1. What type of phenolics is extensively used as objects of art and jewellery?
a) laminated phenolics
b) cast phenolics
c) oil-soluble phenolics
d) resols
Explanation: Due to their attractive colours and transparency, self-lubricating properties and good machinability, the cast phenolics are used as objects of art and jewellery and as handles of tools and umbrella, knobs, etc.
2. How is the cross-linking of novolacs better accomplished along with the presence of additional formaldehyde?
a) use of acidic catalyst
b) use of basic catalyst
c) additional phenol
d) none of the mentioned
Explanation: The cross-linking of novolacs is better accomplished using a basic catalyst. An insoluble, infusible, cross-linked polymer products is then formed in a single step.
3. 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
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.
4. 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
Explanation: Metal stearate like zinc stearate, aluminium stearate, etc. (quantity about 1%) is used as a lubricant in the moulding powder.
5. 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
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.
6. What is the ratio of urea o formaldehyde to produce useful resins?
a) 1:2
b) 2:1
c) 1:1
d) 1:3
Explanation: Urea is potentially tetrafunctional and the use of 1.5 to 2 moles of formaldehyde for each mole of urea yields useful resins.
7. What is the pH requirement for the preparation of adhesive resins from urea formaldehyde resin?
a) 8
b) 7
c) 7.5
d) 9
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%.
8. 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
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.
9. 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
Explanation: Dicyandiamide is produced by heating cyanamide at a temperature of about 70-80 C.
10. 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
Explanation:An initial molar ratio of 1:3 for melamine to formaldehyde is used in commercial resinification reactions.