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ABSTRACT
Effects of urea addition to oriented strandboard (OSB) binder phenol-formaldehyde (PF) resol resins were investigated at 0, 10, 18, and 26% urea addition levels. PF resins were synthesized at these urea levels with the resin solids levels and viscosities being kept approximately constant at 50% and 150 − 250 cP, respectively. Analysis results of synthesized resins indicated that the urea additions lowered the free formaldehyde content and increased the degree of polymerization but decreased the curing rates. Evaluation of the laboratory OSBs manufactured using the synthesized resins as binders showed that the internal bond (IB) strength and the water soak properties were decreased gradually as the urea addition level was increased.