Page 308 - Handbook of Adhesives and Sealants

272 Chapter Seven

Figure 7.4 Effect of silane adhesion promoter on the durability of
a mild steel joint bonded with epoxy adhesives. 32

TABLE 7.8 Lap-shear Strengths of Several Structural Adhesives Incorporating Silane
Adhesion Promoters 28
Percentage Lap
of shear,
Adhesive type Adhesion promoter promoter psi
Nitrile phenolic None — 1450
Nitrile phenolic Gamma-aminopropyltriethoxysilane 1 2350
Nitrile phenolic Gamma-mercaptopropyltrimethoxysilane 1 3120
Epoxy None — 1410
Epoxy Gamma-aminopropyltriethoxysilane 1 1675
Epoxy Gamma-mercaptopropyltrimethoxysilane 1 1580
2024T3 aluminum, 0.063 inch thickness, 1/2 inch overlap
Tests run at 73F; appropriate cure schedule used

step. The main disadvantage is that there could be stability problems
in storage due to hydrolysis and polymerization. Figure 7.5 shows the
improvement in T-peel strength to aluminum caused by the introduc-
tion of silanes into a urethane adhesive. Silanes are also commonly
used in caulks and sealants to improve adhesion. The addition of
0.25% by weight silane (A-187) is reported to improve the wet and dry
peel strength of an acrylic caulk to both glass and wood substrates. 27
Water-stable epoxy silane promoters have recently been developed to