This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Thermoplastics – 1”.
1. Thermoplastics are formed by ________
a) Addition polymerization
b) Copolymerization
c) Condensation polymerization
d) Isomerism
View Answer
Explanation: Thermoplastics are plastic polymer substances formed by the addition polymerization process. They are linear polymers containing chain molecules. These plastics tend to become soft when heated and harden when cooled.
2. Which of the following is not a property of thermoplastics?
a) Recyclable
b) Soft and weak
c) Easy to mold
d) Can be used at high temperatures
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Explanation: Thermoplastics tend to become soft when heated due to weak secondary forces and become hard on cooling. This makes it easier to mold them into any required shape any number of times, and therefore makes them recyclable. They are, however, not suitable for use under high temperatures.
3. Which of the following is an example of a thermoplastic?
a) Urethane
b) Melamine
c) Acetal
d) Epoxide
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Explanation: Acetal is an example of engineering thermoplastics. These are the plastics which are typically employed in engineering applications due to high strength, environmental resistance, and physical properties. Other examples of engineering thermoplastics are ethenic, cellulose, polyether etc. Urethane, melamine, and epoxide are examples of engineering thermosetting plastics.
4. Which of the following is not an example of a commodity thermoplastic?
a) Polyethylene
b) Polypropylene
c) Polystyrene
d) Phenolic
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Explanation: Commodity thermoplastics are the most widely used plastics and are available at a lower cost. Phenolic is an example of thermosetting commodity plastic. The remaining choices, along with PVC, are examples of commodity thermoplastics.
5. Which of these is not a type of polyethylene?
a) Low-density polyethylene
b) High-density polyethylene
c) Linear high-density polyethylene
d) Ultra-high molecular weight polyethylene
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Explanation: Polyethylene is a plastic made by the polymerization of ethylene (ethene). Based on molecular weight, the method of manufacturing, and density, they are classified into various types. Low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and ultra-high molecular weight polyethylene (UHMWPE) are the four types of polyethylene.
6. To overcome the brittleness of polypropylene ______ is used.
a) Polyallomer
b) Polyethylene
c) Polyvinyl chloride
d) Polystyrene
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Explanation: Polypropylene tends to become brittle at low temperatures. Therefore, polyallomer is used to beat this disadvantage. Polyallomer is a block copolymer of polyethylene and polypropylene.
7. Which of the following is not a type of polystyrene?
a) Structural Polystyrene
b) High Impact Polystyrene
c) Styrene Acrylonitrile
d) Acrylonitrile Butadiene Styrene
View Answer
Explanation: Polystyrene is a plastic polymer made from ethylbenzene. They are brittle, cheap, and are extremely easy to mold. The commonly used polystyrenes are High Impact Polystyrene (HIPS), Acrylonitrile Butadiene Styrene (ABS), and Styrene Acrylonitrile (SAN).
8. ________ is an example of dichloro-ethylene.
a) Plasticized PVC
b) Un-plasticized PVC
c) Chlorinated PVC
d) Polyvinylidene chloride
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Explanation: Polyvinyl chloride (PVC) is a polymer made by the polymerization of monomer vinyl chloride. They are low-cost polymers which have good resistance to chemical, oil, electrical attacks. The common forms of PVC are plasticized PVC (PPVC), un-plasticized PVC (UPVC), chlorinated PVC (CPVC), and polyvinylidene chloride (PVDC).
9. Which is the most commonly used fluorocarbon polymer?
a) PTFE
b) PVDF
c) PVF
d) PFA
View Answer
Explanation: Polytetrafluoroethylene (PTFE) is regarded as the most common among all fluorocarbon polymers. They possess excellent electrical properties and are chemically inert. PTFE finds application in chemical pipes, valves, non-stick coatings etc.
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