Tests uncured state

Physical-property tests are used to measure the properties of adhesives in the liquid or gelled states prior to curing and in the solid state after curing. Tests for the uncured state such as viscosity, visual examination, and surface energy or contact angle assure that fillers, if used, have not settled out, that the material has not exceeded its pot life or shelf life, and that the supplier has not changed the formulation. Visual examination and density after cure are performed to verify that voids are not present or, if present, meet specification requirements. Finally, light transmission and index of refraction measurements are important for adhesives used in optoelectronic applications. 

The potential for corrosion caused by adhesives requires evaluations in both cured and uncured states. In one test, the adhesive components or the cured adhesive are applied to aluminized-Mylar film and examined after 48 hours for etching or transmittance of light through the Mylar. A second test involves embedding copper wire with the adhesive and measuring corrosion by resistance changes in copper wire. Because of the wide variety of tests and the fact that they are closely related to adhesive reliability issues discussed in Chapter 6, the reader is referred to that chapter. 

The potential for corrosion caused by adhesives requires evaluations in both the cured and uncured state. In one test, developed for NASA MSFC-SPEC-5 92, the adhesive components orthe cured adhesive are applied to... 

In this part of the work, the composition was tested in the uncured state at 50°C. For each set of tests, a sample was first subjected to a small sinusoidal strain ( 1% for 3 sec at 1.6667Hz), then immediately thereafter a larger strain ( + 50% for 3 sec at 1.6667 Hz) then, immediately thereafter, the small strain ( 1% for 3 sec at 1.6667 Hz) was repeated and then repeated several times after various periods of time. (This sequence is illustrated schematically by Fig. 23). As noted previous in this report, the moduli are lower with greater values of DR. This was found in the case of low-strain, high-strain, or prestrained low-strain moduli. 

The three propellants listed in Table I have been tested in the cured state and classed propellant explosive (solid) Class B by the Interstate Commerce Commission (6). The aluminized formulation, Arcite 373D, gave the same test results when uncured. In addition, Arcite 373D and Arcite 386, both cured and uncured, tested zero cards in the standard Naval Ordanance Laboratory card-gap test (I, 2). 

The ODR, with its ability to show complete cure curves in a very short period of time, has led many rubber manufacturers to use this type of instrument as a batch-control test [2,3]. A standard test is documented in ASTM D-2084 and BS1763, Part 10, 1977. The three phases in transforming rubber compound from the uncured to the cured state can be characterised by the cure curve produced (Figure 9.4). 

While viscosity measurements are typically carried out on uncured adhesives that are still in their liquid state or on partially cured materials that can still exhibit flow, measuring the basic stress-strain behavior is one of the most fundamental tests conducted on polymeric adhesives in their cured or solid state. In their simplest form, these tests are intended for characterizing materials with very large Deborah numbers, where the time scale of the test is short compared to any relaxation times within the material, or for crosslinked materials tested at time scales much longer than their characteristic times. Just as with viscosity tests and because of the very broad characteristic time scale of typical polymers, however, stress-strain tests are often conducted in a manner that captures some of the inherent time dependence of the materials being evaluated. 

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