Page 504 - Handbook of Adhesives and Sealants

436 Chapter Eleven

produces bonds stronger than the wood itself, but they are generally
not resistant to moisture or high temperature. Common adhesives
used for bonding wood are identified in Chapter 16 (Table 16.23).
An accelerated aging test, ASTM D-3434, is convenient for evalu-
ating adhesive performance and predicting durability of bonded wood
joints. Samples are subjected to 800 cycles of exposure to boiling water.
This is equivalent to approximately 16 years of outdoor exposure for
a good wood adhesive. Figure 11.3 compares the performance of var-
ious wood adhesives in this test as well as solid, unbonded wood.
Epoxies have been used for certain specialized applications such as
metal to wood bonds. Newer adhesives have also been introduced in
the industry with very strong and reliable bonds in addition to proc-
essing ease. These include hot melt polyurethane adhesives, moisture
cure urethanes, and silicone adhesives.
Rubber based contact adhesives are also used for wood, especially
for laminating decorative panels. Mastic adhesives have been used in
construction industry and are usually applied by caulking guns. These
are based on elastomers, including reclaimed rubber, neoprene, buta-
diene-styrene, polyurethane, and butyl rubber.

Figure 11.3 Strength reduction curves for the automation boil
test: (1) solid wood; (2) fast cure epoxy, slow cure epoxy, phenolic-
resorcinol, urethane, phenolic; (3) casein, melamine-urea, mela-
mine; (4) urethane, urea. 5