Learning Aims:
  • To develop criteria for wrapping material
  • To develop mental models
Suggestions for use:

This activity is a thinking exercise that leads to the aspect of producing polymer films. The starting question could be: When preparing a sandwich, what’s the best material to use to wrap it? What criteria would you apply? Below are possible factors that pupils might suggest: availability, cost, environmental impact (biodegradable, combustible, ...), insoluble in water, impermeable to fat and water, non-reactive (e.g. with acids in various foods), odorless and tasteless, keeps odours in (or out), ..., breathable or not?

The students should then rank the criteria they have named in order of importance and find out if there were materials that have the properties of higher ranked criteria. This ranking and questioning will lead to the suggestion of a plastic (cling film). Analyse what properties plastics have from the list of criteria. Water will not pass through it; therefore it is impermeable, maybe inferring that there are ‘no holes’.

To get students to start thinking at a deeper level get them to draw what a sheet of cling film looks like.

Ask them about the size and the number of atoms.

Invite the students to imagine to shrink themselves down to the size of an atom and ask them what the plastic will look like.

Experimentally - show briefly that cling film will hold water.

Show Cling Film as an example of a polymer, made up of monomer units, each monomer is long chain. The students could be invited to think again about the size of the chains, the polymers, the atoms, etc.

Possible questions:

A following question could be on the making of films and if it was possible to make films without holes (see extra activities 2.5). The following questions could then lead to further investigations:

  • Will anything else pass through holes e.g. oxygen?
  • Can we make films with different sized holes?
  • When a sandwich is wrapped, lots of other compounds present – e.g. fat, oil, ketchup etc. What are these compounds?
  • If you are wrapping a hot dog, then temperature is important. So how does temperature affect the film?