2. Materials and methods
2.1. Raw materials
Paper sludge was provided from Mazandaran Wood & Paper mill (CMP1 and NSSC2 processes). The characteristics of the paper sludge used in this study are given in Table 1. Wood particles were purchased from North Wood Composite mill. Two synthetic adhesives were used, namely urea formaldehyde (UF) at levels of 10% and 12%, and methylene diphenyl diisocyanate (MDI) at levels of 3% and 4% (oven dry solid wood basis). The characteristics of the adhesives used are given in Table 2. Ammonium chloride (NH4CL) was added as a hardener in urea-formaldehyde adhesive at a level of 2% (dry resin basis).