1. Polymers Noadswood Science, 2012

2. Polymers To be able to explain the properties and uses of different polymers Saturday, June 18, 2016

3. Polymers What are polymers Polymers are huge molecules which are made up of lots of smaller molecules (monomers) which have been joined together

4. Properties Different polymers can be made by using different monomers – these polymers can have very different properties… Polymers have properties that depend on the chemicals they are made from, and the conditions in which they are made Modern polymers have many uses, including: - ▫Waterproof coatings ▫Fillings for teeth ▫Dressings for cuts ▫Hydrogels for making soft contact lenses and disposable nappy liners ▫Shape memory polymers for shrink-wrap packaging

5. Polymer Uses PolymerUse PolyethenePlastic bags and bottles PolypropeneCrates and ropes Polychloroethene Water pipes and insulation on electricity cables

6. Polymer Branches Polymer molecules can have branches coming off them, which change their properties, e.g. LDPE and HDPE… LDPE – low-density poly(ethene) HDPE – high-density poly(ethene) Branches on polymerManyFew Relative strengthWeakStrong Maximum useable temperature ( o C) 85 o C120 o C

7. Plasticisers & Slime Plasticisers are substances that let the polymer molecules slide over each other more easily making the polymer softer and more flexible Poly(chloroethene) or PVC is a hard polymer: - ▫Unplasticised PVC (uPVC) is used to make pipes and window frames ▫PVC with plasticisers is soft and flexible and is used for floor coverings, raincoats and car dashboards Poly(ethenol) is a polymer that dissolves in water to make slime: the viscosity of the slime can be changed to make it thick or runny by varying the amount of water

8. Thermosoftening & Thermosetting Polymers can fall into two categories: - ▫Thermosoftening – can be heated and shaped many times ▫Thermosetting – can only be heated and shaped once Thermosetting polymers have their chains cross linked by covalent bonds – the polymer is originally placed into a mould and heated causing cross links to form (further heat will not cause the polymer to soften or change shape) Thermosoftening (top right) and thermosetting (bottom right) showing the cross link bonds which causes it to hold it’s shape

9. Polymer Problems One of the useful properties of polymers is that they are unreactive, so they are suitable for storing food and chemicals safely, but this property makes it difficult to dispose of polymers Most polymers, including poly(ethene) and poly(propene) are not biodegradable meaning that micro-organisms cannot break them down, so they may last for many years in rubbish dumps However, it is possible to include chemicals that cause the polymer to break down more quickly – carrier bags and refuse bags made from such degradable polymers are already available

10. Polymer Problems Polymers can be burnt or incinerated – they release a lot of heat energy when they burn and this can be used to heat homes or to generate electricity There are problems with incineration as carbon dioxide is produced, which adds to global warming Toxic gases are produced unless the polymers are incinerated at high temperatures

11. Polymer Problems Many polymers can be recycled reducing the disposal problems and the amount of crude oil used It is crucial different polymers are separated from each other first, and this can be difficult and expensive to do

12. Slime Complete the slime experiment: - Add a few drops of the borax solution to a warm solution of PVA glue (you can add some food colouring if you wish to enhance the appearance) Stir well for at least 2 minutes… *The glue becomes slimy because the borax makes the long polymer chains in the glue link together, forming a jelly-like substance