Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Orientation of Thermoplastic Films”.
1. The term BOPP in packaging stands for _____
a) Biaxially Oriented Polypropylene
b) Biaxially Oriented Propylene Alcohol
c) Biaxially Oriented polyphenol
d) Biaxially Operated Packaging Printing
Answer: a
Clarification: The term BOPP in packaging stands for Biaxially Oriented Polypropylene. It is generally used for packaging labels. BOPP is produced by stretching the polypropylene film in both directions. It results in higher strength and higher resistance to stress cracking and puncture.
2. Which of the following is used for shrink bundle?
a) BOPP
b) PVC
c) LLDPE
d) Cast PP
Answer: c
Clarification: LLDPE-Linear Low Density Polyethylene is used for shrink bundling. LLDPE is a copolymer made up of ethylene and another longer olefin, whereas LDPE is a homopolymer made only of ethylene monomers. LLDPE has a greater tensile strength or resistance to harsh environment.
3. Oriented films have better sealability.
a) True
b) False
Answer: b
Clarification: The above statement is false. Oriented film cannot be easily heat sealed because it shrinks and puckers at temperatures below the sealing temperature.
4. LDPE is generally irradiated before moulding into film.
a) True
b) False
Answer: a
Clarification: The given statement is true. LDPE is generally irradiated before moulding into film, because radiation cross-links the molecules and the film can be stretched without becoming fluid at the melting point of a non-irradiated film, resulting in greatly improved tensile strength and shrink tension compared to non-irradiated LDPE.
5. __________ is the process which reduces the residual strain after the extrusion process.
a) Lacquering
b) Canning
c) Electroplating
d) Annealing
Answer: d
Clarification: Annealing is the process which reduces the residual strain after the extrusion process. Films can be annealed by the application of heat to partially relax the forces while maintaining the film in a highly stretched condition. It is then cooled to room temperature and the restraint on the film released.
6. The film after annealing is called ________
a) Strict film
b) Film set
c) Heat set
d) Heat film
Answer: c
Clarification: The film after annealing is called heat set. Heat set does not shrink even if heated below the annealing temperature. Heat set has more desirable properties. Annealing results in some reduction in dimension in the stretched direction or directions.
7. Which of the following methods are used for orientation of plastic films?
a) Tenter frame and bubble frame
b) Tenter frame and Double bubble
c) Tenter bubble and Double bubble
d) Tenter bubble and Double Frame
Answer: b
Clarification: Tenter frame and Double bubble are the two methods are used for orientation of plastic films. It generally includes heating of the film and stretching it in uniaxial or biaxial direction on a tenter or double frame. The orientation decides the use of the film.
8. 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
Answer: d
Clarification: 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.
9. Orientation increases permeability.
a) True
b) False
Answer: b
Clarification: The given statement is false. Orientation decreases permeability. It is because orientation decreases both, the diffusion and solubility coefficient of the plastic film.
10. 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
Answer: c
Clarification: 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.
11. 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
Answer: a
Clarification: 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.
12. The orientation % in BOPP by the double bubble process lies between _________
a) 200-1000
b) 200-800
c) 700-800
d) 700-1000
Answer: c
Clarification: 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.
13. The amount of orientation imparted to a film depends on the amount of quench.
a) True
b) False
Answer: a
Clarification: 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.
14. Films with glass transition temperature below room temperature have more crystallisation rate.
a) True
b) False
Answer: a
Clarification: 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.
15. The property of a thermoplastic film to return to its original size is called ______
a) Elasticity
b) Shrinkiness
c) Elastic memory
d) Shrinkability
Answer: c
Clarification: 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.