Tests on the Curing Adhesive

Many different test methods are used to measure the reactivity or cure rate of the epoxy adhesive. Some of these, such as working life or pot life, are very practical and are used to plan the production process. Others, such as exotherm, are used to determine reaction kinetics. Still others are used to characterize the epoxy network as it cures for the purposes of determining the degree of crosslinking and the rheological properties of the curing adhesive. 

Working life is usually determined on a volume of adhesive that is practical and normally used in production. The mass of the tested material must be defined in the test report because many adhesives have a working life that is dependent on sample mass. 

Structural adhesives usually require curing by the application of heat, the addition of a catalyst, the addition of pressure, or a combination of the three. The strength developed in the adhesive joint at various times during the curing process may be determined by lap shear tensile specimens. This test is commonly used to determine when an adhesive or sealant is fully cured or when the system reaches a handling strength so that the assembled product can be moved with moderate care. 

There are also several methods of determining cure rate on the bulk adhesive material. These are generally analytical procedures that are common in most polymeric materials 

Cure time is very important for sealants as well as adhesives. Often the sealant will be required to function as a barrier or resist the movement of substrates very soon after it is applied. With construction sealants, for example, it may not be possible to delay the environmental conditions until after the adhesive cures. Thus, curing time becomes a critical parameter in selection of the sealant. ASTM C 679 covers a method for determining the time that a mechanic can work the sealant into the joint before the sealant starts to skin or solidify. 

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Tests on the cured adhesive/adherend assembly to determine the bond strength attained. 

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