Use of Short-Retention-Time Blender with Large-Flake Furnishes

Most structural flakeboards have been produced using a powdered phenolic resin. However, it has been difficult to apply more than two to three percent of this powdered resin, since higher levels of resin will not adhere to the flakes under normal conditions. Consequently, it is necessary to use liquid phenolic resin when producing higher-quality boards requiring higher levels of resin. Large rotary blenders can be used for applying liquid resins; however, they are relatively slow and need to be quite large to adequately distribute the resin over the furnish. The use of short-retention-time blenders with large-flake furnishes has been of concern because such blenders may act as attrition mills and break up the flakes. The object of this study was to determine the effect on flake-board properties when using short-retention-time blenders with large-flake furnish and to evaluate the damage to the flakes. Boards were produced using a short-retension-time blenders commonly used in the particleboard process. Variables included three blender speeds, three liquid phenolic resin levels, and three board specific gravity levels. These experimental boards were matched with control boards prepared in a laboratory rotary blender. Large-flake furnish processed with the blender running at 600 rpm had an inadequate coverage of the resin. The furnish at 1800 rpm suffered considerable damage. At the speed of 1200 rpm, flakes suffered little damage and had an adequate resin distribution. Modulus of elasticity values were all similar, including those of the control boards, with the exception of some lower values at 600 rpm. Apparently the long flakes made the modulus of elasticity rather insensitive to resin distribution. Modulus of rupture relationships were basically the same as those for modulus of elasticity. The boards at 0.70 specific gravity made by means of the short-retention-time blender were about 15-30 percent lower in internal bond than the controls, depending on the resin level. These values were considered to be adequate for most applications. Those boards made with the short-retention-time blender running at 1200 rpm exhibited the better values, particularly at the lowest resin level.

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