Particleboards play an important role in the wood industry, since they give added value to recycled and low value wood. Particleboard is made from fine particles in the surface layer and medium size particles in the core layer. Even though they are supposed to be symmetrical, in practice this is mostly not the case. This has been seen in comparisons of the bending strength of the upper and lower sides of panels and through the neutral axis position. In the presented research we investigated the impact of changes in the surface layers on some mechanical properties, as well as on the location of the neutral axis. We made asymmetrical boards from spruce wood with a surface to core layer ratio of 50/50. The difference between panels is in the distribution of the surface layer. In board A the upper and lower parts of the surface layer had an equal mass of particles (50/50), while in panel B the surface layer ratio between the upper and lower sides was 30/70 and in panel C 10/90. We determined the density, density profile, bending strength, modulus of elasticity and internal bonding strength. We also determined the location of the neutral axis with regard to panel structure. The tests were comparable and showed that with different ratios the neutral axis moves from the middle of the board to the lower outer layer. The results of the tests make it possible to determine how a board is made, and how best to use, embed or even make it again.
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