Novel plate rheometer configuration allows monitoring real-time wood adhesive curing behavior

Properties which enable a good insight into the application and performance characteristics of adhesives used for gluing wood to wood are the viscosity level during application, tack development after glue application and the shear (or creep) resistance of the partially cured/dried as well as fully cured/dried glueline. In general, all these properties can be related to the response behavior to the application of stress and, thus, should be possible to be characterized by rheology. In this paper, a new rheometer geometry is presented: it is a plate–plate geometry where at least one of the two plates enables a significant uptake of the resin's solvent (due to diffusion and/or capillary forces). Using this new tool, the application and curing characteristics of different phenol-resorcinol-formaldehyde (PRF) adhesive formulations containing different fillers were analyzed and compared. One of the tested fillers was a Forest Research development, based on thermoplastic microbeads in the micrometer range, which allowed very high substitution levels without disadvantages regarding application and performance (e.g. according to British Standards 1204).