This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Strengthening of Plastics”.
1. ___________ increases with increasing molecular weight of polymer.
a) Degree of entanglement
Explanation: When molecular weight increases, the degree of entanglement of polymer chains increases. It is because of increase in length of polymer chains. While flexibility, cracking and creep decrease.
2. ____________ possess strong intermolecular bonding.
c) Liquid resin
d) Thermosetting plastic
Explanation: Thermosetting plastics possess strong intermolecular bonding. These have cross linking. These don’t soften on reheating.
3. What doesn’t favor the strengthening of polymers?
a) Addition of glass fibers
b) Addition of polar groups in the chain
c) Addition of plasticizers
d) Addition of bulky side groups in the chain
Explanation: Plasticizers soften the polymer. Addition of glass fibers on the other hand provides composite strengthening. Addition of polar and bulky size groups in polymer main chain also causes strengthening.
4. What is the effect of increasing molecular weight on melting temperature of polymer?
a) Increases linearly
b) Increases non-linearly
c) Decreases exponentially
d) Decreases linearly
Explanation: With an increase in molecular weight of polymer, secondary intermolecular bonds increase. Hence melting point of polymer is increased. It increases linearly.
5. What favors strengthening by crystallinity?
a) Trans type structure
b) Cross linking
Explanation: C is type structure favors amorphous structure. Branching and cross linking increases the distance between chains and decreases crystallinity. Copolymerization also decreases crystallinity.
6. Strengthening increases with ____________ in polymers.
a) Increase in crystallinity
b) Decreases in molecular weight
c) Decrease in bulky groups
d) Increase copolymerization
Explanation: Strengthening increases with crystallinity in polymers. Copolymerization decreases crystallinity. Molecular weight and bulky groups also increase strengthening.
7. Which one polymer shows maximum strength among all?
Explanation: Polystyrene shows maximum strength among PE, PP, PVC and PS. It is due to the phenyl pendent group. This group is largest among -H, -CH3 and -Cl.
8. Crystallinity results in increased ___________
a) Tensile strength
b) Impact toughness
d) Creep strength
Explanation: Impact toughness of polymer decreases because of crystallinity. It is because of close packing. While UTS, stiffness and creep strength improve.
9. The degree of crystallinity doesn’t exceed ___________ in polymers.
Explanation: The degree of crystallinity can be achieved as high as 80% in polymers. Polymers can’t be 100% crystalline. In polymers only some regions are crystalline.
10. The intermolecular bending forces are ___________ in nylon 6,6 because of the ___________ bonding.
a) Stronger, covalent
b) Stronger, H bonding
c) Weaker, ionic
d) Weaker, H bonding
Explanation: Nylon 6,6 shows very good mechanical properties. It is due to strong intermolecular bonds. These are hydrogen bonds.
11. Nylon 6,6 have a higher degree of crystallinity than Polyethylene.
Explanation: Intermolecular bonding forces are strong in nylon 6,6. It is because of hydrogen bonding. That’s why nylon 6,6 has higher crystallinity than PE.
12. Low density PE shows a higher degree of crystallinity than HDPE.
Explanation: On crystallization of polymers, interatomic forces become more effective between chains. It causes a decrease in density. So low density PE have less crystallinity.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.