This set of Basic Polymer Engineering Questions and Answers focuses on “Phenolic Resins”.
1. How many methylol groups are present in a typical novolac molecule?
a) 3-5
b) 6-8
c) 0
d) 2
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Explanation: A typical novolac molecule contains around 6 aromatic rings linked through methylene linkages and having practically no methylol groups attached to it.
Thus they are soluble and fusible.
2. If the resinification reaction is stopped at early stages, a low molecular weight product A, having 3-4 aromatic rings and 3-5 methylol groups, which is soluble in alkalis and alcohol is formed. What is the name of the product A?
a) resole
b) resitol
c) resite
d) novolac
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Explanation: If the resinification reaction is stopped at early stages, a low molecular weight product soluble in alkalis and alcohol is obtained. It is known as resole or A-stage resin, which has 3-4 aromatic rings and 3-5 methylol groups. It may be either linear or may be lowly branched.
3. What is the name of the B- staged resin formed in resinification process?
a) resol
b) resitol
c) resite
d) novolac
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Explanation: The reaction of resols with other reactive species and also among each other leads to the production of B-staged resins, known as resitols, which are mildly cross-linked molecules.
4. Resin P, on further heating turns into completely cross-linked resin Q, which is totally insoluble and infusible. Resin P is slightly heat fusible and insoluble in alkalis and alcohols but partly soluble in acetone. What are the names of resin P and Q?
a) resol and resitol
b) resitol and resite
c) resol and resite
d) none of the mentioned
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Explanation: Resitols being slightly heat fusible on further heating turn into fully cured or cross-linked resin known as resite or C-staged resin which is totally insoluble and infusible.
5. Which of the following phenolic resins are suitable for the decorative laminates?
a) caustic soda catalyzed resols
b) ammonia catalyzed resols
c) spirit resols
d) resites
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Explanation: Caustic soda catalyzed resols are suitable for mechanical and decorative laminates while ammonia catalyzed resols are used for electrical laminates.
6. What are the temperature and pressure conditions in compression moulding technique in the moulding of phenolic moulding powder?
a) 160-170 ᵒC and 1500-3000 psi
b) 100-120 ᵒC and 1000-1500 psi
c) 160-170 ᵒC and 500-1000 psi
d) 100-200 ᵒC and 1500-3000 psi
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Explanation: Compression moulding is operated to mould the phenolic moulding powders by using a pressure of about 1500-3000 psi and temperature of 160-170 ᵒC.
7. What is the approximate phenol formaldehyde ratio used is the preparation of casting grade phenolic resins?
a) 1:2.2
b) 2:1
c) 3:1
d) 1:2
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Explanation: The casting grade phenolics are prepared from highly pure grades of phenol and formaldehyde using more than 2 moles of formaldehyde per mole of phenol and employing alkaline catalyst.
8. Why is a stainless steel kettle used in the production of casting grade phenolics?
a) to minimize corrosion’
b) to minimize color formation
c) to maximize color formation
d) to increase strength
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Explanation: To minimize color formation, a stainless steel kettle is used in the process of formation and a mild temperature of 70-75 ᵒC is maintained.
9. 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
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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.
10. 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
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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.
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