Douglas-Fir and Western Hemlock Bark Extracts as Bonding Agents for Particleboard

This study was undertaken to evaluate the suitability of Douglas-fir and western hemlock bark extracts as bonding agent for particleboard. When a small amount of paraformaldehyde was added to wood particles which had been previously 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. Each of the bark extracts produced boards which met specifications for medium-density particleboard and were comparable to some synthetic phenolic resin exterior-type particle boards in moisture resistance. Production costs could be markedly reduced by employing bark extract as bonding agent. The yield of bark extracts from Douglas-fir and western hemlock amounted to about 350 lb. of phenolic-bearing extract solids per ton of dry bark.

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