Wood Adhesives Science and Technology
FS-FPL-4703

Wood Bonding

In this section we put information that will update or supplement what is in the 1999 edition of the Wood Handbook.

First, we have an updated chart of common wood adhesives, both for consumer and industrial use. Click on this link: adhesive selection chart.

Probably the best documents in which to read about the science of wood as a material to be bonded is in Wood as an Adherend, Technology of Wood Bonding, and Gluing of Eastern Hardwoods: A Review.

In bonding wooden pieces or plies with crossed grain directions, or bonding whole wood to reconstituted wood panels (particleboard and MDF principally), swelling or shrinking put great stress on the bondline. For regular wood, the dimensional changes (usually for the tangential dimension) are indicated in tables in the Wood Handbook. Tables 4-3 and 4-5 have shrinkage data between green (freshly cut) wood and 12% moisture content (MC). But for wood that is manufactured for interior use but shipped to various regions of the country, or world, see Table 12-5, which has coefficients of dimensional change between 6% and 14% MC, reflecting dry and tropical environments, respectively. For reconstituted wood panels, cycled between 30% and 90% RH, Table 1.18 of Wood as an Adherend lists the linear expansion in the plane for various particleboards as 0.20% to either 0.65% or 0.85% (for medium density and high density types, respectively) and for various MDFs as 0.35% to 0.62%.

Another aspect of bonding is the amount of warping that species may undergo when they swell and shrink. Warping focuses stresses onto certain parts of the bond, instead of distributing them uniformly. Some information on interlocked grain, which appears to correlate with a high susceptibility to warping, is in the Textbook of Wood Technology (A.J. Panshin and C. DeZeeuw, 4th ed., 1980, New York, McGraw-Hill) or at the web pages of the Center for Wood Anatomy Research at FPL (http://www2.fpl.fs.fed.us) or possibly at the web pages of H.G. Richter and M.J. Dallwitz(“Commercial timbers: descriptions, illustrations, identifications, and information retrieval. In English, French, German, and Spanish. Version: 18th October 2002.” http://biodiversity.uno.edu.delta). A high incidence of tension wood, as in cottonwood (Populus spp.) also seems correlated with excessive warp.

The values in the wood handbook are generally for mature trees. Increasingly, wood coming onto the market is juvenile wood, which has different characteristics from mature wood. We do not know the effect of juvenile wood properties on wood bonding.