Bonding Particleboards with Bark Extracts

Ponderosa and tanoak barks as well as the Douglas-fir bark fraction Silvacon 472 were extracted with hot aqueous carbonate to provide extracts that were used in bonding particleboards. Fresh ponderosa bark was a better source of extract than run-of-mill ponderosa bark. The highest extract yield was obtained from tanoak bark, but this extract was the most unstable. The boards bonded at optimum moisture content of extracts from fresh ponderosa and tanoak barks had moduli of rupture closely approximating those obtained for boards bonded with a urea-formaldehyde resin, but the synthetic-resin bonded group had a lower water absorption. For boards bonded with extract from fresh ponderosa bark, modulus of rupture increased as the moisture content of the board furnish was reduced from 28 to 15 percent, whereas when extract from tanoak bark was used, modulus of rupture de creased as the moisture content of the furnish was reduced from 29 to 19 percent.

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