Engineering materials (polymers)
Polymeric materials now encompass a vast range of biological and synthetic materials that are used in a wide range of applications. The market for polymers involves many large commercial organisations that compete with one another in different market sectors. Thus, polymer nomenclature involves chemistry, from various eras, plus commercial trade names, all of which are used synonymously. The vast majority of the items we call ‘plastic’ are made from one of five ‘families’:
1. PE: polyethylene (low density = LDPE, high density = HDPE), e.g. carrier bags.
2. PP: polypropylene, e.g. drinks cups, kettles, shampoo bottles
3. PS: polystyrene and expanded polystyrene (EPS), e.g. insulating cups, packaging
4. PVC: poly(vinyl chloride), e.g. window frames, insulation cables for domestic wiring.
5. PET: poly(ethylene terephthalate), e.g. transparent water bottles.
The precise polymer chosen for any application depends upon the combination of properties required, such as its glass transition temperature (below which the polymer becomes brittle), its melting point, its toughness, its aging properties, whether it absorbs the chemicals it is to contain, how easily it can be moulded/ shaped and the cost.
The name of a polymer is derived from the monomer, for example propylene or ethylene terephthalate. If the monomer is a simple molecule such as ‘propylene’ then the name of the polymer is ‘polypropylene’ – with no brackets. If it is a combined molecule such as ‘ethylene terephthalate’ then the polymer is ‘poly(ethylene terephthalate)’ – with brackets.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance
Fantastic Plastic
This article can be used to introduce polymers as the ultimate designer material. It looks at polymer chains and considers the future for polymers in manufacturing. Polymers can be made to behave in different ways by the way their long chain molecules are organised and can have a variety of uses.
The article can be used as background information at the start or provide a summary at the end of the topic.
Fantastic Plastic *suitable for home teaching*
This booklet provides a source of ideas and information about polymers. It suggests some activities to demonstrate the properties of different polymers and some of their applications. The practical activities are intended for KS4 students but can be extended to use with Post-16 students.
The following activities are particularly useful in teaching the basic chemistry of polymers:
The difference between Thermoplastic polymers and Thermosetting ploymers is explained on pages 11-12. Activity A2 page 35 can be used to demonstrate the difference between these two types of polymers.
The effect of cross linkages between polymer chains can be illustrated by Activity A4: Making a rubber ball. Rubber is an example of an elastomer. Information about the effects of cross linkage can be found on pages 13 -14 and page 51.
Pages 48 - 53 has further information about polymers and provides useful background information.
Stephanie Kwolek - Polymer Chemist *suitable for home teaching*
This article can be used to introduce the design and use of polymers. Stephanie Kwolek invented the tough polymer Kevlar, used in protective clothing, and developed a method for demonstrating the production of nylon in the classroom which is still used today.
It can be used to prompt discussion with students about the process of designing new materials.
Polymorph
This video clip can be used to demonstrate the properties of thermoplastic polymers.
Polymorph is a thermoplastic polymer that softens and can be moulded at a relatively low temperature. It can be used in a wide variety of engineering contexts.
Activity A5 Testing Bounce (pages 38 -39) from the Fantastic Plastic booklet can be caried out to compare the properties of polymorp with that of rubber.
Cold Formed Plastic
This video clip can be used to demonstrate the properties of cold formed plastic (CFP). It looks like acrylic but has a toughness approaching polycarbonate. It is an example of a shape-memory polymer which will return to its original flat form on application of moderate heat, such as immersion in very hot water.
There is no sound so a commentary will be required to highlight the main teaching points.
Technical Bulletins
Technology Enhancement Programme (TEP) technical bulletins provide quick and accessible guidance on how to get the most from equipment and techniques in a learning environment.
The bulletting most relevant to this topic is:
PODs Thermoforming
This describes how rigid foam PVC sheet and clear acrylic sheet can give outstanding results with shapes conforming closely to that of the mould. It gives examples of products that can be made in the workshop. Sections look at areas such as mould design, handling and health and safety.