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Procedure and notes for teachers (italics refer to the notes for teachers):
- Discuss the topic of materials
- Select 10 random items; write them on a piece of paper.
- Students can select anything, the list can be as follows:
- chair
- car
- rucksack
- jacket
- cup of yogurt
- pencil
- bench
- spectacles
- handkerchief
- school bag
- notice board
- Once the students make their lists, ask them a question concerning the presence of polymers and plastics in the given products:
- For the products listed, highlight those products, where the materials they are made from, contain polymers
- For the products listed it is possible to write e.g. the following description and the students should identify the following materials:
- þ chair – can be wooden, metal legs. Wood is a material consisting mainly (ca about 43 %) of cellulose polymer, which is polymeric glucose. The chair can be from "an artificial material", e.g. from polyethylene or polypropylene, then it naturally contains a polymer, it can also have a cover which is often made of plastic fibres
- þ car – the present car is composed of many polymers, whether the textile fibres on the seats, dashboards, rugs, etc. In today’s cars, a share of plastics reaches 12-15% (http://www.autorevue.cz/automobily-jen-z-plastu-uz-se-to-blizi) and it is still increasing. This is the weight percentage, i.e. the car weighing 2000 kg contains roughly 280 kg of polymers. Since the polymers have a density 4x-8x lower than e.g. steel, a volume share of plastics in the car can be around 50 %.
- þ rucksack – rucksacks are at present made of mainly synthetic fibres, which are naturally the polymers.
- þ jacket – similarly to rucksacks, these products are nowadays made of mostly synthetic polymeric fibres. E.g. today’s very popular Gore-Tex is a polymer polytetrafluoroethylene (PTFE) laminated between the layers of polyamide or polyester. The jacket (or even the rucksack) can also be made of cotton, which is also a polymer (cellulose) or other natural fibres, which are also nearly exclusively polymeric substances.
- þ cup of yogurt – packaging material of our tasty yogurt is very often, indeed almost exclusively, a polymer, often a polystyrene (PS). Yogurt can be packed in glass; however it is not very common.
- þ pencil – a wooden pencil is a polymer (as it contains cellulose), ballpoint pens tend to have a body made of synthetic polymers.
- þ bench – most commonly wooden; i.e. polymeric, there are also the ones made of synthetic polymers.
- þ spectacles – can be polymer-free, e.g. with metal frames and glass, but such spectacles are usually more expensive, moreover also heavier, in particular when the glass is dioptric (and with more dioptres). Therefore even in the production of spectacles, polymers are promoted and frames from synthetic polymers are not an exception as well as the lenses. An advantage of such spectacles is a high variability of the product, low weight and last but not least a reasonable price.
- þ handkerchief – they are usually made of cotton or paper, both composed of polymer - cellulose.
- þ school bag – it is similar to the rucksack, often made of synthetic fibres and synthetic polymers, including also the elements such as buckles, etc. If they are made of natural fibres, these are again, overwhelmingly and almost exclusively, polymers.
- þ Notice board – if it is wooden or cork, it contains polymers, cellulose or suberin (polymer, of which cork is largely composed; it is responsible for its properties)
- Students naturally will not correctly identify all the materials, e.g. they often do not identify wood as a material containing largely a polymer, and the teacher therefore will lead the students to identify a number of items. The teacher can also write the materials on the blackboard and discuss them with the students.
- In conclusion it can be stated that (and our selection was really random) most products contain some polymeric substances, namely in the form of functional material (i.e. not only as packaging or aesthetic matter). This also applies to a yogurt cup (in our examples), it would not be possible or would be difficult to transport, keep it, etc., without a proper packaging. The products that do not contain a polymeric material are not numerous (e.g. purely metal products, ceramics, diamonds, graphite, etc.)
- In conclusion it can therefore be stated that a majority of products around us contain the polymeric material. The importance of polymeric substances is therefore huge and to understand their composition, properties and analysis is extremely important, even necessary for the society and human life.
- We have roughly determined which products contain a polymer. But what is actually a polymer? Create the best possible definition of polymer. You can also use other sources such as e.g. subject-field or other literature or the Internet. If you use a definition already created by somebody else, you have to be able to explain it to the others using examples and be ready to accept their criticism or the revelation that you do not understand the definition.
- Students usually guess what a polymer is but they do not know it exactly. Therefore we let them form a hypothesis in groups and from this hypothesis to create a definition or at least an explanation of the concept. This will be subsequently (e.g. by selected groups) delivered to the other groups. In the discussion guided by the teacher, these groups then confront each other and assess critically their definitions and refine and strengthen the knowledge of the concept. Next we will introduce the concept of plastic:
- Is a plastic the same as a polymer? Try to explain the difference between these concepts.
- The teacher again guides the students’ discussion. They first guess if it is the same or not, and then they try in groups to guess the difference between these concepts. With the help of the teacher they should arrive at the description of the concept “plastic“. Neither generally is the concept of plastic somehow sharply defined, therefore nor the students will probably arrive at a clear conclusion. The concepts of polymer and plastic often coincide with a given product, but the polymer is a more general concept. We are referring to plastics not earlier than at the moment when the polymer represents a multi-component constructional and technical material. If therefore the polymer is not designed for technical processing, we should not call it a plastic. In practice, plastics are often called synthetic polymers, i.e. such materials that are artificially synthesised (therefore they are also often called artificial materials). Natural polymers (paper, wood, cotton) are not called plastics, though they are often for us constructional materials.
- What is a synthetic polymer and which of the selected products contain a synthetic polymer
- By a similar discussion as in the previous cases, the students will determine what it is a synthetic polymer (i.e. a polymer prepared by synthesis from a monomer), they will understand in such a way the concepts of monomer and polymerization reaction (polymerization). The teacher will critically evaluate the definitions and explanations of the concepts given by the students. From the above mentioned list, a synthetic polymer is contained or can often be contained in:
- þ chair – a chair can be made of "an artificial material", e.g. from polyethylene or polypropylene, then it naturally contains a polymer, it can also have a cover, which is often made of synthetic fibres
- þ car – the present car is composed of many polymers, whether the textile fibres on the seats, dashboards, rugs, etc. In today’s cars, a share of plastics reaches 12-15% (http://www.autorevue.cz/automobily-jen-z-plastu-uz-se-to-blizi) and it is still increasing. These are mostly synthetic polymers such as polyethyleneterephthalate (PET), polystyrene (PS) polyethylene and many others.
- þ rucksack – rucksacks are at present made of mainly synthetic fibres, which are naturally the polymers.
- þ jacket – similarly to rucksacks, these product are nowadays made of mostly synthetic polymeric fibres. E.g. today’s very popular Gore-Tex is a polymer polytetrafluorethylene (PTFE) laminated between the layers of polyamide or polyester. The jacket (or even the rucksack) can also be made of cotton, which is also a polymer (cellulose) or other natural fibres, which are also nearly exclusively polymeric substances.
- þ cup of yogurt – packaging material of our tasty yogurt is very often, indeed almost exclusively, a polymer, often a polystyrene (PS). Yogurt can be packed in glass; however it is not very common.
- þ pencil – if we consider a wooden pencil, it does not contain a synthetic polymer but there are also the ones with the body of synthetic polymers (ballpoint pens, micropencils).
- þ bench – most commonly wooden; though benches can be made of synthetic polymeric materials, so far it is not common.
- þ spectacles – can be polymer-free, e.g. with metal frames and glass, but such spectacles are usually more expensive, moreover also heavier, in particular when the glass is dioptric (and with more dioptres). Therefore even in the production of spectacles, polymers are promoted and frames of synthetic polymers are not an exception as well as the lenses. An advantage of such spectacles is a high variability of the product, low weight and last but not least a reasonable price.
- þ handkerchief – they are usually made of cotton or paper, both composed of polymer – cellulose, synthetic polymers are not so far commonly used for the production of handkerchiefs
- þ school bag – it is similar to the rucksack, often made of synthetic fibres and synthetic polymers, including also the elements such as buckles, etc. If they are made of natural fibres, these are again, overwhelmingly and almost exclusively, polymers.
- þ Notice board – if it is wooden or cork, it contains polymers, cellulose or suberin (polymer, of which cork is largely composed; it is responsible for its properties). However there are also notice boards made of polystyrene foam (PS), which is a synthetic polymer
- In conclusion it can be stated that polymeric materials are contained in a large majority of products, synthetic polymeric materials are then a part of a smaller number of products but in spite of this, a half or more than a half of selected products can contain them.
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