1. The temperature of orientation is ______ the flow temperature and _____ the glass transition temperature.
a) above, above
b) above, below
c) below, below
d) below, above
Discussion
Explanation: The temperature of orientation is below the flow temperature and above the glass transition temperature. When the temperature of the film is above glass transition temperature and below flow temperature, the molecules readily glide past one another when the material is stressed. This is the optimal temperature for stretching the thermoplastic film. As a result of this stretching, the direction of the molecules changes toward that in which the material is stressed, and the molecules are extended like springs. The lower temperature enables the setting the configuration of molecules in the strained position.
2. Orientation increases permeability.
a) True
b) False
Discussion
Explanation: The given statement is false. Orientation decreases permeability. It is because orientation decreases both, the diffusion and solubility coefficient of the plastic film.
3. Which of the following does not affect stretch rate in tender frame process?
a) Extent of orientation
b) Divergence angle
c) Feed rate
d) Chain speed
Discussion
Explanation: Feed rate does not affect stretch rate in tender frame process. Stretch rate is determined by the chain speed, divergence angle and extent of orientation. The thermoplastic film is stretched in the machine direction (MD) and the extent of orientation is determined by the ratio of the width of the film entering to the width of the film leaving the system. The film is then fed to a tender frame where a series of clips (mounted side by side on endless chains that diverge at constant angle) grasp both edges of the film and draw it in the transverse direction (TD) as it travels forward at an increasing speed.
4. Draw ratios in tender frame process ranges from ______ to _____
a) 4:1, 10:1
b) 2:1, 10:1
c) 3:1, 10:1
d) 5:1, 10:1
Discussion
Explanation: Draw ratios in tender frame process ranges from 4:1 to 10:1. It is for both the directions- Machine Direction (MD) and Transverse Direction (TD). In the tender frame process, the thermoplastic film is first stretched in the machine direction and then the transverse direction.
5. The orientation % in BOPP by the double bubble process lies between _________
a) 200-1000
b) 200-800
c) 700-800
d) 700-1000
Discussion
Explanation: The orientation % in BOPP by the double bubble process lies between 700-800%. This happens because of the elastic memory of Polypropylene, which leads to shrinkage of the film after orientation.
6. The amount of orientation imparted to a film depends on the amount of quench.
a) True
b) False
Discussion
Explanation: The given statement is true. The amount of orientation imparted to a film depends on the stretching temperature, the amount of stretching, the rate of stretching and the quench. The extent of orientation is increased by decreasing the stretching temperature, increasing the amount of stretch, increasing the rate of stretch and increasing the amount of quench.
7. Films with glass transition temperature below room temperature have more crystallisation rate.
a) True
b) False
Discussion
Explanation: The given statement is true. Films with glass transition temperature below room temperature have more crystallisation rate. PVdC copolymer and PP are an example. They show appreciable crystallization rate even at room temperature and, therefore, have to be quenched and oriented immediately after extruding.
8. The property of a thermoplastic film to return to its original size is called ______
a) Elasticity
b) Shrinkiness
c) Elastic memory
d) Shrinkability
Discussion
Explanation: The property of a thermoplastic film to return to its original size is called elastic memory. It is the potential energy stored in the extended molecules which is a characteristic of oriented, non-heated set thermoplastics. When such a film is reheated to its orientation temperature, it shrinks as the molecules tend to return to their original size and spatial arrangement.
9. Which of the following is not used as a stretch film?
a) Polyolefins
b) PVC
c) PVdC
d) PET
Discussion
Explanation: PET is not used as a stretch film. PET has its greatest use in bottles for juices and soft drink due to its barrier and mechanical properties. Shrink films are composed of three basic categories: polyolefins, PVC and PVdC copolymer.
10.LLDPE is produced by copolymerisation of ethylene with ______
a) Di-olefins
b) Gamma olefins
c) Beta olefins
d) Alpha olefins
Discussion
Explanation: LLDPE is produced by copolymerisation of ethylene with alpha olefins. LLDPE- Linear Low Density Polyethylene has better stretch properties when compared to LDPE- Low Density Polyethylene.