Page 195 - Handbook of Adhesives and Sealants

Standard Test Methods 165

rate of 0.125 in/hr after various exposures to water and hot and cold
temperatures. These conditions are shown in Table 4.5. Typical spec-
imen geometries are shown in Fig. 4.19. The ISO Committee on Con-
struction has also developed a similar test method that differs some-
what from ASTM C 719. It requires extended periods of sustained
elongation (Table 4.6). There are a number of generally recognized
categories of movement capability in which these test methods at-
tempt to place sealants, for example 5%, 10%, 12.5%, 25%,
50%, and 100%/ 50%.
ASTM C 920 describes a bond cohesion test using specimens similar
to ASTM C 719. The test measures initial adhesive strength and cy-
cling after compression and water immersion. Another test includes
cycling after UV exposure. Failure is defined as an adhesive or cohe-
sive separation exceeding 1/10 in. in depth. Values can be obtained
for various extensions. Measured strengths of 5–10 piw are common
for low modulus sealants with extensions of up to 100%; medium mod-
ulus sealants, 15–30 psi; and high modulus sealants, 25–50 psi.

4.5.2 Peel adhesion
The peel adhesion test in combination with the tensile adhesion test
above gives a good indication of how a sealant might perform in ser-
vice. Peel specimens are formed from a substrate of interest and the
sealant which is reinforced with a strip of cotton fabric or fine stainless
wire mesh. Once cured, the cloth or wire is folded back 180 degrees
and peeled at a rate of separation of 2 in/min as shown in Fig. 4.20.
The load is reported in lbs per inch of width. The test is usually run
after the test specimens are immersed in water for three weeks. This

TABLE 4.5 ASTM Movement Capability Test Method C 719 19
Cure cycle Conditions
7 days Standard conditions.
7 days 37.8F, 95% relative humidity.
7 days Standard conditions.
7 days Distilled water.
Interim test Bend 60 deg, examine for failure, if OK, continue.
7 days Compress specimens to required compression (e.g., 25% for
25%). Hold at 70C. After 7 days cool to ambient for 1 hr.
10 cycles Extension/compression at 0.125 in/hr.
10 cycles Place in 26C compartment. Compress while cooling.
Remove, allow to reach room temperature.