The development of new and improved wood adhesives is hindered by an incomplete mechanistic understanding of what makes a wood–adhesive bond able to withstand changes in moisture levels. Although common methods are established to test and report the bulk-level properties of bond lines, such as bond-line shear strength and wood failure analysis, the development of experimental tools to study wood–adhesive bond lines and the effects of moisture at the nanometer to millimeter length scales remains an active area of research. Here we introduce and briefly review four recently developed tools that, when combined, we have found capable to facilitate the study of bond lines and the effects of moisture across these length scales. The tools are X-ray computed tomography, X-ray fluorescence microscopy, nanoindentation, and small-angle neutron scattering. Their combined utility has been demonstrated by studying model bond-line systems made using loblolly pine and phenol-formaldehyde adhesives. The results led to a new insight that adhesive infiltration into cellulose microfibrils at nanometer length scales likely plays an important role in the moisture durability of wood–adhesive bond lines. A new model to facilitate the discussion of potential interactions between adhesive and wood nanostructure was also developed.
Jakes, Joseph E.; Frihart, Charles R.; Hunt, Christopher G.; Yelle, Daniel J.; Plaza, Nayomi Z.; Lorenz, Linda F.; Ching, Daniel J. 2018. Integrating multiscale studies of adhesive penetration into wood. Forest Products Journal. 68(4): 340-348.