Localized Dielectric Cure Monitoring Through the Panel Thickness During Oriented Strandboard Hot-Pressing
Keywords:Dielectric, heat transfer, hot-pressing, moisture, oriented strandboard (OSB), resin cure, temperature
AbstractIn wood composite panel hot-pressing, interactions between resin, wood, and moisture complicate the interpretation of dielectric analysis cure monitoring (also known as impedance cure monitoring) signals. In investigating the application of dielectric cure monitoring to oriented-strandboard (OSB) hot-pressing, pairs of fringe-field dielectric sensors were built into resinless laboratory strand mats at various locations through the thickness and hot-pressed with one sensor exposed to a thin layer of phenol-formaldehyde resin. Temperature and gas pressure probes were also implanted into the mat. The experiments thus yielded base comparisons of localized temperature, gas pressure, and dielectric conditions at various locations ranging from the core to the surface, and an indication of the isolated resin curing effect. The results indicate that the dielectric signal is strongly affected by internal temperature and moisture content gradients as well as by the resin polymerization. Speculation regarding a relationship with the thermo-dynamic energy of the bound water is introduced. Considering this, these experiments advance the understanding and interpretation of dielectric signals, and may subsequently improve the application of such dielectric cure sensors for the optimization of wood composite hot-pressing.
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