1. Table 1 shows some examples of natural polymers and their respective monomers.
2. The structural formula for isoprene is shown below.
The Coagulation Of Latex
1. The colloidal solution containing rubber molecules,water and non-rubber molecules is called latex.
2. The molecule of natural rubber is shown below.
3. The negatively charged protein membrane surrounding the rubber molecules causes the ruber molecules to repel each other.This condition causes natural rubber to remain in a liquid form.
4. Latex can coagulate naturally if left for a few hours due to bacterial activity.
5. Bacterial activity produces acids which contains hydrogen ions which can neutralise the negative charges on the protein membrane.
6. As a result the rubber molecules can come closer and collide with each other.
7. These collisions will break apart the protein membrane ,releasing the rubber polymers which will coalesce to form lumps of rubber.The process that forms the lumps of rubber is called coagulation.
8. Latex can be prevented from coagulating by adding ammonia.
1. Natural rubber is soft and less elastic than vulcanised rubber.
2. | Natural rubber can be vulcanised by the following manner; | |
| (a) | heating natural rubber with sulphur and a little bit of zinc oxide as catalyst.
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| (b) | immersing strips of natural rubber in sulphur monochloride or disulphide dichloride in metylbenzene. |
3. During vulcanisation, the sulphur atoms form disulphide linkages between the rubber polymers preventing them from sliding over each other.
4. The disulphide linkages cause the vulcanised rubber to be harder, more elastic and more resistant to heat. Vulcanised rubber is also more resistant to oxygen and ozone in the atmosphere thus preventing them form being oxidised.
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