38.5 Technical Questions

Q. 1. What are the typical additives used in polymer products ?

Ans: Polymer additives include materials which make and modify polymers. These include surfactants, chain transfer agents, modifiers, plasticizers, stabilizers, initiators and cross – linking agents.

Q. 2. Explain Glass Transition Temperature ?

Ans:Glass Transition Temperature of a non – crystalline material is the temperature at which the material changes its behaviour from its glassy state to a rubbery state. Glassy state refers to the state at which a material is hard and brittle; whereas , rubbery state refers to the state at which the material is flexible and elastic.

Q. 3. Apply your knowledge in Chemical Engineering and outline one problem one may encounter in polymerization processes?

Ans: There are certain compounds like styrene, which are used in the polymerization process. Styrene is an olefin, and is unstable as a pure liquid. Such compounds may explode, even in the absence of oxygen.

Many polymers can be recycled, which reduces the disposal problems. But inorder to do so, the polymers must be separated from each other at first, and this process may be very difficult and expensive.

Incineration is a process which is used in many polymerization processes. But this leads to release of high amount of heat energy , which could otherwise be used for various useful purposes. Moreover, carbon dioxide is produced during incineration , which leads to global warming.

 

Q. 4. Match the polymer processing techniques for making various products?

Group 1	Group 2
a. Rubber sheet	1. Rotational Molding
b. HDPE water storage tanks	2. Compression Molding
c. Bicycle paddle	3. Calendering
d. Glass reinforced thermosetting plastics	4. Injection molding

 

Ans:

• a-3

b-1

c-4

d-2

Q.5 Mention some of the advantages of blow molding as compared to injection molding?

Ans.5 Some of the advantages of blow molding as compared to injection molding are-

1.  Possibility of variable wall thickness.

2.  Low stresses and favorable cost factor.

       

Q.6 What are the different types of injection molding machines that may be used?

Ans.6

1.  Plunger type

2.  Piston type

3.  Reciprocating Screw

 

Q.7 What are the different types of screw zones in a extrusion machine ?

Ans.7

1.  Feed zone

2.  Metering zone

3.  Transition zone

Q.8 In molding process, the polymer material will try to stick to the wall of the mold (container). How can you prevent it?

Ans. 8 The polymeric material can be prevented from sticking to the walls of the mold by changing the viscosity of the polymer. This can be achieved by selecting the MOC of the container (mold) in such a way that it will create substantial viscosity gradient between the walls and the polymeric material. It can also be done by heating the walls of the mold externally.

References :

1. Ullmann F., Encyclopedia of Industrial Chemistry, Wiley – VCH, 1999-2012

2. Kirk R. E., Othmer D. F., Encyclopedia of Chemical Technology, John Wiley and Sons, 1999-2012