Research Brief #23

Prediction of Moisture Content and Moisture Gradient of an Overlaid Particleboard
Louisiana Forest Products Development Center
Louisiana State University
Baton Rouge, LA

Research Objectives

Warping of overlaid particleboards is due to the imbalance of swelling stresses over the cross-section of the panel. Among many variables, asymmetric moisture distribution across the panel thickness plays an important role in causing such a stress imbalance. The purpose of this study was to investigate the sorption behavior of particleboard substrates and high pressure laminate (HPL) overlays; and to examine moisture distribution inside various panels of different construction.

Conclusions

• Nelson's sorption isotherm can be used to describe the equilibrium moisture content data for both particleboards and HPL overlays. The material parameters that define the sorption isotherm varied with types of material and sorption mode.
• Diffusion coefficient of the particleboard face layer was smaller than that of the core layer and decreased at higher moisture contents for both face and core. Diffusion coefficients of HPL and HPL backer increased with increase in moisture content.
• The analytical procedure demonstrated that a highly skewed moisture distribution developed inside a particleboard substrate due to the addition of an HPL overlay to one of its surfaces. It was also shown that by adding one HPL backer to the other surface of the substrate the extent of moisture imbalance within the particleboard was largely reduced.
• The analytical method, coupled with the internal stress analysis, could be used to assess more accurately the warping potential of a multi-ply wood composite panel.

Researchers

Qinglin Wu, Assistant Professor
Forest Products Processing
Louisiana Forest Products Development Center
Louisiana State University
Agricultural Center Baton Rouge, Louisiana

Otto Suchsland, Professor
Department of Forestry
Michigan State University
East Lansing, Michigan

Target Group

Door, furniture and other panel products manufacturers.

Methodology

An interior three-layer, mixed hardwood particleboard (19.1 mm thick), an HPL overlay (1.5 mm) and an HPL backer (0.5 mm thick) were purchased. These three products were used to make two types of laminate (HPL + particleboard and HPL + particleboard + HPL backer).

Test specimens for equilibrium moisture content and diffusion coefficient were produced from first three materials and moisture content samples were made from the particleboard and two laminates. These were used to determine the sorption isotherms, diffusion coefficients, and moisture content changes for various materials.

A model based on diffusion theory was developed to predict moisture content and moisture distribution for a multi-ply wood composite panel. The model's prediction of the mean moisture content for various panels was compared with measurements.