Techniques for Determining Moisture in Wood-Plastic Combinations

Three techniques for determining the moisture content of radiation produced yellow-poplar/styrene-acrylonitrile wood-plastic combinations (WCP) were evaluated against the true moisture content as determined by the Karl Fischer (K.F.) method. These methods were: 1) ovendrying (O.D.) of ground and whole WPC wafers, 2) vacuum drying (Vac.D.) of the same material, and 3) D.C. electrical resistance measurements. The moisture distributions in the WPC samples were also measured. The Vac.D. technique with ground WPC samples gave the most reliable results but there were still some discrepancies between this method and the basic K.F. determinations. Vac.D. of WPC wafers gave satisfactory moisture content measurements in many cases but this technique is not so reliable as Vac.D. of ground WPC samples. The O.D. techniques may be used to give the approximate moisture content of WPC. Direct current electrical resistance measurements were not at all satisfactory for measuring the moisture content of WPC. In the manufacture of the WPC used in this study some of the moisture was driven to the ends of the specimen. This moisture migration caused greater swelling at the ends of the specimens than in the middle.

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