Effect of Shives Content of Hardboard Properties

Five pulps with shives contents of 1, 4, 10, 20, and 50 percent were prepared by systematic addition of shives to a refined base pulp. Hardboards were then produced in the laboratory under the same conditions. The drainage time, expressed as defibrator seconds, of pulps decreases with increasing shives content. An increase in shives content from 1 percent to 30 percent, which is a normal shives content in hardboard mills, reduces the drainage time by about 40 percent. All strength properties are affected by the shives content. The internal bond strength is reduced by about 20 percent and the bending and impact strength by about 10 percent at a 30 percent shives content. The effect on impact strength is greater at higher shives contents, whereas the internal bond and bending strength decrease mainly at low shives contents below 20 percent. The shives content also has a significant influence on the surface smoothness of hardboards, especially after conditioning at 90 percent relative humidity. The surface smoothness of the boards decreases markedly with increasing amount of shives.

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