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Plastics and Polymers

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Introduction

´╗┐Plastics and Polymers Polymers were first made in the early twentieth century and were known as ?plastics?. Polymers are constructed from much smaller molecules (monomers) that are joined together to form long chains (polymers). The economy and many industrial companies rely on polymers as a vital resource. An advantage of using polymers over natural materials is that polymers can be manufactured very specifically with varying degrees of stiffness, density, heat resistance and electrical conductivity. The study of natural polymers has also led to great advances in medicine and nutrition. Polymers have a great many uses: sheets and films, adhesives, paints and inks and also synthetic fibres and yarns. A very common polymer used widely in modern life is polyethylene (the simplest polymer). When it?s made into bags for supermarkets and other uses, it?s typically flexible and transparent. Its monomer (a single unit that is repeated) is Ethene (C2H4). It can be polymerised into polyethylene that generally contains around 105 Ethene monomers within its structure. The diagram shows the polymerisation of ethane into polyethene/polyethylene. ...read more.

Middle

4. Cross Linking ? If polymer chains are linked together by covalent bonds throughout the structure, the polymer is harder and has a higher melting point. The monomers that are required to join together to make the polymer will not usually react with each other under standard conditions (i.e. room temperature and pressure) as they?re too stable. Condensation and addition polymerisation are two methods of polymerising monomers. Condensation polymerisation involves making an extra product, usually water in addition to the required polymer. A common biological condensation reaction is the formation of cellulose from glucose molecules. When two glucose molecules react, a hydroxyl group from each molecule ?condense? to a water molecule, leaving an oxygen atom to link the two monomers together. This is repeated throughout a very large chain of monomers to create the polymer: cellulose. Esters can also be polymerised to create polyesters. These chains are made into fibres and then woven together to create many types of clothing. Polyester fabrics and fibres are very strong and are extremely durable (resistant to most chemicals, stretching and abrasion). ...read more.

Conclusion

Kevlar is formed from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid. Today, with a general opinion that global warming/climate change is being caused by humans, there is more focus than ever on renewable resources, especially in the plastics industry. There are many degradable polymers such as poly(lactic acid) which is used for waste sacks, which when put into a landfill site, will biodegrade. When a polymer is degradable, microorganisms break it down into a mixture of methane and other gases. Some polymers are photodegradable which means the reaction is catalysed by sunlight (UV radiation). Photodegradable polymers break up into small pieces that then do not biodegrade. However this is better than a completely non-biodegradable polymer. Polymers can also be hydrolysed by ?adding? a molecule of water at the ester or amide group to split the polymer. An increasing number of polymers can now be recycled. This reduces disposal problems and the amount of crude oil used to make new products. However, different polymers still need to be collected and separated before they can be recycled, which can prove time consuming and expensive. If incinerated, the polymers can produce toxic gases upon being burnt. For example, poly(vinyl chloride) produces HCl(g). ...read more.

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