Strength and physical properties of structural type particleboards.

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The effects of adding a low molecular weight(Mn=389) phenolic resin to particles on board properties were investigated. Strand particles,prepared from sugi(Cryptomeria japonica)thinnings,were treated with a water-dispersed phenolic resin by the dipping or spraying method. In addition,8% bonding phenolic resin(Mn=962) was sprayed to the particles. On the other hand,the one shot spraying method,which the mixture of impregnating and bonding resin is sprayed to particles,was used. The particles were aligned by means of a mechanical orienter and 10-mm thick single layer boards were produced. The bending properties of the boards increased with the increases in board density and also MOR in the oriented direction was about twice that of random boards. At a board with 10% impregnating resin, the 90 percent of the original MOR was retaianed after a 2-hour boil test. The phenolic resin impregnated particleboards showed greatly improved thickness swelling and exhibited only about one-half the thickness swelling of a control board. Linear expansion (LE) values measured for the range of conditionings at 50 to 90%RH were affected substantially by particle alignment. After six cycles of ASTM accelerating aging,TS of the board with 10% impregnating resin decreased approximately up to 50% of the values observed in control boards and the internal bond strength retention was outstanding. The one shot spraying method is the most effective and it seems to be practical.