This set of Polymer Engineering Interview Questions and Answers for freshers focuses on “Polyethylene-2”.
1. LDPE is more prone to oxidation than HDPE. State true or false.
a) true
b) false
View Answer
Explanation: LDPE is more prone to oxidation than HDPE as is contains higher concentration of tertiary hydrogen (at branch sites), given that it is free from metallic impurities. Uncontrolled oxidation leads to countable incorporation of carbonyl and peroxy groups which can make the polymer more prone to degradation due to absorption of heat and light.
2. What does higher melt flow index (MFI) indicates in polymer system and which type of polyethylene belongs to higher MFI value category?
a) lower molecular weight, LDPE
b) higher molecular weight, LDPE
c) lower molecular weight, HDPE
d) higher molecular weight, HDPE
View Answer
Explanation: The melt flow index (MFI) helps to differentiate between different grades of polymer. A higher value of melt flow index indicates lower molecular weights, and LDPE falls in a MFI range of (0.3-70), whereas HDPE has a relatively lower value (0.02-2.5).
3. Which of following kind of polyethylene has the highest degree of chain-branching?
a) LDPE
b) HDPE
c) LLDPE
d) cannot be determined
View Answer
Explanation: Due to high chain transfer in free radical polymerization effected in high pressure, LDPE has nearly 20-50 branches per 1000 linear carbon atoms in chain molecules, while HDPE contains only about 1-5 branches per 1000 carbon atoms making itself nearly a linear polymer. LLDPE, as the name suggest is a linear polymer.
4. Which of the following category in properties can be considered as a limitation to the application of polyethylene?
a) chemical inertness
b) toxicity
c) softening point
d) insulation properties
View Answer
Explanation: The low softening point or heat distortion temperature of polyethylene is a limiting factor for the application of polyethylene. The contributing factors for its application are excellent chemical inertness and electrical insulation properties, and the non-toxic nature of polyethylene.
5. Which of the following is true case when the stress cracking problem in polyethylene is less critical?
a) high molecular weight and high density
b) low molecular weight and high density
c) high MFI and high density
d) low molecular weight and low density
View Answer
Explanation: Polyethylenes generally show low environment stress cracking resistance problem. Thus, the stress cracking problem is less critical with relatively high molecular weight or low MFI and high density materials.
6. Which of the following is true, when the density of LDPE is increased?
a) crystallinity decreases
b) permeability to liquid and gas decreases
c) toughness increases
d) all of the mentioned
View Answer
Explanation: The crystallinity increases with the density increase of polymer i.e the amount of short chain branching decreases, which on the other hand decreases the toughness and permeability to gas and liquid.
7. Which of the following atom, with its presence in the LDPE chain, can give a rubbery product?
a) Cl
b) S
c) N
d) O
View Answer
Explanation: The introduction of chlorine atom in the chain to the extent of one chlorine atom for at least 7 carbon atoms gives a useful rubbery product. The rubbery products formed are among the best chemical resistant rubbers.
8. LDPE has a superior degree of toughness, stiffness, stress cracking resistance and electrical properties than LLDPE. State true or false.
a) true
b) false
View Answer
Explanation: LLDPE, a copolymer by definition and design, has a superior degree of toughness, stiffness, stress cracking resistance and electrical properties than LDPE. Even the possibilities for LLDPE to take over 30-350% market of LDPE have also increased.
9. What is the range of melting or softening temperature of high density polyethylene?
a) 125-135 ᵒC
b) 110-117 ᵒC
c) 90-110 ᵒC
d) 118-120 ᵒC
View Answer
Explanation: The melting temperature of HDPE (125-135 C) is usually higher in comparison to LDPE and LLDPE, due to the its short and less branching and high density ranges.
10. The films made by copolymer of ethylene and ethyl acrylate are of much better quality than the films made by normal LDPE. State true or false.
a) true
b) false
View Answer
Explanation: The films made from the copolymer of ethylene and ethyl acrylate have a great degree of tensile strength, stress cracking resistance, clarity and flexibility at low temperatures in comparison to the films produced by normal LDPE.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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