Page 192 - Handbook of Adhesives and Sealants

162 Chapter Four

tions. Exposure is typically to elevated temperature, water, salt spray,
or various chemical solutions that are representative of the service
conditions. A number of standard chemicals that are used to soak
bonded specimens for seven days at room temperate are described in
ASTM D 896 (see Table 4.4). The method merely outlines the manner
in which the test specimens are conditioned before testing. After suit-
able exposure, bonds may be tested in whatever manner seems ap-
propriate.
The type of stress and environment should be selected to be a close
approximation of real-life conditions. Two simultaneous environ-
ments, such as heat and moisture, may cause the adhesive to degrade
much faster than when exposed in any single environment because
one condition could accelerate the effect of the other.
Stressed aging tests are important because they more accurately
simulate service conditions than do simple tests where the specimens
are merely hung or placed in a test environment. The Alcoa Stress

TABLE 4.4 Standard Test Exposure of Adhesives 17
Test
Exposure Temperature,
Number F(a) Moisture conditions
1 70 As conditioned
2 30 As conditioned
3 30 Presoaked (b)
4 32 As conditioned
5 73.4 50% relative humidity
6 73.4 Immersed in water
7 100 88% relative humidity
8 145 Oven, uncontrolled humidity
9 145 Over water (c)
10 145 Immersed in water
11 158 Oven, uncontrolled humidity
12 158 Over water (c)
13 180 Oven, uncontrolled humidity
14 180 Over water (c)
15 212 Oven, uncontrolled humidity
16 212 Immersed in water
17 221 Oven, uncontrolled humidity
18 300 Oven, uncontrolled humidity
19 400 Oven, uncontrolled humidity
20 500 Oven, uncontrolled humidity
21 600 Oven, uncontrolled humidity
NOTES:
a-The tolerance for test temperature shall be 1.8F up to 180F and 1% for temperatures
above 180F.
b-Presoaking shall consist of submerging specimens in water and applying vacuum at 20
in. of mercury until weight equilibrium is reached.
c-The relative humidity will ordinarily be 95 to 100%.