Utliization of White Fir Bark and Its Extract in Particleboard

The suitability of white fir bark extract as a bonding agent for particleboard and the use of the bark as core furnish in a three-layer particleboard were evaluated. When paraformaldehyde was added to wood particles which had been sprayed with concentrated bark extract and processed into board, formaldehyde released during the hot press cycle reacted in situ with polyphenolic compounds present in the extract and formed a waterproof bonding agent. The average 3/4-inch three-layer bark extract bonded particleboard had a SG of 0.72, MOR 3104 psi, IB 141 psi, water absorption 14.4 percent, thickness swelling 3.3 percent and 2-hour boiling-in-water thickness swelling of 24.7 percent. Bark containing a small amount of paraformaldehyde was used as core in a three-layer board, and bark extract was used as the bonding agent for the outer wood-particle layers. The average 3/4-inch three-layer bark core board had a SG of 0.72, MOR 2143 psi, IB 119 psi, water absorption 13.7 percent, thickness swelling 4.2 percent and-2-hour boiling-in-water thickness swelling of 18.2 percent. Each type of board met specifications for a medium density particleboard and was comparable to some synthetic phenolic resin exterior-type particleboards in moisture resistance. Production cost could be reduced by employing bark extract as bonding agent and further reduction in costs would be realized by using bark as core in three-layer particleboard. The yield of white fir bark extract solids amounted to around 340 pounds per ton of bark.

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