Hydrochloric acid is emitted from the particleboard mat made with ammonium chloride and aluminium sulphate during hot pressing while sulfuric acid is omitted from the particleboard made with ammonium sulphate. The hardener reacts with the free formaldehyde in the UF resin to generate acid, which decreases the pH; this low pH and hence the acidic conditions enable the restart of the condensation reaction and finally the gelling and hardening of the resin. Since hydrochloric acid is more volatile than sulfuric acid, it spreads more uniformly in all directions. This provides a more uniform curing of the UF resin, which improves the bonding performance among the wood particles in the particleboard [21]. The statistical analysis showed that the use of urea affected only the formaldehyde emission apart from mechanical properties. Urea reacts with certain of free formaldehyde and significantly decreases formaldehyde emission from particleboard in service [22].