Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Thermoforming”.
1. In thermoforming, plastic sheets are heated to ________
a) Boiling point
b) Tg point
c) Sag point
d) Melting point
Answer: c
Clarification: In thermoforming, plastic sheets are heated to Sag point. It is the temperature at which the plastic softens and extends under its own weight, i.e., when the plastic begins to sag.
2. From which of the following processes, canopies for racing vehicles are made?
a) Drape forming
b) Mechanical forming
c) Pressure forming
d) Free blowing
Answer: a
Clarification: Canopies for racing vehicles are made from drape forming. Drape forming is the process by which the plastic sheet is heated, such that it can be bent and shaped into any form without using a vacuum.
3. SPPF in thermoforming stands for ____________
a) Soluble peer pressure forming
b) Soluble phase pressure forming
c) Solid peer pressure forming
d) Solid phase pressure forming
Answer: d
Clarification: SPPF in thermoforming stands for solid phase pressure forming. The SPPF process is primarily used to thermoform PP, a crystalline polymer that is difficult to thermoform uniformly in melt phase machines due to the sharp decrease in melt strength (viscosity) at its melting point.
4. APET is stable till 230°C.
a) True
b) False
Answer: b
Clarification: The given statement is false. CPET (Crystalline PET) is stable till 230°C. Whereas, APET (Amorphous PET) softens over 63°C. The CPET process is based on conventional reheat thermoforming where an extruded PET sheet containing nucleating agents to speed up and maximize crystallization is reheated to around 170°C where it softens. After this, it is transferred in a hot mold and held so the crystallinity develops. Then it is transferred to a second mould for cooling.
5. In drape forming technique _______ is used for forming.
a) Vacuum
b) High pressure
c) High Temperature
d) Low pressure
Answer: a
Clarification: In drape forming technique vacuum is used for forming. In vacuum forming, vacuum is heated below the preheated plastic sheet to draw sheet into cold mold cavity. The steps include heating the plastic sheet, placing the softened sheet is placed over a concave activity. Vacuum draws the sheet into cold cavity. The final product is then cooled.
6. Which of the following material is not thermoformed?
a) HIPS & ABS
b) POM & Nylon
c) PVC
d) PMMA
Answer: b
Clarification: Among the given options, POM & Nylon is not thermoformed. Whereas, HIPS- High Impact Polystyrene, ABS- Acrylonitrile Butadiene Styrene, PVC- Polyvinyl Chloride and PMMA- Poly(methyl methacrylate) are thermoformed.
7. Bath tubs are made by __________ technique.
a) Free forming
b) Pressure thermoforming
c) Match die thermoforming
d) Drape forming
Answer: d
Clarification: Bath tubs are made by drape forming technique. Drape forming is the process by which the plastic sheet is heated, such that it can be bent and shaped into any form without using a vacuum.
8. Thermoforming can be generally classified as ________ and _______ thermoforming.
a) pressure, temperature
b) vacuum, pressure
c) Thick gauge, thin gauge
d) Temperature, vacuum
Answer: c
Clarification: Thermoforming can be generally classified as Thick gauge and thin gauge thermoforming. Thick gauge thermoforming is a term used for making heavy duty parts, such as- plastic pallets, refrigerator liners, etc. Whereas, thin-gauge thermoforming is the term used to describe the manufacturing of lighter and smaller things, such as disposable cups, containers, trays, lids, and other products for the food, medical, and general retail industries.
9. Which of the following is not a mold used in thermoforming?
a) Aluminium mold
b) Steel mold
c) Wooden mold
d) Plastic mold
Answer: b
Clarification: Steel mold is not used in thermoforming. The mould used in thermoforming should be such that the plastic polymer to be thermoformed isn’t affected by it. The mold used in thermoforming are- aluminium mold, plaster of paris mold, plastic mold and wooden mold.
10. Thermoforming is the same as blow moulding.
a) True
b) False
Answer: b
Clarification: The given statemet is false. Thermoforming and blow moulding are totally different processes. Thermoforming is the process in which an article is heated stretched and cooled to give it a desirable shape. Whereas, in blow moulding, the thermoplastic is heated and put into the desired container and then shaped by blowing air through it.
11. The CPET containers, made by thermoforming are stable upto what temperature?
a) 230°C
b) 150°C
c) 300°C
d) 500°C
Answer: a
Clarification: CPET (Crystallized Polyethylene terephthalate)containers, made by thermoforming are stable upto 230°C. The optimum amount of crystallinity is 28%–32%. CPET containers must be crystalline enough to be heat resistant but not so crystalline as to be too brittle for the application, for example, impact resistance at freezer temperatures.
12. The two dominant means of thermoforming sheet for food packaging containers are _____ & _____
a) Solid phase pressure forming, liquid phase pressure forming
b) Liquid phase process, vapour phase pressure forming
c) Melt phase process, liquid phase pressure forming
d) Melt phase process , solid phase pressure forming
Answer: d
Clarification: The two dominant means of thermoforming sheet for food packaging containers are melt phase process and solid phase pressure forming. The melt phase process is most applicable to monolayer structures that have relatively high melt strength at thermoforming temperatures, for example, HIPS, PVC and PC. The SPPF process is primarily used to thermoform PP, a crystalline polymer that is difficult to thermoform uniformly in melt phase machines due to the sharp decrease in melt strength (viscosity) at its melting point.
13. _______ are defined as plastics whose apparent density is decreased.
a) Cellular plastics
b) Polyplastics
c) Thermoplastics
d) Artificial plastics
Answer: a
Clarification: Cellular plastics are defined as plastics whose apparent density is decreased substantially by the presence of numerous cells dispersed throughout their mass. The terms foamed plastic, expanded plastic and plastic foam are also used for cellular plastics. They have desirable properties such as, high strength-to- weight ratio and good insulating and cushioning properties.
14. In general, temperatures for melt phase thermoformed Polypropylene is greater than SPPF Polypropylene.
a) True
b) False
Answer: a
Clarification: The above statement is true. In general, temperatures for melt phase thermoformed Polypropylene is greater than SPPF(Solid phase pressure formed) Polypropylene. It is melt phase thermoformed at 154°C–157°C and SPPF at 141°C–146°C, where it is still virtually a solid with high viscosity, requiring the application of strong forces.