Liquid sorption and swelling behaviour of Norway spruce heartwood and sapwood veneers studied by the multicycle Wilhelmy plate method

The durability of coated wood in outdoor exposure is strongly influenced by the watersorption and liquid permeability properties of the wood substrate. Those properties mayalso influence the ability of a coating to be absorbed into the substrate. It is known thatthere is a significant difference in the water sorption behaviour between spruce heartandsapwood. However, most studies have been concentrated on wood panels, givingthe average behaviour for the whole panel. This study is using smaller wood samplesgiving a more specific information regarding certain influencing factors. Theinfluencing factors could be, e.g. early- and latewood morphology as well as extractivescontent and composition.The aim of this research is to increase the knowledge about water sorption and swellingproperties of Norway spruce. The objective is to study the water uptake behaviour ofheart- and sapwood veneer samples using a recently developed multicycle Wilhelmyplate method. The method enables to follow the sorption and swelling pattern ofrelatively small wood samples during a number of wetting cycles in water and octane. Italso provides a shorter experimental time compared to tests using larger wood panels.The results in the non-swelling liquid octane indicate that a higher wood porosity resultsin higher liquid permeability for both sap- and heartwood. However, no clear differencein permeability can be observed between the sap- and heartwood samples. The result inpermeability is also valid for measurements in water, although the results are moredifficult to interpret. Moreover, the information from liquid mass uptake of octane andwater gives together an indication of the impact from porosity on the overall liquiduptake of heart- and sapwood.QC 20200331EnWoBi