This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Amino Resins”.
1. Which of the following is not a characteristic of a cured urea resin?
a) hard and rigid
b) non-inflammable
c) excellent electrical insulation
d) impart colour and odour to food & drinks
View Answer
Explanation: The cured urea resins do not impart colour and odour to food and drinks with which they may come in contact. They are hard, rigid and non-inflammable but they char around 200 ᵒC. They exhibit excellent insulation properties.
2. Which of the following is used as a lubricant in the moulding powder from urea-formaldehyde resin?
a) zinc stearate
b) ammonium sulphamate
c) trimethyl phosphate
d) none of the mentioned
View Answer
Explanation: Metal stearate like zinc stearate, aluminium stearate, etc. (quantity about 1%) is used as a lubricant in the moulding powder.
3. Which of the following can be used to improve the shelf-life of moulding powders from urea-formaldehyde resin?
a) ammonium sulphamate
b) magnesium stearate
c) hexamine
d) ammonia
View Answer
Explanation: To improve the shelf life of moulding powders, it should be stored in cool place. Incorporation of a small amount of a stabilizer such as hexamine further improves shelf-life.
4. What is the ratio of urea o formaldehyde to produce useful resins?
a) 1:2
b) 2:1
c) 1:1
d) 1:3
View Answer
Explanation: Urea is potentially tetrafunctional and the use of 1.5 to 2 moles of formaldehyde for each mole of urea yields useful resins.
5. What is the pH requirement for the preparation of adhesive resins from urea formaldehyde resin?
a) 8
b) 7
c) 7.5
d) 9
View Answer
Explanation: The adhesive resins are prepared in the water solube form, stabilized by maintaining the pH at 7.5 and a solid content of nearly 50-70%.
6. Which of the following is commonly used as hardening agent for urea-formaldehyde resins?
a) ammonium chloride
b) sodium hydroxide
c) aluminium chloride
d) sodium carbonate
View Answer
Explanation: The resins are hardened under acidic conditions and ammonium chloride is used as most common hardening agent for resins which acts as acid donor.
7. What is the approximate reaction temperature in the formation of melamine, when cyanamide is heated to give dicyandiamide?
a) 300 C
b) 70 C
c) 100 C
d) 180 C
View Answer
Explanation: Dicyandiamide is produced by heating cyanamide at a temperature of about 70-80 C.
8. What is the initial molar ratio for melamine to formaldehyde in commercial resinification reaction?
a) 1:3
b) 1:2
c) 3:1
d) 2:1
View Answer
Explanation: An initial molar ratio of 1:3 for melamine to formaldehyde is used in commercial resinification reactions.
9. What are the temperature and pressure conditions for the compression moulding of m-f resin?
a) 200-250 C and 1000-3000 psi
b) 150-170 C and 2000-8000 psi
c) 150-170 C and 1000-3000 psi
d) 200-250 C and 2000-8000 psi
View Answer
Explanation: The temperatures in the range of 150-170 C and pressure of the order 2000-8000 psi are employed for compression moulding of m-f resins.
10. What is the extensive use of melamine-formaldehyde resins?
a) decorative laminates
b) stove enamels
c) air-drying lacquers
d) art and jewellery
View Answer
Explanation: The exceptional hardness, solvent resistance and heat stability qualities of m-f resin make it suitable to be used as decorative laminates.
11. Which catalyst is used in the production of electrical grade laminates from m-f resin?
a) triethanolamine
b) sodium carbonate
c) sodium hydroxide
d) ethanamine
View Answer
Explanation: The electrical grade laminates are produced by using triethanolamine as condensation catalyst rather than sodium carbonate as catalyst. They are usually made by impregnationg electrical-grade glass cloth with the triethanolamine catalyzed resin.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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