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Fig. 3. Differences in mechanical properties (modulus of rapture (MOR), modulus of elasticity (MOE), and internal bond strength (IB)) of the tested panels
Table 1. General Purpose Boards for Use under Dry Conditions (Type P1) - Requirements for Specified Mechanical Properties (MOE for P1 boards is not defined by the standard) Property Test method Unit Requirement Thickness range (mm, nominal) < 3 3 to 6 > 6 to 13 > 13 to 20 > 20 to 25 > 25 to 32 > 32 to 40 > 40 EN 319 N/mm 2 0.14 NOTE: The values are characterised by moisture content in the material corresponding to a relative humidity of 65 % and a temperature of 20 °C. 0.31 0.31 0.28 0.24 0.20 0.17 0.14 It should be also noted that all the variants of panels in terms of MOR and MOE met the requirements for lightweight particleboard LP1 (CEN/TS 16368 (2014)), while the IB requirement was met by poplar-pine particleboard. It is commonly agreed that the MOR of a panel is strongly correlated with the density of the face layers and mat compression, which are in turn determined by the chip geometry and their density. Lower density leads to a higher compression ratio of a mat and higher contact surface between chips is developed, so that the total bondline surface is larger (Grigoriu 1981; Xu et al. 2004). The data indicated that the highest MOR and MOE values were obtained for the panels containing poplar face layers, while the highest IB were observed for the mixed poplar-pine and neat pine panels. Higher MOR and MOE for poplar series resulted primarily from the higher chip compaction and lower porosity in a layer, while the densities of the face layers remained similar to each other (Fig. 2, Fig. 4). Figure 4 indicates that the structure of the poplar boards was more compact, which resulted from lower bulk density of poplar raw material and its easier compaction. Thus, internal empty spaces volume is minimized and no clear boundary between face and core layers can be observed. The porosity of core of the pine and mixed boards was Bending strength (MOR) Internal bond (IB) EN 310 N/mm 2 11.5 11.5 10.5 10 10 8.5 7 5.5
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Boruszewski et al . (2016 ). “Particleboard density ,” B io R esources 11(3), 6909-6919.
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