Free Adhesives MCQs with Answers

1. An adhesive works by

• A. melting the two surfaces together
• B. forming intermolecular forces or chemical bonds with both surfaces while cohering strongly within itself
• C. removing all air from between the surfaces only
• D. converting one surface into the other

Explanation: A good adhesive must both adhere, sticking to each surface, and cohere, holding together internally, and it usually starts as a liquid so that it can flow into the microscopic irregularities before setting. Failure at the interface is adhesive failure while failure within the glue itself is cohesive failure. Welding, by contrast, does melt the surfaces and is not adhesion.

2. Epoxy resin adhesives are supplied as two tubes that must be mixed before use because

• A. one tube contains the solvent that evaporates
• B. the two components are the same substance at different concentrations
• C. mixing lowers the temperature of the joint
• D. the resin and the hardener react together to form cross links, setting the adhesive

Explanation: Setting is a chemical reaction between the resin and a hardener that builds a rigid cross linked network, so the two must be kept apart until the moment of use. Because no solvent has to evaporate, epoxies set even in a sealed joint and bond metals, glass and ceramics strongly. Adhesives that set by solvent evaporation, such as rubber cement, work on a quite different principle.

3. Thermoplastic adhesives such as hot melt glue set by

• A. cooling and solidifying, with no chemical change
• B. reacting chemically with the surface
• C. absorbing water from the air
• D. releasing carbon dioxide

Explanation: The adhesive is applied molten, flows into the surface irregularities and then simply freezes as it cools, so the change is physical and reheating the joint softens it again. This makes such adhesives quick and convenient but unsuitable where the joint may become warm. Thermosetting adhesives such as epoxies form permanent cross links instead.