Screw Withdrawal Resistance and Surface Soundness of Three-Layer Fiberboard Having Coarse Fibers in Core Layer

Screw withdrawal resistance (SWR) and surface soundness of three-layer MDF were investigated and the results were compared to the single-layer MDF. For this aim, effects of various formulation variables such as coarse fiber length (24.4 to 4.3 mm), resin content (10.5 to 6.5 wt%) in the core layer, average panel density (730 to 650 kg/m3), and surface/core layer ratio (70/30 to 30/70) were determined. The face and edge SWR and surface soundness of three-layer MDF panels were determined according to EN 320 and EN 311 standards, respectively. The results showed that the face SWR and edge SWR of MDF panels improved as the fi ber length increased from 4.3 to 11.5 mm in the core layer. Similar results were determined for the surface soundness. The surface soundness of MDF panels improved with increasing fiber length in the core layer up to 17.8 mm. SWR and surface soundness improved with increasing resin content in the core layer, shelling ratio, and panel density.