This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Structure and Properties of Elastomers”.
1. Plastics and elastomers differ due to their properties of ________
a) Resistivity
b) Dielectric strength
c) Acoustic insulation
d) Extensibility
View Answer
Explanation: Elastomers are polymeric materials similar to plastic resins. They are otherwise known as rubbers. The difference between plastics and elastomers lies in their ability to stretch.
2. Which of the following is not a characteristic of rubber?
a) Non-crystalline
b) Electrical conductivity
c) Chemical resistance
d) Low softening temperature
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Explanation: Elastomers are hydrocarbon polymeric materials that are non-crystalline in nature. These materials possess high chemical and corrosion resistance, and a relatively low softening temperature. However, they are poor conductors of heat, which in effect make them non-conductors of electricity.
3. Which kind of polymer arrangement does the below diagram represent?
a) Unvulcanized
b) Vulcanized
c) Stretched vulcanized
d) Stretched unvulcanized
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Explanation: Polymer structures in elastomers are classified as vulcanized (unstretched), unvulcanized, or stretched vulcanized rubber. The vulcanization process involves cross-linking of covalent bonds. This results in a material similar to a thermoset.
4. Which polymeric arrangement does the figure represent?
a) Unvulcanized
b) Vulcanized
c) Stretched vulcanized
d) Stretched unvulcanized
View Answer
Explanation: Polymer structures in elastomers are classified as vulcanized (unstretched), unvulcanized, or stretched vulcanized rubber. In the unstretched state, these elastomers are amorphous. This is due to the arbitrariness of the polymer arrangement.
5. How does the crystallinity of an elastomer affect its strength?
a) Increases with increase in crystallinity
b) Increases with decrease in crystallinity
c) Decreases with increase in crystallinity
d) No effect
View Answer
Explanation: When elastomer polymers are stretched, the chains tend to straighten and align. This increases the crystallinity of the elastomer, which in turn increases the strength.
6. The loss of heat in elastomers due to friction is known as ________
a) Resilience
b) Hardness
c) Resistivity
d) Hysteresis
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Explanation: Resilience is defined as the ability of an elastomer to accumulate energy. Some of this energy is lost due to internal friction or frictional heat. This loss of heat is known as hysteresis.
7. How is the hardness of an elastomer measured?
a) Bloom
b) Brinnell hardness test
c) Rockwell hardness test
d) Shore durometer
View Answer
Explanation: Shore durometer is a standard test conducted to measure the hardness of an elastomer. This scale ranges from values of 0 to 100, indicating a higher hardness for the higher number.
8. What is the thermal conductivity of rubber?
a) 0.04 W/m oC
b) 0.16 W/m oC
c) 0.64 W/m oC
d) 1.12 W/m oC
View Answer
Explanation: Elastomers are regarded as materials having low heat conduction and electrical conduction abilities. They have a low thermal conductivity of 0.16 W/m oC and a specific gravity of 1.0-1.8. The resistivity of elastomers ranges from 106 to 1010 ohm/oC m.
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