Active and intelligent packaging

This activity requires students to use their existing knowledge of redox reactions, word equations, respiration and micro-organisms, as well as knowledge of polymer structure and function, and to apply this knowledge in a new context – that of packaging materials.

The student sheet guides them through some of the research and development chemists have carried out in recent years in the area of food packing. They may need access to texts to assist them in recalling what they have learnt previously. The activity provides an example of a positive contribution science is making to people’s everyday lives, even though they are largely unaware of it.

Suggestions for running the activity

Students could work on their own or in small discussion groups. They could either all write down the answers to the questions or have one scribe and then work together to produce a leaflet or poster to explain the new packaging to customers. At the end of the activity, students are asked for their opinions and feelings on the issues raised. Question 27 on the student sheet could be set as a follow-up homework task.

Questions

1. Write a list of 10 good reasons why food is put in packages.
2. Write a list of things that a supermarket or a customer might like a food package to be able to do. Be creative and imaginative
3. Why do you think more drinks (cappuccinos or milkshakes, for example) are not sold with a widget? (The widget is a ball containing nitrogen gas at high pressure.)
4. Why do many people prefer to eat fresh food? What do they think are the benefits of it?
5. What are the problems with fresh food?
6. What causes food to spoil or go off?
7. What conditions make food spoil or go off quickly?
8. Many foods are made of living cells that are respiring. Complete an equation to show what happens during respiration. (Equation is provided on download sheet)
9. What happens if you leave your wet swimming kit in a plastic bag for a few days?
10. Why does this happen?
11. Why does this happen to fruit and vegetables when they are left in a plastic bag? (Hint: look at the equation in Q8.)
12. Which gas do moulds need to survive?
13. What is an ‘oxygen scavenger’?
14. Why might you want one in the packaging of your food?
15. What does the word ‘oxidise’ mean?
16. Write a word equation to show what happens when iron is oxidised.
17. Why do you think consumers ‘don’t like finding a sachet marked “Don’t eat!” in their food’?
18. Why might consumers feel differently about the new method of oxygen scavenging than they do about the old one?
19. Why might some food retailers be keen to have this new type of packaging?
20. Why do you think retailers might not want to use it?
21. What do the terms polymer and side chain mean?
22. As the solid polymer is warmed up, what happens to the movement of the molecules?
23. Will a polymer molecule with long side chains need more or less energy to move apart from the other polymer chains? Why?
24. Will a polymer whose molecules have long side chains melt at a lower or higher temperature than one with short side chains? Why? Explain your answer in terms of intermolecular forces.
25. Why might a supermarket want to have labels like this (contains a chemical in the label that changes colour from light to dark when it reacts) on their produce? 
26. Do you think it would be a good thing for consumers if these labels were widely used? Why?
27. Write a paragraph explaining what active packaging is and what you think about it.

Answers

1. Reasons could include: keeps liquids in one place, prevents spillages, protects food, standardises the amount in a pack, allows marketing/branding of products, can put list of ingredients on pack, helps stop the food going off, hygiene, convenience, improves how food looks.
2. Possible aims for packaging include: pre-weighed packs, stop food going off/increase shelf-life, increase speed at check-outs. Students might give a range of other answers.
3. Widgets are expensive so they are only used in relatively expensive products and where there is really no alternative.
4. The reasons people like fresh food include: taste, texture, contains more vitamins and minerals, they enjoy cooking it.
5. Fresh food goes off. Since you cannot keep it for a long time, you either have to go shopping more often or accept a certain amount of wastage.
6. Moulds and bacteria grow on the food and cause it to go off. (Another cause is oxygen reacting with the food, but students will probably not give this answer based on their previous knowledge of science.)
7. Warm, damp conditions make food go off quickly.
8. Glucose + oxygen → carbon dioxide + water C₆ H₁₂ O₆ + 6O₂→ 6CO₂ + 6H₂ O
9. Wet swimming kit left in a plastic bag for a few days starts to smell.
10. Micro-organisms, especially moulds, grow on the kit because there is plenty of water for them. They release the gases that you smell.
11. Fresh fruit and vegetables contain living cells which are respiring. They produce water which cannot escape from the bag. The water encourages micro-organisms (especially moulds) to grow.
12. Moulds need oxygen to survive.
13. An oxygen scavenger is something that removes oxygen.
14. If you remove oxygen from the pack, moulds are less likely to grow because they need oxygen to respire.
15. Oxidise in this context means to react with oxygen.
16. Iron + oxygen → iron oxide
17. They might think their food could get contaminated with a non-edible/poisonous substance.
18. If consumers cannot see the oxygen scavenger, they will not know it is there. Consumers are used to seeing food wrapped in clear plastic and will not notice a difference.
19. Retailers might like the packaging because it will help make the food last longer so less will go past its ‘sell-by’ date before it is sold. This will reduce the retailer’s waste and save money.
20. The new packaging might be more expensive than conventional packing.

Questions 21–24 require knowledge of polymers, their structure and function. If this topic has not been covered, you may wish to direct students to leave these questions out or remove them from the worksheet.

21. Polymer: a long chain molecule made of lots of small molecules (monomers) joined together. Side chain: a group of atoms sticking off/attached to the main polymer chain.
22. As the polymer warms up, the molecules move more and vibrate faster.
23. A polymer with long side chains needs more energy to move apart from the other polymer molecules. This is because there are stronger intermolecular forces holding the molecules with long side chains together so it will take more energy to pull them apart.
24. Long side chains are likely to lead to a higher melting point as there are stronger attractions between the polymer chains. The side-chained polymers move more as the material warms up, leading to the opening of pores in the polymer film.
25. Supermarkets might want to use the labels to give consumers confidence in what they are buying.
26. Various answers are possible here – students might answer ‘yes’ because the labels would allow consumers to see if what they are buying is fresh or not; they might answer ‘no’ because unscrupulous supermarkets could just change the labels.
27. Paragraph about students’ own reaction to the information. Mark by impression.