4. Conclusions
The quality properties of the particleboards were significantly affected by the hardener type, urea usage, and conditioning period. Although the incorporation of the urea into the UF resin significantly decreased the formaldehyde emission of the particleboards, other properties were not significantly affected by the urea application. The incorporation of urea into the resin slightly decreased the mechanical properties and increased thickness swelling. The best quality properties were obtained from the particleboards made with ammonium chloride, followed by ammonium sulphate and aluminium sulphate, respectively. Increasing conditioning time of particleboards from one day to one month significantly improved the mechanical strength and surface quality properties, and decreased the formaldehyde emission and thickness swelling. Based on the findings obtained from the present study, it can be said that the lowest thickness swelling and highest strength values were obtained from one month conditioned particleboards made with ammonium chloride without urea. The lowest formaldehyde emission was obtained from one month conditioned particleboards made with ammonium chloride with urea.