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9.5 Option - Polymers: 3. Plastics are
synthetic polymers
| Syllabus
reference (October 2002 version) |
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| 3. Plastics are synthetic polymers
that can be moulded and coloured |
Students learn to: |
Students: |
Extract from Senior Science Stage 6
Syllabus (Amended October 2002) © Board of Studies, NSW.
[Edit: 16 Sept 08]
Prior learning: Science Stages 4–5 Syllabus 4.11.1.
Background information: There is a huge range of synthetic polymers and more uses are being found for them all the time. Plastic is one group of synthetic polymers. Their uses are very diverse according to their properties. Because they can be shaped so easily plastics have a huge range of uses such as bottles and jars, toys, combs, plastic bags and wraps, prosthetics, furniture, crockery, especially for picnics, cases for electronic devices.
describe
plastics as synthetic polymers that can be moulded and shaped
- “Plastic” means that an object is pliable, or can be modelled or moulded into different shapes.
- Today several of the synthetic polymers are called plastics.
identify
that plastics can be either– thermosetting, which is hardened
permanently by heat
– thermoplastic, which is softened
by heat and hardened by cooling
Background
Information
Thermoplastics consist of linear
molecules held together by weak forces. When heated these molecules
can be separated.
In thermosetting plastics the chains
are strongly linked (bonded) together. The cross-linking in a thermosetting
plastic makes the substance rigid.
- Plastics can be either thermosetting or thermoplastic.
- Thermoplastics can be repeatedly melted, have their shape changed, then harden when cooled again.
- Thermosetting plastics are hardened by heat, then don’t melt when heated again but may char or burn if the temperature is high enough.
plan, choose equipment or resources for, and perform a first-hand investigation to identify the effect of temperature and dye on different polymers.
- You may choose to consider the effect of temperature and dye separately.
- Consider the background information below when planning your investigation.
- Choose what polymers to use. This will partly depend on what is available.
- When you have decided the format of the investigation and have chosen the appropriate equipment, perform the investigation.
Background information
Heating (Effect of temperature)
Thermoplastic polymers behave in a different way when heated compared to thermosetting polymers.
Thermoplastics melt and thermosets char (or burn).
All heating of polymers must be done in an efficient fume cupboard.
When heating polymers appropriate safety equipment must be worn (eg safety glasses, labcoat or apron etc.) and exhaust fans should be turned on.
When heating polymers, characteristics to observe
include
- whether the substance melts or burns
- if it burns, the colour of
smoke
- appearance of residue.
Background information
Dyeing fibres
Fibres are dyed to make them more attractive.
Different fibres react differently to dyes.
A possible procedure for testing the take up of a dye by different polymers (fibres) is :
- Obtain a range of polymers (fibres) and record the type of polymer each on is. If any of your fibres are a blend, try to find out the percentage of each polymer in the blend. Some polymers chosen could be polyester ( polypropylene and polyethylene), nylon, rayon, acrylic, olefin and spandex.
- Cut out the same sized pieces of the fibres chosen to study.
- Consult instructions on the packet of the commercial dye being used.
- Make up a solution as per instructions.
- Place material pieces in dye and bring the mixture to the required temperature.
- Leave the polymers in the dye for the required time.
- Lift each piece (using tongs) from dye and rinse in cold water.
- Examine samples and record colour and general appearance of fabrics.
Make a note of which, if any, polymers
don’t take up the dye. You might decide to grade the polymers from best
to worst at taking the dye. The ones that are darkest take up the dye the best.
(NB “Ultrastain HD is a commercial
preparation that can identify some fabrics by the specific colours that they
turn in this dye.)
identify examples of thermoset plastics and thermoplastics.
- thermosetting plastics include bakelite (phenol-formaldehyde), araldite (epoxy resin), formica (melamine formaldehyde).
- thermoplastics include polyvinyl chloride (PVC), polystyrene, nylon, teflon , polytetrafluoroethene, (PTFE), perspex, (polymethyl methacrylate).
discuss the properties of plastics to assess their versatility and impact on society including the energy required in their production and transportation.
- Not all plastics have the same properties.
- Plastics can be: cheap, flexible, tough, hardwearing, insulating, water-resistant, coloured, made into fibres, shaped, etc.
- Plastics do not always have as pleasing an appearance or feel as natural products.
- It takes less energy to produce a product out of plastic than most other materials.
- Plastics are usually lighter than the materials they replace and can be cheaper to transport.
- Because plastics are so versatile they have replaced many natural polymers and other materials.
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