Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Diffusivity and Permeability in Plastics”.
1. Arrange the following in correct order of WVTR.
a) EVOH > PET > HDPE > Al
b) Al > EVOH > HDPE > PET
c) PET > EVOH > HDPE > Al
d) EVOH > HDPE > PET > Al
Answer: a
Clarification: The correct order of decreasing Water Vapour Transmission Rate is Ethylene Vinyl Alcohol > Polyethylene Terephthalate > High Density Polyethylene > Aluminium. Hence, amongst the given films, Aluminium is the best water vapour barrier.
2. The term OTR related to packaging films stands for ________
a) Overall Thermal Resistance
b) Outer Tear Resistance
c) Oxygen Transmission Rate
d) Odour Transfer Rate
Answer: c
Clarification: The term OTR related to packaging films stands for oxygen transmission rate. It is the rate by which oxygen permeates through a plastic film. The plastic films having a greater oxygen transmission rate are a poor barrier against gases, especially oxygen.
3. The term WVTR related to packaging films stands for ________
a) Water vapour transmission rate
b) Water vapour transient rate
c) Water vapour transfer rate
d) Water to vapour total ratio
Answer: a
Clarification: The term WVTR related to packaging films stands for Water vapour transmission rate. It is the rate by which water vapour/moisture permeates through a plastic film. The plastic films having a greater water vapour transmission rate is a poor barrier against water vapour or moisture.
4. WVTR is expressed as _________
a) gm2/hr
b) g/m224hr
c) g/m2hr
d) g/cm224hr
Answer: b
Clarification: WVTR – Water vapour transmission rate is expressed as gm2/24hr. WVTR is the quantity of water vapour in gram that will permeate from one side of a film of an area 1m2 to other in 24 hours.
5. Arrange the following in correct order of OTR
a) EVOH > PET > LDPE > HDPE
b) PET > EVOH > LDPE > HDPE
c) LDPE > HDPE > EVOH > PET
d) LDPE > HDPE > PET > EVOH
Answer: d
Clarification: The correct order of decreasing Oxygen Transmission Rate is Low Density Polyethylene > High Density Polyethylene > Polyethylene Terephthalate > Ethylene Vinyl Alcohol. Hence, amongst the given films, Ethylene Vinyl Alcohol is the best oxygen barrier.
6. Permeability is calculated using ________ and _________
a) diffusion, solubility
b) permeance, solubility
c) diffusion, permeance
d) transmittivity, solubility
Answer: a
Clarification: Permeability is calculated using Diffusion and Solubility. Permeability is the product of diffusion and solubility. When a gas/vapour passes through the plastic film, it solubilizes first and then diffuses through the film.
7. Permeability is calculated by the formula P=D/S.
a) True
b) False
Answer: b
Clarification: Permeability is the multiplication of diffusion coefficient and solubility coefficient. P=D*S. P,D,S stands for Permeability coefficient, Diffusivity Coefficient and Solubility Coefficient respectively. It is because, vapour/gas solubilizes and then diffuses through the film to reach it’s other side.
8. What is the unit of coefficient of Diffusion coefficient?
a) m2/s
b) cm2/s
c) m/s
d) m2s
Answer: a
Clarification: The unit of coefficient of Diffusion coefficient is m2/s. Diffusion coefficient is a measure of how fast a permeate moves through the plastic polymer. It depends on degree of crystallinity of polymer.
9. What is the unit of coefficient of Solubility coefficient?
a) m2s
b) m2/s
c) m/s
d) ms
Answer: b
Clarification: The unit of coefficient of Solubility coefficient is m2/s. Solubility coefficient is a measure of how much permeate solubilises through the plastic polymer. It depends on degree of interaction between polar water molecule and polymer molecular structure.
10. What is the unit of coefficient of Permeability?
a) s/m2
b) m2/s
c) m/s
d) m2
Answer:c
Clarification: The unit of coefficient of Permeability is m2. Permeability can be calculate by the formula- P=Qk/(AtΔP), where, P:Permeability, Q:Quantity of permeant, k:thickness, A:area, t:time, ΔP:pressure drop across polymer.
11. If a plastic film has high OTR, it will have a high WVTR too.
a) True
b) False
Answer: b
Clarification: The given statement is false. There are many plastics which act as a good water vapour barrier and a poor gas barrier. It is because of different Water Vapour Transmission and Oxygen Transmission rates. For example, EVOH has low Oxygen Transmission Rate but higher Water Vapour Transmission Rate.
12. Permeability can also be calculated by the formula _____________
a) P=Qk/(AtΔP)
b) P=Qt/(AkΔP)
c) P=Q/(AktΔP)
d) P=QA/(ktΔP)
Answer: a
Clarification: Permeability can also be calculated by the formula- P=Qk/(AtΔP). Where, P:Permeability, Q:Quantity of permeant, k:thickness, A:area, t:time, ΔP: pressure drop across polymer. Permeability is directly proportional to Quantity of permeant and thickness and inversely proportional to area, time and pressure difference.
13. The uptake of food components such as aroma and flavour by plastic films is known as ________
a) Scavenging
b) Broiling
c) Scalding
d) Scaling
Answer: d
Clarification: The uptake of food components such as aroma and flavour by plastic films is known as Scaling. Such plastics have a greater permeability and hence are not suitable for primary packing. Such packaging materials are either used for tertiary or pellet packing.
14. Which of the following is the best Oxygen barrier?
a) EVOH
b) PS
c) PE
d) PP
Answer: a
Clarification: Amongst the following, EVOH is the best Oxygen barrier as it has low Oxygen transmission rate. Plastic films with low oxygen transmission rate are good barriers and plastic films with higher oxygen transmission rates are poor barriers.
15. Permeability can be related to which law of Food Engineering?
a) Fourier Law
b) Kohlrausch’s Law
c) Fick’s Law
d) Newton’s Law
Answer: c
Clarification: Permeability can be related to Fick’s law of diffusivity. It relates the diffusion flux (J) to the steepness of concentration gradient, where D is diffusion coefficient, C is concentration and x is the distance. It is given by the formula: J = -δC/δx.