Dimensional variation of three softwood due to hygroscopic behavior

With the aim of monitor the hygroscopic behavior of three softwood species in situations of changes in its moisture content, an experimental program based on dimensional measurements, hygrometer readings and weightings procedure, was carried out. Maritime Pine (Pinus pinaster), Spruce (Picea abies) and Scots Pine (Pinus sylvestris) specimens were evaluated and compared. For each wood species, half of specimens were previously dried while the other half was previously saturated. Three main variables studied during the period of specimen’s adjustment to an external environment of 20ºC and 57.5% relative humidity (RH) were: mass, dimensional and moisture content variations. Based on the obtained experimental results, the equilibrium moisture content, as well as coefficients of linear shrinkage and expansion, were determined. Experimental results confirmed that besides RH and temperature, the equilibrium moisture content of wood depends on its moisture history. Moreover, using the obtained values it was possible to identify differences between the hygroscopic behavior of the softwood species studied.Fundação para a Ciência e a Tecnologia (FCT