Improvement of Properties of Particleboard by Impregnation with Phenolic Resin.

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Particleboards(PB)were treated with a low molecular-weight phenolic resin and their properties were evaluated. Particles were dipped into aqueous solutions of resin or sprayed with resin solutions before spraying the conventional phenolic resin adhesive, or sprayed with a mixture of low molecular-weight resin and the adhesive resin in a single step. Though mechanical properties and dimensional stability of the phenolic resin treated boards were affected considerably by the incorporated resin loadings(IRL), the methods of treatment did not produce significantly different results. After boiling for 2-hours, the boards treated at 10 % IRL retained 80 % of their strength values in the dry condition. The internal bond strength(IB)increased with increasing IRL values, and the boards with 20 % IRL showed twice the value of untreated controls at the same level of board density. Treated PBs showed a dramatic reduction in the rate of swelling even at low resin loading. Results obtained from accelerated laboratory tests of biodegradation suggested that incorporated resin-solids worked well to enhance decay and termite resistance of boards. For a brown-rot fungus, the weight loss was substantially reduced at 15 % IRL, whereas attack was suppressed almost entirely even at low resin loadings for the white-rot fungus.The specimens of treated and untreated PBs were subjected to various accelerated aging treatments, and thickness swelling(TS)and IB were measured after each step of each cycle. The TS after the 6-cycle ASTM D-1037 exposure was affected greatly by the addition of low molecular-weight phenolic resin ; the TS value of the PB with only 5 % IRL was about a half of that of the control boards. The spring back was rarely observed for the treated PBs with 20 % IRL after the cyclic exposure test.The combination of low- and high-molecular weight resin was found to be much more effective in improving the strength properties and the dimensional stability of PBs.