Determining the degree of equilibrated moisture content for 12 mm southern pine strandboard: A time constant approach

Document Type

Article

Publication Date

1-1-2007

Abstract

When wood samples are measured for physical and mechanical properties, they first should be equilibrated at specified MC levels. Since MC levels can fluctuate as equilibrium MC (EMC) is approached, determining EMC can be difficult and time-consuming. This exercise attempts to answer the question, "How much time is needed to equilibrate 12 mm southern pine strandboard panels?" Since complete equilibration can take months, it would be helpful to estimate this answer and know how much progress has been made within a week or two after equilibration starts. Trees from first thinnings of loblolly pine (Pinus taeda) in Louisiana were used. Homogeneous strandboard panels were made from flakes obtained from log billets segregated by diameter: 3 to 10 cm and 11 to 20 cm. Two replicate panels from each diameter category were made with 4 percent liquid phenol-formaldehyde resin at 0.72 g/cm3 nominal densities. The weight and dimensional changes (and thereby, MC) were monitored daily as samples from the boards equilibrated from 30 percent to 90 percent relative humidity. From the experimental time series measurements, the time constant functions, along with accompanying power and exponential models, were generated. For these Strandboard panels, one time constant of 10 days was needed to assure that at least 63.2 percent of the MC change toward equilibrium had been accomplished. Since wood specimens are generally considered fully equilibrated after four or five time constants, this means that at least 40 to 50 days are needed for 12 mm pine Strandboard panel samples to reach at least 98 percent EMC at a particular environmental condition. © Forest Products Society 2007.

Publication Source (Journal or Book title)

Forest Products Journal

First Page

43

Last Page

46

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