Plastics- A Benefit or a Disaster? (Science research coursework)

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Plastics- A Benefit or a Disaster

Introduction

A plastic is scientifically known as a polymer. A polymer is a large molecule made by linking lots of small molecules (monomers) together. In this report I am going to investigate the opinions of two people, Alan and Susie, to find out who is more accurate when they talk about the facts of plastics. Alan states that “Plastics are a great modern invention because: They are lightweight, cheap, energy saving, tough and durable.” However Susie disagrees and she states “Plastics are a disaster for the environment because: They are not biodegradable and litter everywhere for years.”  So by the end of this report I will have found evidence which shows who is correct, either Alan, Susie or both.

How are plastics made?                                                                                                                        

Plastic tends to be made largely from crude oil which is a mixture of many different hydrocarbons.  Crude oil is a natural compound that is found in rock formations within the earth's surface. A complex combination of organic compounds, petroleum is composed of carbon, hydrogen, nitrogen and oxygen, along with trace metals, resulting in a unique chemical composition that produces oil-based crude oil for extraction. Crude oil is obtained from oil rigs. Crude oil is a fossil fuel which means that it is non-renewable and in order to make sure you get the most out of it as it is a mixture, you need to separate it into its more useful fractions, such as petrol.

Fractional distillation is used to separate different parts of the crude oil, via a fractionating column. Distillation works because each substance in the mixture has its own unique boiling point. So, as a mixture is heated, the temperature of the mixture rises until it reaches the temperature of the lowest boiling substance in the mixture. The lowest boiling substance boils away. Meanwhile, the other components of the mixture remain in their original phase until the lowest boiling component has all boiled off. Only then does the temperature of the remaining mixture rise and other components are boiled off. The supply of fractions with small molecules, like petrol, is less than the demand for them.

Cracking is a chemical reaction that takes the useless fractions of crude oil with long chains, breaks them up and turns them into useful short chains, so you will end up with an alkene and an alkane.

Fractional distillation and cracking make the raw materials for plastics. Cracking is used to produce a mixture of smaller alkanes and alkenes from larger alkanes. These smaller hydrocarbons are more useful as fuel because they ignite more easily. However alkenes are also useful as raw materials for making other substances, in particular polymers (plastics).

Plastics are made by a process called polymerisation. This is when the small alkenes join together to form large molecules. The small alkenes are called monomers and the large molecules are polymers. As this process is when the two mix it is called polymerisation. For example, if you take ethane which is the monomer and mix it with a polymer, you will get polyethene.

 

This information above supports Susie as it proves that plastics are not energy saving. This is because it takes a lot of energy to continually fractionate crude oil, and if there is not much demand for the fractions being produced, therefore much of the energy is wasted as it isn’t needed. This does not support Alan as the information is not relevant to his statement.

Examples of plastics and uses

There are two main types of polymers: Thermosetting and thermoplastic. They both have very different properties as shown in the table below.

Thermoplastics and thermosetting differ in many different ways. Some of these differences are that thermoplastics are made from a polymer called polyethene whereas thermosetting plastics are made from a polymer called melamine.

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 Polythene was the first of the polymers to be discovered. Polyethene is a polymer produced by reacting oxygen and ethene, in this reaction the small ethene molecules attach together to form long chain polymer molecules. This process is known as addition polymerisation. Melamine is an organic base molecule. It contains 66% Nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred.

Thermoplastics can stretch or bend whereas thermosetting is rigid and breaks when bent. Thermoplastic softens and melts when heated whereas thermosetting chars and decomposes. Thermoplastic ...

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