Page 430 - Handbook of Adhesives and Sealants

372 Chapter Ten

Epoxy-phenolic adhesives were developed primarily for bonding
metal joints in high-temperature applications. They were one of the
first adhesives developed for high temperature aircraft applications in
the early 1950s. They are also commonly used for bonding glass, ce-
ramics, and phenolic composites. Because of their relatively good flow
properties, epoxy phenolics are also used in bonding honeycomb sand-
wich composites.

10.3.2.3 Epoxy-nylon. Epoxy-nylon adhesives, introduced in the
1960s, were one of the first structural adhesives designed specifically
to have high shear strength and extremely high peel strength. These
characteristics were achieved by blending epoxy resins with co-
polymers from the polyamide (or nylon) resin family that is noted for
toughness and tensile properties. The nylons used as modifiers for
epoxy adhesives are soluble co-polymers made from conventional ny-
lon monomers. Conventional crystalline nylon polymers, such as nylon
6 or nylon 66, would be incompatible with epoxy resins.
Epoxy-nylon resins are one of the best materials to use in film and
tape adhesives for applications where the service environment is not
severe. Their main advantages are better flexibility and a large in-
crease in peel strength compared with unmodified epoxy adhesives.
Epoxy-nylon adhesives offer both excellent tensile lap shear and peel
strength. In addition, epoxy-nylon adhesives have good fatigue and
impact resistance. They maintain their tensile lap shear properties at
cryogenic temperatures, but the peel strength is poor at low temper-
atures. They are limited to a maximum service temperature of 180 F,
and they exhibit poor creep resistance. Possibly their most serious
limitation is poor moisture resistance because of the hydrophilic nylon
(polyamide) constituent. The degradation by exposure to moisture oc-
curs with both the cured and uncured adhesives.
Epoxy-nylon adhesives are generally available as film or as solvent
solutions. A pressure of 25 psi and temperature of 350 F are required
for 1 hr to cure the adhesive. Because of their excellent filleting prop-
erties and high peel strength, epoxy-nylon adhesives are often used to
bond aluminum skins to honeycomb core in aircraft structures.

10.3.2.4 Epoxy-polysulfide. Polysulfide resins combine with epoxy res-
ins to provide adhesives and sealants with excellent flexibility and
chemical resistance. These adhesives bond well to many different sub-
strates. Shear strength and elevated temperature properties are low.
However, resistance to peel forces and low temperatures are very good.
Epoxy-polysulfides have good adhesive properties down to 150 F, and
they stay flexible to 85 F. The maximum service temperature is
about 122 F 180 F depending on the epoxy concentration in the for-