3. Results and discussion
The acidity of the particles, physical and mechanical properties, formaldehyde emission, surface roughness, and contact angles of the particleboards are presented in Table 2, Table 3, Table 4, Table 5 and Table 6. The pH of the wood particles before the blending process was found to be 5.39 while it was found to be 4.32–5.02 after the blending with the UF resin depending on the hardener type and urea usage. The pH of wood particles with urea was slightly higher than that of the wood particles without urea. The urea usage was not found to be effective on the acidity of the particles according to the Newman–Keuls test results (Table 6). However, the acidity of the wood particles was significantly affected by the hardener type. The lowest pH value was found for the particles with ammonium chloride while the highest pH value was found for the particles with aluminium sulphate (Table 2). The pH values of wood particles with the UF resin were decreased by the hardener because the hardener acted as an acid catalyst for the curing reaction of the UF resin. The wood partices with aluminium sulphate had the lowest pH value among the studied hardener types due to the fact that its acidity level was lower than ammonium sulphate and ammonium chloride.