Characterization of adhesive penetration in wood bond by means of scanning thermal microscopy (SThM)

The penetration characteristics of phenol formaldehyde (PF) resin, modified by two different nanomaterials (PFmod), has been studied by means of scanning thermal microscopy (SThM). The thermal conductivity (ThC) of the two PFmod was lower than that of the cell wall (CW), but the ThC of both PF resins was basically the same. SThM imaging revealed the penetration of parts of PFmod into the CW by a ThC transitional region, which exists between the CW and the resin. In the transitional zone, the ThC changed obviously in a region about 2 mu m in width. This region includes two subregions, one about 0.7 mu m and another 1.3 mu m in width. The first one is the interface, where PFmod and the CW are in direct contact where the ThC changes rapidly. In the second subregion, the PFmod and CW are in interaction, and ThC changes slowly. Regarding the adhesives' penetration into the cell lumen, the ThC of the penetrating adhesive was higher than that in the glue line, and this is an indication that SThM is a useful tool to detect the differences of adhesive penetration at the micro-scale level.