar tests indicated the characteristics of the shear properties of panels made of different elements.Part of this paper was presented at the Fourth International Wood Science Symposium, Serpong, Indonesia, September 2002     

检测条件对人造板吸水厚度膨胀率测定结果的影响

研究了恒温恒湿处理和浸渍温度对人造板吸水厚度膨胀率检测结果的影响.结果表明:中密度纤维板和刨花板的测定值随着浸渍温度的升高而增大,两者存在着一定的线性关系,而胶合板则受水温影响很小;在浸渍前试件进行恒温恒湿处理与否会影响测试结果.对于刨花板和薄型中密度纤维板,进行恒温恒湿处理是必要的.     

我国人造板出口现状及目标市场形势分析

2011年我国人造板出5 245 911 541美元,品种包括胶合板、细木工板、刨花板、中密度纤维板等。笔者依据2007～2011年我国人造板出口贸易情况,分析了我国人造板出口所面临的机遇与挑战,提出了国拓展人造板国际市场的思路。     

Fatigue in wood-based panels. Part 1: The strength variability and fatigue performance of OSB, chipboard and MDF

Wood-based panels used as floor decking can be exposed to fatigue as well as creep loading. The strength and fatigue performances of three wood-based panel products OSB, chipboard and MDF have been determined in four-point bending. The mean bending strengths were found to decrease in the following order MDF>OSB>chipboard. The bending strength variation within the OSB was considerably greater than that for chipboard and MDF. Normalised with respect to the static strengths, the fatigue performance of the chipboard was superior to that of the OSB, although the two materials have very similar performances at low stress levels. Normalised with respect to the static strengths, the fatigue performance of the MDF was inferior to both materials and at lower stress levels the fatigue performance deteriorated to a greater extent. However, in terms of absolute applied stress, the fatigue performance of the MDF was superior to that of the OSB, which was superior to that of the chipboard. However, as the stress was reduced the difference between the three materials reduced. At low stresses the performances of the three materials were quite similar. Received 5 August 1999     

一种脲醛树脂胶粘剂的设计

鉴于对文献的分析和实验验证,本文提出一种脲醛树脂胶粘剂的设计原则。即:1)脲醛树脂最终摩尔比应取1.40～1.20:1,这样可以使制成的板材具有足够的胶接强度;2)为了使人造板的甲醛释放量达到10mg/100g(穿孔法)以下,树脂中的游离尿素应在10%以上;3)在脲醛树脂的分子中引入尿素的环状衍生物,如三嗪环或Uron。环状化合物含量最好在10%左右。按此原则合成了三种树脂,在试验室按标准刨花板和中密度纤维板工艺制成板材,其甲醛释放量在10mg/100g左右,板材物理力学性能均超过国家标准和企业标准。     

定向刨花板在建筑中的应用前景

本文扼要介绍了国外木材制品在建筑中的应用情况，探讨了木材制品特别是定向刨花板(OSB)在中国建筑中的应用前景，为扩大中国的OSB市场提出建议。     

Fatigue in wood-based panels. Part 2: property changes during fatigue cycling of OSB, chipboard and MDF

Wood-based panels are viscoelastic so when a load (stress) is applied to them there is a time lag before a deflection (strain) is produced, which results in hysteresis (a loss of energy). The capture of stress versus strain hysteresis loops is a non-interruptive method of monitoring the damage produced during fatigue testing. Hysteresis loops were captured throughout the flexural fatigue testing of OSB, chipboard and MDF in four-point bending allowing the development of fatigue damage to be followed. The MDF tested had a greater mean bending strength than the OSB and chipboard. When stresses were applied to the materials as a percentage of their bending strengths, the stresses applied to the MDF samples were larger than those applied to the OSB and chipboard samples. As a result the microstrains were greater for MDF than for the chipboard and OSB. The OSB was stiffer than the chipboard and MDF, which were both of similar stiffness. The information gained from the hysteresis loops indicates that the OSB, chipboard and MDF all had fatigue limits just below 20% of their bending strengths. The fatigue limit for the MDF is likely to be slightly lower than for the chipboard and the OSB.     

Deterioration of wood-based boards subjected to outdoor exposure in Tsukuba

Various types of wood-based boards were analyzed for deterioration after being exposed to an outdoor environment for 5 years in Tsukuba, Japan. In phenol–formaldehyde resin bonded particleboard (PB(PF)) and aspen oriented strand board (OSB(aspen)), longer exposure caused a greater reduction in the modulus of rupture and internal bond strength, an increase in the coefficients of variation, and a decrease in 95 % lower tolerance limit at the 75 % confidence level (95TL). Nail-head pull-through and lateral nail resistance were also reduced by outdoor exposure, but their coefficients of variation and 95TL were not significantly affected. In contrast, methylene diphenyl diisocyanate bonded medium density fiberboard (MDF(MDI)) only showed a slight deterioration of these properties even after 5-year exposure, and the coefficients of variation and 95TL hardly changed. After 5-year exposure, the retention of shear load in one-plane at relative displacement of 1.0 mm was high in MDF(MDI) and OSB(aspen) at 93.5 and 78.5 %, respectively, but low in PB(PF) at 41.1 %. As with PB(PF), OSB(aspen) also showed a sharp decrease in the modulus of rupture and internal bond strength, but only slightly reduced shear load in one-plane.     

Veneer strand flanged I-beam with MDF or particleboard as web material IV: Effect of web material types and flange density on the basic properties

The balance of strength between the flange and web parts of veneer strand flanged I-beam was investigated by the following methods: (1) use of different web material types, such as plywood, oriented strand board (OSB), particleboard (PB), and medium density fiberboard (MDF), that have different strength properties; and (2) fabrication of I-beams with low-density flanges using low-density strands with PB web material. Replacing PB or MDF with plywood showed slight significant improvement in the modulus of rupture but not in the modulus of elasticity of the entire I-beam. However, PB and MDF showed competent performance in comparison with OSB, thus strengthening the promising future of the use of PB or MDF as web material to fabricate I-beams. Hot-pressing conditions used for I-beam production exerted slightly adverse effects on the bending properties of PB, but not on MDF, OSB, and plywood web materials. The flange density of 0.60 g/cm³ was considered to be the lower limit that provides I-beams with balanced mechanical properties and dimensional stability.     

定向结构刨花板产品市场现状与展望

详述近10年来全球范围定向结构刨花板(OSB)的生产能力、实际产量、主要用途、进出口贸易情况,分析和预测未来几年OSB的全球发展趋势,指出中国OSB的发展存在可观的潜在市场.     

表面型电磁屏蔽木基复合材料的制备及性能

选用镀镍布和粗化铜箔,制备具有电磁屏蔽功能的复合人造板。根据接合面的特点,分别选用聚醋酸乙烯乳液和环氧树脂,将镀镍布和粗化铜箔胶贴于人造板表面。性能检测结果表明,所制得的复合人造板的力学性能比人造板基材增强,镀镍布复合板的电磁屏蔽效能约60dB,铜箔复合板大于70dB,可满足屏蔽室建造用材的要求。     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard

The static strength, stiffness and fatigue life of MDF, OSB and chipboard have been measured in a 65%RH environment and a 85%RH environment. Chipboard is commonly utilised as a flooring material and OSB is also used in structural applications, for example floor decking and webs of I-beams. The mean static strengths of MDF, OSB and chipboard at 65%RH were 47.9 MPa, 27.9 MPa and 21.0Mpa, respectively, compared with 34.59 MPa, 21.70 MPa and 10.61 MPa at 85%RH. However, MDF has mostly been used in non-structural applications, such as furniture, so its resistance to fatigue loads as a structural panel is of considerable interest. In a 65%RH environment dynamic modulus values showed that whilst MDF and chipboard exhibit similar stiffness values (4 GPa), OSB is approximately 50% stiffer. However, at 85%RH MDF was the stiffest of the three materials, followed by OSB and chipboard. The fatigue life performance of all three panel products was markedly lower at 85%RH compared with 65%RH. Overall, the high RH environment had a noticeably detrimental effect on the MOE (modulus of elasticity), MOR (modulus of rupture) and fatigue lives of OSB and chipboard. This is attributed to these panels retaining more of the original characteristics of the original wood, i.e. larger particle sizes (flakes/chips) compared with the homogeneous fibrous composition of MDF. Received 5 November 1999     

A multiple criteria analysis of factors affecting markets of engineered wood products with respect to customer preferences: a case study of particleboard and MDF

Of considerable importance and a principal goal in business is the creation of customer satisfaction. Evalu- ation of end user preferences for producers of particleboard and medium density fiberboard (MDF) requires indices for the assessment of markets and modification of product quality. However, only sporadic research has been carried out in this field. Therefore, the goal of this survey was to identify indices with respect to the points of view of: 1) consumers in order to select particleboard and MDF, 2) suppliers in order to consider production strategies, improve product quality, improve competitive ability of domestic producers in the market and help industry to be more customer oriented. This survey consisted of two stages. In the first stage, factors affecting customer preferences in the selection of particleboard and MDF were determined using a Delphi method, with the help of experts and a group of principal users of these prod- ucts. Then these factors were categorized in three groups: qualitative, technical and technological and marketing factors. Furthermore, questionnaires were prepared and distributed among consumers and responses evaluated and weighted by using an analytic hierarchy process (AHP) using expert choice software. Our results show that at both stages, the consistency ratio was less than 0.1, indicating that all results and judgments were stable and acceptable. The results obtained from questionnaires about particleboard rank the priorities for factors in the selection by consumers as follows: nail and screw holding ability, homogeneity in structure, edge strength of panel, durability and bending strength. The most important factors for MDF were machinability of panels, homogeneity in structure, nail and screw holding ability, edge strength of panel, durability and bending strength.     

Dimensional stability of MDF panels produced from fibres treated with maleated polypropylene wax

Medium-density fibreboard (MDF) was produced from fibres treated with maleated polypropylene wax. The objectives of this study were to improve the dimensional stability of MDF panels by this treatment; to observe the maleated polypropylene wax distribution within the MDF panels using conventional fluorescence microscopy; and to determine the effects of the treatment on the mechanical properties and vertical density profile of the panels. MDF panels were produced from two resin types (urea-formaldehyde and melamine-urea-formaldehyde) and three maleated polypropylene wax contents (0, 3 and 5%). Photomicrographs show that maleated polypropylene wax forms agglomerates within the MDF panels which is an evidence of its poor distribution in our experimental conditions. Our results show an important reduction on thickness swelling and water absorption after water soaking for panels produced from treated fibres. Linear expansion and contraction in adsorption and desorption conditions between 80 and 50% relative humidity increased following fibre treatment. However, thickness swelling and shrinkage in similar conditions showed an important reduction following fibre treatment. The fibre treatment did not have negative effects on the mechanical properties or the vertical density profile of MDF panels. The modulus of rupture and modulus of elasticity in bending were increased by the treatment independently of maleated polypropylene wax content. The internal bond strength increased following the addition of 5% maleated polypropylene wax content.     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard.

The fatigue and creep performance of MDF, OSB and chipboard have been examined in two environments, namely 65%RH (standard environment) and 85%RH (high humidity). Parallel fatigue and creep tests have been performed in four-point bending on the three wood-based panel products in the two environments. The constant 65%RH environment is service class 1 and the constant 85% RH environment is indicative of a service class 2 environment as detailed in Eurocode 5. The non-interruptive technique of stress-strain hysteresis loop capture has been utilised to follow property changes of the fatigue samples during cyclic loading at a stress ratio of R equal to 0.1. Loop parameters such as loop area, dynamic modulus, and fatigue modulus have been used to characterise the response of these materials to fatigue loads in the two environments. Creep microstrains for the creep samples were recorded in parallel with the fatigue parameters. Fatigue and creep results at 85%RH were more variable than those reported at 65%RH for MDF, OSB and chipboard. In general, at R=0.1 and 85%RH, fatigue and creep microstrains were higher, dynamic stiffnesses were lower and hysteresis loop areas were higher than corresponding properties measured at 65%RH. MDF and chipboard were less moisture tolerant than OSB, this is reflected in the large changes in fatigue and creep parameters.     

酸碱处理对制备再生桉木颗粒板的影响

废弃人造板中的胶黏剂影响人造板的回收利用。笔者利用化学法对废弃桉木颗粒板中的胶黏剂进行处理,分别探究不同浓度的硫酸、甲酸、硝酸、氢氧化钾分解废弃木颗粒板中脲醛树脂的最佳条件。结果表明,在90℃,水浴处理2 h条件下,甲酸浓度大于60%,硫酸浓度大于25%,或硝酸浓度大于25%可完全分解固化后的脲醛胶黏剂;对酸处理后的木颗粒的颜色、形貌、化学性质进行分析,甲酸对木颗粒的形态、颜色影响较小。用酸处理后制得的再生木颗粒板,力学性能相对于未经处理的再生木颗粒板得到显著提高。     

热压工艺参数对三聚氰胺饰面刨花板甲醛释放量的影响

以市售刨花板和三聚氰胺浸渍纸为原料,制备三聚氰胺饰面刨花板.采用L9（34）正交试验考察热压温度、热压时间、热压压力3个热压工艺参数对三聚氰胺板甲醛释放量的影响.采用国家标准（GB/T 17657-1999）《人造板及饰面人造板理化性能试验方法》干燥器法检测甲醛的释放量.试验结果表明,热压温度对甲醛释放量影响最大、热压时间其次、热压压力影响最小,其中热压温度对甲醛释放量有显著影响,热压时间和热压压力的影响并不显著.热压工艺参数提高,会引起热压后的三聚氰胺板前期的甲醛释放量明显升高.确定饰面刨花板甲醛低释放的最优化生产工艺参数为热压温度170℃、热压时间40s、热压压力2.5 MPa.     

Comparison of internal bond strength and compression shear strength of wood-based materials

The purpose of this study was to design a compression shear device for easy and fast measurement of the bonded shear strength of wood-based materials to replace the conventional method used to evaluate internal bond strength (IB). To assess the performance of this device, five differently sized specimens, included group I (dimension 5 × 1 cm), group II (5 × 2 cm), group III (5 × 3 cm), group IV (5 × 4 cm), and group V (5 × 5 cm) cut from commercial particleboard and medium-density fiberboard (MDF) (1.8 cm thick) were tested in compression shear. Only group V (5 × 5 cm) was prepared for the IB test. Results indicated that the compression shear strengths (CS) of particleboard and MDF, loaded in the horizontal or the diagonal direction, were greater than the IB, although a significant correlation existed between the two. This finding suggests that the IB of particleboard and MDF could be accurately estimated from the data collected by the CS test.Part of this report was presented at the Third Pacific Rim Bio-based Composites Symposium, Kyoto, December 2–5, 1996     

Comparative study on measurement of elastic constants of wood-based panels using modal testing: choice of boundary conditions and calculation methods

Modal testing based on the theory of transverse vibration of orthotropic plate has shown great potentials in measuring elastic constants of panel products. Boundary condition (BC) and corresponding calculation method are key in affecting its practical application in terms of setup implementation, frequency identification, accuracy and calculation efforts. To evaluate different BCs for non-destructive testing of wood-based panels, three BCs with corresponding calculation methods were investigated for measuring their elastic constants, namely in-plane elastic moduli (E _x , E _y ) and shear modulus (G _xy ). As a demonstration of the concept, the products used in this study were oriented strand board (OSB) and medium density fiberboard (MDF). The BCs and corresponding calculated methods investigated were, (a) all sides free (FFFF) with one-term Rayleigh frequency equation and finite element modeling, (b) one side simply supported and the other three free (SFFF) with one-term Rayleigh frequency equation, (c) a pair of opposite sides along minor strength direction simply supported and the other pair along major strength direction free (SFSF) with improved three-term Rayleigh frequency equation. Differences between modal and static results for different BCs were analyzed for each case. Results showed that all three modal testing approaches could be applied for evaluation of the elastic constants of wood-based panels with different accuracy levels compared with standard static test methods. Modal testing on full-size panels is recommended for developing design properties of structural panels as it can provide global properties.