Effect of thermally conductive fillers on the internal bond strength of strandboard

The manufacture of strandboard could be improved by developing a method to shorten the cure time of resin during hot-pressing, which might either speed production or improve overall board quality. This paper explores whether adding thermally conductive fillers could increase the internal bond (IB) strength of strandboard, which is often considered as an indirect measure of degree of resin cure. It was speculated that the thermally conductive fillers would facilitate heat transfer during hot-pressing, causing a greater degree of resin cure and thereby increasing the internal bond strength. Five thermally conductive fillers were studied and added at a level of 1 g filler/100 g dry strands, including three different types of synthetic graphite, one type of natural graphite, and one type of boron nitride powder. Strandboard 18.3 mm thick was manufactured using phenol-formaldehyde resin at a loading of 4 g resin solids/100 g dry strands, a total press time of 5 minutes, and a press temperature of 216?C. IB results of the boards containing filler were compared with control boards that did not contain any filler. At the 95 percent confidence level, the results showed that the IB strength of strandboard containing boron nitride powder (Advanced Ceramics Corporation Grade HCP) was higher than that of the control boards. At the 90 percent confidence level, the IB strength of the boards containing Conoco?s coarse ThermocarbTM Specialty Graphite (synthetic graphite) or Lonza?s KS-75-250 Manufactured Graphite (synthetic graphite)was higher than the IB strength of the control.

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