Microstructural Changes in Wood Plastic Composites Due to Wetting and Re-drying Evaluated by X-ray Microtomography

An extruded wood polypropylene composite subjected to soaking-drying cycles in distilled water was investigated nondestructively using an X-ray microtomography. The representative elementary volumes of the material were examined and discussed using means/median of image intensity values and void contents in 3D XMT images. A 2 mm cube was determined as the representative elementary volume for this material. There were some differences for means in the dry, wet, and re-dried states. The specimen cutting position, i.e., surface or core, affects the results because there was a “resin rich/glazed” surface layer formed during extrusion and the WPPC material had a larger scale heterogeneity, which relates to the difference in flow rate between the core and face of a die. The void contents of re-dried specimens were higher than those of dry specimens.