Quiz Unit V

What is the significance of the glass transition temperature (Tg) in polymers?

• It indicates the melting point of the polymer.

• It indicates the density of the polymer.

• It measures the flexibility of a polymer.

• It determines the color of the polymer.

Answer explanation

The glass transition temperature (Tg) is crucial as it indicates the temperature range where a polymer transitions from a hard, glassy state to a more flexible, rubbery state, thus measuring its flexibility.

Which of the following is a thermosetting polymer?

• Polyethylene

• Bakelite

• Polycarbonate

• Nylon

Answer explanation

Bakelite is a thermosetting polymer, meaning it hardens permanently when cured. In contrast, polyethylene, polycarbonate, and nylon are thermoplastics, which can be remolded upon heating.

What is the primary application of epoxy resins?

• Used as adhesives for various materials.

• Used in the production of textiles.

• Used for making food containers.

• Used in the manufacture of biodegradable plastics.

Answer explanation

Epoxy resins are primarily used as adhesives due to their strong bonding properties with various materials, making them ideal for construction, automotive, and manufacturing applications.

Which polymer is known for its high impact resistance and transparency?

• Polyethylene

• Nylon

• Polycarbonate

• Bakelite

Answer explanation

Polycarbonate is known for its high impact resistance and transparency, making it ideal for applications like eyewear lenses and safety glasses. In contrast, polyethylene, nylon, and Bakelite do not possess the same level of clarity and impact strength.

What is the main advantage of biodegradable polymers?

• They are cheaper than synthetic polymers.

• They degrade naturally in the environment.

• They have higher tensile strength.

• They are more flexible.

Answer explanation

The main advantage of biodegradable polymers is that they degrade naturally in the environment, reducing pollution and waste, unlike synthetic polymers which can persist for a long time.

Which of the following is a method for synthesizing poly lactic acid (PLA)?

• Ring opening polymerization of lactide.

• Both A and C.

• Condensation of phenol and formaldehyde.

• Direct polycondensation of lactic acid.

Answer explanation

Poly lactic acid (PLA) can be synthesized through ring opening polymerization of lactide and direct polycondensation of lactic acid. Therefore, the correct answer is 'Both A and C'.

What type of fibers are used to reinforce polymer composites for increased mechanical properties?

• Natural fibers

• Synthetic fibers

• Glass fibers

• All of the above

Answer explanation

All types of fibers, including natural, synthetic, and glass fibers, can be used to reinforce polymer composites, enhancing their mechanical properties. Therefore, the correct answer is 'All of the above'.

Which ASTM standard is used for testing tensile properties of polymer composites?

• ASTM D 790

• ASTM D 3039

• ASTM D 256

• ASTM D 2344

Answer explanation

ASTM D 3039 is the standard specifically used for testing the tensile properties of polymer composites, making it the correct choice. The other standards listed pertain to different testing methods.

What is the primary role of a curing agent in epoxy resins?

• To reduce weight.

• To initiate cross-linking.

• To improve flexibility.

• To enhance color.

Answer explanation

The primary role of a curing agent in epoxy resins is to initiate cross-linking, which transforms the liquid resin into a solid, durable material. This process is essential for achieving the desired mechanical properties.

Which polymer is characterized by its high toughness and temperature stability?

• Nylon

• Bakelite

• Polyether sulfone

• Polycarbonate

Answer explanation

Polyether sulfone is known for its exceptional toughness and high temperature stability, making it suitable for demanding applications. In contrast, other options like nylon and polycarbonate do not match its thermal performance.